bluuebunny/crossref_metadata_2025 huggingface dataset:
Microtubule organization during the development of the mitotic apparatus in cultured mesophyll protoplasts of higher plants – an immunofluorescence microscopic study
Authors: Meijer Eltjo G. M. , Simmonds Daina H.
Published: May 2006

Microtubule organization in the course of the interphase‐mitosis transition, karyokinesis and cytokinesis in cultured mesophyll protoplasts of Medicago sativa L. cv. Regen S and Nicotiana tabacum L. cv. Wisconsin 38 was investigated during the early culture stages. A prominent circular band of microtubules, the prophase band of microtubules (PB) was seen in the cell cortex during prophase in most cells. The band appeared during very early prophase and disappeared during late prophase. Other prophase microtubule arrays were nuclear‐envelope associated microtubule fluorescence (perinuclear fluorescence, PNF) and groups of microtubules radiating from the nuclear envelope into the cytoplasm. These radiating microtubutes (perinuclear radiating microtubules, PNR) were particularly long and prominent in the PB plane appearing to link the PNF with the PB network. The possible functions of the PNR are discussed. The role of the PB is discussed in the light of the unorganized nature of these cells.
Cytological abnormalities and aberrant microtubule organization during early divisions in mesophyll protoplast cultures of Medicago sativa and Nicotiana tabacum
Authors: Meijer Eltjo G. M. , Keller Wilfred A. , Simmonds Daina H.
Published: May 2006

Karyokinetic and cytokinetic irregularities were examined in cultured mesophyll protoplasts of Medicago sativa L. cv. Regen S and Nicotiana tabacum L. cv. Wisconsin 38 during the early cell divisions. Spindle anomalies, laggine chromalids during anaphase, displaced phragmoplasts during telophase and incomplete cross‐walls following the completion of cytokinesis were scored in these cultures. The abnormalities, however, occurred at low frequencies when compared to those found in suspension culture‐derived protoplasts of Vicia hajastana. It is suggested that abnormalities are reduced because the mesophyll protoplasts regenerate a substantial cell wall prior to the onset of the first division.

An entirely different class of cytological aberration occurring in 40–50% of the cells was caused by localized protruding of the cytoplasm (budding). The nucleus was often positioned at the site of constriction of the bud. The association of budding with mitosis has led us to postulate a mechanism which may be a cause of budding and to suggest a possible way to prevent it.
Changes in NO3− and K+ uptake by four species in flowing solution culture in response to increased irradiance
Authors: Macduff J. H. , Wild A.
Published: May 2006

Net rates of NO3− and K+ uptake were compared for oilseed rape (Brassica napus L. cv. Jet neuf), perennial ryegrass (Lolium perenne L. cv. S23), Italian ryegrass (Lolium multiflorum Lam. cv. Augusta) and wheat (Triticum aestivum L. cv. Fen‐man) in flowing solution culture during a 4‐day sequence of low‐low‐high‐high natural irradiance. Concentrations of NO3− (10 μM) and K+ (2.5 μM) in solutions were maintained automatically and hourly variation in net uptake of these ions was measured. During the 2 days of low irradiance (<1 MJ m−2 day−1) the uptake rates of both ions by all species were low at <1 mmol NO3−, m−2 h−1 and <0.4 mmol K+ m−2 h−1. Uptake increased in each species during the first day of high irradiance (7.90 MJ m−2 day−1) to >4 mmol NO3− m−2 h−1 and >1.4 mmol K+ m−1 h−1. These higher rates were maintained throughout the following night. The lag‐time between maximum irradiance and the onset of the highest acceleration in uptake was greater for NO3− (5–8 h) than for K+ (≤1 h) in rape, wheat and Italian ryegrass. Uptake of NO3−, by perennial ryegrass showed an almost constant acceleration for 18 h following maximum irradiance. In all species the measured maximum inflows (uptake rate per unit root length) of both ions were greater than theoretical maximum potential inflows to a non‐competing infinite‐sink root in soil, by factors of 7 and 36, respectively, for NO3− and K+, averaged over all species.
Effect of temperature on electron transport activities of glutaraldehyde‐fixed pea thylakoids
Authors: Nolan William G.
Published: May 2006

Temperature‐induced changes in Hill activity of glutaraldehyde‐fixed pea (Pisum sativum L. cv. Alaska) thylakoids have been examined. Using ferricyanide as electron acceptor, a temperature‐induced change occurred at ca 12–14°C for both control and fixed thylakoids. In contrast to the controls, fixed thylakoids not only showed a change in slope of the Arrhenius plots but also a discontinuity which has not been observed in previous studies. A drop in activity coincided with the decrease in slope: the extent of the reduction depended on the concentration of glutaraldehyde used for fixation. Using a lipophilic electron acceptor, a temperature‐induced change also occurred at 12–14°C, but there was no reduction in activities of fixed thylakoids at temperatures above the change in slope.

The results indicate that a temperature‐induced change in fixed thylakoids restricts the access of ferricyanide to its reductant(s) in the membrane but that fixation does not affect the temperature‐induced change per se. The results confirm that temperature has a general effect on the functioning of thylakoid membranes. The data demonstrate that calculations of the extent of inhibition by glutaraldehyde of Hill activity with ferricyanide should take into account the temperature at which assays are performed.
Effect of the osmotic environment of the seed coat on sucrose and amino acid transport into developing seeds of Lunaria annua, Acer pseudoplatanus and Glycine max
Authors: Wolswinkel Pieter , Ammerlaan Ankie
Published: May 2006

In contrast to the data reported for developing seeds of pea and broad bean, assimilate transport into empty kernels of maize is not reduced by a low osmolality of the substitute medium. Therefore, additional data were collected from representatives of other taxonomical groups. In pulse‐labelling experiments with Lunaria annua L. and Acer pseudoplatanus L., sucrose and amino acid transport into empty ovules was strongly reduced by a low osmolality of the medium filling an empty ovule, compared to that seen with high osmolality. In experiments of 8 h without radioiso‐topes, a very low osmolality of the medium (about 0 mM) reduced the rate of sugar and amino acid release from attached seed coats of soybean [Glycine max (L.) Merr. cv. Fiskeby V], in comparison with a 300 mM mannitol medium. It can be concluded that in all dicotyledonous plants studied (five species), a low osmotic potential of the seed apoplast is one of the most important factors controlling the rate of assimilate transport into developing seeds. At this moment, the data reported for maize have an isolated position.
Inhibition of photosynthesis and transpiration in relation to mercury‐induced root damage in spruce seedlings
Authors: Godbold Douglas L. , Hüttermann Aloys
Published: May 2006

Spruce seedlings [Picea abies (L.) Karst.] were exposed in nutrient solutions to a range of concentrations of HgCl2 and CH3HgCl for 7 weeks. The mineral, chlorophyll and water contents of the needles, and dry weights of root and needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plants were determined using a Li‐cor portable photosynthesis‐measuring system. CO2 uptake decreased as the supply of both forms of Hg increased. Rates of transpiration were significantly reduced only after exposure to CH3HgCl. Similar concentrations of Hg were found in needles independent of the form of Hg supplied. Decreased rates of CO2 uptake at 100 nM HgCl2 and 1 nM CH3HgCl could be explained by lower levels of chlorophyll, and by lower levels of chlorophyll and closed stomata at all other CH3HgCl concentrations. Only at 1000 nM HgCl2 were other photosynthetic parameters affected.

Decreased rates of transpiration and the lower chlorophyll levels in the needles did not appear to be due to the direct action of Hg, but rather to root damage that leads to a decrease in water supply and nutrient levels in the needles.
Vulnerability of xylem to embolism in a mangrove vs an inland species of Rhizophoraceae
Authors: Sperry John S. , Tyree Melvin T. , Donnelly John R.
Published: May 2006

Vulnerability of xylem conduits to cavitation and embolism was compared in two species of Rhizophoraceae, the mangrove Rhizophora mangle L. and the tropical moist‐forest Cassipourea elliptica (Sw.) Poir. Cavitation (water column breakage preceeding embolism) was monitored by ultrasonic detection; embolism was quantified by its reduction of xylem hydraulic conductivity. Acoustic data were not predictive of loss in hydraulic conductivity, probably because signals from cavitating vessels were swamped by more numerous ones from cavitating fibers. Rhizophora mangle was the less vulnerable to embolism of the two species, losing 80% of its hydraulic conductivity between – 6.0 and – 7.0 MPa. Cassipourea elliptica lost conductivity in linear proportion to decreasing xylem pressure from – 0.5 to – 7.0 MPa. Species vulnerability correlated closely with physiological demands of habitat; the mangrove Rhizophora mangle had field xylem pressures between – 2.5 and – 4.0 MPa. whereas the minimum for Cassipourea elliptica was – 1.6 MPa. Differences in vulnerability between species could be accounted for by differences in the measured air permeability of intervessel pit membranes. According to this explanation, embolism occurs when air enters a water‐filled vessel from a neighboring air‐filled one via pores in shared pit membranes.
Diurnal export and carbon economy in an expanding source leaf of cucumber at contrasting source and sink temperature
Authors: Verkleij Frans N. , Challa Hugo
Published: May 2006

Effects of contrasting temperatures of an expanding leaf (source) and of remaining plant parts (sink) on diurnal export and distribution of carbon were studied in seedlings of Cucumis sativus L., cv. Farbio. The time course of the rate of export was calculated by measuring simultaneously the exchange of 14CO2 and the amount of 14C in the source leaf by means of a Geiger‐Müller detector using a steady‐state labelling technique.

In all treatments average export rate during the night (16 h) was maximally 50% of the average rate during the 8‐h day. Temperature affected the diurnal course of export via the source leaf and the sink in different ways. At a source leaf temperature of 25 or 30°C export stopped 12 h after start of the night, whereas at 20°C export continued throughout the night. However, the total amount of carbon exported during a 24 h cycle, expressed as a proportion of the amount of carbon assimilated, was the same at source leaf temperatures of 20 or 30°C. Thus source leaf temperature did not affect the distribution of assimilates between source and sink, in contrast to sink temperature. After 24 h at a sink temperature of 30°C, 20% more 14C was exported to plant parts below the source leaf than with a sink temperature of 20°C, at the expense of carbon remaining in the source.

During the day less starch and more structural dry matter was formed at a source leaf temperature of 30°C than at 20°C. After a complete day/night cycle, however, there was no difference between the treatments. Starch was the primary carbon source during the night, and the decline in the rate of export coincided with the depletion of starch. Thus the decline in the rate of export at a source leaf temperature of 25 or 30°C at 12 h after the start of the night was due to the depletion of starch at that time. Similarly, at 20°C export could continue until the end of the night as the starch degradation supplied assimilates during the whole night.
Hydroxycinnamoyl amides in stem explants from flowering and non‐flowering Nicotiana tabacum
Authors: Wyss‐Benz Markus , Streit Luc , Ebert Edith
Published: May 2006

Flower formation in stem explants was chosen as an experimental system for the study of the function of hydroxycinnamoyl amides (HCAs) in plants. The explants, derived from flowering and non‐flowering Nicotiana tabacum L. var. Xanthi nc., differentiated to two types of callus and afterwards to flower buds. A novel reversed‐phase high performance liquid chromatography method, following sample clean‐up on CM‐Fractogel columns, enabled us to examine HCA concentrations in small tissue samples. Two different groups of HCA could be distinguished during in vitro flower formation: Firstly, feruloyl‐ and diferuloyputrescine, the major detectable HCAs that accumulated during callus proliferation; secondly, caffeoylputrescine, which accumulated during the later stage of flower differentiation and reached higher concentrations than feruloylputrescine.
Influence of aluminium on phosphate and calcium uptake in beech (Fagus sylvatica) grown in nutrient solution and soil solution
Authors: Bengtsson Bengt , Asp Håkan , Jensén Paul , Berggren Dan
Published: May 2006

The effects of AICI3 on uptake of Ca2+ and phosphate in roots of intact beech (Fagus sylvatica L. provenance Maramures) plants were studied in nutrient solution and soil solution. Aluminium reduced the concentrations of Ca, Mg and P in plants and increased that of K. In short term experiments, uptake of Ca2+(45Ca) was reduced by exposure of the roots to Al. The effect of aluminium on Ca2+(45Ca) uptake was immediate and primarily of a competitive nature, preventing Ca2+ from being adsorbed. Uptake of 32P‐phosphate increased with increasing Al concentration up to 0.1 mM and then decreased at higher Al concentrations. The effect of Al on 32P‐phosphate uptake was most pronounced during the first hours of exposure. Growth of plants for 15 days in soil solution, collected from the upper A horizon of a beech forest soil, had no effect on uptake of Ca2+(45Ca) and 32P‐phosphate, probably because of a low concentration of labile bound monomeric Al and binding of Al to organic compounds. Soil solution from the deeper B horizon reduced Ca2+(45Ca) uptake and increased 32P‐phosphate uptake in a manner similar to that with Altreatment in nutrient solution. It is concluded that in soil solution from the deeper regions of the soil, mineral uptake by roots was affected by Al.
Effect of drought, on transport and metabolism of abscisic acid in aeroponically grown Helianthus annuus
Authors: Hubick Kerry T. , Reid David M.
Published: May 2006

The effect of drought on transport and metabolism of radioactive abscisic acid (ABA) in roots and shoots of sunflower (Helianthus annuus L. cv. Russian) was observed. Radioactivity from ABA moved freely all over the plants. Young shoot tissues, such as the growing apical bud or axillary buds released from apical dominance, were strong sinks for ABA. Mature tissues were effective exporters. Drought‐induced alterations in the pattern of transport of radioactivity do not appear to be a major factor in the control of drought‐induced changes in ABA levels. Metabolism of ABA occurred in all organs examined in stressed and unstressed plants. Labelled ABA and its metabolites moved in the xylem. Drought altered the quantity of radioactive metabolites and reduced the amount of radioactive ABA in extracts from the stressed plants.
Comparison of the specific activity of ribulose‐1,5‐bis‐phosphate carboxylase‐oxygenase from some C3 and C4 plants
Authors: Rintamäki Eevi , Keys Alfred J. , Parry Martin A. J.
Published: May 2006

The specific activity of ribulose‐1,5‐bisphosphate carboxylase‐oxygenase (Rubisco, EC 4.1.1.39) was measured from the crude extracts of five C3 plants consisting of wheat (Triticum aestivum L. cv. Maris Mink), spinach (Spinacia oleracea L.), pea (Pisum sativum L. cv. Greenfeast), pumpkin (Cucurbita pepo L. cv. Jättiläismeloni) and Ceratodon purpureus (Hedw.) Brid., and two C4 plants, maize (Zea mays L. ETA F1) and sugar sorghum [Sorghum saccharatum (L. emend, L.) Moench]. The amount of Rubisco in the crude extracts was estimated by polyacrylamide gel electro‐phoresis with the Coomassie Brilliant Blue staining procedure. The amounts of the dye bound to the purified Rubisco of different higher plants were similar. The method gave a linear response for both purified enzyme and crude extracts, and the results agreed with those observed by immunochemical methods. The addition of positive effectors such as inorganic phosphate was necessary to obtain maximal activity in the crude extracts of all the studied plants except in that of maize. No significant differences in the specific carboxylase activity at 25°C were found between the C3 and C4 plants.
The effects of illumination sequence, CO2 concentration, temperature and acclimation on the convexity of the photosynthetic light response curve
Authors: Leverenz Jerry W.
Published: May 2006

It was shown previously that the convexity (curvature or rate of bending) of the photosynthetic light response curve was strongly correlated with chlorophyll content in shade acclimated conifer needles (Leverenz 1987, Physiol. Plant. 71: 20–29), in agreement with an hypothesis that gradients of light within leaves affect the convexity. In the present study it is shown that the convexity at any given chlorophyll content can be altered when leaves of Pinus sylvestris L. Picea glauca (Muench), Picea mariana (M.II.) BS.P. and Picea abies (L.) Karst pre‐treated with less shade. This probably induced a differential acclimation of cells on the top and bottom sides of the leaves to their local light environment. Leaves were illuminated on i) their top surface, ii) their bottom surface, or iii) uniformly in a light integrating sphere during measurements of photosynthesis. After shoots had been transferred from their growth environment to a new measuring environment, the convexity increased from the first to the second day towards a maximum of 0.97. The rate of increase towards this maximum was 55 to 62% per day and probably is the result of re‐acclimation of cells within the leaves. The data shown that the act of measuring photosynthesis induces a significant alteration in the experimental material when measurements are made for more than one day.

The convexity of the light response curve of photosynthesis, was independent of whether the steady state measurements were made beginning in the dark and sequentially increasing photon flux density or beginning at high light and sequentially lowering photon flux density. Neither variation of CO2 concentration from 35 to 200 Pa, nor of temperature from 5° to 32°C affected the convexity.
A measurement system to detect small plant movements
Authors: Eidesmo T. , Johnsson A.
Published: May 2006

A measurement system based on a photodiode array technique is presented, together with some results from recordings of phototropic responses of Avena sativa L. (cv. Seger I) coleoptiles.

A commercial photodiode array (RL‐256G) was used, controlled by a likewise commercial control board RC‐301. Electronic circuits were built to connect the control board to the interface card IO‐801 of an Apple IIe microcomputer. The circuits constitute a fast temporary memory, which mainly contains two shift registers and two timers. Programs, which control the measurements, have been written and are presented.

Detailed recordings of blue light induced phototropic movements are presented: resolution and other features of the equipment are discussed.
Imposition of water stress in wheat seedlings improves the efficacy of uniconazole‐induced thermal resistance
Authors: Fletcher R. A. , Santakumari M. , Murr D. P.
Published: May 2006

Winter wheat (Triticum aestivum L. cv. Fredrick) seedlings (seed) treated with different concentrations of uniconazole (S‐3307) were water stressed by withholding water for 2, 4 and 6 days. Subsequently, the water‐stressed seedlings were exposed to heat shock at 45°C for 3 h. Chlorophyll fluorescence, stress‐ethylene and percentage survival were the parameters used to monitor the efficacy of protection against thermal stress by uniconazole. In the control seedlings, water stress for 2 days prior to heat shock provided minimal protection, whereas uniconazole protected both water‐stressed and non‐stressed seedlings from heat injury. However, the degree of protection by uniconazole was enhanced if the seedlings were subjected to water stress (2–4 days) prior to the heat shock. In addition to protection against heat injury, uniconazole also reduced stress‐induced (water and heat) ethytene levels.
Drought effects on photosynthesis and fluorescence in hard wheat cultivars grown in the field
Authors: Di Marco Giorgio , Massacci Angelo , Gabrielli Roberto
Published: May 2006

Net photosynthesis of the flag leaf of hard wheat (Triticum durum L. evs Valforte, Produra, Adamello, Karel, Appulo and El Amel from the collection of the Instituto di Cerealicultura. Foggia, Italy) of different water potential has been studied on three consecutive years. Net photosynthesis was measured in natural conditions with a LI‐COR portable instrument and in saturating CO2 with an oxygen electrode. Net photosynthesis and stomatal conductance were significantly lower in the unirrigated leaves. However, the ratio of intercellular CO2, concentration (C1) to ambient CO3 concentration (Ca) around the stressed plants was similar to the irrigated control. The maximal rate of photosynthesis in saturating CO2, (Pnmax). measured in the second year of the experiment, was quite close to photosynthesis under natural conditions, indicating that CO2 supply was not limiting. These results suggest that altered mesophyll photosynthetic capacity, rather than stomatal closure, causes the observed reduction in photosynthesis in the unirrigated plants. The variable fluorescence yield (v/Fm) in predarkened leaves measured for two consecutive years, did not show differences between treatments or between cultivars. However, the analysis of the slow transients, measured the last year of the experiment, showed a linear relation between the fluorescence decline from the maximum initial level (P) and maximum photosynthesis (Pnmax).
Vitamin D and related compounds as plant growth substances
Authors: Buchala A. J. , Pythoud F.
Published: May 2006

Vitamin D and related compounds (hydroxylated derivatives and glycosides) occur naturally in certain plants. The metabolism of vitamin D3 in Solanum malacoxylon Sendtn. is similar in certain respects to that in animal systems. There is also evidence that vitamin D3, plays a role in processes regulated by Ca2+ in plants. Vitamin D3 possesses plant growth substance activities and in particular enhances adventitious root formation.
Proline accumulation and nitrate reductase activity in contrasting sorghum lines during mid‐season drought stress
Authors: Sivaramakrishnan S. , Patell Villoo Z. , Flower D. J. , Peacock J. M.
Published: May 2006

Six lines of sorghum (Sorghum bicolor L. Moench) with differing drought resistance (IS 22380, ICSV 213, IS 13441 and SPH 263, resistant and IS 12739 and IS 12744, susceptible) were grown under field conditions in the semi‐arid tropics and analysed for proline and nitrate reductase activity (NRA; EC 1.6.6.1) during a mid‐season drought. The resistant lines accumulated high levels of proline, while the susceptible lines showed no significant proline accumulation. Most of the proline was accumulated after growth of the plants had ceased. In a separate greenhouse experiment, most of the proline was found in the green rather than the fired portions of leaves. The levels returned to that of irrigated controls within 5 days of rewatering. Proline levels increased as leaf water potential and relative water content fell, and there was no apparent difference among the different sorghum lines with change in plant water status. Susceptible lines accumulated less proline than resistant lines as leaf death occurred at higher water potentials. Proline accumulation may, however, contribute to the immediate recovery of plants from drought. Leaf NRA reached high levels at about 35 days after sowing in both the stressed and irrigated plants, after which it declined. The decline in NRA was more pronounced in the stressed than in the irrigated plants and closely followed changes in the growth rate. Upon rewatering, NRA increased several‐fold in all the lines and, in contrast to proline accumulation, genotypic differences in NRA were small, both during stress and upon rewatering. The high sensitivity of NRA to mild drought stress was reflected in the rapid decline of activity with small changes in leaf water potential and relative water content. The results are discussed in the light of a possible role for proline during recovery from drought, and the maintenance of NRA during stress and its recovery upon rewatering.
Characterization of an l‐aspartate aminotransferase activity in Chlamydomonas reinhardtii
Authors: Muñoz‐Blanco Juan , Lain‐Guelbenzu Blanca , Torres Jacobo Cárdenas
Published: May 2006

The isolation and characterization of an l‐aspartate aminotransferase (AAT) activity (EC 2.6.1.1) in the unicellular green alga Chlamydomonas reinhardtii 6145c are reported for the first time. The enzyme transaminates aspartate with the 2‐oxoglutarate‐glutamate system, and exhibits maximum aminotransferase activity at pH 7.8 and 37°C. It has an Mr of 138 kDa, contains pyridoxal 5′‐phosphate, and has a Km apparent for oxalacetate of 0.55 mM and exhibits positive co‐operativity with l‐aspartate with an S0.5 of 2.53 mM and a Hill coefficient of 1.57. In vivo, activity levels were affected by the carbon and nitrogen sources and by the change in the dark‐light conditions. All these responses are interpreted in terms of a possible physiological regulation of AAT activity to keep the intracellular pools of glutamate and aspartate within margins compatible with environmental fluctuations.
Production and organ distribution of succinate in rice seedlings during anoxia
Authors: Menegus F. , Cattaruzza L. , Chersi A. , Selva A. , Fronza G.
Published: May 2006

Anaerobic production of succinate, a common feature in animals able to sustain anoxia, has seldom been reported in plants. By the use of 1H‐nuclear magnetic resonance spectroscopy we show here that succinate is produced by rice seedlings (Oryza sativa L. cv. Arborio) subjected to anoxic conditions. Starting from levels below I μmol (g fresh weight)−1 in air, after 48 h of anoxia the levels of alanine, succinate and lactate had increased to 23.8, 5.2 and 1.0 μmol (g fresh weight) −1, respectively, in shoot tissues. Succinate was accumulated in shoots, notably in the coleoptiles, but not in roots of the rice seedlings, suggesting its involvement in rice coleoptile elongation under anoxia. Other possible functions of succinate production in rice seedling, an organism highly tolerant to anoxia, are discussed.
Effect of irradiance and plant age on the dimensions of the growing shoot of poplar
Authors: Pieters George A. , van den Noort M. E.
Published: May 2006

Populus euramericana (Dode) Guinier cv. Robusta plants were cultivated at irradiances of 7.5, 15 and 30 W m−2 (32.5, 65 and 130 μmol m2 s−1), 400–700 nm at 22°C and a relative humidity between 40 and 60% on a gravel culture subirrigated with Hoagland's nutrient solution. The basal diameter of the growing shoot, a measure of the number of apical cells participating in growth, increased proportionally to irradiance and was correlated with mature leaf length. The development of the length of the growing shoot (Lgs) depended also on the nutritional status of the (young) shoot. Lgs was strongly correlated with the rate of height growth.
Flowering requirements of Scandinavian Festuca pratensis
Authors: Heide O.M.
Published: May 2006

Flowering requirements of three Scandinavian cultivars of Festuca pratensis Huds, have been studied in controlled environments. At 3 and 6°C, primary induction was independent of photoperiod, while short days (8 h) were more effective than long days (24 h) at higher temperatures. The critical temperature for induction was about 15°C in short days and about 12°C in long days. Saturation of induction required 18–20 weeks of exposure to optimal conditions. At temperatures below 12°C both induction and initiation of inflorescence primordia took place in long days, while a transition to long days was required for inflorescence initiation after primary induction in short days. A minimum of 8 long‐day cycles were required for flowering of plants primary induced in short days and saturation of flowering required more than 16 cycles. The critical photoperiod for secondary induction was about 13 h. High temperature (21°C) had some devernalization effect in primary induced plants, suppressing flowering compared with 15°C.
Nitrogen concentration, ammonium/nitrate ratio and NaCl interaction in vegetative and reproductive growth of peanuts
Authors: Silberbush M. , Lips S. H.
Published: May 2006

Peanuts (Arachis hypogaea L. cv. Shulamit) grown with NO3− and saline water in hydroponics responded positively to addition of nitrogen (N) in their vegetative growth, but not in desert dune sand. In order to clarify these conflicting results, peanut plants were grown in a greenhouse pot experiment with fine calcareous sand. The nutrient solution contained 0 or 50 mM NaCl and 2 or 6 mM N in the form of Ca(NO3)2, NH4NO3 or (NH4)2SO4. Three replicates were harvested after 48 days (beginning of reproductive stage) and three after 109 days (pod filling). In addition, gynophores were treated with 0, 50, 100, 150 or 200 mM NaCl outside the growth pot to check their sensitivity to salt. Shoot dry weight became greater with increasing NH4+/NO3− ratio. Increasing the N concentration from 2 to 6 mM did not change shoot dry weight of the NH4NO3 or NH4+‐fed plants, but caused a reduction in shoot dry weight of NO3−‐fed plants. Shoot dry weight was not affected by increasing the NaCl concentration to 50 mM. Salt caused an increase in the number of gynophores per plant and a reduction of the mean pod weight. A NaCl concentration of 100 mM and above reduced gynophore vitality. It is concluded that the salt sensitivity of peanut plants resides mainly in the sensitivity of the reproductive organs.
Galactolipase activity and free fatty acid levels in chloroplasts of domestic and wild tomatoes with different chilling tolerance
Authors: Gemel Joanna , Saczyńska Violetta , Kaniuga Zbigniew
Published: May 2006

In order to establish differences in the chilling sensitivity of domestic and wild Lycopersicon species, galactolipase (EC 3.1.1.26) activity, free fatty acid (FFA) level and Hill reaction activity were measured in chloroplasts isolated from control and cold treated leaves of L. esculentum Mill., cv. Norton, L. hirsutum Humb. and Bonpl., L. peruvianum var. glandulosum Mill. Galactolipase activity was higher in chloroplasts from Lycopersicon species with high chilling sensitivity than in chloroplasts of more chilling‐resistant ones. A similar relationship was observed for FFA level in chloroplasts from both cold‐stored and control leaves. Decrease in Hill reaction activity due to cold stress was greater in chloroplasts of more chilling‐sensitive species. The changes are accompanied by a decline of photochemical activity. Considering the changes in the three parameters noted above, an increasing order of chilling tolerance was established: L. esculentum < L. hirsutum (700 m) < L. hirsutum (3100 m) < L. peruvianum (3400 m). It is suggested that measurements of galactolipase activity and FFA may be useful in an evaluation of differences in resistance to chilling injury of closely related species.
The epiphytic lichen Evernia prunastri synthesizes a secretable cellulase system that degrades crystalline cellulose
Authors: Yagüe E. , Estévez M. P.
Published: May 2006

Evernia prunastri (L.) Ach. produces a cellulase system capable of solubilizing crystalline cellulose. The enzyme is secreted into the incubation medium in response to the presence of 0.5% (w/v) cellobiose. Cellulase secretion is pH dependent, the maximum occurring at an initial pH of 9.0, which is rapidly decreased by the action of the lichen. The effect of cellobiose on the cellulase system is inhibited by cycloheximide and 8‐azaguanine. The cellulasc activity increases with the metabolic reactivation that is initiated by thallus hydration. Several functions of cellulase in this lichen are discussed.
Cytoplasmic pH of Dunaliella parva and Dunaliella acidophila as monitored by in vivo 31P‐NMR spectroscopy and the DMO method
Authors: Gimmler H. , Kugel H. , Leibfritz D. , Mayer A.
Published: May 2006

In connection with investigations of the pH‐stat mechanism of the unicellular, halotolerant green algae Dunaliella parva and the acid‐resistant species D. acidophila, a comparative study on the in vivo measurement of the cytoplasmic pH of Dunaliella cells was carried out, using the so‐called dimethyloxazolidine‐2,4‐dione (DMO) method (distribution of a weak acid between the cells and the medium) and 31P‐NMR spectroscopy. As judged by the effects of the external pH, light, anaerobiosis, nitrogen nutrition, permeable weak acids and bases and of ATPase inhibitors, both methods yield reproducible and in principle similar results, although absolute pH values obtained by the NMR method were always slightly higher than those obtained by the DMO method: 1) D. parva is able to maintain a cytoplasmic pH close to 7.0 at external pH 5–8, whereas D. acidophila maintains a neutral pH even at an external pH of 1. 2) The pH‐homeostasis requires ATP. 3) During illumination the cytoplasm and the stroma is alkalized. 4) Anaerobiosis induces reversible acidifications of the cells. The physiological importance of these effects is discussed. Advantages of the NMR method for the assessment of the cytoplasmic pH of D. parva are: 1) Better resolution of kinetic effects. 2) Independence of volume determinations. 3) Information about phosphate, phosphomonoester, nucleotide and polyphosphate contents of the cells. However, the ability of 31P‐NMR spectroscopy to monitor pH values in different compartments of cells could not be exploited with Dunaliella cells: Although a light‐induced alkalization of the cells was observed, differences in the pH of the cytoplasm and the stroma of illuminated cells could not be detected. The disadvantages of the 31P‐NMR method are the low sensitivity in comparison to the DMO method and the requirement for an appropriate calibration matrix. Advantages of the DMO method are the high sensitivity and the possibility of measuring many samples in parallel. Disadvantages of the DMO method are the poor resolution of kinetic effects and the need to know the osmotic volume of the cells.
Hexose kinases of avocado
Authors: Copeland Les , Tanner Gregory J.
Published: May 2006

The subcellular location and properties of enzymes concerned with the phosphorylation of glucose and fructose in avocado (Persea americana Mill. cv. Hass) have been studied. A substantial amount of glucose‐phosphorylating activity was particulate and fractionation of extracts by sucrose density gradient centrifugation indicated that most of this activity was associated with the mitochondria. Three hexose‐phosphorylating enzymes were resolved by DEAE‐cellulose chromatography of the cytosolic fraction. These were a hexokinase (EC 2.7.1.1), which had strong preference for glucose as substrate, and two specific fructokinases (EC 2.7.1.4). ATP was the preferred phosphoryl donor for the hexose kinases of avocado.
Ca2+ dependence and La3+ interference of ultraviolet radiationinduced K+ efflux from rose cells
Authors: Murphy Terence M.
Published: May 2006

A low fluence of ultraviolet radiation (UV) causes cultured cells of Rosa damascena Mill cv. Gloire de Guilan to lose intracellular K+. This effect required the presence of Ca2+ in the medium. A reduction in the concentration of free Ca2+ to 10−5M with ethyleneglycol‐bis‐(β‐aminoethyl‐ether)‐N.N.N′,N′‐tetraacetic acid (EGTA) buffer inhibited the UV‐stimulated efflux; this was correlated with a discharge of the membrane potential and a stimulation of the leakage of K+ from unirradiated cells. All the same effects were seen with La3+ at 0.2 mM. At 0.02 mM La3+, the UV‐stimulated efflux of K+ was blocked without concomitant effects on the membrane potential or K+ efflux from control cells. It is suggested that removal of Ca2+ blocks or masks the UV‐induced leakage of K+ by destabilizing the plasma membrane. In addition, La3+ may specifically inhibit the UV‐stimulated opening of K+ or anion channels.
Phytochrome is not involved in the red‐light‐enhancement of the stomatal blue‐light‐response in wheat seedlings
Authors: Karlsson Per Erik
Published: May 2006

The stomatal response to blue light (BL) in wheat seedlings (Triticum aestivum L. cv. Starke II, Weibull) was enhanced by background red light (R). This enhancement was only slightly affected by the addition of background far‐red light (FR). Under similar light treatments, the addition of FR induced a 43% transformation from the far‐red‐absorbing form towards the red‐absorbing form of phytochrome from etiolated oat (Avena sativa L. cv. Sol II), immobilized on phenyl‐sepharose. Furthermore, the enhancement of the stomatal BL‐response by 15 min R was not reversed by a subsequent irradiation with 5 min FR. It is concluded that the red‐light‐enhancement of the stomatal blue‐light‐response in wheat seedlings does not involve a change in the photostationary state of phytochrome.
Inhibition of photosynthesis in Nicotiana tabacum leaves treated with tabtoxin and its relation to pigment loss
Authors: Turner John G.
Published: May 2006

Tabtoxin is the chlorosis‐inducing dipeptide toxin produced by Pseudomonas syringae pv. tabaci, causal agent of the wildfire disease of Nicotiana tabacum L. cv. White Burley. In plant tissue it is hydrolysed to yield the amino acid tabtoxinine β‐lactam, which inactivates glutamine synthetase (EC 6.3.1.2). This study sought to identify those physiological alterations caused by the inactivation of glutamine synthetase and which were involved in the development of the chlorotic symptom. In tobacco (Nicotiana tabacum L. cv. White Burley) leaves injected with concentrations of taboxin that caused the inactivation of glutamine synthetase, photosynthesis was rapidly inhibited when the tissue was illuminated. This was closely followed by losses in leaf pigments, particularly chlorophyll a, and the ratio of chlorophyll a/b declined, indicating photochemical destruction. The rapid inhibition of photosynthesis in green tissue was due to reduced quantum efficiency, indicating a lesion in the light reactions. In chlorotic tissue, photosynthesis was limited by the chlorophyll level. The results indicated that the inhibition of photosynthesis may be instrumental in development of the chlorotic symptoms.
Comparison of movement and metabolism of indole‐3‐acetic acid and indole‐3‐butyric acid in mung bean cuttings
Authors: Wiesman Zeev , Riov Joseph , Epstein Ephraim
Published: May 2006

Indole‐3‐butyric acid (IBA) was much more effective than indole‐3‐acetic acid (IAA) in inducing adventitious root formation in mung bean (Vigna radiata L.) cuttings. Prolonging the duration of treatment with both auxins from 24 to 96 h significantly increased the number of roots formed. Labelled IAA and IBA applied to the basal cut surface of the cuttings were transported acropetally. With both auxins, most radioactivity was detected in the hypocotyl, where roots were formed, but relatively more IBA was found in the upper sections of the cuttings. The rate of metabolism of IAA and IBA in these cuttings was similar. Both auxins were metabolized very rapidly and 24 h after application only a small fraction of the radioactivity corresponded to the free auxins. Hydrolysis with 7 M NaOH indicates that conjugation is the major pathway of IAA and IBA metabolism in mung bean tissues. The major conjugate of IAA was identified tentatively as indole‐3‐acetylaspartic acid, whereas IBA formed at least two major conjugates. The data indicate that the higher root‐promoting activity of IBA was not due to a different transport pattern and/or a different rate of conjugation. It is suggested that the IBA conjugates may be a better source of free auxin than those of IAA and this may explain the higher activity of IBA.
Photoinhibition of photosynthesis. An evaluation of damaging and protective mechanisms
Authors: Krause G. Heinrich
Published: May 2006

Inhibition of photosynthesis by excess excitation energy is initiated in the reaction center of photosystem II. The primary site of photoinhibition in the reaction center (components of primary charge separation or secondary electron acceptor QB) is still disputed. Photoinhibition is characterized by quenching of variable chlorophyll flurescence (Fv), resulting from increased thermal dissipation of excitation energy. Varying responses of initial fluorescence (F0), however, seem to indicate involvement of different mechanisms. As far as photoinhibition is reversible within minutes to hours, it can be viewed as a controlled protective mechanism that serves to dissipate excessive energy, Supposedly, another dissipative mechanism, distinguished by its faster kinetics (response within seconds), is related to the energy‐dependent fluorescence quenching.
The action of tentoxin on membrane processes in plants
Authors: Klotz Martin G.
Published: May 2006

Tentoxin, a fungal phytotoxin, with its complex mode of action on plant membrane processes, is currently the best known example of a phytotoxic substance, with the literature going back more than 20 years and including a number of conflicting reports, which have not yet been adequately reconciled. This minireview covers all effects of tentoxin obtained at different levels of organization in several plant species (chloroplast structure and function, stomatal movements and guard cell protoplasts, leaf and root plasmalemma, ion uptake and translocation and internal ion concentrations) and suggests a number of targets for tentoxin which merit investigation. Besides the demonstration of the complexity of phytotoxin action and its possible relationship with other signal exchange mechanisms operating between microorganisms and plants, tentoxin may also provide a valuable tool for obtaining further information about the regulation of ion transport in plants.
Short‐term pH regulation in plants
Authors: Felle Hubert
Published: May 2006

Cellular pH regulation consists of two features: (i) Long‐term pH homeostasis, which ensures that all H+ or OH− produced in excess is ultimately removed from the cell and which requires metabolic energy; (ii) short‐term reactions of the cell(s) to sudden shifts in intracellular pH, in order to prevent acute disturbances of metabolism. Recent progress in measuring and understanding of mainly short‐term cellular regulation is summarized, including cellular responses to pH loads that arise from different sources such as external pH, weak acids/bases, protonophores, metabolic inhibitors, H+/cotransport, light and phytohormones. Whereas the plasma membrane H+ pump and metabolic adjustments may serve both long‐ and short‐term pH control, physico‐chemical buffering and the translocation of H+ from and to cellular compartments render only time‐limited capacity for the neutralization of pH loads and seem exhausted within minutes. In spite of the widespread opinion that, because of tight regulation, intracellular pH does not vary with time, there is good evidence for long‐lasting pH changes in plant cells, i.e. after hormonal stimulation, light/dark changes or carboxylation during crassulacean acid metabolism (CAM). This emphasizes that cytoplasmic pH, besides being well regulated, is essential not only for the regulation of membrane transport but also as a cellular messenger.
Carbon and nitrogen partitioning in young nodulated pea (wild type and nitrate reductase‐deficient mutant) plants exposed to NH4NO3
Authors: Taylor David C. , Shelp Barry J. , Nelson Louise M. , Grodzinski Bernard
Published: May 2006

Carbon and nitrogen partitioning was examined in a wild‐type and a nitrate reductase‐deficient mutant (A317) of Pisum sativum L. (ev. Juneau), effectively inoculated with two strains of Rhizobium leguminosarum (128C23 and 128C54) and grown hydroponically in medium without nitrogen for 21 days, followed by a further 7 days in medium without and with 5 mM NH4NO3. In wild‐type symbioses the application of NH4NO3 significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [14C]‐labelled (NO3−, NH4+, amino acids) in roots. In nodules, there was a decline in amino acids together with an increase in inorganic nitrogen concentration. In contrast, symbioses involving A317 exhibited no change in nitrogenase activity or nodule carbohydrates, and the concentrations of all nitrogenous solutes measured (including asparagine) in roots and nodules were enhanced. Photosynthate allocation to the nodule was reduced in the 128C23 symbiosis. Nitrite accumulation was not detected in any case. These data cannot be wholly explained by either the carbohydrate deprivation hypothesis or the nitrite hypothesis for the inhibition of symbiotic nitrogen fixation by combined nitrogen. Our result with A317 also provided evidence against the hypothesis that NO3− and NH4+ or its assimilation products exert a direct effect on nitrogenase activity. It is concluded that more than one legume host and Rhizobium strain must be studied before generalizations about Rhizobium/legume interactions are made.
Serine hydroxymethyltransferase from spinach leaf mitochondria. Purification and characterization
Authors: Henricson Dag , Ericson Ingemar
Published: May 2006

A mitochondrial serine hydroxymethyltransferase (EC 2.1.2.1) has for the first time been purified close to homogeneity from a photosynthetically active tissue, spinach (Spinacea oleracea L. cv Viking II) leaves. The specific activity of the enzyme was 7.8 μmol (mg protein)−1 min−1 using L‐serine as substrate. The enzyme was stable for at least 8 weeks at 4°C in the presence of folate. The pH optimum was at pH 8.5 where the enzyme had a Km for L‐serine of 0.9 mM. Carboxymethoxylamine was a strong competitive inhibitor with a K1 of 1.4 μM. An absorption spectrum taken of the enzyme in the presence of glycine and tetrahydrofolate showed a peak at 492 nm, probably originating from a substrate‐enzyme complex. The molecular weight obtained by gel filtration was 209 kDa. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis of the purified enzyme showed that the apparent molecular weight of the subunit was 53 kDa, indicating four subunits.
Apical dominance inPhaseolus vulgaris. The triggering effect of shoot decapitation and leaf excision on growth of the lateral buds
Authors: McIntyre Gordon , Damson Erich
Published: May 2006

It was postulated that the release of lateral buds from apical dominance is triggered by the immediate increase in apoplastic water potential (hydrostatic pressure) that is produced by shoot decapitation and that is rapidly transmitted throughout the plant. In experiments conducted to test this hypothesis the use of a strain gauge transducer capable of measuring bud growth with an accuracy of ± 0.1 μm, showed that growth of the inhibited lateral bud at the primary leaf node ofPhaseolus vulgaris(L.) ev. Canadian Wonder was initiated within 1 to 5 s following shoot decapitation or excision of the primary leaves. When only the apical bud was excised the lateral bud showed a brief, transitory growth response of ca 1 min duration, but the axillary buds of the first and second trifoliate leaves were released from inhibition. Decapitation of the shoot just below the first trifoliate leaf induced a lateral bud response characterized by three distinct stages: a) a rapid initial growth response with a mean duration of 4.9 min b) a period of arrested growth, which varied in duration from 2 min to 4 h and c) the subsequent resumption of growth.

Excision of both primary leaves induced a rapid but transitory bud response of considerably greater duration than that induced by apical bud excision. Excision of the primary leaves prior to decapitation of the shoot eliminated the phase of arrested growth, which characterized the bud response to decapitation of the intact plant. The rapidity of the bud response to both shoot decapitation and leaf excision and the interaction between the effect of these two treatments are consistent with the hypothesis that competition for water plays a major role in the correlative inhibition of lateral buds.