bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of combined NaCl and CaCl2 salinity on photosynthetic parameters of barley grown in nutrient solution
Authors: Morales Fermín , Abadía Anunciación , Gómez‐Aparisi Joaquín , Abadía Javier
Published: May 2006

The changes caused by NaCl− and CaCl2‐induced salinity on several leaf parameters have been measured in two cultivars of barley (Hordeum vulgare L.) growing in a growth chamber in nutrient solution. Salinity was induced by adding to the nutrient solution equal weights of NaCl and CaCl2, to obtain conductivities of 2, 6, 12, 19 and 26 dS m−1. Salinity induced decreases in the leaf water potential and in the osmotic potential. Salinity did not induce significant changes in the relative photosynthetic pigment composition of barley leaves, the photosynthetic pigment stoichiometry for neoxanthin:violaxanthin cycle pigments:lutein:β‐carotene:Chl b:Chl a being close to 3:6:14:12:25:100 (mol:mol). Salinity per se did not induce interconversions in the carotenoids within the violaxanthin cycle in most barley leaves. The PSII photochemistry of most barley leaves was unchanged by salinity. However, some apparently healthy leaves growing in high salinity exhibited sudden decreases in PSII photochemistry and increases in zeaxanthin (at the expense of violaxanthin), that preceded rapid leaf drying. Salinity induced significant changes in the slow part of the chlorophyll fluorescence induction curve from barley leaves.
After‐ripening and phytochrome action in seeds of dormant lines of wild oat (Avena fatua)
Authors: Hou J. Q. , Simpson G. M.
Published: May 2006

The effects of a short exposure to red, far‐red or alternate red/far‐red light on the germination of seeds after‐ripened for different periods of time were studied in dormant lines of wild oat (Avena fatua L.). Three stages were distinguishable in the after‐ripening period in the response of germination to light. Seeds stayed dormant and showed no response to light during stage I. Phytochrome‐mediated germination was observed in seeds during stage II. The phytochrome action disappeared during stage III, i.e. seeds fully germinated following treatments of all light qualities. When the seeds were imbibed in polyethylene glycol solutions, dark germination was reduced and phytochrome again had an effect, which suggested the involvement of phytochrome in water uptake of the seed.
Cell wall glycanases and their activity against the hemicelluloses from pine hypocotyls
Authors: Acebes José Luis , Zarra Ignacio
Published: May 2006

Glycanases associated with the cell walls of Pinus pinaster Aiton from Northern Spain (29QT638, altitude 1000 m) were extracted with 1 M LiCl solution, and their effect on the hemicellulosic polysaccharides from the same material was studied. The extracted proteins were able to increase the amount of reducing sugars and to decrease the viscosity of the hemicellulosic polysaccharides extracted with both 4 and 24% (w/v) KOH, suggesting the presence of exo‐ and endo‐type glycanases. The extracted proteins released arabinose, galactose and xylose from both hemicellulosic polysaccharides, and caused an important depolymerization of xyloglucan. The results indicate that the changes in the hemicellulosic polysaccharides, i.e., xyloglucan depolymerization, found during cell elongation are caused by an enzymic system associated with the cell wall.
Light‐quality effects on Arabidopsis development. Red, blue and far‐red regulation of flowering and morphology
Authors: Eskins Kenneth
Published: May 2006

Arabidopsis thaliana(L.) Heynh. race Columbia plants were grown in red. blue, red + far‐red, blue + far‐red and various light mixtures of red + blue + far‐red light under 14 h light/10 h dark photoperiods. Each single light source and light mixture maintained a constant irradiance (50 μmol m−2 s−1) and the mixtures of red + blue + far‐red maintained a constant ratio of red/far‐red light, but varied in the ratio of blue to red + far‐red light. Depending on the method used for calculation, values of the fraction of phytochrome in the far‐red absorbing form (Pfr/Ptot) for these light mixtures were either constant or decreased slightly with increasing percentage of blue light in the mixtures. Arabidopsis flowered early (20 days) in blue, blue + far‐red and red + far‐red light and late (55 days) in red light. In mixtures of red + blue + far‐red light, each of which established a nearly constant Pfr/Ptot flowering was in direct relation to time and irradiance level of blue light. Leaf area and petiole length were also correlated with blue light irradiance levels.
Analysis of the decrease in photosynthesis on desiccation of mosses from xeric and hydric environments
Authors: Seel W. E. , Baker N. R. , Lee J. A.
Published: May 2006

Three moss species [Tortula ruraliformis (Besch.) Grout. Bryum pseudotriquetrum (Hedw.) Schaegr and Dicranella palustris (Dicks.) Crund. ex. E. F. Warb. (D. squarrosa (Starke) Schp.] collected from a range of habitats differing in water availability were desiccated in controlled conditions. All species became photosynthetically inactive when dried below a water content of 100–200% dry weight. Only Tortula ruraliformis, a moss from arid sand dunes. was able to recover fully to pre‐desiccated rates of photosynthetic electron transport during subsequent rehydration. The rate of recovery was influenced by irradiance during desiccation. Mosses from hydric habitats showed some resumption of photosynthetic electron transport (following rehydration) if dried in the dark. but did not do so if dried even in low light. In these circumstances the mosses showed evidence of lasting photoinhibition of photosynthesis after rehydration. The desiccation‐tolerant T. ruraliformis became significantly photoinhibited only when continually exposed to high irradiance (1200 μmol m−2 s−1) in the hydrated state. If allowed to desiccate whilst exposed to high irradiance this species showed less evidence of photoinhibition after rehydration, and was not at all affected by desiccation in low irradiance. Photon flux absorption in dry moss was 50–60% less than that in hydrated moss as a result of leaf curling. However, the reduction in absorption of photosynthetically active radiation cannot account for the total loss of photosynthetic oxygen evolution and variable chlorophyll fluorescence observed in the desiccated mosses.
Cadmium effects on leaf transpiration of sugar beet (Beta vulgaris)
Authors: Greger Maria , Johansson Monica
Published: May 2006

Seedlings of sugar beet (Beta vulgaris L. cv Monohill) were cultivated for 4 weeks in nutrient solution containing different concentrations of CdCl2 (0 to 10 μM). The effects of Cd on appearance and function of stomata and leaf cuticle were investigated by water loss measurements and microscopy. The leaf transpiration rate increased with increasing Cd concentrations while the sum total of stomatal aperture area per unit leaf area decreased. Already at low Cd levels. an increase of defective and undeveloped stomata was found in Cd treated plants. These stomata are closed or have small apertures and probably lack a functional closing mechanism. The number of intact stomata per unit leaf area was lower in leaves of Cd treated plants than in controls, and Cd induced closure of intact stomata. The total number of stomata per leaf area slightly increases with increasing Cd concentration. as does the percentage of small stomata. Furthermore. specific leaf area increased, while the density of leaf structure was decreased by Cd. From this observation we conclude that the increase in transpiration rate caused by Cd is primarily due to effects on the permeability of the leaf cuticle to water.
Activities of enzymes involved in lignification during the postharvest storage of etiolated asparagus spears
Authors: Hennion Stéphane , Anthony Little C. H. , Hartmann Claude
Published: May 2006

The content of lignin and the activities of 5 enzymes involved in lignification were monitored along the length of etiolated spears of asparagus (Asparagus officinalis L., INRA Fl male hybrid n°156) stored for 22 h with their base in air (control), water or water containing the ethylene antagonist, silver thiosulfate (STS). At the time of harvest the lignin content increased basipetally, as did the activity of all the enzymes studied, viz., phenylalanine ammonia lyase (PAL; EC 4.3.1.5), hydroxycinnamate: CoA ligase (HCoAL; EC 6.2.1.12), cinnamoyl‐CoA reductase (CCR: EC 1.2.1.44), cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) and syringaldazine oxidase (SyrOx. a peroxidase [POD; EC 1.11.1.7] with syringaldazine as substrate). Neither the lignin content nor the activity of any enzyme changed in the spear apex during storage, regardless of treatment. In the spear base. all enzyme activities decrased during the first 2 to 4 h in every storage treatment. Subsequently. PAL and HCoAL activities remained constant. whereas the activities of CAD and SyrOx gradually increased. Lignification in the spear base was not affected by storage in air. However, storage in water increased lignin formation and SyrOx activity, whereas treatment with STS prevented both of these increases. The results indicate that postharvest lignification in etiolated asparagus spears is caused primarily by enhanced SyrOx activity, and that ethylene is involved in the control of this activity.
Light and temperature action in germination of seeds of the empress tree (Paulownia tomentosa)
Authors: Grubišicá Dragoljub , Konjević Radomir
Published: May 2006

Seeds of the empress tree (Paulownia tomentosa Steud.) were imbibed for two weeks in darkness at constant temperatures (18, 23 or 28°C), and then irradiated with red light for 5 min. Germination was poor if it took place at the same temperature as imbibition, but a high percentage was achieved if the seeds were exposed to higher or lower temperatures before they were irradiated. Maximum germination was obtained when the difference between pretreatment and imbibition was about 10°C. The effect increased with the duration of the pretreatment and was optimal at 24 h. The effect decreased as the time lapse between temperature pretreatment and red light irradiation increased, and it was lost after two days. If pretreatment was shorter than 24 h (12 h). a high percent of germination was obtained by alternating pretreatment and imbibition temperatures. The germination of seeds imbibed in 40% heavy water was also stimulated by temperature pretreatments. Light and temperature also exhibited an interactive effect in the germination of seeds that were imbibed in darkness for only 3 days. For each of the germination phases there was a temperature at which the time needed for 50% germination was the shortest, namely 35°C during imbibition, 37.5°C in the period of Pfr activity. and 32.5°C during radicle protrusion. The data obtained are shortly discussed in relation to the domestication of empress tree in Southern Europe.
Pyruvate carboxylase inLeptosphaeria michotü. Isolation, properties, intracellular localization and cyclic variations of its activity in relation to polypeptide level
Authors: Tozo Koffi , Séjalon‐Delmas Nathalie , Jerebzoff‐Quintin Simonne , Jerebzoff Stephan
Published: May 2006

Pyruvate carboxylase (EC 6.4.1.1) was obtained from the fungusLeptosphaeria michotü(West) Sacc. and enriched 543‐fold by a 5‐step purification procedure as an a4‐β4 tetramer of Mr440000, composedof a Mr60000 α‐subunit, containing bound biotin, and a Mr50000 β‐subunit. The enzyme was active from pH 6.5 to 12.0, with a maximum between pH 8.0 and 8.5. Its specific activity was 125nkat (mg protein)−1: it was not affected by acetyl CoA. A rabbit antiserum raised against the yeast pyruvate carboxylase was specifically reactive against the α‐subunits of theL. michotüenzyme. The enzyme was localized into the cytosol by gold‐labelled streptavidin and immunogold staining of thin sections of Lowicryl‐K4M‐embedded colonies. Pyruvate carboxylase and acetylCoA carboxylase inL. michotühad synchronous activity rhythms at constant temperature and in darkness; these rhythms were suppressed by cycloheximide or avidin supply. The pyruvate carboxylase level was quantified along the activity rhythm by gel electrophoresis using35S‐streptavidin. and by enzyme‐linked immunosorbent assay (ELISA) using serum against the yeast pyruvate carboxylase. The cyclic variations of pyruvate carboxylase activity were correlated with cyclic variations in the enzyme level. Suppression of pyruvate and acetyl CoA carboxylase activities by avidin had a no important effect on the transaminase rhythms ofL. michotü.
Hydroxycinnamoylputrescines are not causally involved in the tuberization process in potato plants
Authors: Leubner‐Metzger Gerhard , Amrhein Nikolaus
Published: May 2006

The possible role of hydroxycinnamoylputrescines in the tuberization process of potato plants was studied using in vitro tuberization systems. Minitubers in shoot cultures of Solanum tuberosum ssp. andigena and S. tuberosum ssp. tuberosum were obtained in vitro within 3 weeks of dark incubation after increasing the sucrose concentration in the Murashige‐Skoog (T. Murashige and F. Skoog. 1962. Physiol. Plant. 15: 473–497.) medium (without hormones) from 60 to 240 mM. both in the presence and absence of benzylaminopurine (BAP). Feruloylputrescine (FP) and caffeoylputrescine (CP) increased with tuberization, with a sharp maximum at day 9 in the shoot, but only when the medium contained BAP. When inhibitors of phenylalanine ammonia‐lyase (PAL) and of polyamine biosynthesis were added to the medium containing BAP, the levels of FP and CP were reduced to values lower than those observed in the absence of BAP, but there was no significant effect on the number and dry weight of tubers formed. Addition of BAP without increasing the sucrose content also resulted in CP and FP accumulation. but failed to induce tuberization of the cultures. Experiments with in vitro stolon cultures and leaf cuttings also supported the conclusion that CP and FP accumulated as a response to the application of BAP, without having any effect on optimal tuberization. These results indicate that the increase of hydroxycinnamoylputrescines during tuber formation is unlikely to be causally involved in the tuberization process in potato plants.
Alterations in carbohydrate levels in leaves of Populus due to ambient air pollution
Authors: Bücker J. , Ballach H.‐J.
Published: May 2006

Cuttings of Populus nigra L. cv. Loenen and Populus maximowiczii Henri ×Populus nigra L. cv. Rochester were exposed for 6 weeks in open‐top chambers to investigate effects of realistic mixtures of ozone, sulphur dioxide, and nitrogen oxides on carbohydrate levels. Whereas the total main nonstructural carbohydrates in the leaves were reduced, those in the roots were nearly not affected. The reduction in leaf carbohydrates was associated with a significant decrease in starch. In contrast, sucrose and especially glucose were increased, causing a shift in the starch to sucrose and the starch to glucose ratios. The effects were strongest in the older leaves of both cultivars, with cv. Loenen, especially, responding to ozonic mixtures. In the petioles, sucrose and glucose were unchanged or, in some cases, decreased. The alterations in carbohydrate levels were coupled to a reduction in both total fresh weight of leaves and total dry matter of roots, and were attributed to an air pollution‐dependent demand for energy and carbon in leaves.
Temporal changes in root growth and 15N uptake and water relations of two tussock grass species recovering from water stress
Authors: BassiriRad Hormoz , Caldwell Martyn M.
Published: May 2006

Physiological responses of Agropyron desertorum and Pseudoroegneria spicata, two common cold desert perennial tussock grass species of the North American Great Basin, were evaluated during and after a period of imposed drought in a pot study. The timing and the pattern of response of leaf water potential (Ψ1), stomatal conductance (gs), and root growth were strikingly similar in both species during and after drought. The severity of stress influenced the magnitude of Ψ1 and gs, but had little effect on the timing of these responses. Although drought inhibited total root length in prestressed plants, within 4 days after relief of drought both species showed similar increases in root growth which exceeded those of the control. Despite similarities in their root growth responses to increased soil water availability, the two grasses differed in their capacity to restore N uptake following drought. By 14 days after rewatering, N uptake in the prestressed Agropyron had recovered to levels of control plants, although both root biomass and root lenght were much less than those of the controls. This is attributed to elevated root uptake kinetics. Restoration of N uptake by prestressed Pseudoregneria was much less effective during the same period.
5′‐Methylthioadenosine nucleosidase and 5‐methylthioribose kinase activities in relation to stress‐induced ethylene biosynthesis
Authors: Kushad M. M. , Orvos A. , Ferro A. J.
Published: May 2006

The activities of 5’‐methylthioadenosine (MTA) nucleosidase (EC 2.2.2.28) and 5‐methylthioribose (MTR) kinase (EC 2.7.1.100) were related to changes in ethylene biosynthesis in tomato (Lycopersicon esculentum Mill. cv. Rutgers) and cucumber (Cucumis sativus Mill. cv. Poinsett 76) fruit following wounding and chemically induced stresses. Stress ethylene formation in wounded tomato and cucumber tissue continued to increase after wounding, reached its peak by 3h, and then declined. The activities of MTA nucleosidase and MTR kinase increased parallel to stress ethylene in both tissues. At peak ethylene formation, MTA and MTR kinase activities were 2‐ to 4‐fold higher in wounded than in intact tissue. Wounded, mature‐green tomato tissue treated with specific inhibitors of MTA nucleosidase and MTR kinase showed a significant reduction in the activities of these enzymes, which was concomitant with a decline in stress ethylene biosynthesis. When mature‐green tomato discs were infiltrated with [14CH3] MTA and wounded, radioactive MTR and methionine were formed. Incubation of mature‐green tomato discs with Cu2+ and Li+ in the presence of kinetin increased ethylene biosynthesis. MTA nucleosidase activity was higher than that of the control in the presence of Cu2+ but not in the presence of Li+, while MTR kinase activity was lower than that of the control in both Cu2+ and Li+ treatments. Data indicate that MTA nucleosidase and MTR kinase are required for wound‐induced ethylene biosynthesis but not for chemical stress‐induced ethylene by Cu2+ or Li+ treatments.
Effect of temperature regimes on gibberellin levels in thermosensitive dwarf apple trees
Authors: Steffens G. L. , Hedden P.
Published: May 2006

Orchard‐grown dwarf apple (Malus domestica Borkh.) trees selected from a hybrid population were propagated by tissue culture but had a growth pattern similar to standard cv. Golden Delicious plants when grown at constant 27°C instead of the expected dwarf pattern of growth. Shoot elongation was markedly reduced, with or without gibberellin A1 (GA1) or GA4 treatment, when trees were grown in an environment where day temperature was maintained at 35°C for 2 h in a ramped regime (night 20°C day ramped to 35°C, held for 2 h and ramped down to 20°C night over a 14‐h photoperiod). Application of GA1 or GA4 partially overcame growth retardation resulting from prior paclobutrazol treatment of both standard and dwarf trees grown at constant 27°C and of standard trees grown in the ramped environment. However, these GAs had no effect on paclobutrazol‐treated or untreated dwarfs grown in the ramped regime. Gas chromatography‐mass spectrometry with labelled internal standards was used to quantify GA1, GA3, GA8, GA19, GA20 and GA29 in extracts from standard and dwarf plants grown either at a constant 27°C or in a 20‐30‐20°C ramped temperature regime. Standard plants, which elongate quite rapidly in either environment, had similar levels of these GAs in both temperature regimes. The slowly growing dwarfs in the ramped temperature environment contained three times more GA19 than the rapidly elongating dwarfs grown at 27°C. The concentrations of the other GAs were reduced to ca 40% or less in plants grown in the ramped temperature regime compared with those grown at 27°C. These data suggest that shoot elongation of dwarf plants is sensitive to elevated temperatures both as a result of reduced responsiveness to GAs and because of a reduction in the concentration of GA1, apparently as a result of a lower rate of conversion of GA19 to GA20. It is possible that the altered GA metabolism may be a consequence of the change in GA sensitivity.
Effects of vanadate, N2 and light on the membrane potential of motor cells and the lateral leaflet movements of Desmodium motorium
Authors: Antkowiak Bernd , Engelmann Wolfgang , Herbjørnsen Rut , Johnsson Anders
Published: May 2006

The lateral leaflets of Desmodium motorium (Houtt.) Merr. exhibit ultradian up‐ and down movements, which are paralleled by oscillations of the membrane potential of motor cells in the pulvinus. By different treatments we have tested the hypothesis that both that both oscillation‐types are causally related. The reactions of the leaflet movement and the membrane potential were evaluated by the following approaches. (1) Application of vanadate. an inhibitor of the proton pump in the plasmalemma. and N2 suppressed leaflet movements and finally arrested the leaflet in the lower position. Before the oscillations damped out, a strong lengthening in period was found. This indicates that the pump is part of the ultradian clock. A period lenthening and a final suppression of the rhythm by vanadate was also seen in the extracellular electric potential of the pulvinus. Intracellular recordings in situ showed that vanadate application depolarized the motor cells. (2) Light of high fluence rates diminished the amplitude of the oscillations of the membrane potential of single motor cells and shortened the period. The same effects were observed when monitoring the lateral leaflet movement. The leaflet always moved towards the direction of the light. whether it was applied from the abaxial or from the adaxial part of the pulvinus. (3) When light was applied to the pulvinus of lateral leaflets. which had spontancously stopped moving in an upper position. oscillations were induced transiently. This effect was also found for the membrane potential of motor cells in the pulvinus. ‐ Our results thus provide further evidence that the membrane potential controls the volume state of the motor cells in the pulvinus of lateral leaflets of Desmodium motorium.
Effect of long term fumigation with ozone on the turnover of the D‐1 reaction center polypetide of photosystem II in spruce (Picea abies)
Authors: Godde D. , Buchhold J.
Published: May 2006

Long term fumigation of 4‐year‐old spruce trees with ozone concentrations up to 200 nl l−1 has only minor effects on the photosynthetic activities measured as chlorophyll a fluorescence. Nevertheless, it drastically changes the turnover of the D‐1 reaction center polypeptide of photosystem II. During summer, fumigation with ozone for 2 weeks resulted in an almost 4‐fold stimulation of the light dependent incorporation of [14C] leucine into the D‐1 protein in the exposed trees. The amount of immunodetectable D‐1 protein remained constant when based on chlorophyll. This indicates that exposure to ozone stimulates both the synthesis and the degradation of the D‐1 protein. When spruce trees were exposed during winter for 4 weeks to 100 and 200 nl l−1 ozone, respectively, an almost 3‐fold increase of the amount of immunodetectable D‐1 protein per chlorophyll in the exposed trees was observed. This can be explained by a varying stimulation of D‐1 protein synthesis and degradation depending on the different physiological conditions. Since so far the D‐1 protein has been found only as a component of photosystem II reaction centers, one has to assume that the relative content of photosystem II reaction centers also increases under certain stress conditions. The increased turnover of the D‐1 protein in trees exposed to ozone explains the synergistic effects of stress conditions and high light intensities often observed in the field.
Floral morphogenesis in Rudbeckia hirta in relation to polyamine concentration
Authors: Harkess Richard L. , Lyons Robert E. , Kushad Mosbah M.
Published: May 2006

Changes in polyamine concentration in the long day (LD) plant Rudbeckia hirta were examined over the course of floral initiation and development. Plants of R. hirta were grown to maturity under 9h, non‐floral‐inductive photoperiods. At maturity, half the plants were placed in ambient day length plus a 4‐h night interruption. Plants were sampled at 0, 4, 8, 12 or 16 days for polyamine content and floral initiation. Polyamines were extracted from fully expanded leaves and the meristems were examined histologically. In another experiment, polyamines were extracted from the meristems under paired LD and short day (SD) conditions every 2 days from 0 to 22 days. A rise in free polyamines was linked to important cytological events during floral initiation. Free putrescine and spermidine levels increased after 4 LD and continued until 14 to 16 LD when the levels in the meristem began to decline. Events of floral initiation began between 4 and 8 LD with cell proliferation and the start of stem elongation. Initiation was irreversible after 14 to 16 LD, the period when putrescine and spermidine began to decline. After 4 LD, the polyamine level was consistently higher in the photoinduced plants. Our results from this study, using direct histological comparisons of meristematic development and polyamine concentration, clearly demonstrate a correlation of polyamines and flowering.
An endogenous growth inhibitor, 3‐hydroxy‐β‐ionone. I. Its role in light‐induced growth inhibition of hypocotyls of Phaseolus vulgaris
Authors: Kato‐Noguchi Hisashi
Published: May 2006

The effects of 3‐hydroxy‐β‐ionone on the growth of hypocotyls of dark‐grown dwarl bean (Phaseolus vulgaris L. cv. Morocco) and tall bean (cv. Kentucky Wonder) were examined. 3‐Hydroxy‐β‐ionone inhibited growth of the hypocotyl of both cultivars at doses higher than 3 ng per plant. Seedlings of the tall cultivar responded to a slightly lesser extent to 3‐hydroxy‐β‐ionone than those of the dwarf cultivar. Changes in the levels of 3‐hydroxy‐β‐ionone in hypocotyls of both cultivars 24 h after the onset of light irradiation, were determined by high‐performance liquid chromatography and the results compared with the results of light‐induced inhibition of growth. The difference in levels of 3‐hydroxy‐β‐ionone between the two cultivars was considerable, and the changes in its levels in the hypocotyls of each cultivar reflected the light‐induced inhibition of growth of the hypocotyls of the respective cultivars. These results suggest that the endogenous growth inhibitor. 3‐hydroxy‐β‐ionone, may play an important role in the inhibition by light of hypocotyl growth of the two cultivars and may serve to distinguish the growth habits of these cultivars.
Pigment formation in potato tubers (Solanum tuberosum) exposed to light followed by darkness
Authors: Virgin Hemming I. , Sundqvist Christer
Published: May 2006

Potato tubers (Solanum tubersoum cvs Bintje and King Edward). never exposed to light, lack chlorophyllous pigments. Continuous irradiation results in chlorophyll (Chl) formation and induces the ability for protochlorophyll (Pchl) formation when the tubers are brought back to darkness. Pigment synthesis takes place in both blue and red light, but blue light is more effective than red in starting the greening process. The pigment formation is strongest in the layers just below the periderm with a steep gradient inwards. Small amounts of Chl formed after irradiation. slowly fade away during extended darkness. However, the Chl formed after long time of irradiation is remarkably stable. Irradiated potatoes, placed in darkness, form Pchl with a fluorescence emission peak at 633 nm. A maximal level is reached after ca 7 days. Resolution of the Pchl spectrum suggests the presence of small amounts of a pigment with an emission maximum at around 642 nm. No sign of the Pchl with emission maximum at 657 nm, which dominates in etiolated leaves, is found. A faint Chl fluorescence indicates that some Pchl, probably the 642 nm form, is phototransformed into Chl in weak light. The Chl formation in the potato tuber is discussed in relation to that of roots and leaves.
Effects of chilling on tomato fruit texture
Authors: Jackman Robert L. , Gibson Henry J. , Stanley David W.
Published: May 2006

The effects of chilling on tomato (Lycopersicon esculentum Mill cv. Caruso) texture were investigated using fruit stored at 22°C (nonchilled) or 5°C (chilled) for 28 days. or at 5°C for 15 days before transfer to 22°C to facilitate ripening during and additional 13 days (prechilled). Prechilled fruit exhibited symptoms of slight chilling injury, i.e. development of mealiness, accelerated softening relative to that of nonchilled fruit and nonuniform surface colour development. The firmness of all fruit decreased during ripening and chilled storage when measured by flat plate compression and puncture, especially during the early stages of ripening of nonchilled and prechilled fruit. The compression firmness of pericarp tissue similarly decreased during ripening of nonchilled and prechilled fruit, but was maintained during chilling. Total moisture content (ca 94%) of tissue, uronide content (32‐35% w/w) and extracted β‐galactosidase activity did not differ significantly (P > 0.05) among fruit during ripening and chilled storage. The degree of uronide methyl esterification in ethanol‐insoluble solids prepared from pericarp tissue (EIS) was relatively low for all fruit. i.e. <40%. EIS from which greater levels of pectinesterase were extracted (i.e. nonchilled>chilled>prechilled) exhibited decreased levels of uronide methyl esterification. Markedly elevated levels of β‐glucosidase activity were extracted from prechilled EIS. Total polygalacturonase activity (mainly as PGI) and autolysis of enzyme‐extracted EIS were inversely correlated (P≤ 0.05) only with the loss of nonchilled fruit and tissue firmness and prechilled fruit firmness. Results suggest a possible role for β‐glucosidase in textural changes of prechilled fruit and tissue (e.g. loss of firmness, development of mealiness) and also implicate loss of skin strength in the softening of whole fruit during chilling.
The regulation of nitrogen accumulation in the grain of wheat plants (Triticum aestivum)
Authors: Barneix Atilio J. , Arnozis Patricia A. , Guitman Maria R.
Published: May 2006

Nitrogen accumulation in the ear of wheat plants (Triticum aestivum L. cv. Klein Chamaco) during ear growth was studied under 4 experimental conditions. Plants were grown in pots with Perlite or soil, and fertilized with nutrient solutions. In one experiment the plants were grown in a greenhouse and supplied with high (16mM) or low (1.6 mM) N in the nutrient solutions until anthesis, and then with or without nitrogen supply until ripening. In a second experiment the plants were grown with high N supply until anthesis, and then for half of the plants light intensity was decreased by 50%, and at the same time. N supply was terminated for half of the plants within each light treatment. A third experiment was similar to the previous one, but was carried out in a growth cabinet under 20% of the maximal irradiance in the greenhouse. In a fourth experiment half the ear was excised at anthesis in half of the plants, and these plants were then supplied with or without nitrogen.

In all experiments there was a linear relation between the rate of N accumulation and the rate of ear growth. A wide range of final individual grain weights and N concentration was observed among the experiments. The same maximum N concentration was observed for all grain sizes, although the N concentration could be different between grains of the same size. The grain N concentration correlated with the rate of N accumulation per unit of ear weight increase during ear growth. It is suggested that in wheat plants there is a dependence of nitrogen transport on carbon transport to the ear, and to the ear, and that the final grain N concentration is determined by the N/C ratio exported from the vegetative tissues.
Pyrophosphate‐dependent phosphofructokinase from pollen: properties and possible roles in sugar metabolism
Authors: Nakamura Norio , Suzuki Yoshiomi , Suzuki Hiroshi
Published: May 2006

To evaluate the role of pyrophosphate‐dependent phosphofructokinase (PFP. EC 2.7.1.90) in the sugar metabolism of pollen. its occurrence and properties were studied in pollen grains of several plants including camellia (Camellia japonica L.). In all pollen samples, PFP was strongly activated by fructose‐2,6‐bisphosphate (F2,6BP), and the activity of F2,6BP‐activated PFP was higher than that of phosphofructokinase (PFK. EC 2.7.1.11). PFP partially purified from camellia pollen required Mg2+ for activity with an optimum at 1 mM. and was almost unaflected by a variety of metabolites at 1 mM. Its molecular mass was around 220 kDa, and apparent Km values for F6P, PPi. F1, 6BP and Pi were 294, 4, 20 and 580 uM, respectively. The levels of F2.6BP. PPi and F6P in camellia pollen were sufficent to support the forward reaction by PFP, and PFP, was 20‐ to 40‐fold more active than PFK during pollen growth. These results suggest that pollen PFP plays a role in glycolysis but not gluconeogenesis. and the possible relevance of this to pollen tube growth is discussed.
The role of thylakoid lipids in the photodamage of photosynthetic activity
Authors: Sharma Prabhat Kumar , Singhal Gauri S.
Published: May 2006

The effect of excess light at 10 or 30°C under aerobic or low O2 condition on peroxidation of thylakoid lipids and primary photochemistry of photoinsynthesis was studied in wheat (Triticum aestivum L. cv. HD 2329). Photoinhibitory damage to photosythesis was directly proportional to the peroxidation of thylakoid lipids. Photoinhibitory treatment given under low O2 conditions resulted in significantly less peroxidation of the primary photochemistry of photosythesis measured using chlorophyll fluorescence and photosythetic electron trasport. Short term recovery of Fv/Fm ratio was fast while thylakoid lipids did not show much recovry. However, recovery (of Fv/Fm ratio and thylakoid lipids) was almost complete within 12 h after photoinhibition treatment. A possible relationship between peroxidation of thylakoid lipids and photodamage to photosynthesis is discussed.
Changes in pigment levels, Rubisco and respiratory enzyme activity of Ficus benjamina during acclimation to low irradiance
Authors: Lance C. J. , Guy C. L.
Published: May 2006

The objective of the present study was to determine the influence of reduced irradiance on the activities of ribulose bisphosphate carboxylase‐oxygenase (Rubisco) and respiratory enzymes. Rooted cuttings of the tropical epiphyte. Ficus benjamina L., were grown in a shaded environment that excluded approximately 50% of the natural photosynthetically active irradiance (890 μmol m−2 s−1) for 4 months. Established plants were transferred and grown for 10 months under a range of irradiance levels with daily average maxima varying from a full‐sun environment to 20% full sun (100%−1735; 50%−890; 40%−695; and 20%−303 μmol m−2s−1). Chlorophyll, carotenoid and soluble protein content increased in Ficus leaves as irradiance level decreased, while Rubisco increased on a fresh weight basis but decreased on a protein basis. Glycolytic enzymes, enolase and pyruvate kinase, showed higher activities in full‐sun plants on a protein and fresh weight basis. However, the activity of two mitochondrial enzymes, aconitase and malate dehydrogenase, was not different under the various irradiance levels. When transferred to a very low irradiance environment (18 μmol m−2 s−1), mature leaves exhibited increased chlorophyll and carotenoid levels regardless of previous irradiance treatment. Exposure to very low irradiance resulted in a large increase in enolase and pyruvate kinase activities. Only plants grown under full sun conditions showed a decline in Rubisco activity following growth at very low irradiance. Together, these studies demonstrate the ability of mature leaves of Ficus to biochemically adjust photosynthetic and respiratory components over a wide range of irradiance.
Cytokinins in cut carnations. X. The effect of stem length and holding time on the transport and metabolism of [8‐14C]6‐(benzylamino)purine
Authors: Upfold S. J. , van Staden J.
Published: May 2006

Stem length and to a lesser extent holding time influenced the transport of [8‐14C]6‐(benzylamino)purine (BA) within the carnation flower (Dianthus caryophyllus L.). A stem length of 40 cm as compared to one of 10 cm resulted in a lower amount of BA reaching the carnation flower head when the flowers were held in solution for 3 to 24 h. There was also a slight delay in cytokinin movement from, as well as increased metabolism within, the stem tissues. Consequently levels of radioactivity and the nature of metabolites produced in the upper floral components were influenced by movement through the stem. In the flower head the receptacle was the strongest sink for flowers with 10 cm stem lengths. A metabolite tentatively identified as ribosyl‐benzylaminopurine [9R]BA was the major compound formed in all flower components. This metabolic step appeared to be reversible. Various minor stable metabolites and possible breakdown products were also produced.
Low temperature influence on flowering in Citrus. The separation of inductive and bud dormancy releasing effects
Authors: García‐Luís A. , Kanduser M. , Santamarina P. , Guardiola J. L.
Published: May 2006

The flowering response of Owari Satsuma mandarin (Citrus unshiu Marc) to low temperature treatments has been determined using potted trees and in vitro bud cultures. In potted trees the chilling treatments released bud dormancy and enhanced both sprouting and flowering, but these two responses could not be separated. However, bud cultures showed no dormancy, and a specific effect of low temperature on flower induction was demonstrated. Low temperature appears to have a dual effect, releasing bud dormancy and inducing flowering. Potential flower buds have a deeper dormancy than vegetative buds, and the first stages of flower initiation seem to occur before the winter rest period.
Expression of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase activity in maize tissues
Authors: Ji Wan , Hatzios Kriton K. , Cramer Carole L.
Published: May 2006

The activity of the enzyme 3‐hydroxy‐3‐methlglutaryl‐coenzyme A reductase (HMGR, EC 1.1.1.34) is highly expressed in 4‐day‐old etiolated seedlings of normal (cv. DeKalb XL72AA), dwarf (d5) and albino (lw3) maize (Zea mays L.). HMGR activity of maize seedlings appeared to be exclusively associated with the microsomal rather than the plastidic fraction of maize cells. Maize tissues with high meristematic activity such as germinating seeds, leaf bases, root tips and the site of origin of lateral roots contained high levels of microsomal HMGR activity. The activity of HMGR extracted from leaf tips of normal, dwarf and albino maize seedlings is regulated by light. Microsomal HMGR activity from leaf tips of 4‐day‐old maize seedlings was inhibited significantly following exposure to strong light (600 μmol m−2 s−1) for more than 10 h. By comparison, microsomal HMGR activity from leaf bases and root tips of maize was not inhibited by exposure to strong light. These results suggest that the microsomal HMGR which is highly expressed in maize may be related to sterol biosynthesis and membrane biogenesis rather than plastidic‐associated isoprenoid synthesis and that light may regulate HMGR activity indirectly by increasing cell differentiation.
Aluminium effects on Scenedesmus obtusiusculus with different phosphorus status. I. Mineral uptake
Authors: Greger Maria , Tillberg Jan‐Eric , Johansson Monica
Published: May 2006

Synchronously growing cultures of the unicellular green alga Scenedesmus obtusiusculus were cultivated for 24 and 72 h in the presence or absence of phosphorus. Aluminium chloride (37, 74, 111, 148, 185, or 222 μmol) was added daily to 1 l cell suspension at the end of the cell division phase. As AlCl3 decreases the pH of the growth medium, controls were run in media with low pH in the absence of AlCl3. Samples for analysis of the internal (net uptake) and external (bound to cell surface) levels of Al, Mg, P, Ca, and Fe were taken every second hour during a 24 h period or once after 72 h.

The investigation shows that the intracellular aluminium in Scenedesmus affects the nutrient status of the cells. A high intracellular level of Al is in consort with an enhancement of the intracellular fractions of Mg, P, Ca and Fe. The increase in net uptake of the minerals measured in the presence of Al is not due to an Al‐induced lowering of the pH, caused by Al. The concentrations of Al, Mg, P, Ca and Fe in the cells are generally lower during the dark period of the cell cycle, when the cells are dividing, than during the light period. A peak in mineral concentration of the cells could be monitored in the middle of the 24 h life cycle of the cells. The intracellular Al level is higher when the growth medium is low in P than in phosphorus‐rich medium, due to precipitation of aluminium‐phosphate both in medium and at cell surfaces. The extracellular Al and P fractions are thus higher in the presence than in the absence of P. The highest Al content monitored in the cells is about 100 nmol Al (106 cells)−1. A large fraction of Al initially taken up after addition to the medium is subsequently released from the cells during the 24 h cell cycle. The results are interpreted as Al effects on the plasma membrane, thus indirectly affecting various mechanisms for ion transport across the membrane. There are also indications that a surface covered with aluminium‐phosphate, formed at high P level in the medium, may prevent ion uptake.
Metabolism of [14C]‐indole‐3‐acetic acid by soybean callus and hypocotyl sections
Authors: Lee T. T. , Starratt A. N.
Published: May 2006

Metabolism of indole‐3‐acetic acid in soybean [Glycine max (L.) Merr.] was investigated with [1‐14C]‐ and [2‐14C]‐indole‐3‐acetic acid (IAA) applied by injection into soybean hypocotyl sections and by incubation with soybean callus. Free IAA and its metabolites were extracted with 80% methanol and separated by high performance liquid chromatography with [3H]‐IAA as an internal standard. Metabolism of IAA in soybean callus was much greater than that in tobacco (Nicotiana tabacum L.) callus used for comparison. High performance liquid chromatography of soybean extracts showed at least 10 metabolite peaks including both decarboxylated and undecarboxylated products. A major unstable decarboxylated metabolite was purified. [14C]‐indole‐3‐methanol (IM) was three times more efficient than [2‐14C]‐IAA as substrate for producing this metabolite. It was hydrolyzable by β‐glucosidase (EC 3.2.1.21), yielding an indole and D‐glucose. The indole possessed characteristics of authentic IM. Thus, the metabolite is tentatively identified as indole‐3‐methanol‐β‐D‐glucopyranoside. The results suggest that soybean tissues are capable of oxidizing IAA via the decarboxylative pathway with indole‐3‐methanol‐glucoside as a major product. The high rate of metabolism of IAA may be related to the observed growth of soybean callus with high concentrations of IAA in the culture medium.
Effects of estrone and 17 β‐estradiol on vegetative growth of Medicago sativa
Authors: Shore Laurence S. , Kapulnik Yoram , Ben‐Dor Bruria , Fridman Yechezkial , Wininger Smadar , Shemesh Mordechai
Published: May 2006

Alfalfa (Medicago sativa L.) plants were grown in the absence or presence of the steroidal estrogens, estrone and 17β‐estradiol, under varying conditions. Plants were analysed for the following parameters: plant weight, estrogen content, phytoestrogen content, degree of nodulation and nitrogen fixation activity. It was found that under controlled greenhouse conditions: (1) Treatment with estrogens in the range of 0.005 to 0.5 μg 1−1 increases both shoot and root dry weitht. In contrast, estrogen in concentrations of 50 to 500 μg 1−1 decreases plant growth. (2) The effect of estrogen of growth is most marked in the absence of nitrogen. (3) Estrone is more effective in increasing growth than 17 β‐estradiol. (4) In the plants where estrogen induced growth there was no significant increase in nitrogen fixation activity and nodule number. (5) Endogenous estrogen content of the plant did not increase at concentrations (0.005‐0.5 μg 1−1) which increased vegetative growth. (6) Endogenous estrogen content of the plant did increase at concentrations of estrogen (50‐500 μg 1−1 which inhibited vegetative growth and nodule weight. It can be concluded that estrogen in concentrations found in sewage water (0.3 μg estrogen 1−1) can affect the vegetative growth of alfalfa plants.
Enhancement of NaCl tolerance in Arabidopsis thaliana by exogenous L‐asparagine and D‐asparagine
Authors: Lehle Fredric R. , Chen Futai , Wendt Karen R.
Published: May 2006

The tolerances of Columbia Arabidopsis thaliana (L.) Heynh. to NaCl, L‐asparagine (L‐Asn) and D‐asparagine (D‐Asn) during seedling establishment on sterile agar medium were determined. Germination and the establishment of upright seedlings with expanded green cotyledons were increasingly inhibited by NaCl concentrations from 20 to 180 mM and radicle growth was prevented at 225 mM NaCl. Tolerance of established seedlings to NaCl was similar at these concentrations. Seedling establishment was prevented at 20 mM L‐Asn and 60 mM D‐Asn, but L‐Asn was not toxic to established seedlings. At lower concentrations, exogenous L‐ and D‐Asn enhanced NaCl tolerance during germination and seedling establishment. Inhibition of seedling establishment by NaCl concentrations below 225 mM was reduced by the addition of L‐ and D‐Asn to the medium. Maximal reduction of NaCl inhibition occurred between 2 and 4 mM for both L‐ and D‐Asn. Higher concentrations of NaCl prevented establishment whether exogenous Asn was present or not. Reduction of NaCl inhibition occurred to the same extent whether L‐Asn was presented simultaneously with the NaCl or preloaded for up to 24 h. The total seedling content of Na+ increased about 4‐fold to 55 μg (mg dry weight)−1 as the medium concentration of NaCl was increased from 9 μM to 150 mM NaCl. Total K+ content declined about 80% from about 34 μg (mg dry weight)−1 over the same range of NaCl concentrations. The Na+ uptake and K+ efflux by whole seedlings were similar whether or not NaCl tolerance was increased by exogenous Asn.