bluuebunny/crossref_metadata_2025 huggingface dataset:
Seed germination of a tropical rain forest pioneer tree (Heliocarpus donnell‐smithii) in response to diurnal fluctuation of temperature
Authors: Vázquez‐Yanes C. , Orozco‐Segovia A.
Published: April 2006

The tropical rain forest pioneer tree Heliocarpus donnell‐smithii Rose establishes itself only in light gaps of the forest canopy. A series of experiments with fluctuating temperatures have shown that the germination is increased if the temperature rises above 31°C during a few hours each day. The laboratory experiments were complemented with determinations of the seed viability in the soil each month during one year, and with determinations of germination under the natural diurnal fluctuation of temperature in a forest gap. Germination increases under fluctuating temperatures, and the seeds can remain dormant when buried in the soil during several months. The diurnal heating of the soil of light gaps as contrasted with the almost constant temperature under undisturbed canopies may be a precise environmental indicator of appropriate conditions for germination and establishment of the pioneer heliophytes of the rain forest.
Sensitivity to drying in vitro of enzymes in mitochondrial subfractions from Vicia faba seed
Authors: Priestley David A. , Bruinsma Johan
Published: April 2006

In order to investigate the persistence of membrane and matrix functions following desiccation, enzymic activities were studied in Vicia faba L. seed mitochondrial subfractions subjected to drying and rehydration in vitro. Mitochondria were prepared after 0, 12 and 24 h of seed imbibition. These were fractionated into inner membranes (“submitochondrial particles”), outer membranes (12 and 24 h only) and the soluble matrix. Enzyme activities associated with the inner membrane and matrix were found to increase several‐fold during the first 12 h of imbibition. The two matrix enzymes examined, malate dehydrogenase and glutamate dehydrogenase, were insensitive to in vitro drying at all stages of imbibition. The membrane‐bound activities from 12 h and 24 h imbibed material, antimycin A‐sensitive NADH: cytochrome c oxidoreductase and (Fo‐F1)‐ATPase of the inner membrane and antimycin A‐insensitive NADH: cytochrome c oxidoreductase of the outer membrane, were moderately sensitive to dehydration. The F1‐ATPase solubilized from the inner membrane (Fo‐F1) complex was much less sensitive to drying, provided this was done at room temperature.

Mitochondria posessing their outer membranes could not be prepared from dry seed. The antimycin A‐sensitive NADH: cytochrome c oxidoreductase from inner mitochondrial membranes of unimbibed seed was extremely sensitive to desiccation in vitro, about 75 to 80% of the activity being lost. This loss could be somewhat reduced by addition of glycerol or sucrose before drying.

It is concluded that uncontrolled desiccation results in major damage to some of the membrane‐bound enzymic systems in mitochondria, whereas activities in the soluble fraction are remarkably tolerant of desiccation.
Adenosine nucleotides and ATP synthesizing enzymes in conidia of Aspergillus niger
Authors: Perl M.
Published: April 2006

In crude conidia extracts of Aspergillus niger, 650 pmol AMP/mg protein was found but no ADP or ATP could be detected. Cell‐free extracts from the conidia produce ATP in the presence of AMP and phosphoenolpyruvate. The system is Mg2+ ‐dependent and highly stimulated by increases in the viscosity of the incubation media. The examination of enzymes involved in the ATP synthesis, revealed the presence of adenylate kinase (EC 2.7.4.3) and pyruvate kinase (EC 2.7.1.40) activity. The pyruvate kinase is stimulated in viscous incubation media. A 30% polyethyleneglycol concentration was found to be an optimal viscous medium. Adenylate kinase was unaffected by viscosity changes.
Light‐dependent rubidium uptake into isolated mesophyll protoplasts from leaves of Pisum sativum
Authors: Leurs C. J. , Winter H. , Wiersema P. K. , Helder R. J.
Published: April 2006

A method is described for the isolation of large amounts of physiologically active protoplasts from leaves of Pisum sativum L. Rubidium uptake was determined after separation of the intact protoplasts from the loading medium by rapid centrifugation through a phthalate step gradient. In freshly isolated mesophyll protoplasts of Pisum sativum, rubidium uptake was carbonylcyanide‐p‐trifluoromethoxyphenylhydrazone reduced by metabolic inhibitors such as 5 μM, 0.1 mW cyanide, 2 μM DCMU and 5 mM arsenate and by dark incubation. Reduction of rubidium uptake by inhibition of aerobic respiration or the photosynthetic electron transport system demonstrates that both processes play a role in the energy supply for membrane transport in these protoplasts.
Accumulation and localisation of sodium ions within the shoots of rice (Oryza sativa) varieties differing in salinity resistance
Authors: Yeo A. R. , Flowers T. J.
Published: April 2006

Oryza sativa L. (rice) is a salt‐sensitive crop species which is relatively ineffective in controlling the influx of sodium and chloride ions to the shoot. Nonetheless, there is considerable varietal and individual variability in salinity resistance, much of which must derive, therefore, from differences in the fates and subsequent effects of saline ions after they have entered the plant. The destination of sodium ions within the plant has been investigated, in saline conditions, by examining the time‐course of sodium ion concentrations in different leaves of four varieties and breeding lines of rice of differing salinity resistance. Radionuclide tracers were employed to study short term effects and the degree of retranslocation of these sodium ions. Sodium was not distributed uniformly but accumulated in the older leaves before the younger ones. At least some leaves were maintained at sub‐lethal salt concentrations in at least the more salt resistant varieties. Radionuclide tracer studies showed that the discontinuous distribution of sodium (from leaf to leaf) is constitutive, and cannot be explained by time of exposure or differential leaf growth rates, and that significant quantities of sodium were not subsequently retranslocated, either within the plant or to the root medium.
Sterols and frost hardening of winter rape
Authors: Sikorska Elzbieta , Farkas Tibor
Published: April 2006

Winter rape (Brassica napus L., var. olifera cv. Górczanski) seedlings were exposed to hardening conditions and the content and composition of free sterols as well as the ratio of free sterols to total phospholipids were determined. There was a reduction in free sterol content in the leaves at the most advanced stage of hardening. The ratio of free sterol to total phospholipids was significantly reduced by hardening due to a decrease in the level of the former and an increase in that of the latter compounds. There was a negative correlation between this ratio and the temperature at which half of the seedlings died. Thus, adaptation of membranes to temperature takes place also at the level of sterol‐phospholipid interactions. Exposing seedlings already hardened to freezing temperatures caused injury higher than 50%, and brought about a drastic increase in the level of free sterols and an elevation in the ratio of free sterols to phospholipids. The results are discussed in terms of a possible role of the molecular architecture of membranes in surviving at subzero temperatures.
Elongation and gravireaction of intact and segmented roots: light effects
Authors: Beffa Roland , Pilet Paul‐Emile
Published: April 2006

Using a macrophotographic technique, kinetic studies were performed on growth and gravireaction, both measured on maize (cv. LG 11) roots. When using intact roots, it was found that the growth rate decreased two hours after the beginning of the gravistimulus, the rate of root curvature being optimal at that time. These two processes are greater in light than in the dark. Subsequently, the curvature rate decreased rapidly to zero in the dark but, in light, it continued for at least a further three hours. There was then a recovery of elongation in darkness whereas in light growth rate remained low. A comparative analysis between root segments and intact roots suggests that the correlation between the growth and the gravireaction rates differs according to the system studied and that light has a greater effect on growth rate when the roots are subject to gravitational stimuli. Present data are discussed in terms of hormone balance between several endogenous regulators.
Gas exchange in a 20‐year‐old stand of Scots pine
Authors: Troeng E. , Linder S.
Published: April 2006

The rates of net photosynthesis and transpiration of one‐year‐old shoots were measured in situ in five different positions within the crown of a young Scots pine (Pinus sylvestris L.). Measurements were carried out on south‐ and north‐facing shoots on the third and sixth whorls, respectively, and on an east‐facing shoot on the ninth whorl. In another investigation the rates of gas exchange of one‐year‐old shoots on the third whorl of eight different trees were studied. The measurements were made during June and July, 1977, under non‐limiting conditions of soil water. The daily rates of net photosynthesis in whorls three and six followed the light conditions closely, with higher rates for the south side of each whorl and higher for whorl three than six. On whorl nine the shoot had a higher light compensation point and a low rate of photosynthesis at light saturation compared to the other shoot positions. The quantum yield for the shoot on the lowest whorl, as estimated from the linear part of the light response curve, was 50% lower than for shoots on whorl three and six.

The variation in transpiration rates was pronounced within the crown as an effect of differences in the absolute value and diurnal course of stomatal conductance. The variation in net photosynthesis was small between different trees while the variation in transpiration was much higher. Thus the variation in water use efficiency was great. It is concluded that it is possible to extrapolate measurements of net photosynthesis from individual trees up to a stand level without introducing large errors in the estimate. More caution must be paid before extrapolating tree transpiration up to stand transpiration. However, before an extrapolation of gas exchange is made from tree to stand level the variation in net photosynthesis and transpiration rate within the crown must be known.
Effect of L‐methionine‐DL‐sulphoximine, a specific inhibitor of glutamine synthetase, on ammonium and nitrate metabolism in the unicellular alga Cyanidium caldarium
Authors: Di Martino Rigano Vittoria , Vona Vincenza , Fuggi Amodio , Rigano Carmelo
Published: April 2006

In the unicellular alga Cyanidium caldarium nitrate utilization is strongly inhibited by ammonium and it is resumed when ammonium has been depleted. In the presence of L‐methionine‐DL‐sulphoximine (MSX), which prevents ammonium assimilation through a specific irreversible inhibition of glutamine synthetase, nitrate reduction is no longer inhibited by ammonium, and most of the ammonium derived from nitrate reduction is excreted into the external medium. However, in the presence of MSX, nitrate reduction to ammonium proceeds at a reduced rate (45 to 70% of the control); this is particularly marked at low nitrate concentration. It is hypothesized that either MSX or accumulating ammonium bring about decrease in the rate of nitrate entry into the cell.
Effects of cyanide, salicylhydroxamic acid, and temperature on respiration and germination of spores of the fern Sphaeropteris cooperi
Authors: Reynolds Thomas L.
Published: April 2006

During the first 96 h of culture, germinating spores of the fern Sphaeropteris cooperi (F. v. Muell.) Tryon showed a gradual rise in respiratory activity to a maximum of about 6.5 μl 02 h−1 mg−1 dry wt. This was followed by a transitory decline in rate, concluded by a second respiratory rise preceding the emergence of the rhizoid after 192 h of culture. Oxygen uptake during the first 120 h of germination was insensitive to 1 mM potassium cyanide (KCN) but was inhibited by 1 mM salicylhydroxamic acid (SHAM); however, beyond this time cyanide showed increasing inhibitory effectiveness whereas SHAM became less effective. Regardless of time of application, KCN had no effect on germination. Maximum inhibition of germination by SHAM was achieved if applied up to 120 h after culture initiation, after which spores became insensitive to SHAM. Heat treatment (50°C for 90 min) during the cyanide‐resistant phase of respiration (0 h–120 h) induced cyanide‐sensitive respiration and completely inhibited spore germination. Elevated temperatures had little effect if applied during the cyanide‐sensitive phase (beyond 120 h). Temperature inhibited spores regained their ability to germinate if maintained in culture until the cyanide‐resistant pathway was restored and then subjected to a second photoinductive light treatment. These results suggest the presence and possible involvement of the cyanide‐resistant, alternative respiratory pathway during germination of Sphaeropteris cooperi spores.
Influence of 2,4‐D and low pH on potassium, ammonium and nitrate uptake by rice roots
Authors: Haunold Ernst
Published: April 2006

The uptake of the auxin type herbicide 2,4‐D into rice seedlings (Oryza sativa L. cv. Dunghan Shali) and its effects on the K+, NH+4 and NO3 ion uptake and the K+ content were investigated at different pH values. A short incubation of the roots in 0.01 mM 2,4‐D caused a marked ion uptake inhibition only at low pH. The non‐auxin type herbicide benthiocarb did not produce such an inhibitory effect. Lowering of the pH in the external medium led to an increased 2,4‐D uptake by the roots. These results can be explained by the increased H+ permeability of the membranes, allowing a more rapid entrance of 2,4‐D into the root cells, thereby inhibiting the active ion uptake. Rice roots not subjected to 2,4‐D treatment responded to H+ stress with an increased anomalous K+ uptake and a decreased K+ content. With reference to the effects of pH changes on the ion and 2,4‐D uptake, possible transport mechanism of NH+4 and 2,4‐D are briefly discussed.
Glutamine synthetase isoforms in leaves of a C4 plant: Sorghum vulgare
Authors: Hirel Bertrand , Gadal Pierre
Published: April 2006

In Sorghum vulgare L. (cv. INRA 450) leaves, two isoforms of glutamine synthetase GS1 and GS2 were identified by DEAE Sephacel chromatography and polyac‐rylamide gel electrophoresis. GS1 was present both in etiolated and green leaves and its activity remained constant during the greening process. In green leaves another isoform GS2 was identified that was responsible for a 33% increase in total glutamine synthetase activity after light exposure. The two isoforms differed in their heat stability but exhibited similar pH optima and Km values for L‐glutamate. The total glutamine synthetase activity was equally distributed between mesophyll and bundle sheath cells; moreover in the two types of cells both GS1 and GS2 were present in the proportions of 67% and 33% of the total respectively. In mesophyll cells the two isoforms had a different subcellular distribution: GS2 was localized in the chloroplast and GS1 in the cytosol.
Artificial ice crystal formation in excised short shoots of Pinus silvestris L.
Authors: von Fircks H. A. , Christersson L.
Published: April 2006

Controlled freezing methods adopted for Thermal Analysis (TA) and Differential Thermal Analysis (DTA), were used to investigate the capacity for subcooling short shoots of Pinus silvestris L. of various ages. Both methods showed that there were no differences in subcooling temperature along the length of the short shoots. Differences in age and water content have a significant effect on the freezing profiles. Short shoots of the current years growth were able to subcool to about −13°C. One‐year‐old short shoots subcooled to about −9°C. There were no apparent variations in subcooling temperatures from June to September. Rainfall or dry periods had no effect on subcooling temperatures. The freezing profiles of living material was characteristic and was not repeated during subsequent freezing cycles. Detection of ice crystal formation during refreezing experiments indicated whether short shoots were alive or dead.
Effect of potassium on the water potential, the pressure potential, the osmotic potential and cell elongation in leaves of Phaseolus vulgaris
Authors: Mengel Konrad , Arneke Wilhelm‐Wolfgang
Published: April 2006

The effect of potassium on the water potential, the osmotic potential and the pressure potential in younger and older leaves ofPhaseolus vulgarisgrown in hydroponic culture was studied. Inadequate potassium supply resulted in an increase of the osmotic potential. In the older leaves the water potential was raised, in the younger leaves the pressure potential was depressed in the treatment insufficiently supplied with potassium as compared with leaves with an adequate potassium supply. Cell size of the younger leaves was smaller in the treatment with the low K+supply in comparison with the leaves well supplied with K+. Potassium had a beneficial effect on plant growth, especially on fresh matter production. The water status of leaves (water content, pressure potential, osmotic potential) responded more sensitively to potassium supply than dry matter production. Besides organic N and organic anions, K+was the most abundant solute found in the press sap of the leaves. From the results it is concluded that K+is indispensible for attaining an optimum potential (turgor) in young leaves which in turn has an impact on plant growth.
Photooxidative inhibition of nitrate reductase during chilling
Authors: Bakker Niek , Van Hasselt Philip R.
Published: April 2006

The effect of a temperature close to the freezing point (chilling) on the nitrate reductase system of leaf discs of Cucumis sativus L. cv. Kleine Groene Scherpe was determined in the absence and presence of light. The capacity of leaf discs in the light (250 μE m−2s−1) at 20°C to increase in vivo and in vitro nitrate reductase activity, was unaffected by chilling pretreatment in the dark, but 4 h of chilling pretreatment in the light (250 μE m−2s−1) decreased the capacity to less than 50% of the unchilled control. The chilling inhibition of the capacity to increase nitrate reductase activity was of a photooxidative nature since it only occurred in the presence of light and oxygen. Plants grown at a low light intensity (65 μE m−2s−1) lost 95% of their capacity to increase nitrate reductase activity, while plants grown at 195 μE m−2s−1 retained 80% of their nitrate reducing capacity after 6 h chilling pretreatment in the 250 μE m−2s−1 light. Previously induced nitrate reductase activity was also affected by light during chilling. A lag phase of 7 h preceded a fast phase of decrease in activity. Both in vivo and in vitro activity decreased to 15% of the control value after 18 h of chilling in the light. It is concluded that the induction mechanism of nitrate reductase is primarily affected by photooxidation during chilling. The decrease in nitrate reductase activity is attributed to a decrease in the amount of activity enzyme.
The physiological basis of seed dormancy in Avena fatua L. I. Action of the respiratory inhibitors sodium azide and salicylhydroxamic acid
Authors: Upadhyay Mahesh K. , Naylor James M. , Simpson Graham M.
Published: April 2006

The dormancy breaking effect of sodium azide was studied in seeds of several genetically pure lines of Avena fatua L. isolated from field populations. Sodium azide (0.8 and 1 mM) induced germination in several dormant lines (characterized by long term dormancy) after two weeks of treatment. By about five weeks, germination was nearly complete in azide treated seeds as compared to little or no germination in controls. (2‐chloroethyl) trimethylammonium chloride (an inhibitor of gibberellin biosynthesis) completely inhibited the azide effect suggesting that stimulation of germination by azide requires gibberellin biosynthesis. Azide was very effective in breaking dormancy in lines AN‐51, AN‐86, AN‐127 and AN‐265, but failed to induce germination in Montana 73. In this line there was a synergism between azide and gibberellic acid in promotion of germination. Thus, at least two metabolic blocks are involved in the stimulation of germination in this line. Salicylhydroxamic acid (an inhibitor of alternative respiration) at 3 mM completely inhibited the germination induced by 1 mM azide. At this concentration, salicylhydroxamic acid did not inhibit germination in 1) genetically nondormant seeds (line SH‐430), 2) afterripened seeds of a dormant line (AN‐51), and 3) gibberellic acid‐treated dormant seeds. These findings suggest that salicylhydroxamic acid‐sensitive process(es), presumably alternative respiration, is necessary for the stimulation of germination in the presence of azide, but not in the germination of genetically nondormant, gibberellic acid‐treated dormant, or afterripened seeds.
Transport and metabolism of labelled abscisic acid in broad‐bean plants (Vicia faba L.)
Authors: Everant‐Bourbouloux Andrée
Published: April 2006

The movement of 2‐14C‐abscisic acid applied to a mature leaf of broad‐bean plants (Vicia faba L. cv. Aguadulce) was investigated by liquid scintillation counting and autoradiography. The radioactivity was readily transported into the whole plant by the phloem after 90 min. Thereafter, radioactivity moved towards the upper part of the plant, where it accumulated in the young growing leaves and in the apical bud. During transport, 2‐14C‐ ABA was slightly metabolized, and a subsequent rapid metabolism occurred in the young leaves of the apical part of the plant and in the axillary buds released from apical dominance in decapitated plants. Transport of exogenous ABA from the apical bud presented the characteristics of a diffusion transport.
Endogenous abscisic acid levels in stems and axillary buds of intact or decapitated broad‐bean plants (Vicia faba L.)
Authors: Everat‐Bourbouloux Andrée , Charnay Dominique
Published: April 2006

Endogenous levels of abscisic acid (ABA) were measured by gas‐liquid chromatography (electron capture) in stems and axillary buds of intact or decapitated broad‐bean plants (Vicia faba L. cv. Aguadulce). Endogenous ABA was distributed in the main axis according to a concentration gradient from the apical part of the stem towards the base. Axillary buds contained ABA levels which were from 4 to 9 times higher than those in the corresponding nodes and internodes. Decapitation of the plant was followed within 6 h by a large decrease of ABA levels in all the parts of the main axis. The diminution of ABA content was the most important in axillary buds released from apical dominance. Twenty‐four hours after the decapitation, the ABA concentration further decreased in the upper parts of the stem, while no modification was observed in the basal parts of the stem containing the smallest levels of ABA.
Carbon metabolism of Frankia spp. in root nodules of Alnus glutinosa and Hippophaë rhamnoides
Authors: Huss‐Danell Kerstin , Roelofsen Wim , Akkermans Antoon D. L. , Meijer Piet
Published: April 2006

The occurrence and localization of enzymes involved in glycolysis, tricarboxylic acid cycle and glyoxylate cycle in root nodules of Alnus glutinosa (L.) Vill. and Hippophaë rhamnoides L. ssp. rhamnoides were studied. The following enzymes, catalyzing reversible steps in the glycolysis, were found in both the endophyte Frankia spp. and the plant cytosol of Alnus nodules: fructose‐1,6‐diphosphate aldolase, glyceralde‐hyde‐3‐phosphate dehydrogenase, phosphoglycerate kinase and enolase. The enzymes catalyzing irreversible steps in glycolysis, viz. hexokinase and pyruvate kinase, were detectable only in the plant cytosol. Similar results were obtained with nodule homogenates of Hippophaë. This indicates the absence of a complete glycolysis in the endophyte. Vesicle clusters of the nodule endophyte of Alnus contained various dehydrogenases of the tricarboxylic acid cycle and showed activity of glutamate oxaloacetate transaminase. Respiration studies showed that vesicle clusters take up oxygen when supplied with NAD, glutamate and malate together. No oxygen uptake was found when any of these compounds was omitted. Vesicle clusters from both Alnus and Hippophaë nodules showed no detectable activity of the glyoxylate cycle enzymes isocitrate lyase and malate synthase. Since these enzymes are known to be present in Frankia Avcll, when grown in a medium with Tween 80 as carbon source, it is suggested that the glyoxylate cycle enzymes are repressed in the root‐nodule symbioses.
The effects of diclofop‐methyl on root growth of wild oat
Authors: Donald W. W. , Parke R. V. , Shimabukuro R. H.
Published: April 2006

Diclofop‐methyl severely reduced the growth of seminal roots of wild oat (Avena fatua L.) when applied in hydroponics at 0.01 and 0.05 μM. Lateral roots emerged closer to the seminal root apex than in the controls, but coronal root number and length were unaffected at 0.01 μM. However, doses of 0.05 to 0.1 μM induced more but shorter coronal roots to emerge than for controls. At 1 μM the number and length of coronal roots were less than for controls. Root‐applied diclofop‐methyl at 1 μM inhibited emerging second leaf growth to the same extent as a foliar dip in 1 μM diclofop‐methyl without causing chlorosis as foliar treatment does. Because of limited basipetal transport of foliarly‐applied diclofop‐methyl, shoot treatment was ineffective in inducing abnormal root morphogenesis of the seminal and lateral root systems, although it caused abnormalities of the coronal root system. Time course studies were initiated to examine the effect of root‐applied diclofop‐methyl at 0.05 μM. Seminal root growth was inhibited (by diclofop‐methyl) soon after treatment, while controls continued elongating. The distance between the seminal root apex and the first lateral primordia increased in the controls within one day after treatment, but decreased in the herbicide‐treated roots. The distance between the seminal root apex and the first emerged lateral root was reduced by three days after treatment. The number of lateral primordia and emerged roots was unaffected three days after treatment. These dose‐response and kinetic results suggested that diclofop‐methyl caused a loss of apical dominance in the seminal root.
Changes in invertase activities during the photoperiodically induced bulb formation of onion (Allium cepa L.)
Authors: Lercari Bartolomeo
Published: April 2006

Onion (Allium cepa L.) tissues contain both acid and neutral invertase activity with pH optimum at 5.2 and 7.0, respectively. The acid invertase was distributed between the pellets and the supernatant while neutral invertase activity was found only in the supernatant fraction of homogenate. A decrease in acid invertase activity both in the pseudostem and in the leaf‐blade was induced by long day conditions. Under long photoperiod the neutral invertase activity disappears in the pseudostem, while the neutral invertase activity in the leaf‐blades of bulbing plants is almost constant. Thus the activity of acid and neutral invertase change during the photoperiodic‐induced bulb development but independently of each other.
Maintenance and growth respiration in shoots and roots of sunflower plants grown at different root temperatures
Authors: Szaniawski R. K. , Kielkiewicz M.
Published: April 2006

Continuous measurements of CO2‐evolution and dry matter accumulation were carried out on shoots and roots separately of intact Helianthus annuus L. cv. Autumn Beauty plants grown in nutrient solution at different root temperatures. The data were used to distinguish between growth and maintenance components of respiration. The maintenance and growth coefficients were higher in the root system than in the shoots. The overall efficiency of assimilate utilization was within the range reported in the literature. An increase in root temperature increased the maintenance part of root respiration and, to a lesser degree, also shoot maintenance respiration. Neither root nor shoot growth respiration coefficients were affected by root temperature. It is concluded that the study of whole‐plant respiration masks differences in energy utilization between shoots and roots.
Activity and properties of ribulose‐1,5‐bisphosphate carboxylase of sugarbeet plants grown under saline conditions
Authors: Heuer Bruria , Plaut Zvi
Published: April 2006

Activity and properties of sugar beet (Beta vulgaris var. Polyrave) leaf ribulose‐1,5‐bisphosphate (RuBP) carboxylase were investigated following the exposure of plants to NaCl in the range of 45 to 270 mM for 7 days. An enhancement in RuBP carboxylase activity was found both in crude extracts and in purified preparations following plant exposure to 180 mM NaCl. Kinetic properties of the enzyme were significantly affected by salinity as determined by a 4.5 fold increase in Km [HCO‐3] and Km [CO2], and a Vmax increase of 50%. Data based on polyacrylamide‐gel‐electrophoresis suggest that the molecular weight of the small subunit of RuBP carboxylase was reduced from 15,500 to 12,500 in plants grown under salinity. The large subunit was much less affected and no change was found in the whole enzyme. The enzyme isolated from plants exposed to salinity contained about 50% fewer titratable SH groups as compared with the control. The results indicate that in this plant, mild salt concentrations induced conformational changes in RuBP carboxylase which may be responsible for its tolerance to semi‐salinity.
Light‐induced absorbance changes in the fungus Verticillium agaricinum
Authors: Hsiao K. C. , Björn L. O.
Published: April 2006

Light‐induced absorbance changes were investigated in vivo in the fungus Verticillium agaricinum (Link) Corda. There was a broad light‐induced absorbance decrease in the blue and near UV with a maximum at 384 nm. An action spectrum indicated that the absorbance changes were due to photo‐bleaching of a pigment with an absorption spectrum that was similar to the action spectrum. Neither redox reactions nor energy metabolism were involved in the photo‐bleaching process. A direct comparison of action spectra for light‐induced absorbance changes and photo‐induction of carotenogenesis suggests that the photo‐bleaching may not be related to photo‐induction of carotenogenesis.
High‐performance liquid chromatographic identification and quantitation of cyclic adenosine 3′:5′‐monophosphate in higher (Phaseolus vulgaris L.) and lower (Chlorella sp.) plants
Authors: Van Onckelen H. A. , Dupon M. , De Greef J. A.
Published: April 2006

Cyclic adenosine 3′:5′‐monophosphate (cAMP) was extracted from Phaseolus vulgaris L. cv. Limburg seedlings and Chlorella sp. The cAMP was purified by charcoal adsorption, polyvinylpyrrolidone (PVP) and Dowex 50 W × 8 column chromatography and by preparative high‐performance liquid chromatography (HPLC). Quantitation was achieved by combining phosphodiesterase (PDE) treatment with analytical HPLC (reversed phase ion‐pair partition chromatography) and cAMP‐dependent protein kinase activation. This provided a very specific, accurate and sensitive assay for cAMP determinations. The cAMP content found in Chlorella (70–90 pmol/g dry wt) was comparable with previous reports using other quantitation methods, whereas the endogenous concentration found in bean seedlings (92 pmol/g dry wt) was considerably lower than previously reported data.
Influence of chloramphenicol on growth and respiration of soybean (Glycine max L.) suspension cultures
Authors: de Klerk‐Kiebert Yvonne M. , Kneppers Tarcies J. A. , van der Plas Linus H. W.
Published: April 2006

By addition of chloramphenicol (CAP) to the growth medium of green soybean (Glycine max L.) cells in batch culture, growth is inhibited and the activity of the cytochrome oxidase decreases to 60% of the value found in control cells. The presence of CAP induces an enhancement of the contribution of the alternative pathway to total respiration. This enlarged contribution results both from a higher capacity of the alternative pathway and from a greater part of this capacity being used. Also in mitochondria isolated from cells treated with CAP, a higher capacity of the alternative pathway has been found, while the part of this capacity which is really used is comparable with the values found in control cells.
Physiological and biochemical changes associated with cotton fibre development. II. Auxin oxidising system
Authors: Rao N. Rama , Naithani S. C. , Singh Y. D.
Published: April 2006

Changes in IAA oxidase, and in cytoplasmic and ionically wall‐bound peroxidase activities were studied in the developing fibres of three cotton cultivars (Gossypium hirsutum L. cv. Gujarat‐67, cv. Khandwa‐2 and G. herbaceum L. cv. Digvijay), designated as long, medium and short staple cultivars, respectively. In all the three cultivars IAA oxidase activity was low during the fibre elongation phase, while the activity increased significantly during the secondary thickening phase. The increase in IAA oxidase activity in the three cultivars showed close correspondence with their respective total period of elongation. No relationship between cytoplasmic peroxidase activity and fibre development was discernible. The ionically bound wall peroxidase activity, however, recorded low levels during the elongation phase and higher levels during the secondary thickening phase. The role of wall peroxidase in cessation of elongation growth is discussed.
Cytokinin‐induced activation of polyribosomes in the protonema of Ceratodon purpureus
Authors: Gwóźdź Edward A. , Szweykowska Alicja M.
Published: April 2006

A ribosomal preparation from N6‐isopentenyladenine‐treated protonema of Ceratodon purpureus (Hedw.) Brid. exhibited an increased activity of protein synthesis in a cell‐free system as compared to a control preparation. The ratio of polyribosomes to monoribosomes was the same in both preparations, and it is assumed that an activation of pre‐existing polyribosomes was responsible for the increased efficiency in protein synthesis. An electrophoretic fractionation of the in vitro translation product showed an enhanced synthesis of some polypeptide fractions in the cytokinin variant.
Photoperiodic response of Coprinus congregatus: Effects of light breaks on fruiting
Authors: Durand Roger
Published: April 2006

Light initiated fruit‐body primordia of Coprinus congregatus Bull, ex Fr. were subjected to different dark periods (4 h to 24 h) and exposed to short blue light pulses at different times. The light break inhibited the development of primordia as did continuous light. The time of maximum sensitivity to a light break was dependent on the duration of the dark period. A short light break imposed two‐thirds of the way through the dark period produced strong inhibition of fruiting. The higher the temperature during the dark period, the lower the irradiance required for 50% inhibition of fruiting at the time of maximal sensitivity. During a very long dark period (48 h) a light break was no longer inhibitory. The light break fulfilled the light requirement for normal morphogenesis and defined the time the fruit‐bodies sporulated.
Some physiological and growth responses of Betula papyrifera seedlings to flooding
Authors: Tang Z. C. , Kozlowski T. T.
Published: April 2006

Betula papyrifera Marsh, seedlings adapted very poorly to flooding for up to 60 days. Responses to flooding included increased ethylene production; stomatal closure; leaf senescence; drastic inhibition of shoot growth, cambial growth, and root growth; decay of roots, and death of many seedlings. Flooding inhibited growth of leaves that formed prior to flooding, inhibited formation of new leaves, and induced abscission of old leaves. As a result of extensive leaf abscission, fewer leaves were present after flooding than before flooding was initiated. The drastic reduction in leaf area was associated with greatly decreased growth of the lower stem and roots. No evidence was found of adaptive morphological changes to flooding. The data indicate that intolerance of B. papyrifera seedlings to flooding is an important barrier to regeneration of the species on sites subject to periodic inundation.
The relationship of abscisic acid metabolism to stomatal conductance in Douglas‐fir during water stress
Authors: Johnson John D. , Ferrell William K.
Published: April 2006

Changes in abscisic acid and its metabolites were followed through two drought cycles in Pseudotsuga menziesii (Mirb.) Franco seedlings to determine the metabolic pathway of the hormone and its relationship to branch (stomatal) conductance. Three year‐old, intact seedlings were water‐stressed, watered, and restressed over a period of 30 days. Water potential was sampled with a pressure chamber and branch conductance with a steady‐state porometer. Needle content of abscisic acid and 2‐trans‐abscisic acid and their saponifiable conjugates were quantified with gas‐liquid chromatography. The typical water potential threshold in branch conductance, decreasing abruptly at ‐2.0 MPa, corresponded to an increase in abscisic acid content of 240 ng g−1. The relationship between abscisic acid and water potential was not definitive, though the general trend was an increase in the hormone with intensifying stress until water potential was ‐5.0 MPa, when concentration sharply declined. No adjustment to stress was observed in the relationships, but stress during the second cycle progressed more slowly. A linear relationship between abscisic acid and its conjugate indicated the importance of the interconversion of the two compounds for storage and supply of the free acid.
Endocellular distribution of calcium and Ca‐ATPases in horse‐bean roots: Possible relation to the ecological status of the plant
Authors: Monestiez M. , Lamant A. , Heller R.
Published: April 2006

The endocellular distribution of calcium has been determined and Ca‐ATPase activity measured in subcellular fractions of various species: horse‐bean (Vicia faba L., var. minor), barley (Hordeum vulgare L., var. Astrix), wheat (Triticum vulgare L., var. Hardy), lupine (Lupinus luteus L., var. Weiko III), oat (Avena sativa L. var. Zelma) which grow differently on calcareous media. The vacuolar calcium concentrations are below thermodynamic equilibrium with the medium for all plants. The deficit in vacuolar calcium is accentuated in plants which prefer calcareous soils. Membranes of such plants show weak affinity for calcium and also considerable Ca‐ATPase activity. It is suggested that low vacuolar concentration is a consequence of low cytoplasmic concentration. The role of Ca‐ATPases and the physicochemical properties of membranes in counteracting high external calcium is discussed.
Somatic embryogenesis in the opium poppy, Papaver somniferum
Authors: Nessler Craig L.
Published: April 2006

A procedure is described for the induction of somatic embryos in the opium poppy. Papaver somniferum L. Callus was obtained from seedling hypocotyls on an agar solidified medium [Murashige and Skoog (1962) Physiol. Plant. 15: 473–497] containing 0.25 mg/l (1.2 μM) kinetin and 2.0 mg/l (10.7 μM) naphtalene acetic acid (NAA). Suspension cultures were initiated from callus using a liquid medium in which 2.0 mg/l (9.0 μM) 2,4‐dichlorophenoxyacetic acid was substituted for NAA. Meristemoids, spheres of closely packed cells, developed in suspensions and on the surface of a few callus cultures. Differentiation of meristemoids into somatic embryos was accomplished by removing growth regulators from the liquid medium. Embryoids appeared morphologically normal and similar to torpedo stage embryos, however, they possessed mature tracheary elements and laticifers in areas that should have contained only procambium. Whole plants have been obtained by placing embryos in the light on solid medium that also lacked growth regulators.
Tentoxin does not cause chlorosis in greening mung bean leaves by inhibiting photophosphorylation
Authors: Duke Stephen O. , Wickliff James L. , Vaughn Kevin C. , Paul Rex N.
Published: April 2006

Effects of the fungal toxin, tentotoxin, on development and chlorophyll accumulation of plastids of primary leaves of mung bean [Vigna radiata (L.) Wilczek cv. Berken] were studied using spectrophotometric, electrophoretic, and microscopic procedures. In etioplasts of control tissues both prolamellar bodies and prothylakoids occurred, whereas small vesicles were associated with structurally distinct prolamellar bodies in tentoxin‐affected etioplasts. As determined by in vivo spectrophotometry, tentoxin‐affected etioplasts had 25% less phototransformable protochlorophyll(ide) and 35% less non‐phototransformable protochlorophyll(ide) than had control etioplasts after 5 days of dark seedling growth. Tentoxin had no effect on the rate of the Shibita shift. Protochlorophyll(ide) resynthesis in the dark immediately after protochlorophyll(ide) phototransformation was five to six times slower in tentoxintreated than in control tissues. Effects on chlorophyll(ide) content were observed within 30 min of the beginning of continuous white light exposure. In vivo measurement of cytochrome f redox activity revealed that this cytochrome was linked to light‐driven electron flow in control tissues within 20 min of the beginning of continuous white light, whereas in the tentoxin‐treated tissues there was no linkage (despite the presence of cytochromef) at any time. Coupling factor 1 was present and had potential ATPase activity in both control and tentoxin‐affected plastids. There was about sixteen times more chlorophyll in control than in tentoxin‐treated tissues in continuous as well as in intermittent (2 min light/118 min dark) light. These data are consistent with the view that tentoxin disrupts normal etioplast and chloroplast development through a mechanism unrelated to photophosphorylation.
Leaf senescence and lipid peroxidation: Effects of some phytohormones, and scavengers of free radicals and singlet oxygen
Authors: Dhindsa Rajinder S. , Plumb‐Dhindsa Pamela L. , Reid David M.
Published: April 2006

During in vitro senescence (chlorophyll loss) of oat (Avena sativa L. cv. Victory) leaf segments and of leaf discs of Rumex obtusifolius L, the activity of catalase decreases and lipid peroxidation increases. The activity of superoxide dismutase (SOD) decreases in Rumex leaf discs but changes little in oat leaf segments. Kinetin treatment of oat leaf segments, and GA3 treatment of Rumex leaf discs, inhibit decline in the enzyme activities and increase in the level of lipid peroxidation and strongly inhibit senescence. In either leaf tissue a treatment with ethanol or vitamin E (scavengers of free radicals) or with diphenylisobenzofuran (scavenger of singlet oxygen) results in a strong inhibition of lipid peroxidation and senescence, but does not affect much the decline in the SOD and catalase activities. It is concluded that, i) senscence‐associated lipid peroxidation is induced by free radicals and singlet oxygen; and, ii) kinetin and GA3 inhibit senescence mainly by a modulation of lipid peroxidation through maintaining high levels of such cellular scavengers as SOD and catalase.
Effect of cytokinin on the distribution of 14C‐glyphosate in Xanthium pennsylvanicum
Authors: Foley Michael E. , Wax Lloyd M.
Published: April 2006

Cytokinin N6‐(δ2‐isopentenyl) adenosine (i6A) was applied five times to runoff on the first leaf of Xanthium pennsylvanicum Wallr. After a 24 h application period the second leaf was treated with the herbicide methyl‐14C‐glyphosate, [N‐(phosphonomethyl)glycine]. The distribution of radioactivity was determined after 12 and 24 h. At no time after treatment did 14C‐glyphosate move preferentially into the i6A treated leaf. Radioactivity accumulated in all plant parts, but in i6A‐treated plants, there were more counts in the actively growing areas after 12 h. The primary effect of i6A after 24 h was enhanced uptake of 14C‐glyphosate into the plant. To determine if the increased uptake and altered movement of 14C‐glyphosate was due to a cytokinin‐induced transpiration increase, leaf diffusive resistance was measured. Leaf diffusive resistances were unaffected by i6A during the 48 h after application. By 12 h after the application of glyphosate, the herbicide was found not to affect the cytokinin content in the Xanthium root tips.
Studies on the mechanisms of ozone tolerance: Cytokinin‐like activity of N‐[2‐(2‐oxo‐1‐imidazolidinyl)ethyl]‐N'‐phenylurea, a compound protecting against ozone injury
Authors: Lee E. H. , Chen C. M.
Published: April 2006

The cytokinin‐like activity of the growth regulating chemical EDU, N‐[2‐(2‐oxo‐1‐imidazolidinyl)ethyl]‐N′‐phenylurea, was determined and compared with the actitivity of kinetin using the tobacco callus bioassay. EDU has a pronounced stimulatory effect on callus growth at concentrations of 5 × 10−4 and 1 × 10−3M but was 5 000 times less potent than the synthetic cytokinin, kinetin. Senescence regulation and oxidant resistance induced by EDU and kinetin were also studied. EDU retarded the breakdown of chlorophyll, protein and RNA in 03‐sensitive tobacco leaf discs during senescence. EDU was much more effective in arresting senescence and in protecting against 03 injury than kinetin. Results indicate the EDU‐induced plant tolerance to 03 phytotoxicity may be indirect through enzyme induction regulation.
Light‐dependence of paraquat‐initiated membrane deterioration in bean plants. Evidence for the involvement of superoxide
Authors: Chia L. S. , McRae D. G. , Thompson J. E.
Published: April 2006

Treatment of primary bean leaves with 10 mg/I paraquat induces the formation of gel phase lipid in microsomal and chloroplast membranes and enhances the activity of superoxide dismutase, but only if the leaves are exposed to light. These light‐dependent changes in membrane lipid phase properties show a close temporal correlation with enhanced O27 production by illuminated chloroplasts and the onset of lipid peroxidation. Malondialdehyde and ethane, which are both formed during lipid peroxidation, are produced in large amounts by paraquat‐treated leaves exposed to light, but not by those maintained in the dark. Electron spin resonance measurements indicate that production of O27 by illuminated chloroplasts is more than 2‐fold greater in the presence of paraquat than in its absence. The identity of the radical formed by illuminated chloroplasts in the presence of paraquat was confirmed by using the diagnostic spin trap 5,5′‐dimethyl‐l‐pyrroline‐l‐oxide and by establishing that its formation is sensitive to superoxide dismutase. The observations collectively indicate that paraquat‐mediated membrane deterioration is light‐dependent and attributable to enhanced O27‐production.
Cytokinins as inhibitors of root growth
Authors: Stenlid Göran
Published: April 2006

The elongation of roots of wheat (Triticum aestivum L. cv. Diamant II), flax (Linum usitatissimum L. cv. Concurrent) and cucumber (Cucumis sativus L. cv. Favör) seedlings in the dark was strongly inhibited by various native and synthetic cytokinins (kinetin, benzyladenine, isopentenyladenine, zeatin and their corresponding 9‐ribosides). An inhibition of 50% was obtained for wheat roots with 3 · 10−9M zeatin and for flax roots with 6 · 10−9M isopentenyladenine. The ribosides were in all cases less inhibitory. The inhibition was reversed by various types of ‘antiauxins’ and ‘antiethylenes’ (such as structural auxin analogues, uncouplers, specific inhibitors of ethylene synthesis, free radical scavengers, inhibitors of ethylene action). These substances as a rule counteract also inhibitions caused by auxins. Auxins and cytokinins stimulate ethylene production synergistically, and the similar inhibitory effects of these two types of hormone can be understood if it is assumed that their effect is at least partly mediated through ethylene. The cytokinins must be considered as possible natural inhibitors and regulators of root growth.