bluuebunny/crossref_metadata_2025 huggingface dataset:
Light‐induced linear dichroism in photoreversibly photochromic sensor pigments. – III. Chromophore rotation estimated by polarized light reversal of dichroism
Authors: Sundqvist Christer , Björn Lars Olof
Published: April 2006

Phytochrome from oats (Avena sativa L. cv. Sol II), partially purified on brushite, was immobilized on Sepharose beads to which antiphytochrome immunoglobulin had been covalently linked. The immobilized phytochrome was first brought to the Pr form with unpolarized far‐red light. The change in linear dichroism at 660 nm induced by plane polarized red light, and its reversal by plane polarized far‐red light were then studied using a dual‐wavelength spectrophotometer equipped with polarizing filters. The far‐red light was most effective in reversing red‐induced dichroism when the angle between the planes of polarization of red and far‐red light was approximately 23°. From this it was computed that the long‐wavelength transition moment of phytochrome rotates about 29° (or 180°–29°) with respect to the protein during conversion from Pr to Pfr. The reverse experiment, using unpolarized red light followed first by polarized far‐red light and then polarized red light, with dichroism monitored at 730 nm, also gives most effective reversal for an angle of about 23° between polarization planes, but this corresponds to a transition moment rotation of about 36° (or 180°–36°). The present method is more straightforward but less accurate and confirms our earlier conclusion that the rotation angle is close to 32° (or 180°–32°) in contrast to the “in vivo” value of 90° found by several workers.
Resolution of components of the absorption spectrum of chlorophyll‐protein 668 and its phototransformation product in Atriplex hortensis
Authors: Hagar William G. , French C. S.
Published: April 2006

The absorption spectra of a highly purified water‐soluble chlorophyll‐protein, CP 668, obtained from upper leaves of Atriplex hortensis L., and its phototransformation product have been measured and analyzed as sums of component curves. The difference spectrum before and after transformation has the same major peaks as those previously reported for a preparation from Chenopodium. The curve resolution indicates that, unlike some previous studies with preparations from other species of CP 668 from Atriplex, the main red band is a single, though somewhat unsymmetrical, component very much like the chlorophyll α 670 (Ca 670) common to all green plants. The “740” band of the phototransformed material, however, appears to have at least two components. The amounts of photoconversion of this pigment‐protein was more extensive than any complex previously studied. The converted material had a far‐red to red absorbance ratio of 2.6.
Effects of ultraviolet‐B irradiation on plants during mild water stress.
Authors: Teramura Alan H. , Tevini M. , Iwanzik W.
Published: April 2006

Cucumber (Cucumis sativus L. cv. Delikatess) and radish (Raphanus sativus L. cv. Saxa Treib) were grown in a factorial design under two ultraviolet‐B (UV–B) irradiances and three levels of water stress. On a weighted, daily dose basis the UV–B radiation treatments were equivalent to ambient levels during the beginning of the growing season (controls) and those predicted for an 11.6% ozone depletion during the summer solstice at 49°N latitude. Water stress was achieved by varying the frequency of watering. The combination of UV–B radiation and water stress resulted in large species differences in the pattern of stomatal resistances. This study indicated that Cucumis is one of the most sensitive crop species to UV–B radiation yet identified and that the primary effect of UV–B radiation in this species is a decrease in the leaf diffusive resistance to water vapor. This, therefore, may result in reductions in growth via increased water stress.
Distribution of cytochrome b photoreductions mediated by endogenous photosensitizer or methylene blue in fractions from corn and cauliflower
Authors: Widell S. , Larsson C.
Published: April 2006

Light‐induced absorbance changes [LIAC; measured as Δ(A428–A410)] reflecting the reduction of a b‐type cytochrome and mediated by an endogenous blue light absorbing receptor have been proposed to be related to blue light physiology of fungi and higher plants. It has also been suggested that the same cytochrome specifically can be reduced by red light in the presence of methylene blue. We have investigated the distribution of LIAC between different membrane fractions from corn (Zea mays L.) coleoptiles and cauliflower (Brassica oleracea L.) inflorescences. The membrane fractions were obtained by differential centrifugation followed by partition in an aqueous polymer two‐phase system. By this procedure fractions rich in plasma membrane were obtained from both mitochondrial and microsomal fractions obtained by centrifugation. LIAC was by far most enriched in fractions also enriched in plasma membranes (identified by silicotungstic acid staining), but LIAC could be obtained also in other fractions. Our conclusion is that LIAC undoubtedly is caused by a b‐cytochrome bound to the plasma membrane, but that LIAC also may be due to other b‐cytochromes, one of which is probably located in the endoplasmic reticulum. Thus, the two assay procedures used for LIAC (blue and red light induced) could not disciminate between different b‐cytochromes giving rise to LIAC.
Transplanting shock in white spruce; effect of cold‐storage and root pruning on water relations and stomatal conditioning
Authors: Blake T. J.
Published: April 2006

White spruce [Piceae glauca(Moench) Voss] seedlings were pre‐conditioned by cold storage and root pruning and a study was made of the effects of conditioning on root regeneration and stomatal adaptation following transplanting.

Root pruning (0 to 75% of the initial root area) of dormant seedlings immediately prior to transplanting did not confer any detectable physiological advantage in either cold‐stored or freshly‐lifted seedlings. Transpiration rates and stomatal resistance were not greatly affected by root pruning in the 6 week period after planting and root pruning did not greatly alter the response to drought.

Cold‐stored seedlings appear better able to avoid transplanting shock and an early drought despite delayed root growth as evidenced by a) a delay in flushing of new shoot growth and b) pre‐conditioning of the stomatal apparatus which reduced water loss after planting and when moisture was limiting. Seedlings freshly‐lifted in the spring did not show these adaptive responses and their stomata were poorly adapted to reduce water loss in the post‐planting period after a drought.
Sugar uptake in soybean (Glycine max) cells in suspension culture
Authors: de Klerk‐Kiebert Y. M. , Kneppeis T. J. A. , Matthijs H. C. P. , Verieur J. D.
Published: April 2006

In chlorophylkras soybean (Glycine max L.) cell suspensioo cultures glucose uptake has been studied using the analogue 3‐O‐methyIglucose. Uptake could be distinguished into: a) a high affinity phase with Km= 0.06 mM and b) a low affinity phase with Km 2.0 mM. The uptake of glucose was accompanied by H+‐cotransport with a stoichiometry of 0.3 H+ per molecule 3‐O‐methylglucose. Experiments in which sugar uptake was measured in the presence of various inhibitors of respiration and photosynthesis demonstrated that the glucose uptake system was dependent on energy metabolism and the ATP‐content of the cells. Efflux experiments in the presence of the uncoupler dinitrophenol confirmed this energy dependency. Glucose uptake did not decrease before the ATP‐content of the cells had decreased considerably.
In vitro and in vivo regulation of chloroplast glyceraldehyde‐3‐phosphate dehydrogenase isozymes from Chenopodium rubrum. II. In vitro modulation of the isozyme pattern
Authors: de Looze Stephen , Wagner Edgar
Published: April 2006

Isozymes of chloroplast glyceraldehyde‐3‐phosphate dehydrogenase (GPD, EC 1.2.1.13) from Chenopodium rubrum were separated using inverse discontinuous ammonium sulphate gradient solubilization. Leaves were extracted at the 9th h of light and the 9th h of darkness of a 12 h light/12 h dark cycle. The ratio of “NADP‐GPD I” to “NADP‐GPD II” varied with the light/dark cycle. However, the “light” isozyme pattern could be obtained from “dark” plants by including NADP + or NAD + kinase in the extraction buffer. Similarly, the “dark” isozyme pattern was produced in “light” plants extracted in the presence of NAD+. Pyridine nucleotides had no effect on the separated, purified isozymes. It is concluded that differential binding of the isozymes at the moment of extraction to pelletable material in the crude extract determines the isozyme pattern, and that this binding is regulated by the pyridine nucleotide ratio.
Comparison of two methods for the preparation of a membrane fraction of cauliflower inflorescences containing a blue light reducible b ‐type cytochrome
Authors: Caubergs R. , Widell S. , Larsson C. , De Greef J. A.
Published: April 2006

Presumptive plasma membrane fractions containing a light‐sensitive flavocyto–chrome b ‐protein complex from cauliflower inflorescences were isolated by two different procedures. In the first procedure a density gradient centrifugation was used, while in the second the separation was carried out using an aqueous polymer two phase system based on the specific surface properties of the membranes. This latter method is much faster and its yield is as good as a purification on a linear sucrose density gradient in terms of light inducible cyt b reduction. When the LIAC‐containing membranes obtained through a sucrose gradient are further purified on an Urografin gradient, the presence of contaminating cyt b is shown. The distribution of this b type cytochrome, showing no redox change upon illumination, is similar to the distribution as a NADH dependent and antimycin A resistant cytochrome c reduc–tase, a marker enzyme for endoplasmic reticulum. Measurable mitochondrial contamination is indicated by cytochrome oxidase activity. Both contaminants were less pronounced in the fractions obtained after Urografin gradient centrifugation of the membranes prepared by the two phase system method. The isolation procedure based upon the use of the two phase aqueous polymer system allows more rapid preparation of LIAC‐containing presumptive plasma membranes than that obtained with the sucrose density gradient centrifugation. It also yields a purer preparation.
Synergism between gibberellic acid and low Pfr levels inducing germination of Kalanchoë seeds
Authors: Fredericq H. , Rethy R. , van Onckelen H. , de Greef J. A.
Published: April 2006

Sown on water, seeds of Kalanchoëbiossfetdiana Poelln. cv. Feuerblute are absolutely light‐requiring and show full red/far‐red reversibility. In seeds, sown on 2 ×10‐3 M gibberellic acid, red/far‐red reversibility disappears and both short red and far‐red irradiations induce germination. Gibberellic acid alone does not induce germination, but it increases the physiological activity of Pfr to the extent, that the low Pfr level obtained by far‐red irradiation becomes very effective. The synergism between gibberellic acid and far‐red light appears after a two‐day incubation; period. The nature of this lag phase was examined by measuring both germination and uptake of labelled gibberellic acid in intact seeds and seeds with a punctured seed coat. The lag phase was shown to be independent of the uptake kinetics of gibberellic acid and allows development to a specific stage, necessary for germination after phytochrome‐phototransformation. The kinetics of the uptake of gibberellic acid by intact seeds and embryos of intact seeds are different. In intact seeds most of the gibberellic acid is retained in the seed coat; only a small fraction actually penetrates to the embryo where it can exert its physiological activity.
Blue light induces stomatal transpiration in wheat seedlings with chlorophyll deficiency caused by SAN 9789
Authors: Karlsson Per Erik , Höglund Hans‐Olof , Klockare Rune
Published: April 2006

Wheat seedlings (Truicum aestivum L. cv. Starke II, Weibull) grown in a solution of the herbicide SAN 9789 axe deficient in chlorophyll and carotenoids. Such seedlings were used in order to isolate a blue light response of stomata, not mediated by photosynthesis. When illuminated with blue light (430‐505 nm) SAN‐grown seedlings showed a considerable transpiration response, whereas red light (>590 nm) gave no response whatsoever with the intensities used. The transpiration was measured with hygrometers in an open air‐flow system. Furthermore, blue light had a superior effect, relative to red, in causing a transpiration response in untreated green seedlings. The transpiration level after two hours of illumination was higher in blue than in red light, although the blue light had its major effect immediately after the light was switched on. The difference between the effects of blue and red light was most pronounced at low light intensities. This, together with the high sensitivity of SAN‐grown seedlings to low ntensity blue light, led to the conclusion that blue light is of special importance at low quantum fluxes. Because of the very low carotenoid content in the SAN‐grown seedlings, the role of the carotenoids as photoreceptors for the blue light response of stomata was excluded.
Effets physiologiques de ľ atrazine à doses sublétales sur Lemna minor, VII. Incorporation ?acétate‐l,2‐[14C] dans les groupes de lipides et leurs acides gras
Authors: Grenier Gilles , Beaumont Gaston
Published: April 2006

Physiological effects of sublethal doses of atrazine on Lemna minor. VII. 1,2‐[14C] acetate incorporation into the groups of lipids and their fatty acids.

The lipids and the fatty acids of ten‐day old duckweed (Lemna minor L.), cultivated aseptically in mineral solution containing sublethal concentrations of 0,10 and 0,50 ppm (0.46 and 2.3 μM, respectively) of atrazine, were analyzed by thin‐layer chromatography and gas‐liquid radiochromatography after 1,2‐[14C] acetate feeding. Sublethal concentrations of atrazine increased the incorporation of radioactivity in total lipids, diacylgalactosylglycerol (DGG), diacyldigalactosylglycerol (DDG), sul‐folipids (SL), phosphatidylglycerol (PG), diacylglycerol (DAG) and triacylglycerol + steroll esters (TAG+SE). The incorporation of acetate‐1,2‐[14C] decreased in phos‐phatidylcholine (PC) and in phosphatidylethanolamine (PE) in the presence of atrazine. The radioactivity increased in total Transic‐hexadecenoic, linoleic and α ‐linolenic acids while it decreased in the other fatty acids. This indicates that the sublethal concentrations of atrazine stimulate the desaturation of fatty acids of L. minor. The radioactivity was strongly incorporated in the α ‐linolenic acid of DGG in the presence of atrazine. The specific radioactivity of α‐linolenic acid was greater in DAG than in PG > TAG + SE > PC > PE > DGG > SL > DDG and it increased in all groupd of lipids analyzed under the influence of sublethal doses of atrazine. The labelling of Translchexadecenoic acid of PG and its specific radioactivity increased in the presence of atrazine. These changes suggest that the sublethal concentrations of atrazine stimulate especially the lipid metabolism of the chloroplasts of L. minor and they could explain the increase in the number of grana per chloroplast in treated L. minor. The results are discussed in relation to the biosynthesis of galactolipids.
Synthèses ?acides nucléiques et de protéines au cours de ľinitiation de bourgeons adventifs sur des explantats de Cichorium intybus cultivés in vitro
Authors: Vasseur Jacques , Roger Véronique
Published: April 2006

Synthesis of nucleic acids and proteins during initiation of vegetative buds from explants of Cichorium intybus cultivated in vitro.

Explants of 6 mm diameter and 2 mm thickness from roots of Cichorium intybus L. (var. WitIoof cv. “Zoom”), grown in vitro in the presence of kinetin (l0–6M), produced only buds. By comparing the histological events and the biochemical modifications which occurred during the neoformation of buds, it is possible to distinguish two distinct phases. The first phase starts immediately after the excision of the explants and continues for 30 h, when the mitotic index is at its highest. This corresponds to a phase of cellular activation, which is characterized by early synthesis of RNA, permitting the synthesis of proteins necessary for duplication of DNA and cell divisions. The second period starts after 30 h and ends after approximately 72 h of culture, at which time the first bud meristematic nodules were detected. This is a preparatory phase for organogenesis and above all related to synthesis of RNA and proteins.
Hormonal control of cambial activity and vessel differentiation in Quercus robur
Authors: Zakrzewski Jacek
Published: April 2006

Cambial activity and vessel differentiation of the Quercus robur stem were investigated in relation to concentration of growth regulators and sucrose, seasonal changes in the sensitivity of cambial cells, and axial polarity of the stem. Basipetal efflux of natural auxin was measured in the oak stem cambial region. IAA, GA3, kinetin and sucrose affected cambial activity and/or initiation of vessel differentiation differently, depending upon concentration. Depending upon the season, kinetin increased or reduced the stimulation of cambial activity caused by IAA and GA3, but it did not affect the differentiation of vessels. Supply of sucrose in higher concentrations reduced the number of differentiated vessels but did not decrease the stimulation of cambial divisions.Unlike stimulation of cambial activity by GA3, auxin stimulation of cambial divisions and differentiation of vessels were highly dependent upon stem polarity, 2,3,5‐triiodobenzoic acid (TIBA) inhibited formation of vessels, but not cambial activity. The oscillations in basipetal efflux of natural auxin from the cambial stem region of successive 6 mm long sections substantiate the hypothesis that the histogenesis of xylem tissue in ring‐porous species is under control of the vectoriat field that is associated with oscillatory phenomena in polar auxin transport.
Regulation of glutamate dehydrogenase activity by amino acids in maize seedlings
Authors: Singh Rana P. , Srivastava H. S.
Published: April 2006

Root or secondary leaf segments from maize (Zea mays L. cv. Ganga safed‐2) seedlings were incubated with 9‐amino acids and two amides separately, each at 5 mM for 24 h, to study their effects on glutamate dehydrogenase (GDH) activity. Most of the compounds tested inhibited the specific activity of NADH‐GDH and increased that of NAD+‐GDH in the roots in the presence as well as in the absence of ammonium. In the leaves, such effects were recorded only with a few amino acids. Total soluble protein in the root and leaf tissues increased with the supply of most of the amino compounds. The effect of glutamate on enzyme activity and protein was concentration dependent in both tissues. When the enzyme extracts from root or leaf tissues were incubated with some of the amino acids, NADH‐GDH declined while NAD+‐GDH increased in most cases. The inhibition of NADH‐GDH increased with increasing concentration of cysteine from 1 to 5 mM. The experiments demonstrate that most of the amino acids regulated GDH activity, possibly through some physicochemical modulation of the enzyme molecule.
Evaluation of freezing injury and freeze‐thaw injury to membranes of Saskatoon serviceberry twigs by measuring HCN release
Authors: Stout Darryl G.
Published: April 2006

The influence of thawing on freeze‐injured Saskatoon serviceberry (Amelanchier alnifolia Nutt.) twigs was evaluated by refreezing freeze‐thawed twigs and comparing the HCN release at ‐5°C fro these twigs to the HCN release at ‐5°C from twigs that had not been thawed. An effect of thawing depended on the physiological state of the twigs, on the degree of freezing stress, or on both. Manifestation of membrane injury does not have an absolute dependence on thawing. Post‐thaw temperature influences manifestation of injury, since twigs warmed to 30°C released more HCN than twigs warmed to 1°C when refrozen to ‐5°C. Although thawing and post‐thaw conditions can influence the magnitude of membrane injury, the critical event leading to injury occurs while plants are frozen.
Quantitative and qualitative changes in cell wall polysaccharides in relation to growth and cell wall loosening in Lactuca sativa hypocotyls
Authors: Katsu Noriko , Kamisaka Seiichiro
Published: April 2006

The correlation between hypocotyl elongation, cell wall loosening and changes in cell wall polysaccharides was studied using intact lettuce seedlings grown in the dark or in light together with gibberellic acid (GA) and/or 5‐fluorodeoxyuridine (FUDR). The following results were obtained:

1) The production of pectic, hemicellulosic and cellulosic polysaccharides look place in parallel with hypocotyl elongation, which was substantially affected by different growth conditions.

2) The mole percentage sugar composition of pectic and hemicellulosic polysaccharides changed in response to dark, light, GA, or FUDR treatments.

3) The amounts of xylose and glucose in hemicellulosic polysaccharides and those of galactosc, rhumnose and uronic acid in pectic polysaccharides increased in parallel with hypocotyl elongation.

4) Statistical analysis of the quantitative relationship between sugars composing polysaccharides revealed that the uronic acid content changed in parallel with those of rhamnose and galactose in pectic polysaccharides, and the content of xylose varied in parallel with those of fucose and glucose.

5) The content of hemicellulosic polysaccharides was correlated with cell wall loosening represented by a decrease in the minimum stress‐relaxation time. Changes in the stress‐relaxation time value were correlated with those in the content of araltinose and galactose in hemicellulosic polysaccharides.

Based on these results, the relationship between hypocotyl elongation, changes in cell wall polysaccharides, and cell wall loosening is discussed with respect to the effect of GA and FUDR on hypocotyl elongation.
The mechanism of auxin uptake and accumulation in moss protonemata
Authors: Rose Stefan , Rubery Philip H. , Bopp Martin
Published: April 2006

Protonemata of the moss Funaria hygrometrica Sibth. (L.) show a strong pH dependence for auxin accumulation. IAA uptake is enhanced when the pH of the incubation medium is lowered from 7.6 to 4. In low light intensity grown protonemata (0.56 W m−2) a component of IAA uptake could be saturated by IAA; efflux of IAA could be inhibited by 2,3,5‐triiodobenzoic acid. This is explained by the presence of influx and efflux carriers for IAA. In protonemata grown at high light intensity (2.00‐2.30 W m−2) these carriers could not be shown to be present. These results are discussed with regard to the different physiological behavior of moss protonemata grown under different light conditions.
Uptake and polar transport of indoleacetic acid in moss rhizoids
Authors: Rose Stefan , Bopp Martin
Published: April 2006

Rhizoids of the moss Funaria liygrometrica Sibth. (L.) accumulate auxin in a manner similar to whole protonctnata. In the base of rhizoids auxin accumulation is always higher than in the tip. Auxin is transported in rhizoids from the tip to the base. The auxin transport is strictly polar. This can be explained by the different pattern of auxin accumulation in tip and base of rhizoids which represents a good model for the chemiosmotic hypothesis of polar auxin transport. The involvement of such a polar transport in moss development is discussed.
A malate‐oxaloacetate shuttle linking cytosolic fatty acid α‐oxidation to the mitochondrial electron transport chain in uncoupled fresh potato slices
Authors: Wu Shu‐yi , Laties George G.
Published: April 2006

The possible existence of a malonate‐sensitive dicarboxylate‐mediated electron shuttle between microsomal NAD‐linked fatty acid α‐oxidation and the mitochondrial electron transport chain in uncoupled fresh potato slices was investigated. Uncoupled slice respiration is inhibited by benzylmalonate and butylmalonate, inhibitors of dicarboxylate transport into mitochondria. Uncoupled slice respiration is also inhibited by rotenone, an indication of intramitochondrial NADH oxidation. Since fatty acid α‐oxidation per se is rotenone insensitive, rotenone and benzylmalonate inhibition of the oxidation of carboxyl‐labeled myristate in slices points to a dicarboxylic acid shuttle linking microsomal fatty acid a‐oxidation with intramitochondrial NADH dehydrogenase.

Malonute inhibits both respiration and 14CO2, release from carboxyl‐labeled myristate in fresh uncoupled slices, as do inhibitors of dicarboxylate transport. Mitochondrial studies show that malonate inhibits malate oxidation but not malate dehydrogenase per se. Furthermore, malonate inhibits malate transport more severely than malate oxidation. Accordingly, mulonate inhibition of uncoupled slice respiration in the absence of tricarboxylic acid cycle activity is attributed to its interference with mitochondrial malate transport, and its consequent curtailment of a putative malate‐OAA shuttle linked to cytosolic NAD‐mediated fatty acid α‐oxidation.
Role of aminocyclopropane‐l‐carboxylic acid in ethylene release by distal tissues following localized application of ethephon in Cucurbita pepo
Authors: Hume Bob , Lovell Peter
Published: April 2006

The application of ethephon to a single leaf of Cucurbita pepo L. cv. Trailing Marrow plants caused a huge increase in ethylene production from the treated organ and an increased rate of ethylene production from other parts of the plant. These increases were particularly marked in the shoot apex and expanding leaf. Prior treatment with aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor, blocked the increased production of ethylene at sites distant from the point of ethephon application. This strongly suggests that the increased ethylene production at these distant sites is due to ethylene biosynthesis and not a result of the translocation of ethylene released by the breakdown of ethephon at the site of application. Assays of 1‐aminocyclopropane‐l‐carboxylic acid (ACC), an ethylene precursor, showed that it increased substantially after ethephon application but was at undetectable levels in the presence of AVG. It is proposed that the application of ethephon stimulates ethylene biosynthesis, but that transport through the plants is effected by ACC which is then converted to ethylene at the shoot apex and leaves.
Interaction between chloroplast and cytoplasmic factors in the inhibition of l‐phenylalanine ammonia‐lyase activity
Authors: Podstoiski Andrzej
Published: April 2006

Components of the system inactivating cytoplasmic l‐phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5.) in barley seedlings (Hordeiim vulgare L. cv. Polon) were investigated. In vitro light‐activated chloroplasts and two cytoplasmic factors participate in the enzyme inhibition. One role of the chloroplasts is to mediate the reaction between PAL and the cytoplasmic factors, resulting in inactivation of the enzyme. Uncoupling (carbonyl cyanide m‐chlorophenyl hydrazone, valinomycin) or inhibiting [3‐(3,4‐dichlorophenyl)‐l,l‐dimethylurea] photosynthetic electron transport showed that electron transport is necessary to enable chloroplasts to mediate PAL inhibition. Preliminary results also indicate that mitochondria are able to mediate the inhibition. The role of this inhibiting system in the regulation of PAL activity in vivo is discussed.
Instability during storage of phosphogluco‐isomerase isoenzymes from ryegrasses (Lolium spp.)
Authors: Jones Thomas W. A.
Published: April 2006

The stability during storage of phosphogluco‐isomerase (D‐glucose‐6‐phosphate ketol isomerase EC 5.3.1.9) isoenzymes coded for at the PGI/2 locus has been examined. Extracts were prepared from leaves of several diploid and tetraploid Italian (Lolium multiflorum Lam.) and perennial (Lolium perenne. L.) ryegrass cultivars, as well as from interspecific hybrids. It was clearly demonstrated that extracts from plants homozygous for a specific PGI/2 allele could quickly generate new band forms upon storage. The novel forms were not due to aggregation or disintegration of the original enzyme molecule, and some of the generated bands electrophoresed to gel positions characteristic of other alleles of the same locus. An assessment was also made of the effects of a range of compounds added to the storage buffer. The most likely explanation was that the observed changes were due to the action of proteases, and the implications, especially for those using isoenzymes as genetic markers, are discussed.
Implications of water stress‐induced changes in the levels of endogenous ascorbic acid and hydrogen peroxide in Vigna seedlings
Authors: Mukherjee S. P. , Choudhuri M. A.
Published: April 2006

Vigna cutjang Endl. cv. Pusa Barsati seedlings, subjected to increasing degrees of water stress (−0.5, −1.0, −1,5 MPa), produced an approximately proportional increase in glycolate oxidase activity, hydrogen peroxide (H2O2) and proline content but a decrease in catalase activity, ascorbic acid and protein content. Leaf water potential (leaf ψ) and relative water content (RWC) were also lowered with increasing stress. Pretreatment with l‐cysteine and reduced glutathione (10‐3 M) decreased glycolate oxidase activity, H2O2 content, ascorbic acid oxidase activity, proline content and also slightly improved the water status of leaves stressed (−1.0 MPa) for 2 days. Pretreatment of non‐stressed seedlings with these antioxidants had little or no effect. These studies indicate that treatment with antioxidants makes the plant tolerant against water stress by modulating the endogenous levels of H2O2 and ascorbic acid in stressed tissue.
Changes in the uptake and assimilation efficiency for sulfate and nitrate in maize hybrids selected during the period 1930 through 1975
Authors: Cacco Giovanni , Saccomani Massimo , Ferrari Giovanni
Published: April 2006

Sulfate and nitrate uptake capacity, ATP sulfurylase (ATPS) and nitrate reductase (NR) activity were determined in a set of maize hybrids representative of selection cycles carried out during the period 1930 through 1975. All the above metabolic parameters together with the grain yield were improved by the selection. The annual rate of the improvement was higher (double) for sulfate uptake than for ATPS and similar for NR and nitrate uptake. Significant correlations were evidenced between the uptake efficiency of the roots and the enzyme activity in the leaves both for sulfate and nitrate pathways, and also between the uptake and enzyme steps of nitrate and those of sulfate. This offered good evidence of a coupled genetic regulation between nitrogen and sulfur metabolism in maize.
Thigmomorphogenesis: membrane lipid and protein changes in bean plants as affected by mechanical perturbation and Ethrel
Authors: Erner Y. , Jaffe M. J.
Published: April 2006

When bean plants (Phaseolus vulgaris L. cv. Red Cherokee Bush) are mechanically perturbed by rubbing, their stem elongation is inhibited and the stem thickness increases. The decrease in cell elongation and the increase in lateral cell divisions, which are partially responsible for this syndrome, were correlated with a decrease in the tree fatty acids and in the phospholipids of the membranes of microsomal fractions of first and second internodes of mechanically stimulated plants. This was true even though only the first internode was mechanically stimulated.

Of the microsomal free fatty acids, mechanical perturbation induced an increase in myristic acid and large decreases in stearic, oleic, linoleic and linolenic acids. It also reduced the unsaturated:saturated ratio of the fatty acids. It induced a decrease in phosphatidyl choline but an increase in phosphatidyl ethanolamine. When the fatty acids were cleaved from the microsomal phospholipids, mechanical perturbation caused only a slight decrease in the unsaturated:saturated ratio and no significant changes in the double bond index.

Mechanical perturbation induced an increase in the total microsomal protein and of membrane‐associated latent IDPase. However, the activity of membrane‐associated KCN‐insensitive NADPH cytochrome‐c reductase was decreased by mechanical perturbation.

Treatment of the first internode with exogenous Ethrel produced results that were very similar in all respects to those obtained by mechanical perturbation. The factors inducing hardening against frost and drought, as achieved by mechanical perturbation and Ethrel treatment, are not only related to sterols or the polar head‐groups of phospholipids but may also be related to the protein components, and all may have an effect on the fluidity of a bilayer membrane model. These data support the hypothesis that ethylene mediates thigmomorphogenesis and that mechanical perturbation of the first internode results in the acropetal transport of a translocatable thigmomorphogenetic factor.
Ethylene production by carob (Ceratonia siliqua) callus cultures on varying media
Authors: Martins‐Loução M. A. , Rodríguez‐Barrueco C.
Published: April 2006

Carob callus from hypocotyl segments produced ethylene in different amounts which were related to the composition of the medium and age of the callus. Both light and darkness stimulated high levels of ethylene production. No correlation was found between growth rate and ethylene production under dark conditions. In the light, a significant correlation was found, indicating that ethylene production and growth rate follow one another. Culture medium was the most important factor in controlling the growth rate and ethylene production. The highest values of ethylene production were obtained on media showing highest callus growth rate. These studies seem to indicate that most of the ethylene produced is a by‐product of metabolic changes during carob callus development, though, under certain conditions, the initial evolution could regulate growth.
Levels of endogenous abscisic acid in achenes of Rosa rugosa during dormancy release and germination
Authors: Tillberg Elisabeth
Published: April 2006

Germination experiments on isolated embryos and intact achenes from Rosa rugosa L. var. rubra revealed the existence of both coat‐induced and embryo dormancy. Studies were made on the quantitative changes in abscisic acid (ABA) of achenes during both a stratification period at 4°C and a subsequent germination period at 20°C. Controls were run in parallel at 17°C. Dormant, unimbibed achenes contained large amounts of ABA. The level fell rapidly during the early stages of stratification at 4°C, mainly due to leakage, and then the decline levelled off. The reduction of ABA content during germination was less and followed a tri‐phasic pattern. Under the control conditions, the ABA level also fell although still faster, the amounts present being consistently below those detected in the corresponding cold‐stratified samples. The content of alkali‐hydrolysable ABA was low and not affected either by the duration or by the temperature of stratification. The investigation shows that termination of dormancy is not simply a consequence of a fall in the content of endogenous ABA and supports the current debate questioning the central role of ABA in regulation of dormancy breakage and of germination.
Effect of cycloheximide on IAA‐induced proton excretion and IAA‐induced growth in abraded Avena coleoptiles
Authors: Pope David G.
Published: April 2006

IAA‐induced proton excretion in peeled or abraded oat (Avena saliva L. cv. Victory) coleoptiles is closely associated with IAA‐induced growth. It was attempted to separate these two processes by using cycloheximide to inhibit them differentially. Growth of abraded coleoptile segments was measured by a shadow graphic method, and their IAA‐induced acidification of the external solution was monitored with a pH meter. IAA stimulated proton excretion in abraded Avena coleoptile segments after a 13 min lag. IAA‐induced proton excretion was inhibited within 5 min by cycloheximide at concentrations of 1.8 × 10−6, 3.6 × 10 or 3.6 × 10−5 M. Cycloheximide at these concentrations, added within 4 min of IAA, prevented IAA‐induced acidification of the medium for at least 60 min. However, it did not prevent IAA‐induced growth during this time. It is concluded that some of the initial IAA‐induced growth seen in Avena coleoptiles is independent of detectable IAA‐induced proton excretion.
The role of ethylene in the induction of amylase activity in wheat aleurone tissue
Authors: Varty K. , Arreguín L. B. , Lopez T. P. J. , Sanchez F. C. J. , Garcia H. E. , Gomez L. M. A.
Published: April 2006

When wheat aleurone layers (Triticum aestivum L. var. Potam S‐70) incubated in medium containing gibberellic acid were exposed to ethylene, the synthesis and release of amylase were enhanced relative to layers incubated in the presence of mercuric perchlorate. Exogenous ethylene stimulated gibberellic acid‐induced amylase synthesis by approximately 2.2‐fold. The ethylene‐mediated stimulation of amylase formation was dependent upon the tissue being exposed to the gas during the lag phase of gibberellic acid action. Ethylene appeared to promote only quantitative changes in amylase synthesis and release, since the isoelectric focusing patterns of amylase is enzymes were not significantly altered by ethylene. Ethylene had no effect on the incorporation of [methyl‐14C]choline into aleurone phospholipids, but stimulated the accumulation of [U‐14C]adenine into poly(A) RNA of gibberellic acid‐treated tissue by about 80%.
The penetration of ultraviolet radiation to the ground
Authors: Green A. E. S.
Published: April 2006

The evolution of analytic formulas for characterizing the ultraviolet spectral ir‐radiance penetrating to the ground is briefly described. Analytic spectral functions for the extraterrestrial solar spectral irradiance, the ozone absorption coefficient, Rayleigh scattering coefficients and aerosol scattering and absorption coefficients, which are used as basic inputs, are given. With Beer's law, these give immediately the direct solar spectral irradiance. A ratio technique described in quantitative detail gives a procedure for calculating the skylight component of the UV radiation reaching the ground. The influence of ground reflectivity, clouds and a possible connection between photobiology and radiological physics are discussed. Finally the advantages of multiwavelength monitoring are described, using monochromators similar to those used in satellite ozone sounding to serve the needs of the photobiology and the atmospheric science communities.
Use of action spectra for identifying molecular targets and mechanisms of action of solar ultraviolet light
Authors: Peak Meyrick J. , Peak Jennifer G.
Published: April 2006

The use of action spectra in the elucidation of the mechanisms of biological action of solar ultraviolet radiation that reaches the surface of the earth is reviewed, and precautions in the preparation and interpretation of such action spectra are discussed. Original experiments are also described which show correlations between lethality and DNA breakage caused by monochromatic solar ultraviolet (UV) wavelengths in Escherichia coli and Bacillus subtilis, which may constitute evidence for an important biological role of DNA breaks leading to lethality in these microorganisms.
Effects of pH, NADH, succinate and malate on the oxidation of glycine in spinach leaf mitochondria
Authors: Bergman Anders , Ericson Ingentar
Published: April 2006

The effect of external pH on several reactions catalyzed by glycine decarboxylase in spinach leaf mitochondria was investigated. Glycine‐dependent oxygen consumption showed a pH optimum at 7.6, whereas the release of CO2 and NH3 from glycine in the presence of oxaloacetate both showed pH maxima at 8.1. Glycine‐dependent reduction of 2,6‐dichlorophenolindophenol. on the other hand showed a pH optimum at 8.4. It is concluded that these three reactions have different rate‐limiting steps. The rate of the glycine‐bicarbonate exchange reaction catalyzed by glycine decarboxylase showed no optimum in the pH range investigated, pH 7–9, but increased with decreasing pH. This suggests that CO2 may be the true substrate in this reaction.

The oxidation of glycine inhibited the oxidation of both malate, succinate and external NADH since the addition of malate, succinate or NADH to mitochondria oxidizing glycine in state 3 resulted in a rate of oxygen consumption which was lower than the sum of the rates when the substrates were oxidized individually. The addition of malate, succinate or NADH did not, however, decrease the rate of CO2 or NH, release from glycine. It is suggested that the preferred oxidation of glycine by‐spinach leaf mitochondria may constitute an important regulatory mechanism for the function of leaf mitochondria during photosynthesis.
Purification and properties of NADP‐dependent glutamate dehydrogenase from Sphaerostilbe repens
Authors: Balton Bernard , Msatef Yamina
Published: April 2006

NADP‐dependent glutamate dehydrogenase (EC 1.4.1.4) extracted from Sphaerostilbe repens was purified to homogeneity by using ammonium sullate fractionation hydroxyapatite and DEAE‐cellulose column chromatography and, finally, preparative polyacrylamide gel electrophoresis. The turnover number of the enzyme for the amination reaction was about 66000 mol substrate transformed min‐1 (molecule of GDH)‐1. Molecular weight of the native enzyme was estimated to be 280000 dalton by polyacrylamide gradient gel electrophoresis. The same technique in the presence of sodium dodecyl sulfatc gave a single protein band that corresponded to the subunit molecular weight of 48000 dalton. Thus, it is concluded that NADP‐GDH is composed of six identical polypeptidic chains.

The pH optimums were 6.9 and 8.4 for the forward and reverse reactions respectively. The NADP‐GDH lost practically none of its activity for ten days at 4°C and for 15 h at room temperature, but was inactivated by higher temperatures. Thiol compounds such as 2‐mercaptoethanol and dithiolhrcitol protected the enzyme from rapid inactivation. The Michaelis constants for GDH were 0.64, 0.049. 0.043 and 5.5 mM for α‐ketoglutaratc. NADPH, NADP and glutamate, respectively. The enzyme had a negative cooperativity for ammonium (Hill number of 0.66), and its Km value increased from 2.6 to 21.2 mM when the ammonium concentration exceeded 16 mM. The deamination reaction was highly sensitive to inhibition by ammonium, while the amination reaction was only slightly inhibited by glutamate. These results, considered together with the Km values, indicate that the NADP‐GDH in Sphaerostilbe repens is primarily concerned with glutamate biosynthesis.
Nucleolar dissolution induced by aluminium in root cells of Allium
Authors: Fiskesjö Geirid
Published: April 2006

Acidification of natural waters and soils leads to the release of aluminium, causing damage to living organisms. In the present experiments, growing roots of Allium cepa L. were exposed to water solution of AICl3 in concentrations from 10‐5 to 10‐1M. After a few days in concentrations around 10‐3M. the roots showed macroscopical signs of being affected; they became bent and their terminal portions tended to loosen and drop off. Microscopically, the affected zone of the roots revealed a new cellular phenomenon: Nucleolar material was extruded from the nuclei into the cytoplasm forming elongated, rod‐like bodies, which eventually divided into two, one distinct body at each pole of the cell. The derivation of these bodies from the nucleoli was further strengthened by the observation that they absorbed light green differentially Apparently, aluminium has a specific effect on the nucleoli of certain root cells.
The effect of triacontanol on growth, photosynthesis and photorespiration in Chlamydomonas reinhardtii and Anacystis nidulans
Authors: Haugstad May , Ulsaker Liv Kari , Ruppel Anneke , Nilsen Stein
Published: April 2006

Chlamydomonas reinhardtii Dangerad 11–32(90) (−), which exhibits C3 properties, and Anacystis nidulans (Strain no. UTEX 625), which exhibits C4 properties, were used to study the effects of triacontanol on growth, photosynthesis and photorespiration. Photosynthetic rate was measured as CO2 uptake and the O2 inhibition of photosynthesis was used as a measure of photorespiration. Triacontanol dissolved in chloroform and dispersed in Tween‐20 and triacontanol colloidally dispersed in an aqueous solution of sodium tallow alkyl sulfate were tested. Chlamydomonas cultures increased significantly in cell number after 4 days, and in chlorophyll content after 3 days of treatment with 2.3 × 10−8 M TRIA in chloroform/Tween‐20. In cultures of Anacystis the chlorophyll content became significantly higher 3 days after treatment with 2.3 × 10−9 M TRIA and the cell number was noticeably higher than the controls.

CO2 uptake by triacontanol‐treated Chlamydomonas cultures was about the same in both 2 and 21% O2, and the O2 inhibition was significantly reduced as compared with the controls. Photosynthesis in Anacystis was O2‐insensitive under the experimental condition used. When Anacystis was treated with triacontanol there was no change in the rate of CO2 uptake and no change in the O2 sensitivity of its CO2 uptake. It appears that triacontanol affects some process which regulated the balance between photosynthesis and photorespiration, but other processes which result in increased growth are probably also affected.
Effects of light flashes on the dark closure of Albizzia julibrissin pinnules
Authors: Tanada Takuma
Published: April 2006

An electronic flash unit is used to deliver, at the beginning of a 10 min dark period and within a few ms, large doses of light to Albizzia julibrissin pinnules, to ascertain their effects on the rate of pinnule closing. In a series of alternating light flashes at 710 and 550 nm, the first 710 nm light flash significantly retards closing. A following light flash at 550 nm negates the far‐red induced delay. The second 710 nm light flash delays closing less effectively than the first when given within 4 s after the green flash, but is just as effective when given after 30 s. The delay brought about by the second 710 nm light flash is again abolished by a light flash at 550 nm. A light flash at 660 nm has no effect on pinnule closing by itself and is also ineffective in reversing the far‐red induced delay. A series of ten 710 nm light flashes becomes most effective in delaying closure when there is a dark interval of one min between flashes. The closing delay induced by a 710 nm light flash escapes reversal by a 550 nm light flash when the dark interval between the two flashes exceeds 2–3 min. A 750 nm light flash has no retarding effect on pinnule closing, but it becomes effective when preceded by a 660 nm or 550 nm light flash. The results obtained are suggested to be due to light absorbed by phytochrome and an unknown photoreceptor with green, far‐red photoreversal property.
Purification and characterization of lectins from Vicia hirsuta
Authors: Solheim Bjern
Published: April 2006

The presence of three lectins in the seeds of Vicia hirsuta (L.) S. F. Gray, a wild‐growing vetch, was shown. The main lectin was purified to homogeneity by buffer extraction, ammonium sulfate precipitation, affinity chromatography on Sephadex G‐100 and isoelectric focusing in granulated gel. By chromatofocusing instead of isoelectric focusing the yield was increased 5‐fold. The lectin has a pi of 6.4. It is composed of large β‐subunits (Mr 19.200) and small α‐subunits (Mr 12.800) in a 1:1 ratio. The subunits can be separated on Sephadex G‐75 when equilibrated with 6 M guanidine‐HCl. The amino acid composition of the two different subunits has been determined. No sulfur‐containing amino acids are present. The lectin resembles the lectins from legumes from the same cross‐inoculation group, i.e. Lens culinaris, Lens esculenta, Pisum satiyum and several Vicia spp. by the same type of sugar specificity and amino acid composition.