bluuebunny/crossref_metadata_2025 huggingface dataset:
Free amino acids of Nicotiana alata anthers during development in vivo
Authors: Krogaard Helle , Andersen A. Skytt
Published: April 2006

The variation of free amino acids in anthers and pollen of Nicotiana alata Link et Otto has been examined during pollen development in vivo. The purpose was to find clues for optimizing an in vitro medium for cultivation of haploid plantlets from N. alata pollen. The quantitatively most important amino acids were proline, glutamic acid/glutamine, alanine and aspartic acid/asparagine. These exhibited similar patterns of variation during pollen development: first maximum (0.5 to 1.7 μmol per flower) at mitosis, then decrease during early binucleate stage (0.6 to 2.0 mmol per flower). Other amino acids were found in much smaller quantities (max 0.25 μmol per flower).
Lipid composition in leaves of cucumber genotypes as affected by different temperature regimes and grafting
Authors: Horváth I. , Vigh L. , van Hasselt Ph. R. , Woltjes J. , Kuiper P. J. C.
Published: April 2006

The lipid composition of leaves has been investigated in different genotypes of cucumber (Cucumis sativus L.), which differ in temperature requirement for cultivation. In addition the effects of hardening by low but non‐chilling temperature, soil heating and grafting (on the chilling‐resistant C. ficifolia L.) on lipid composition have been studied. Content and composition of phospholipids and sterols were determined as well as phospholipid/sterol ratio, and fatty acid composition of total lipids and the different phospholipids.

The effects of genetic differentiation and of the various culture treatments on lipid composition of the leaves were very different. Genetic differentiation was evident as higher levels of Iinolenic acid in several phospholipids in the more cold‐tolerant cultivars. Hardening the plants by low temperature resulted in a higher phospholipid level (especially phosphatidyl choline), more unsaturated phospholipid, and lowering of the sterol/phiospholipid ratio, all properties which may contribute to a higher membrane fluidity and lower growth temperature limit. Soil healing reduced the phospholipid level of the leaves slightly, and a higher content of 3‐trans‐hexadece‐noic acid in phosphatidyl glycerol was observed. Grafting cucumber on the cold‐resistant rootstock of C. ficifolia also raised the level of trans‐hexadecenoic acid in phosphatidyl glycerol. The role of this fatty acid in the functioning of the chloroplast is discussed.
Root growth and gravireaction: Influence of the shoot
Authors: Beffa Roland , Pilet Paul‐Emile
Published: April 2006

The kinetics of root gravicurvature of intact maize (Zea mays L., cv. LG 11) seedlings can be separated into two steps. From 0 to 2 h, a rapid downward bending, enhanced by light, occurred. During the next 4 h (2 to 6 h) no further curvature appeared in the dark, whereas it continued in light. The final root gravicurvature was greater for light‐than dark‐treated seedlings. Growth was particulary inhibited during the first 2 h.

When intact seedlings were placed horizontally and returned to the dark after a 4 h light pretreatment in a vertical position, only the second step (2 to 6 h) was changed. A negative gravitropism, associated with a stimulation of growth, appeared. Thus, when gravireaction took place in darkness, the final root gravicurvature was similar for the light‐pretreated intact seedlings and the dark control. Using apical root segments, this phase of negative gravicurvature was not observed although the stimulation of gravicurvature of light‐pretreated roots remained. Similar experiments were performed with seedlings having coleoptile or endosperm removed, after intact seedlings had been exposed to a light pretreatment, and gravireaction took place in the dark. Results indicated that these two organs could play an essential role in the development of gravicurvature and in the regulation of the light effects, respectively.
Protein and nucleic acid synthesis during germination of the asexual spores of the aquatic fungus, Aphanomyces astaci
Authors: Soderhall Kenneth , Cerenius Lage
Published: April 2006

Macromolecular synthesis of asexual spores of Aphanomyces astaci Schikora, strain is, was studied during the germination phase. Germination of the spores was completely inhibited by aclinomycin D (20 ug/ml) or cycloheximide (100 ug/ml) as was incorporation of labeled uridine and leucine, respectively. During spore germination protein synthesis was almost linear, whereas incorporation of [3Hl‐uridine and [3H1‐thymidine showed lag phases. Initial protein synthesis is therefore suggested to take place without concomitant RNA‐synthesis in this species. Germlings were not developmentally competent to sporulate before 8 h of germination.
Blue light induced inhibition of seed germination: The necessity of the fruit coats for the blue light response
Authors: Tanno Noriaki
Published: April 2006

The seeds (achenes) of Laportea bulbifera require a chilling to break their dormancy and are negatively photoblastic. Their germination is inhibited by both continuous blue light and continuous or prolonged far‐red radiation. The germination of de‐coated seeds, prepared by removing the fruit coats, however, was strongly inhibited by continuous far‐red, but not by continuous blue light. Photoreversible germination by a brief irradiation with red light occurred when the chilled seeds were exposed to prolonged far‐red light. These results suggest that far‐red light may regulate the germination of L. bulbifera seeds through the phytochrome system which exists in the regions other than fruit coats and that the blue light reaction may be governed by other photoreceptor system(s).
Distribution of a lectin in tissues of Phaseolus vulgaris
Authors: Borrebaeck Carl A. K. , Mattiasson Bo
Published: April 2006

The distribution of lectin in various tissues of Phaseolus vulgaris L. (var. red) has been investigated with the use of a sensitive solid phase enzyme immunoassay. Plants were divided into roots, stems and leaves with a further dissection of the stem into internodes. Isolated tissues, from plants 3‐10 weeks old, were screened for their lectin content, and the development of the lectin over this period determined. Stems and roots contained significant amounts of lectin, whereas the leaves only exhibited very low levels. Furthermore, a pronounced and differential increase in the biosynthesis of the lectin was observed in stem sections between 6 and 10 weeks, where the third internode displayed the highest lectin level.
Effects of frost‐hardening and salinity on glutathione and sulfhydryl levels and on glutathione reductase activity in spinach leaves
Authors: de Kok Luit J. , Oosterhuis Fenny A.
Published: April 2006

In frost‐hardened spinach leaves (Spinucea oleracea L. ev. Vroeg Reuzenblad) an enhanced content of water‐soluble non‐protein sulfhydryl compounds was observed. The enhancement was due to higher levels of glutathione as well as to other non‐protein‐bound sulfhydryl compounds. In addition glutathione reductase activity was increased upon hardening. The affinity of the enzyme for oxidized glutathione was slightly lowered during hardening. The significance of glutathione accumulation during frost‐hardening is discussed. Exposure of spinach to NaCl‐stress did not affect the levels of glutathione and glutathione reductase of the leaves. In addition the kinetic properties of the enzyme remained unaltered by salinity. It is suggested that glutathione and glutathione reductase activity are not involved in adaptation of spinach to saline conditions.
Identification of the ammonium‐dependent isoenzyme of glutamate dehydrogenase as the form induced by senescence or darkness stress in the first leaf of wheat
Authors: Laurière C. , Daussant J.
Published: April 2006

The level of glutamate dehydrogenase activity increases nearly 3 fold in detached wheat (Triticum aestivum L. cv. Capitole) leaves during 72 h incubation with 15 mM ammonia. De novo synthesis of one of the glutamate dehydrogenase isoenzymes is shown to be correlated with the activity increase, by using an immunochemical approach. The identification of the ammonia inducible isoenzyme as the form previously reported induced by darkness stress or senescence (Laurière et al. 1981, Physiol. Plant. 52: 151‐155), provides new information on the possible physiological significance of the response to ammonia.
Involvement of ethylene in the abscission of flowers and petals of Leptospermum scoparium
Authors: Zieslin Naftaly , Gottesman Varda
Published: April 2006

Excised vegetative and flowering shoots of Leptospermum scoparium Forst. emanate ethylene in a climacteric time course. Relatively high concentrations of applied ethylene were required to cause flower abscission. Flowers and petals dropped only if they were exposed to a high relative humidity, while at a low relative humidity the flowers dried out and shrivelled without abscission. Silver thiosulphate prevented ethylene‐induced, but not natural abscission of mature flowers. A rise in ethylene evolution followed treatment with silver thiosulphate in both young and mature flowers. Benzyl adenine prevented natural abscission and inhibited ethylene evolution, while ethylene‐induced abscission remained unaffected.
The physiological basis of seed dormancy in Avena fatua. II. On the involvement of alternative respiration in the stimulation of germination by sodium azide
Authors: Upadhyaya Mahesh K. , Naylor James ML , Simpson Graham M.
Published: April 2006

Sodium azide, an inhibitor of cytochrome oxidase, has been shown to stimulate germination in several genetically pure lines of wild oats (Avena fatua L.). This effect of azide is completely inhibited by salicylhydroxamic acid, an inhibitor of alternative respiration. Sodium azide treatment, which induced germination, stimulated oxygen uptake by as much as 200 to 400%. The dose‐response curves for the stimulation of germination and of oxygen uptake by azide were very similar. The stimulation of oxygen uptake was completely inhibited by salicylhydroxamic acid and was not due to lipoxygenase activity. Thus, stimulation of salicylhydroxamic acid‐sensitive oxygen uptake (alternative respiration) is associated with and is necessary for the stimulation of germination in the presence of azide. However, it remains to be shown whether the induction of alternative respiration by azide is the direct cause of stimulation of germination.

In the Montana 73, unlike other pure lines investigated, azide stimulated alternative respiration, but not germination. The lack of germination response in this line is considered to be due to an additional metabolic block in the processes leading to germination.
Nitrate uptake and respiration in roots and shoots: A model
Authors: Johnson I. R.
Published: April 2006

Respiration in plants is often divided into growth and maintenance components. From the growth respiration it is possible to estimate the efficiency of conversion of substrate to plant material. Analysis of recent experimental data on this basis suggests that the conversion efficiency is considerably lower in roots than in shoots, which conflicts with biochemical analysis. The conventional method for describing respiration data is developed to incorporate root activity and is applied to a set of experimental data. The model provides a means for estimating the respiratory cost of nitrate uptake and also a possible explanation for the inconsistency between experimental observations and theoretical analysis.
Reversal of abscisic acid‐inhibited betacyanin synthesis by phenolic compounds in Amaranthus caudatus seedlings
Authors: Ray S. D. , Guruprasad K. N. , Laloraya M. M.
Published: April 2006

Abscisic acid inhibits light‐induced betacyanin synthesis in Amaranthus caudatus seedlings. Kinetin antagonizes ABA action and restores betacyanin synthesis. Similarly, phenolic compounds also antagonize ABA action and restore the synthesis of betacyanin. When present together phenolic compounds have an additive effect with kinetin in restoring ABA‐inhibited betacyanin synthesis.
Effects of temperature and moisture stress on the accumulation of abscisic acid in bean
Authors: Eze J. M. O. , Dumbroff E. B. , Thompson J. E.
Published: April 2006

Levels of abscisic acid (ABA) and several indicators of leaf‐water status were measured in excised and intact primary leaves of bean (Phaseolus vulgaris cv. Kinghorn) exposed to different temperature and moisture regimes. After 2 h at 5°, 25° or 45°C under moist conditions, the water status of detached leaves showed only minor changes, and there was no increase in ABA. Under conditions favoring water loss, ABA rose over 10‐fold at 25°C, and trends towards higher ABA levels were observed at 5° and 45°C. When intact leaves on whole plants were exposed to the same temperatures for 10 h, there was still no evidence of a temperature‐dependent rise in ABA that was not associated with a disturbance in the water balance of the plant. These data suggest that the rapid accumulation of ABA during temperature stress is a function of induced moisture deficits and does not result from high or low temperatures per se.
Diurnal variations of nitrate reductase activity and stability in barley leaves
Authors: Lillo Cathrine
Published: April 2006

Diurnal variations of nitrate reductase (NR) activity and stability have been studied in leaves of barley seedlings (Hordeum vulgare L. cv. Herta) grown in an 8 h light/16 h darkness regime. Stability (decay) of NR was tested both in the extracts and in the plants. In the morning, when the plants were transferred to light, NR activity increased rapidly during the first hour and then remained constant. After the photoperiod, activity decreased rapidly during the first hour of darkness and then remained fairly constant during the rest of the dark period. The high NR activity during the photoperiod was associated with low NR stability both in the extracts and in the plants. On the other hand the low NR activity during the dark period was associated with high stability in the extracts and in the plants.
Evaluation of the significance of malic acid secretion in chickpea
Authors: Koundal K. R. , Sinha S. K.
Published: April 2006

Leaves of chickpea (Cicer urietinum L.) secrete malic acid hut the significance of this secretion is not known. Our studies have confirmed that secretion of malic acid was mostly confined to the day time. PEP carboxylase activity and the secretion of malic acid are associated with the presence of glands on the surface of leaves and fruit wall. PEP carboxylase activity increased while malic acid secretion and MDH activity decreased in water stressed plants. The secretion of malic acid did not influence the reflectance properties of the crop canopy thereby discounting the possibility of reducing radiation load. It is suggested that the significance of malic acid secretion in chickpea should be considered in relation to insect pests which are very few on this plant.
Independent mode of action of cyanide and light on lettuce seed germination
Authors: Zagórski Slawomir , Lewak Stanislaw
Published: April 2006

Gaseous hydrogen cyanide stimulated subsequent lettuce seed (Lactuca sativa L. cv. Grand Rapids) germination in darkness when applied for 1 or 22 h. Optimum concentrations were 5 × 10‐5 M and 10‐6 M, respectively. However, seeds did not germinate in the presence of HCN even at 10‐8 M. The effects of unsaturating red light (R) and HCN (1 μM) showed a slight synergism. On the other hand, there was no difference between the effects of the sequences HCN – R and R – HCN. Stimulation of lettuce germination by an HCN pulse was practically not affected by far‐red illumination, independently of the sequence of treatments. It was concluded that the primary stimulatory effect of HCN is of a regulatory character. Cyanide controls a regulatory point different from that affected by activated phytochrome.
Cherry fruit development: Indoleacetic acid oxidase isoenzymes in the seed
Authors: Valpuesta Victoriano , Bukovac Martin J.
Published: April 2006

Two anionic indoleacetic acid oxidase isoenzymes were separated by polyacrylamide gel electrophoresis from an acetate buffer (0.2 M, pH 4.0) extract of sour cherry (Prunus cerasus L. cv. Montmorency) seed. One isoenzyme migrated to Rf 0.25 (I1) and the other to Rf 0.78 (I2). Isoenzyme I, exhibited hyperbolic kinetics and was found during all three stages of fruit development with the highest levels during early stage II. The isoenzyme I2 showed sigmoidal kinetics and was found only during stages II and III of fruit growth with highest levels during stage III. The activities of both isoenzymes were markedly enhanced by addition of Mn2+ and 2,4‐dichloro‐phenol to the reaction mixture. Isoenzyme I, showed higher affinity for indoleacetic acid than isoenzyme I2. The significance of these isoenzymes in cherry fruit growth is discussed.
Effects of benzyladenine and abscisic acid on superoxide dismutase in fronds of the duckweed Lemna gibba
Authors: Vaughan D. , DeKock P. C. , Ord B. G.
Published: April 2006

The growth‐promoting (benzyladenine) and growth‐inhibiting (abscisic acid) plant hormones, when used at concentrations of 0.4 and 4.0 μM, affect the development of superoxide dismutase (SOD) activity of Lemna fronds in opposite ways, the former hormone decreasing the activity and the latter increasing it. The effect of both growth substances is on de novo synthesis of the enzyme. In addition abscisic acid also causes the Zn, Cu and protein contents of the fronds to increase, while benzyladenine has the opposite affect.
Structural modifications and δ‐aminolevulinate dehydratase synthesis/transport in cotyledons of far‐red irradiated radish
Authors: Brangeon Judy , Balangé Alain P. , Forchioni Arlette
Published: April 2006

δ‐Aminolevulinate dehydratase (ALAD) is synthesized in the cytoplasm and subsequently transported into the plastids in cotyledons of tar‐red irradiated radish (Raphanus sativus L. ev. Longue Rave Saumonée). The intra‐cellular localization of ALAD activity was determined under far‐red irradiation and darkness. After 60 h far‐red, ALAD was essentially eytoplasmic; 96 h far‐red corresponded to a peak in total ALAD activity, as well as the onset of massive ALAD transfer into the plastids, and after 120 h a maximum enzyme activity was located in the plastids. Under dark conditions, essentially no transport of ALAD was noted.

Structural modifications of plastid‐eytoplasmic relationships were analysed at the three developmental periods under dark and far‐red conditions. 60 h far‐red induced a change in the “elasticity” of plastid envelopes leading to envelope proliferations and amoeboid shaped plastids. After 96 h tar‐red, membrane proliferations formed a highly evaginated plastid periphery. It is suggested that these membranes form a transport network between the two compartments. Also at 96 h, numerous vesicles, which appear to originate from the endoplasmic reticulum (ER), surround the plastid profile. On the basis of the structural observations, it is proposed that ALAD would be synthesized within the ER and transported toward the plastids via ER extensions, which take the form of smooth vesicles. Our hypothesis is that the transition vesicles and proliferations of the outer envelope membrane undergo a fusion process emptying the content of the vesicle into the intermembrane space of the envelope.
Apoplastic mobility of sucrose in storage parenchyma of sugar beet
Authors: Richter Ekkehard , Ehwald Rudolf
Published: April 2006

The apoplastic movement of sucrose through storage parenchyma discs (2.4 mm thick) from roots of sugar beet (Beta vulgaris var. altissima) was investigated in order to evaluate the suitability of the apoplast for transcellular sugar transport. The sucrose permeability of the discs (P = 5.7 × 10−8 cm s−1 at 25°C) was more than two orders of magnitude lower than that of an equally thick layer of unstirred water. This is due to the small volume fraction of free space (3.1%) and the decreased diffusion coefficient D of sucrose in the cell walls. The effective diffusion coefficient of the apoplast (6 to 9 × 10−7 cm2 s−1 at 25°C) was determined independently of the cross sectional area of free space by treating the time course of fluxes according to Fick's second law. The high diffusion resistance of the apoplast has to be considered in models of native parenchyma transport.
Acyltransferase capacity of membranes from cotyledons of germinating peas
Authors: Macey M. J. K.
Published: April 2006

The incorporation of 1‐[14C]‐palmitate into the lipids of microsomal and mitochondrial membranes from peas (Pisum sativum L., var. Massey Gem) and the relative effects of ATP and coenzyme A(CoA) on the process have been examined. Both mitochondrial and microsomal pellets possessed acyltransferase capacity, which responded similarly to additions of ATP and CoA. Incorporation of 1‐[14C]‐palmitate into phospholipid was promoted by ATP alone, but incorporation into triacylglycerols was not. The addition of CoA alone did not promote incorporation. The addition of CoA and ATP further promoted incorporation into phospholipids and also stimulated incorporation into triacylglycerol. It was concluded that some CoA must be membrane‐bound and available for phospholipid but not for triacylglycerol synthesis. Phospholipase A, treatment of microsomal and mitochondrial phospholipids, previously labelled with 1‐[14C]‐palmitate in the presence of ATP and coenzyme A, showed that incorporation occurred only into the 2‐position of phosphatidyl choline and phosphatidyl ethanolamine.

There was enough lyso‐phosphatidyl choline in the phospholipids of microcomal membranes (obtained from a 100 000 g pellet) to account for the observed incorporations of palmitate. Using microsomal membranes whose fatty acyl groups were pre‐labelled by incubation of tissue with 1‐[14C]‐acetate, no evidence of acyl exchange was found during subsequent incubations with unlabelled palmitate. Similar observations were made using oleate instead of palmitate. It was concluded that acyl‐CoA: 1‐acylglycerophosphocholine o‐acyltransferase (E.C. 2.3.1.23) was responsible for the observed acyl transfer to phosphatidyl choline.

Sucrose gradient analysis of whole homogenates and of the 10 000 g pellet showed that both mitochondrial and rough endoplasmic reticulum possessed acyltransferase capacity, with the bulk of this residing in the mitochondria. The possible significance of this widely distributed membrane activity is briefly discussed.
Physiological changes in, and phosphate uptake by potato plants during development of, and recovery from phosphate deficiency
Authors: Cogliatti Daniel H. , Clarkson David T.
Published: April 2006

The development of phosphate deficiency (P‐stress) was observed in rooted sprouts of Solanum tuberosum L. cv. Desiree growing in solutions without phosphate. Shoot growth was inhibited by P‐stress within 3 to 5 days of terminating the phosphate supply, while significant effects on root growth were not recorded until 7 to 9 days. Thus, the shoot:root dry weight ratio decreased from 4.3 to 2.6 over a 10‐day period. Growth in the absence of an exogenous phosphate supply progressively diluted the phosphorus in the plant. The proportional decrease in concentration was similar in roots and shoots over a 7‐day period, even though the former were growing more quickly.

The potential for phosphate uptake per unit weight of root increased rapidly during the first 3 days of P‐stress. When the plants were provided subsequently with a labelled, 1 mol m−3 phosphate solution, the absorption rate was 3 to 4‐fold greater than that of control plants which had received a continuous phosphate supply. The increased rate of uptake by P‐stressed plants was accounted for by an increase (3‐fold) in the Vmax of system 1 for phosphate transport and by a marked increase in the affinity of the system for phosphate (decrease in Km). In the early stages of P‐stress, before marked changes in growth were measured, the proportion of labelled phosphate translocated to the shoots increased slightly relative to the controls when a phosphate supply was restored. In the later stages of stress a greater proportion was retained in the root system of P‐stressed plants than in that of controls.

In plants with roots divided between solutions containing or lacking a phosphate supply, the increased absorption rate was determined by the general demand for phosphate in the plant and not by the P‐status of the particular root where uptake was measured. By contrast, the poportion translocated was strongly dependent on the P‐status of the root.

The restoration of a phosphate supply to P‐stressed plants was marked by a rapid increase in the P concentration in snoots and roots which returned to levels similar to unstressed controls within 24 h. The enhanced uptake rate persisted for at least 5 days, resulting in supra‐normal concentrations of P in both shoots and roots, and in the formation of extensive necrotic areas between the veins of mature leaves. Autoradiographs showed accumulations of 32P in these lesions and at the points where guttation droplets formed on leaves.
Action spectra and estimation of biologically effective UV radiation
Authors: Rundel Robert D.
Published: April 2006

The use of action spectra in calculating biologically effective ultraviolet radiation fluence is reviewed. In predicting biological damage due to ozone depletion, the most reliable action spectra are those derived from experiments utilizing polychromatic irradiation filtered by sharp cut‐off UV filters. A new method is presented for optimum estimation of an action spectrum from data obtained in such experiments. Details of the mathematical procedures are discussed, and examples of their use on data from both plant and animal objects are given.
Influence of physiological conditions on DNA repair and mutagenesis in higher plants
Authors: Soyfer Valery N.
Published: April 2006

In barley (Hordeum vulgare L.) and grass pea (Lathyrus sativus L.), caffeine, an inhibitor of DNA repair activity, and Na2ethylenediaminetetraacetate, an inhibitor of DNA‐endonucleases, sharply decreased the excision repair of pyrimidine dimers induced in DNA by ultraviolet irradiation. An inhibitor of RNases, diethylpyro‐carbonate, did not inhibit the process of excision, and in one experiment it even enhanced excision. Caffeine markedly increased the frequency of mutations and inhibited the growth of seedlings after UV‐radiation. Such enhancement was greater with the higher UV fluence. Results of chemical inhibition were further confirmed by the suppression of repair by low temperatures: the frequency of chromatid aberrations induced with propyl methanesulfonate was increased more than 3 times and chromatid aberrations 1.5 times. Evidence for participation of repair enzymes in the modification of mutation processes was also obtained in the experiments which combined γ‐irradiation and treatment with propyl methanesulfonate. Conditions favouring repair activity caused a drastic reduction in the frequency of aberrations, whereas with conditions preventing enzyme function the mutation frequency increased. In one of the experiments of this series we were able to demonstrate, with identical mutagenic treatment, that by changing post‐mutagen conditions (wetting and drying of seeds, storage after mutagenic treatment) it was possible to alter the mutation frequency and to obtain below‐additive, additive and synergistic mutational response.
Membranes as targets of ultraviolet radiation
Authors: Murphy Terence M.
Published: April 2006

In non‐photosynthetic cells, evidence for UV (ultraviolet radiation) damage to membranes comes from electron microscopy, chemical analysis and observations of transport processes. Specific perturbations in transport across membranes occur quickly after a relatively low fluence of UV. As an example, irradiation of suspension‐cultured rose cells with 500‐2000 J m−2 (at 254 nm) causes an appearance of K+ in the extracellular medium at the rate of 5 × 10−10μmol cell−1 min−1 for 30 to 60 min and more slowly thereafter. The early, rapid phase of appearance of K+ reflects both an increase in efflux and a decrease in influx. The appearance of K+ is matched by an appearance of HCO−3 in the medium. The HCO−3 comes from respiratory CO2, which hydrates and dissociates in the cytoplasm, leading to a decrease in cytoplasmic pH. Overall, these results not only demonstrate UV damage to membrane function, but also suggest several ways by which UV may alter the general metabolic state of the cell. A demonstration of direct effects of UV on membrane components requires a purified system. At lower fluence, < 1800 J m−2 (254 nm), the ATPase of membrane vesicle preparations is inactivated in a two‐phase process that suggests the presence of enzymes with different UV sensitivities. The existence of two non‐mitochondrial enzymes in rose cell vesicles has been confirmed by solubilizing the vesicle proteins with 1% cholic acid and separating the components on G‐150 Sephadex. One component of relatively high molecular weight is especially sensitive. The fact that it is still sensitive when it is dissolved in cholic acid strongly suggests that its sensitivity is intrinsic and does not depend on sensitization by other membrane components. The action spectrum for the inactivation of the ATPase has a major peak at 290 nm and extends into the UV‐C and UV‐A regions. The physiological effects of UV‐stimulated membrane changes are uncertain. There is little evidence that the UV damage to membranes is responsible for cell death. A UV‐induced loss of K+ from guard cells may result in lower stomatal conductance. UV‐stimulated membrane changes may play a role in the UV‐induced synthesis of anthocyanins.
Comparative study of the action of ultraviolet‐C and ultraviolet‐ B radiation on photosynthetic electron transport
Authors: Kulandaivelu G. , Noorudeen A. M.
Published: April 2006

The effect of ultraviolet‐C (UV‐C, mainly 254 nm radiation) and ultraviolet‐B (UV‐B, 290‐320 nm) radiation on the photosynthetic electron transport reactions has been investigated. The rates of Hill activity mediated by ferricyanide and dichlorodimethoxy‐p‐benzoquinone (DCDMQ) were differently sensitive to UV‐C but equally inhibited by UV‐B. Replacement of water with diphenylcarbazide was ineffective in restoring the activity of dichlorophenol indophenol (DCPIP) Hill reaction in UV‐B treated chloroplasts, but had significant effect in UV‐C treated chloroplasts.

Photobleaching of carotenoids in the presence of carbonyl cyanide‐m‐chlorophenyl‐hydrazone, an indicator of the photochemical reaction associated with the reaction centre of photosystem II, was suppressed and is paralleled by the changes in Hill activity only in UV‐B‐treated chloroplasts. Carotenoid photobleaching occurred even in UV‐C treated chloroplasts showing no measurable Hill activity. UV‐C and UV‐B irradiation diminished variable fluorescence. With UV‐B treated, but not with UV‐C treated chloroplasts, an increase in the fluorescence yield was observed upon the addition of 3‐(3,4‐dichIorophenyl)‐l,l‐dimethylurea (DCMU) and/or Na dithionite.

Photosystem I activity was found to be unaffected by both UV‐C and UV‐B radiation at the fluences tested. Kinetics of P700 photooxidation and dark reversal in UV treated chloroplasts indicate that only the electron flow from photosystem II to photosystem I is impaired. It is concluded that while UV‐B radiation inactivates specifically the photosystem II reaction centre, UV‐C radiation acts at plastoquinone, the quencher Q, and the water oxidizing enzyme system.
Action of UV‐B radiation on photosynthetic primary reactions in spinach chloroplasts
Authors: Iwanzik W. , Tevini M. , Dohnt G. , Voss M. , Weiss W. , Gräber P. , Renger G.
Published: April 2006

Spinach (Spinacia oleracea L. cv. Matador) chloroplasts were irradiated with several levels of UV‐B radiation. Measurements which reflect characteristic steps of photosynthetic electron transport were made to localize the site of impairment of photosynthesis by UV‐B radiation.

Variable fluorescence, the μs‐kinetics of the 320 nm absorption changes and also oxygen evolution were substantially reduced in chloroplasts irradiated with UV‐B. It was not possible to restore the amplitude of the 320 nm absorption changes nor the signal of the transmembrane electric field measured at 520 nm by adding the photo‐system II donor couple hydroquinone/ascorbate to UV‐B treated chloroplast samples. This indicates that impairment of photosystem II activity is not caused by selective inhibition of the water‐splitting enzyme system Y, but rather is due to blockage of photosystem II reaction centers. Photosystem 1 is inferred to be highly resistant to UV‐B radiation.

These results suggest that the reaction centers of photosystem II are transformed into dissipative sinks for excitation energy by action of UV‐B radiation.
Coaction between phytochrome and blue/UV light in anthocyanin synthesis in seedlings
Authors: Vlohr Hans , Drumm‐Herrel Helge
Published: April 2006

Light‐mediated mass production of blue/UV absorbing pigments, anthocyanin and/or other flavonoid compounds, can be considered an adaptive mechanism to protect a plant against high levels of short wavelength sunlight. Comparative studies of light‐mediated formation of anthocyanin in seedlings of higher plants have been performed. As a result of Darwinian evolution, a seedling may be expected to form considerable amounts of pigment only when necessary and only to the extent required for protection ('economy principle'). The four species investigated with regard to light‐mediated synthesis of anthocyanin in seedlings (mustard, milo, tomato, wheat), differ greatly with regard to their photoperception. Phytochrome is involved in the photoresponse in all cases. We conclude that the Pfr‐mediated differential gene activation leading to anthocyanin synthesis is the core of the response. However, the different species differ greatly with regard to the red, blue and UV light dependent processes they perform in order to establish sensitivity towards phytochrome (Pfr), or to amplify sensitivity towards Pfr.
Effects of ultraviolet‐B radiation on the growth and yield of crop plants
Authors: Teramura Alan H.
Published: April 2006

This paper reviews growth chamber, greenhouse, and field studies on the effects of ultraviolet‐B (UV‐B. between 280 and 320 nm) radiation on agricultural crop plants. Our understanding of the physiological effects of UV‐B radiation comes primarily from growth chamber studies, where UV‐B is artificially supplied via filtered lamps. Both photosystems I and II, as well as carboxylating enzymes, are sensitive to UV‐B radiation. Ultraviolet‐B radiation also affects stomatal resistance, chlorophyll concentration, soluble leaf proteins, lipids, and carbohydrate pools. In general, the effects of UV‐B radiation are accentuated by the low levels of visible radiation typically found inside growth chambers.

Ultraviolet‐B radiation has also been shown to affect anatomical and morphological plant characteristics. Commonly observed UV‐B induced changes include plant stunting, reductions in leaf area and total biomass, and alterations in the pattern of biomass partitioning into various plant organs. In sensitive plants, evidence of cell and tissue damage often appears on the upper leaf epidermis as bronzing, glazing, and chlorosis. Epidermal transmission in the UV region decreases in irradiated leaves. This decrease is primarily associated with a stimulation in flavonoid biosynthesis and is thought to be a protective, screening response to the deleterious effects of UV‐B. A considerable degree of variability exists in sensitivity to UV‐B radiation between different species. Approximately 30% of the species tested were resistant, another 20% were extremely sensitive, and the remainder were of intermediate sensitivity, in terms of reductions in total dry weight. In addition to this sizable interspecific variability, there appears to be a similarly wide intraspecific variability in UV‐B response.

The effects of UV‐B radiation on crop yield have only been examined in a limited number of field studies, with ambient levels of UV‐B radiation being supplemented with fluorescent sun lamps. Due to various deficiencies, all these field experiments to date have only limited utility for assessing the potential impact of enhanced levels of UV‐B on crop productivity.
Impact of solar ultraviolet‐B radiation (290‐320 nm) upon marine microalgae
Authors: Worrest R. C.
Published: April 2006

For years scientists and laymen alike have casually noted the impact of solar ultraviolet radiation upon the non‐human component of the biosphere. It was not until recently, when human activities were thought to threaten the protective stratospheric ozone shield, that researchers undertook intensive studies into the biological stress caused by the previously neglected short‐wavelength edge of the global solar spectrum. Stratospheric ozone functions effectively as an ultraviolet screen by filtering out solar radiation in the 220–320 nm waveband as it penetrates through the atmosphere, thus allowing only small amounts of the longer wavelengths of radiation in this waveband to leak through to the surface of the earth. Although this ultraviolet radiation (UV‐B radiation, 290–320 nm) comprises only a small fraction (less than 1%) of the total solar spectrum, it can have a major impact on biological systems due to its actinic nature. Many organic molecules, most notably DNA and proteins, absorb UV‐B radiation which can initiate photochemical reactions. It is life's ability, or lack thereof, to cope with enhanced levels of solar UV‐B radiation that has generated the concern over the potential depletion of stratospheric ozone. The defense mechanisms that serve to protect both plants and animals from current levels of UV‐B radiation are quite varied. Whether these mechanisms will suffice for marine microalgae under conditions of enhanced levels of UV‐B radiation is the subject of this review.
Internal filters: Prospects for UV‐acclimation in higher plants
Authors: Caldwell Martyn M. , Robberecht Ronald , Flint Stephan D.
Published: April 2006

Wavelength‐selective absorption of solar radiation within plant leaves allows penetration of visible radiation (400–700 nm) to the chloroplasts, while removing much of the damaging ultraviolet‐B (UV‐B, 280–320 nm) radiation. Flavonoids are important in this wavelength‐selective absorption. Induction of flavonoid synthesis by solar radiation, and specifically by UV‐B radiation, is discussed as this relates to the potential acclimation of plants to enhanced solar UV‐B radiation that would result from stratospheric ozone reduction.
SO2 and assimilatory sulfate reduction in beech leaves
Authors: Brunold Christian , Landolt Werner , Lavanchy Pierre
Published: April 2006

The effect of SO2 on the extractable activity of ATP sulfurylase (EC 2.7.7.4.). adenosine 5′‐phosphosulfate sulfotransferase, ribulosebisphosphate carboxylase, chlorophyll, protein, sulfate, and amino acids was examined in leaves of potted grafts of beech (Fagus sylvatica L.) treated in outdoor fumigation chambers. Addition of 0.025 and 0.075 μl SO2 1−1 to unfiltered ambient air caused a decrease in the extractable activity of adenosine 5′‐phosphosulfate sulfotransferase to about 20 to 30% of the controls. Neither the extractable activity of ATP sulfurylase and ribulosebisphosphate carboxylase nor the content in chlorophyll, total amino acids and protein were significantly affected by SO2, but there was an increase in the sulfate content. Leaves treated with 0.075 μl SO2 1−1 contained more alanine and cysteine and less serine than the controls. After transfer of the SO2‐treated beech trees to control chambers there was an increase in adenosine 5′‐phosphosulfate sulfotransferase activity, but no significant decrease in SO2−4‐sulfur.
Role of 1‐aminocyclopropane‐1‐carboxylic acid in the control of female flowering in Cucurbita pepo
Authors: Hume R. J. , Lovell Peter H.
Published: April 2006

Cucurbita pepo L. cv. Trailing Marrow is monoecious, bearing separate male and female flowers and the first functional flowers are usually male. Treatment with 300 ppm ethephon delayed and greatly reduced male flower production and also increased female flower numbers. When plants were sprayed with aminoethoxyvinylglycine (AVG) no female flowers were produced but male flower production was unaffected. Even when ethephon was applied to AVG‐treated plants there was still complete inhibition of female flower production. Similarly, AVG‐treated plants subsequently exposed to 4000 ppm ethylene for two days never produced female flowers. AVG inhibits the penultimate stage in ethylene biosynthesis i.e. immediately before 1‐aminocyclopropane‐1‐carboxylic acid (ACC). Although spraying AVG‐treated plants with ACC did not reverse the inhibition, application of ACC via a cut petiole for a 72 h period following AVG application did cause female flowers to form. The evidence indicates that ACC and not ethylene is the factor controlling female flower production in C. pepo.
Effect of H2 evolution on 15N2 fixation, C2H2 reduction and relative efficiency of leguminous symbionts
Authors: van Kessel Christopher , Burris Robert H.
Published: April 2006

The (C2H4+ H2(C2H2))/15N2 ratios of 15 clover‐Rhizobium symbionts. soybean, and black medick symbionts were measured. Relative efficiency based on the C2H4 production and on 15N2 incorporation were compared, and in most symbionts there was little difference between the two measures of relative efficiency. Total measurable electron flux through nitrogenase during acetylene reduction and 15N2 incorporation were nearly equal for most symbionts studied. The relative efficiency and the (C2H4+ H2(C2H2))/15N2 ratio showed an inverse correlation. Use of this ratio appears preferable to use of the ratio of C2H2 reduction/N2 reduction. Some evolution of H2 was observed in the presence of C2H2.
Changes in plastid ultrastructure and fluctuations of cellular isoprenoid and carbohydrate compounds during continued etiolation of dark‐grown oat seedlings
Authors: Wellburn Alan R. , Gounaris Ioannis , Fäßler Leobert , Lichtenlhaler Hartmut K.
Published: April 2006

After continued etiolation of oat (Avena sativa L. cv. Arnold) seedlings without greening at any stage, the volumes of both etioplasts and prolamellar bodies were found to increase to a maximum around the 9th day, declining thereafter. Throughout this process a proportion of the early lamellar components is reconverted later into prolamellar body material to account in part for this crystalline accumulation. Starch grains and stroma‐centres arc only prominent in early etioplasts. The pro‐lamellar bodies of such etioplasts are more amorphous in form resembling more closely the semi‐crystalline bodies of dark‐grown algae or light‐grown cereal seedlings. The high levels of total reducing sugars and fructans after ca 7 days of continued etiolation declined rapidly afterwards, although sucrose content was maximal on the ninth day. It is thought that these carbohydrate reserves were partly used to synthesize sterols (mainly desmethyl sterols) and carotenoids (mainly xanthophylls) found in the high concentrations on around the 9th and 10th days of continued etiolation. High levels of the steroidal saponins in etiolated primary leaves after this time declined to less than half due entirely to the disappearance of avenacoside B, which was partially converted into avenacoside A. Only traces of desgluco‐avenacosides A plus B were found in the late stages of continued etiolation. These results demonstrate that etiolated tissue changes constantly with time. Consequently, greening studies starting with etiolated tissue of different ages may differ considerably even within the same cultivar.
Effect of dicarboxylic acids on the peroxidase‐IAA oxidase isozymes of soybean callus
Authors: Forchetti Silvia Milrad de , Tigier Horacio A.
Published: April 2006

Multiple forms of peroxidase with indole‐3‐acetic acid (IAA) oxidase activity were detected in callus cultures from soybean seeds [Glycinc max (L.) Merrill, cv. Acme] using ion‐exchange chromatography and polyacrylamide gel electrophoresis. The properties of the IAA oxidase were studied with a partially purified fraction eluted from a DEAE cellulose column. At pH 5.7. p‐coumaric acid and MnCl2 were required as cofactors and H2O2 was not able to replace them, but H2O2 eliminated the usual lag period of the reaction. Activation effects obtained with some dicarboxylic acids acting only on IAA oxidase are shown. These effects were studied at different pH values and oxalic acid was found to be the most efficient activator, particularly at pH 4.6. Activation by oxalic acid occurred even in the absence of MnCl2, but the presence of this salt produced a synergistic effect. IAA oxidase showed a sigmoidal kinetic behaviour at pH 5.7 changing to hyperbolic at pH 4.6
Isolation and culture of gymnosperm root protoplasts (Pinus pinaster)
Authors: Faye M. , David A.
Published: April 2006

Various factors affecting the yield and isolation of axenic protoplast cultures originating from Pinus pinaster root segments (in which most cells are differentiating) were studied. In spite of the use of plant material collected from germinating seeds under aseptic conditions, an additional sterilization with 0.1 % w/v mercuric chloride in 50% ethanol was a prerequisite for obtaining an axenic protoplast culture. A pretreatment with 30 mM cysteine in 0.7 M sorbitol for I h tripled the yield. Cen‐trifugation at lOOg instead of 40 g further increased the yield to 6 × 103 protoplasts per cm of root segment. Viability ranged from 80 to 91%. Cell divisions occurred after a minimum of 7 days of culture.
Simulation of marked root hair curling in Rhizobium‐legume symbiosis
Authors: van Batenburg F. H. D. , Kijne J. W. , van Iren F. , Libbenga K. R.
Published: April 2006

The soil bacterium Rhizobium infects its leguminous host plants in temperate regions of the world mostly by way of the growing root hairs. Root hair curling is a prerequisite for root hair infection, although sidelong root hair infections occasionally have been observed. The processes underlying Rhizobium‐induced root hair curling are unknown.

Computer simulation of root hair growth indicates that one‐sided tip growth inhibition by Rhizobium can result in root hair curling when three conditions are simultaneously fulfilled: 1) rhizobial growth inhibition is strong enough to prevent removal out of the tip growth range: 2) root hair surface growth between the attached Rhizobium and the root hair top is inhibited; 3) rhizobial growth inhibition is limited to one side of the root hair.

The results predict that root hair curling by stimulation of tip growth is improbable. This study accentuates the need for information about the growth processes contributing to tip growth in leguminous root hairs.
Effect of KCN and p‐chloromercuribenzenesulfonic acid on the release of sucrose and 2‐amino(1‐14C)isobutyric acid by the seed coat of Pisum sativum
Authors: Wolswinkel Pieter , Ammerlaan Ankie , Kuyvenhoven Herbert
Published: April 2006

The process of sugar and amino acid release by the seed coat of Pisum sativum L. cv. Marzia was studied. Prior to measuring the release of solutes by the seed coat of developing ovules, the embryo was removed from each ovule studied. After this surgical treatment, each “empty” seed coat was filled with the appropriate solution (pH 5.5) with or without inhibitor. Both KCN and p‐chloromercuribenzenesulfonic acid (PCMBS) strongly inhibited the release of sucrose and p‐aminoisobutyric acid (AIB) by the seed‐coat. These data support the view that phloem unloading is an energy‐dependent process sensitive to the sulfhydryl group modifier PCMBS. In pulse‐labelling experiments, addition of high concentrations of unlabelled sucrose (200 mM) and AIB (25 mM) to the solution filling the seed coat cavity did not diminish the release of labelled solutes by the unloading sites of the seed coat. This observation presents evidence against the view that phloem unloading into a strong sink is related to low sugar concentrations in the apoplast.