bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Cd2+ and EDTA on young sugar beets (Beta vulgaris). II. Net uptake and distribution of Mg2+, Ca2+ and Fe2+/Fe3+
Authors: Greger Maria , Lindberg Sylvia
Published: May 2006

Levels of Mg2+, Ca2+ and Fe2+/Fe3+ were determined in roots and shoots of sugar beet seedlings (Beta vulgaris L. cv. Monohill) cultured for 5 weeks in a complete nutrient solution to which either Cd2+ (0, 5 or 50 μM), EDTA (0, 10 or 100 μM) or a combination of both was added. The plants subjected to the various treatments showed a variety of deficiency symptoms. Leaves of the Cd2+‐treated plants became thin and chlorotic (Mg‐ and Fe‐deficiency symptoms). The plants showed reduced growth and developed only a few brownish roots with short laterals (Ca‐deficiency symptoms). EDTA treatment resulted in green, stunted, hard leaves and reduced growth (Ca‐deficiency symptoms). The deficiency symptoms observed correspond well with the observed uptake rates and distributions of Mg2+, Ca2+ and Fe2+/Fe3+. Increases in either Cd2+, EDTA or a combination of both in the growth medium, were correlated with increasing Mg2+ levels in the roots and with decreasing Mg2+ levels in the shoots. Cd2+ alone or in combination with EDTA had little influence on Ca2+ levels in the shoots but decreased Ca2+ levels in the roots. Thus, Cd2+ affects Mg2+ and Ca2+ transport in opposite ways: Mg2+ transport to the shoots is inhibited while that of Ca2+ is facilitated. Treatment with EDTA alone did not affect Ca2+ concentrations in either the shoots or the roots. Treatment with Cd2+ lowered Fe2+ concentrations in both roots and shoots.
An analysis of the role of abscisic acid on the differential expansion and chlorophyll synthesis of the two cotyledons of dormant apple embryo in culture
Authors: Le Page‐Degivry Marie Thérèse , Boillot Annie , Loquès Françoise , Bulard Camille
Published: May 2006

In dormant embryos of Pyrus malus L. cv. Golden delicious laid flat on water agar and cultured under light, inhibition of growth, chlorophyll synthesis and pro‐plastid development in the upper cotyledon was complete, whereas they occurred to a notable degree in the cotyledon in contact with the medium particularly between days 5 and 9 of culture. Radioimmunoassay of endogenous ABA showed a marked difference between the two cotyledons during the first days of culture: on day 2 the level in the upper cotyledon could be 8 times higher than in the lower cotyledon. Experiments using isolated cotyledons showed that this early difference may be responsible for the subsequent divergence in development of the two cotyledons. The effects of exogenous ABA differed depending on the physiological state of the material: when applied at the start of culture ABA inhibited subsequent development, but if applied after 5 days of incubation, when plastid differentiation was already established, ABA no longer prevented growth and only partially inhibited chlorophyll production. The results suggest a direct causal relationship between the levels of endogenous ABA and cotyledon development.
Changes in carbohydrates and mineral elements in Citrus leaves during flowering and fruit set
Authors: Sanz A. , Monerri C. , González‐Ferrer J. , Guardiola J. L.
Published: May 2006

Mineral elements and metabolizable carbohydrates in Citrus leaves [Citrus sinensis (L.) Osbeck cv. Washington navel] have been determined from bud sprouting until the end of the June drop and related to fruitlet growth and abscission. Mineral elements in old leaves decreased during the spring flush of growth and reached minimum values at flower opening, coinciding with a peak in abscission. This was followed by a rapid recovery in potassium and nitrogen to the initial values, with little change afterwards. Old leaves accumulate carbohydrates until flowering, and lose them during post‐anthesis at a constant rate for more than 4 months; this rate of export is unaltered by the presence of a nearby growing fruit. Inflorescence leaves accumulate carbohydrates and mineral elements during post‐anthesis; during the June drop there is an interruption in the accumulation of nitrogen and a net loss of phosphorus, potassium and carbohydrates from these leaves, coinciding with the attainment of the maximum growth rate of the fruit.

The two main periods of abscission coincide with minima in the amount of reserves in leaves, suggesting that a limitation in metabolite supply may be the primary cause of drop. There is a closer relationship of the fruit with inflorescence leaves than with old mature ones; however, the regulation of carbohydrate levels in the inflorescence leaves cannot be simply explained in terms of source‐sink relationships with the nearby growing fruit, and the smaller size of inflorescence leaves vs. vegetative ones is not due to the presence of the flower during leaf development.
Indole‐3‐ethanol oxidase in Phycomyces blakesleeanus. Is indole‐3‐ethanol a “storage pool” for IAA?
Authors: Schramm Peter , Rausch Thomas , Hilgenberg Willy
Published: May 2006

Indole‐3‐ethanol (IEt) was extracted from Phycomyces blakesleeanus Bgff. and purified by TLC and HPLC. Identification was performed by mass spectrum. The HPLC‐purified compound showed an UV‐spectrum typical for indoles, with absorption maxima at 220 and 281 nm. The IEt content varied between 1.5 nmol (g fresh weight)−1 and 5.6 nmol (g fresh weight)−1. The observed variations were strongly correlated with certain developmental stages of the fungus. Furthermore, the decrease of IEt between 60 and 84 h of fungal development coincides with a high IEt oxidase activity. The product of the enzyme reaction was indole‐3‐acetaldehyde, which was identified by co‐chromatography with an authentic standard in several TLC and HPLC systems and by chemical conversion to indole‐3‐acetaldoxime.
Wheat endosperm mRNA and polysomes and their in vitro translation products during development and early stages of germination
Authors: Tercé‐Laforgue Thérèse , Sallantin Marc , Pernollet Jean‐Claude
Published: May 2006

We have examined the synthesis of the gliadins (alcohol‐soluble wheat storage proteins) from Triticum aestivum L. cv. Cappelle Desprez as a function of development from 2 days after anthesis until the beginning of seed germination with respect to free and membrane‐bound polysomes, cytoplasmic poly(A)+RNA and their in vitro translation products. The presence of gliadin mRNAs was investigated in mature dry seed and at the early stages of germination in relation to the lifetime of these mRNAs. Only one maximum, occurring at 18/21 days after anthesis, for mRNAs and polysomes as well as for their synthetic capacity, was observed. Nevertheless, some discrete proteins were expressed at different times during endosperm development, synthesized on either free or membrane‐bound polysomes. All gliadins were continuously synthesized from the earliest stages to maturity. Some long‐lived gliadin mRNAs carried over through the quiescent stage of the grain and were finally found in the germinating seed. From these observations, we conclude that the regulation of gliadin synthesis occurs not only at the transcriptional level but is also partly controlled by the activity of the protein synthesis machinery.
Changes in activities of enzymes involved in flavonoid metabolism during the initiation and suppression of anthocyanin synthesis in carrot suspension cultures regulated by 2,4‐dichlorophenoxyacetic acid
Authors: Ozeki Yoshihiro , Komamine Atsushi , Noguchi Hiroshi , Sankawa Ushio
Published: May 2006

When anthocyanin synthesis was induced in cell suspension cultures of carrot (Daucus carota L. cv. Kurodagosun) by transfer to medium lacking 2,4‐dichlorophenoxyacetic acid (2,4‐D), phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5), chalcone synthase (CHS, EC 6.‐.‐.‐), and chalcone‐flavanone isomerase (CHFI, EC 5.5.1.6) activities appeared, reaching maxima 6–7 days after transfer. The maximum specific activity of CHS was much lower than that of PAL or CHFI. In a medium containing 2,4‐D, no anthocyanin was synthesized, PAL and CHFI activities were suppressed and CHS activity could not be detected at all. The activities of PAL and CHS in cells cultured without 2,4‐D for 6 days began to decrease within 3–6 h of 2,4‐D addition. CHS activity was completely repressed 24–36 h after the addition, but CHFI activity was almost unchanged at this time. After culture without 2,4‐D for 6 days, cell suspensions were transferred to fresh media either lacking or containing 2,4‐D. After transfer, PAL increased in both media within 3 h, whereas CHS activity and anthocyanin accumulation were coordinated and both were completely regulated by 2,4‐D. Changes in CHS activity rather than PAL activity correlate with changes in anthocyanin accumulation under various culture conditions.
Isolation of root hairs from seedlings of Pisum sativum. Identification of root hair specific proteins by in situ labeling
Authors: Röhm Mechthild , Werner Dietrich
Published: May 2006

A procedure was developed which allows the large‐scale isolation of root hairs from seedlings of Pisum sativum. L. cvs. Kleine Rheinländerin and Rosa Krone. The method may yield up to 50 g fresh weight of root hairs per 3.104 seedlings. In a modified form considerable amounts of root hair material may be harvested, even after incubation of the roots in aqueous solutions. Thus, detailed biochemical studies on the root hair system have become feasible.

The occurrence of specific proteins in membrane fractions of P. sativum root hairs was demonstrated as follows: Incubation of root hairs in situ with 3‐azidonaphthalene‐2,7‐disulfonate – a strongly anionic, photoactivated fluorescent marker – followed by gel electrophoresis of membrane fractions showed the presence of root‐hair specific proteins which, since the system was intact, suggests that they are on the outer surface of the cells.
Rooting, growth and ethylene evolution of pea cuttings in response to chloroindole auxins
Authors: Ahmad A. , Andersen A. S. , Engvild K.
Published: May 2006

In pea cuttings (Pisum sativum L. cv. Alaska) we measured shoot and root growth and ethylene production in response to 4‐chloroindole‐3‐acetic acid (4‐CI‐IAA) or 4,6‐dichloroindole‐3‐acetic acid (4,6‐Cl2‐IAA). Leafy cuttings treated basally with either of the chlorinated auxins in high concentrations showed permanent epinasty, loss of apical growth and dominance resulting in the outgrowth of laterals from the lower‐most axillary bud. The naturally occurring 4‐CI‐IAA was a better root promoter than the synthetic 4,6‐Cl2‐IAA which inhibited rooting. Both chloroindole auxins induced very high ethylene evolution, which lasted much longer than the ethylene evolution after IAA treatment.
Effects of drought on [1‐14C]‐oleic and [1‐14C]‐linoleic acid desaturation in cotton leaves
Authors: Pham Thi A. T. , Borrel‐Flood C. , Vieíra da Silva J. , Justin A. M. , Mazliak P.
Published: May 2006

The effects of water stress on [1‐14C]‐oleic and [1‐14C]‐linoleic acid desaturations were studied in leaves of two varieties of cotton (Gossypium hirsutum L.), one drought‐sensitive (Reba) and the other more resistant (Mocosinho). After 24 h incorporation, [1‐14C]‐oleate led to the appearance of linoleate in phospholipids and, additionally, of linolenate in galactolipids. [1‐14C]‐Linoleate was desaturated to linolenate only in galactolipid fractions. Water stress markedly inhibited the incorporation of the precursors into the leaf lipids. The two desaturation steps were affected, particularly the transformation of linoleate to linolenate in monogalactosyldiacylglycerol in the drought‐sensitive variety of cotton. The metabolic implications of the inhibition of the biosynthesis of C18‐polyunsaturated fatty acids are discussed.
Invertase and sucrose synthase activity, carbohydrate status and endogenous IAA levels during Citrus leaf development
Authors: Schaffer Arthur A. , Sagee Oded , Goldschmidt Eliezer E. , Goren Raphael
Published: May 2006

Levels of activity of the sucrose catabolizing enzymes, acid invertase (EC 3.2.1.26) and sucrose synthase (EC 2.4.1.13), were measured during development of new leaves of Citrus sinensis (L.) Osbeck cv. Shamouti. Soluble acid invertase showed a peak activity of 32 nkat (g fresh weight)−1 at ca 60% of full leaf expansion and rapidly declined toward and after full expansion. There was no concomitant increase in an insoluble form of the enzyme. Sucrose synthase activity, measured in the synthesis direction, declined from 33% of full leaf expansion [10 nkat (g fresh weight)−1] 10, and following, full expansion. Highest sucrose synthase activity, measured in the cleavage direction, was 6 nkat (g fresh weight)−1 and showed little change during development. Acid invertase has a Km of 5 mMfor sucrose, while sucrose synthase had a Km of 118 mM for sucrose. Changes in acid invertase activity correlated with changes in the reducing sugar:sucrose ratio. These results suggest that soluble acid invertase activity is the primary enzyme responsible for sucrose catabolism in the expanding Citrus leaf. Changes in leaf expansion rate and invertase activity did not correlate positively with changes in endogenous free IAA level, as determined by enzyme linked immunoassay.
Freezing stress and membrane injury of Norway spruce (Picea abies) tissues
Authors: Pukacki Pawel , Pukacka Stanislawa
Published: May 2006

Effects of sub‐zero temperatures (−5 to −35°C) on the tissues of needles, buds and shoots of Norway spruce [Picea abies (L.) Karst.] were studied. The freezing caused increased efflux of cellular electrolytes. Freezing injury of the primordial shoots and 1‐year‐old shoots was the result of the spontaneous freezing of a deep supercooled cellular water. The crystallization injures the cellular membranes leading to the loss of semipermeability and to the drastic efflux of K+. In the needles there was no deep supercooling of water and two patterns of changes in the membranes, depending upon the range of the applied temperatures, could be distinguished. At 0 to – 25°C, which do not kill the cells, we observed a disturbance in the membrane semipermeability as monitored by electrolytes efflux within a few hours after thawing of the needles. At lower temperatures (−35°C) we observed irreversible loss of the membrane semipermeability, and death of the tissue. Those changes occurred 10 h after thawing and were probably caused by the released lytic enzymes and some toxic compounds, which acted on the cellular membranes.
Chlorophyll synthesis in green leaves and isolated chloroplasts of barley (Hordeum vulgare)
Authors: Dehesh Katayoon , Kreuz Klaus , Apel Klaus
Published: May 2006

The photoreduction of protochlorophyllide was studied in leaves and isolated chloroplasts of barley. Leaves of plants which had been preilluminated for varying lengths of time were incubated with [14C]‐δ‐ aminolevulinic acid for 2 h in the dark. The subsequent photoreduction of [14C]‐protochlorophyllide was analyzed by high performance liquid chromatography of pigments extracted from illuminated leaves and plastids. The plastids used in this study were isolated in the dark from leaves at the end of the 2 h labelling period. Three major results were obtained:

The extent of protochlorophyllide reduction in vivo was rapidly reduced as a function of the preillumination period. In 24 h preilluminated plants only a small fraction of the radioactively labelled protochlorophyllide was reduced during the subsequent light period.

The amount of NADPH‐protochlorophyllide oxidoreductase (EC 1.6.99.‐) present in plastids of fully‐green plants was drastically reduced relative to levels in plastids of dark‐grown plants as estimated by the methods of immunoblotting of plastid proteins and immunogold labelling of ultrathin sections of the leaf tissue.

In etiolated plants light seemed to affect the reduction of protochlorophyllide directly through the excitation of protochlorophyllide. In fully green plants, however, light also affected chlorophyll formation indirectly by the supply of NADPH via photosynthetic electron transport.
Dehydration tolerance of leaf tissues of six woody angiosperm species
Authors: Martin U. , Pallardy S. G. , Bahari Z. A.
Published: May 2006

Electrolyte leakage from leaf discs (measured as an index of dehydration tolerance) increased as water potentials of excised leaves declined for field‐grown saplings of six woody species. Until late in the growing season (mid‐August), leaves of Cornus florida L. exhibited greater leakage than those of other species; however, in August and September leakage in this species was much reduced, indicating apparent hardening in response to mid‐season drought. Leaves of Quercus alba L., Q. rubra L. and Q. velutina Lam. generally exhibited less electrolyte leakage than did those of Acer saccharum Marsh, and Juglans nigra L. over the season. Moreover, leaves of Quercus species showed a reduction in electrolyte leakage late in the season similar to (but less accentuated than) that of C. florida. Saplings of A. saccharum and J. nigra showed little and no drought‐hardening response, respectively. The responses shown by the studied species suggest that dehydration tolerance plays a role in plant distribution and that environmentally induced shifts in this tolerance are a significant phenomenon in natural plant communities.
A novel system for rapid high frequency somatic embryogenesis in Medicago sativa
Authors: Meijer Eltjo G. M. , Brown Daniel C. W.
Published: May 2006

A novel, genotype dependent system for rapid high frequency somatic embryogenesis in Medicago sativa L. was developed in which the first embryos are visible as early as 15 days after the explant (hypocotyl, petiole, leaf) is put into culture. The simplest method involves culture of the explants on a single Murashige and Skoog (MS) medium supplemented with 2 g l−1 casein hydrolysate, 9 μM 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 1.2 μM kinetin. An efficient two‐step, two‐medium system was developed to allow separation of the induction and differentiation phases. The explants are cultured on MS with 22.6 μM 2,4‐D and 4.7 μM kinetin (induction medium) for 10 days and then on basal MS for 20 days. Embryo yields and embryo conversion to plantlets were strongly dependent on the 2,4‐D and kinetin concentrations in the induction medium. Both petiole and leaf explants were highly embryogenic and very little callus proliferation occurred when this method was used. Selected clones from three ssp. falcata‐based M. sativa cultivars showed a response very similar to the highly regenerable falcata clone F1.1, but it was not possible to produce large numbers of somatic embryos in tissue cultures of cv. Regen S, which is used in most M. sativa tissue culture research, with this procedure. These results suggest that there are two distinct developmental pathways for somatic embryogenesis in M. sativa, with Regen S cultures requiring extensive dedifferentiation during a prolonged callus phase, while the genotypes described in this report have no such requirement.
Reconstitution and rapid partial purification of the red beet plasma membrane ATPase
Authors: Singh Sashi P. , Sudershan Kesav B. V. , Briskin Donald P.
Published: May 2006

Red beet (Beta vulgaris L., cv. Detroit Dark Red) plasma membrane ATPase solubilized from a deoxycholate‐extracted plasma membrane fraction with Zwittergent 3–14 was reconstituted into liposomes. Detergent removal and reconstitution was carried out by column chromatography on Sephadex G‐200 followed by centrifugation at 100 000 g for I h. Prior to reconstitution, optimal activity in the solubilized preparation was observed when dormant red beet tissue was used in the extraction/solubilization procedure. Following reconstitution into liposomes, ATP‐dependent proton transport could be demonstrated by measuring the quenching of acridine orange fluorescence. Proton transport and ATPase activity in the reconstituted enzyme preparation were inhibited by orthovandate but stimulated by KNO3. This stimulation most likely results from a reduction in the membrane potential generated during electrogenic proton transport by the reconstituted ATPase. The ATPase activity of the reconstituted ATPase was further characterized and found to have a pH optimum of 6.5 in the presence of both Mg2+ and K+. The activity was specific for ATP, insensitive to ouabain and azide but inhibited by N;N‐dicyclohexylcarbodiimide and diethylstilbestrol. Stimulation of ATP hydrolytic activity occurred in the sequence: K+ Rb+ Na+ Cs+ Li+ and the kinetics of K+ stimulation of ATPase activity followed non‐Michaelis‐Menten kinetics as observed for both the membrane‐bound and solubilized forms of the enzyme. Reconstitution of the plasma membrane ATPase from red beet allowed a substantial purification of the enzyme and resulted in the enrichment of a 100 kDa polypeptide representing the ATPase catalytic subunit.
Effects of glyphosate on phenolic metabolism in yellow nutsedge leaves
Authors: Cañal Maria Jesús , Tumés Ricardo Sanchez , Fernández Belén
Published: May 2006

The action of the herbicide glyphosate [N‐(phosphonomethyl)‐glycine] on phenolic metabolism and phenylalanine ammonia lyase (PAL; EC 4.3.1.5) activity was investigated in yellow nutsedge (Cyperus esculentus L.). Glyphosate caused significant increases in the amount of total soluble hydroxyphenolics in the three fractions studied (neutral, acid and residual). Qualitative and quantitative differences in relation to these fractions and the amount of applied glyphosate were observed. Most of the phenolic compounds which increased after glyphosate treatment were benzoic acids (gentisic. p‐OH‐benzoic, salicylic and vanillic). Gentisic acid showed the greatest increase in neutral and acid fractions, being twenty‐ and four‐fold, respectively, of the amount found in the control. PAL activity was not affected by the lowest doses of glyphosate (10−4and 10−3M), but a dramatic decrease in PAL activity was observed after 10−2M treatment. These findings, together with the low levels of cinnamic acids measured in treated yellow nutsedge plants, suggest that PAL activity is only marginally involved in glyphosate action. Since the herbicidal action probably takes place at 5‐enol‐pyruvylshikimate‐3‐P synthase (EC 2.5.1.19), an alternative pathway to PAL in phenolic biosynthesis should be activated yielding benzoic acids.
Recognition of phlorizin by the carriers of sucrose and hexose in broad bean leaves
Authors: Lemoine Remi , Delrot Serge
Published: May 2006

Phlorizin (1‐[2‐(β‐d‐glucopyranosyloxy)‐4, 6‐dihydroxyphenyl]‐3‐(4‐hydroxyphenyl)‐1‐propanone) is a well‐known non‐transported inhibitor of glucose uptake in animal cells. The effects of this compound were studied on the transmembrane potential difference (PD) of broad bean (Vicia faba L. cv. Aguadulce) mesophyll cells, and on the uptake of amino acids and sugars by the leaf tissues. Phlorizin (5 mM) induced a marginal depolarization (7 to 10 mV) of the normal PD (‐140 mV), and a slight decrease in the uptake of glycine and serine. By contrast, phlorizin induced a stronger inhibition of the uptake of glucose and 3–O‐methylglucose, and more particularly of sucrose uptake and phloem loading. In tissues aged for 12 h, 5 mM phlorizin inhibited the absorption of sucrose from a 1 mM solution by 70%. Kinetic experiments demonstrated that phlorizin acted as a competitive inhibitor for the sucrose carrier and for the hexose carrier. Efflux experiments showed that the counter‐exchange of sucrose and of 3–O‐methylglucose was also phlorizin‐sensitive. Overall, the data show that phlorizin is recognized by the hexose carrier and, more efficiently, by the sucrose carrier of the material investigated, but that it is not transported across the membrane.
Germination uniformity of Fraxinus excelsior controlled by seed water content during cold treatment
Authors: Van de Walle Claude
Published: May 2006

The seeds of Fraxinus excelsior L. are dormant after harvest, since they need a period of chilling for germination. Moist treatment at 20°C for 2–3 months followed by stratification at 4°C for 7 months breaks dormancy. We observed that germination occurred during stratification and was spread over a period of 3 months. Germination at low temperature was temporarily inhibited by a moderate reduction of the seed water content initiated after the third month of stratification. This allowed the afterripening process to continue.

The following procedure was developed to suppress dormancy and to induce uniform germination:

Imbibition of the seeds and moist treatment at 20°C for 2–3 months;

stratification for 3 months;

treatment at low temperature and low water potential for at least 4 months, this treatment should not exceed 6 months;

complete rehydration of the seeds at 16°C.
The effects of exogenously applied plant growth substances on the physiological plasticity in Plantago major ssp. pleiosperma: Responses of growth, shoot to root ratio and respiration
Authors: Kuiper Daan , Staal Marten
Published: May 2006

Growth rates, shoot to root ratios and root respiration were studied in plants of Plantago major L. ssp. pleiosperma (Pilger) at two regimes of mineral nutrition. The responses of plants transferred from one condition to the other were compared with similarly transferred plants supplied with a plant growth substance and also with plants permanently grown at the same nutritional level.

The effect of an addition of benzyladenine (BA) depended on the concentration. Changes in the relative growth rates, shoot to root ratios and root respiration as a response to a lowered mineral supply were strongly retarded by 10−8M BA. These effects of BA were very obvious in the first period of 7 days after the transfer of the plants. During the second period of 7 days the hormonal effects disappeared due to limitation of mineral nutrients. Daily spray with abscisic acid or with indoleacetic acid did not significantly affect the measured characteristics. The results from the experiments with BA addition are discussed in relation to a possible regulatory role of cytokinins in physiological plasticity upon mineral nutrition.
Differences in photosynthetic characteristics among northern and southern C4 plants
Authors: Potvin Catherine
Published: May 2006

Both responses to short‐term changes of temperature and to chilling under high light were analyzed in populations of Echinochloa crus‐galli var. crus‐galli (L.) Beauv. from Québec. North Carolina and Mississippi to improve the understanding of C4 photosynthesis at low temperature. Comparison also included plants of Eleusine indica (L.) Gaertn. from Mississippi to provide for differences among species and populations. Plants were grown at two thermoperiods (28/22°C, 21/15°C). After transfer from cool (21/15°C) to warm (28/22°C) growth conditions, Echinochloa from Mississippi achieved the highest photosynthetic rates. Plants from Québec maintained the highest rates of CO2 uptake upon transfer to cool conditions. Exposure to 7°C for 3 days at a photon fluence rate of 1000 μmol m−2s−1 resulted in a reduction in the growth rates of all populations. This reduction was paralleled by a decrease in net photosynthesis and in stomatal conductance. Following chilling under hight light, the reduction in growth parameters was less important for plants from Québec than for the other populations. It suggests that, among other characteristics, northern plants had developed a certain tolerance to chilling under light.
Effect of abscisic acid on exudation of sunflower roots as affected by nutrient status, glucose level and aeration
Authors: Founier José M. , Benlloch Manuel , Díaz de la Guardia Manuel
Published: May 2006

Three‐week‐old sunflower plants (Helianthus annuus L. cv. Halcón) grown in nutrient solution at two K+ levels (0.3 and 2.5 mM) were used to study the effect of 4 μM abscisic acid (ABA) on the transport of K+ (Rb+) and water to the exuding stream of decapitated plants. Other conditions of the bathing medium of the roots were also assayed, such as presence of 10 mM glucose, aeration and time of ABA application. In the first 2 or 3 h after ABA application, ABA always promoted water and ion fluxes, even under the most unfavorable conditions such as low K+ roots without glucose or under anaerobiosis. The ABA‐promoting effect on ion and water flow was higher with glucose in the medium. Under anaerobiosis the ABA effect disappeared after 3 h. With glucose and aeration the ABA‐promoting effect appeared early and continued for several hours, although the effect decreased with time. If ABA was applied 24 h before excision, the effect was small or even negative. We suggest that ABA acts directly on membranes of certain root cells (endodermal or both endodermal and cortical cells) by increasing their permeability and thus releasing ions. This will decrease cell turgor pressure and, indirectly, the hydraulic conductivity of the whole root. Under conditions of higher hydraulic conductivity, the presence of ions and glucose in the root stimulates the transport of ions into the xylem. and thus increases the osmotic water flow.
Changes in the level of oxidized and reduced pyridine nucleotides during cold acclimation of winter rape plants
Authors: Maciejewska Urszula , Kacperska Alina
Published: May 2006

Prolonged cold (2°C) treatment of winter rape plants (Brassica napus L. var. oleifera L. cv. Górczański) markedly modified the pattern of leaf growth and brought about changes in the level of pyridine nucleotides already during the first few days of treatment. The NAD+, NADP+ and NADPH levels markedly increased but there was practically no effect on the NADH level. Changes in the respective nucleotide levels were reflected by changes in anabolic and catabolic reduction charges. The former increased by 70%, whereas the latter decreased by 44%. Alterations in pyridine nucleotide levels and the reduction charges are discussed in terms of possible mechanisms involved, as well as in terms of their role in plant adaptation to cold.
Preparation of extracts from mature spruce needles for enzymatic analyses
Authors: Weimar Maria , Rothe Gunter M.
Published: May 2006

It was possible to extract simultaneously several active enzymes involved in the carbohydrate or the amino acid metabolism from spruce needles [Picea abies (L.) Karst.] when a) a 100 mM Na‐Pi buffer of pH 7.5 containing 5% PVPP and 0.5% Triton X‐100 was used and when b) the resulting crude extracts were freed from lowmolecular‐weight compounds by gel‐chromatography using the separation medium Fractogel TSK HW‐40. Besides Triton X‐100, Triton X‐305, Myrij‐52 and Brij‐35 were tested, but 0.5% Triton X‐100 brought about the most active enzyme extracts. In crude extracts prepared from spruce needles during the early summer a high increase in absorbance at 334 nm was observed when the co‐substrate NADP+ was added, thus making reliable spectrophotometric assays impossible. The interfering low‐molecular‐weight substances could be eliminated by gel chromatography. As separation media Bio‐Gel P‐6 DG, Sephadex G‐25 m, Trisacryl GF 05 and Fractogel TSK HW‐40 (F) were tested, with Fractogel yielding the highest activities.

With the methods described in this paper the activities of the following enzymes were determined: glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49), 6‐phosphogluconate dehydrogenase (EC 1.1.1.44), glucose‐6‐phosphate isomerase (EC 5.3.1.9), shikimate dehydrogenase (EC 1.1.1.25), NAD+‐malate dehydrogenase (EC 1.1.1.37), glutamate dehydrogenase (EC 1.4.1.2), aspartate aminotransferase (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2). The activities estimated for NAD+‐malate dehydrogenase and 6‐phosphogluconate dehydrogenase are in the range of those published for the needle enzymes of white spruce and Scots pine, respectively.
Photosynthesis and stomatal characteristics of Striga hermonthica in relation to its parasitic habit
Authors: Shah N. , Smirnoff N. , Stewart G. R.
Published: May 2006

Photosynthesis and stomatal characteristics of the angiosperm parasite Striga her‐monthica (Del.) Benth. have been compared with those of Antirrhinum majus L. cv. Suttons Yellow Rust Resistant, a related, non‐parasitic species. The concentration of photosynthetic pigments in S. hermonthica leaves was less than 40% of those of A. majus leaves. Light saturated CO2 assimilation rate of S. hermonthica was less than 40% that of A. majus on a chlorophyll basis and under 20% than of A. majus on a leaf area basis.

Stomata of Striga showed only partial closure in darkness, remained open in water stressed leaves and showed little response to exogenously applied abscisic acid. Stomatal conductance and transpiration were considerably higher in Striga compared with Antirrhinum. The high transpiration and low photosynthetic rates of S. hermonthica resulted in a low water use efficiency. The water relations of Striga leaves, while seemingly inappropriate for growth in drought prone environments, do appear to maximise nutrient and water acquisition from the host and as such may be an adaptation to the parasitic habit.
Changes in K+, Cl− and P contents in stomata of Zea mays leaves exposed to different light and CO2 levels
Authors: Lascève G. , Couchat P. , Vavasseur A. , Bossy J. P.
Published: May 2006

Maize plants (Zea mays L. hybrid INRA 508) were placed under controlled conditions of light and CO2 partial pressure. The K+, Cl− and P contents were then determined by X‐ray microanalysis in the bulbous end of guard cells and in the center of subsidiary cells. The results were interpreted in connection with the stomatal conductance at the time of sampling.

In normal air, the K+ and Cl− contents in guard cells only rose from a light threshold of about 300 μmol m−2 s−1 at which stomata were already largely open. At 600 μmol m−2 s−1, the K+ and Cl− levels in guard cells attained values that were 3‐ and 8‐fold greater, respectively, than the values observed in darkness. The K+ and Cl− contents in the subsidiary cells remained quite constant irrespective of the light conditions. CO2‐free air in darkness induced a significant K+ influx towards guard and subsidiary cells. Under light and in CO2‐free air, the K+ and Cl− contents dramatically increased in the guard cells, but slightly decreased in the subsidiary cells. Thus, when subjected to strong light in CO2‐free air, the K+ and Cl− contents in the subsidiary cells were approximately equal to those measured in normal air conditions. In the guard cells, stomatal opening was associated with a marked shift of the Cl−/K+ ratio – from 0.3 for closed stomata to ca 1 for fully open stomata. This could imply a slow change in the nature of the principal counterion accompanying K+ during stomatal opening. The content of P in guard cells appeared, in contrast to that of K+ and Cl−, to be practically independent of stomatal aperture.
Reverse bimodal action of 2,2,2‐trifluoroethanol on Rumex crispus seed germination
Authors: Taylorson R. B.
Published: May 2006

Light‐stimulated germination of R. crispus L. seed is inhibited by pretreatment with 5 mM 2,2,2‐trifluoroethanol, whereas at higher concentrations (0.1 M) germination is greatly enhanced. The action is the reverse of the usual promotion‐inhibition order of bimodal response to applied substances. In darkness, 0.1 M trifluoroethanol promotes germination. Germination of eight other species (including R. obtusifolius L. and R. acetosella L.) is inhibited by levels of trifluoroethanol that promote germination of R. crispus. Ethanol inhibition of light‐stimulated germination of R. crispus can be partially offset by simultaneous treatment with 0.1 M trifluoroethanol. Similarly, inhibition of the light‐stimulated germination of R. crispus seeds by 5 mM trifluoroethanol can be partially offset by simultaneous treatment with 2‐propanol. The inhibitory and promotive actions of trifluoroethanol may be caused by a specific enzyme inhibition and an anaesthetic effect, respectively.
Nitrate metabolism in soybean root nodules
Authors: Heckmann M. O. , Drevon J. J.
Published: May 2006

The nitrate metabolism in nodules induced by Bradyrhizobium japonicum strain PJ17 on roots of soybean [Glycine max (L.) Merr. cv. Hodgson] has been characterized by the nitrate reductase (NR; EC 1.6.6.1 and EC 1.6.6.3) activity of both partners of the symbiosis. NR activities of bacteroids and nodular cytosol were comparable and significantly higher than those of the roots. Nitrate reduction led to nitrite accumulation in root nodules, which was maximum after pod filling. The nodule had the capacity to metabolize nitrite via nitrite reductase (NiR; EC 1.6.6.4), at least in the cytosolic fraction. This activity was partly inhibited by the low content of free O2 in the nodule. Indeed, nitrite accumulation decreased in the presence of an increased external pressure of O2.
Root primordia and endogenous auxin in maize roots cultured in vitro
Authors: Golaz Franck , Pilet Paul‐Emile
Published: May 2006

Quantitative analyses of indol‐3yl‐acetic acid (Iaa) in Zea mays L. (cv. LG 11) root segments cultured in vitro were performed by gas chromatography‐mass spectrometry with selected ion monitoring. The root extracts were first purified by highperformance liquid chromatography. Root primordia initiation in intact and decapitated roots showed different patterns: decapitation strongly enhanced primordia initiation in their first 10 mm. During the culture (5 days), Iaa content decreased in both intact and decapitated roots. No correlation was found between the level of endogenous auxin and the numher of root primordia initiated from either intact or decapitated maize root segments.
Photophobic stop‐response in a dinoflagellate: Modulation by preirradiation
Authors: Ekelund Nils G. A. , Björn Lars Olof
Published: May 2006

Gyrodinium dorsum Kofoid responds photophobically to flashes of blue light. The photophobic response consists of a cessation of movement (stop‐response). Without background light and after a flash fluence above 10 J m−2, 75–85% of the cells show a stop‐response, while only 50% of the cells show this response at 5 J m−2. With a flash fluence of 5 J m−2, background light of different wavelengths either increases (614 nm. 5.5–18.2 μmol m−2 s−1) or decreases (700 nm, 18.4–36.0 μmol m−2 s−1) the stop‐response. Two hypotheses for the mechanism of the modulation by background light of the photophobic response are discussed: an effect of light on the balance of the photosynthetic system (PS I/PS II) or an effect on a phytochrome‐like pigment (Pr/Pfr). This study supports the idea that a phytochrome‐like pigment works in combination with a blue light‐absorbing pigment. It was also found that cells of Gyrodinium dorsum cultured in red light (39.8 μmol m−2) had a higher absorption in the red region of the absorption spectra than those cultured in white light (92.7 μmol m−2).
Induction of nitrate reductase in needles of Scots pine seedlings by NOX and NO3−
Authors: Wingsle Gunnar , Näsholm Torgny , Lundmark Tomas , Ericsson Anders
Published: May 2006

The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine (Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO3−, no such increase could be detected in the needles. Detached seedlings placed in NO3− solution showed increasing NR activities with increasing NO3− concentrations. Exposure of seedlings to NOx (70–80 ppb NO2 and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO2− (g fresh weight)−1 h−1 to about 400 nmol NO2− (g fresh weight)−1 h−1. This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO2− (g fresh weight)−1 h−1. Analyses of free amino acids showed low concentrations of arginine and glutamine in NOx‐fumigated seedlings compared to corresponding controls.
Effect of paclobutrazol and chilling on leaf membrane lipids in cucumber seedlings
Authors: Whitaker Bruce D. , Wang Chien Yi
Published: May 2006

The effects of paclobutrazol on the leaf membrane lipid composition of seedlings of cucumber (Cucumis sativus L. cv. Victory) subjected to chilling temperatures were assessed. At a non‐injurious temperature (12.5°C), there was no difference in the polar lipid fatty acid composition or in the glycolipid, phospholipid or free sterol content of leaves from treated vs untreated seedlings, regardless of whether paclobutrazol was administered 1 or 7 days prior to analysis. In the latter case (7 days pretreatment), there were clear effects of the bioregulator on plant growth and morphology as well as on leaf chlorophyll content. At an injurious chilling temperature (5°C), desaturation of leaf polar lipid fatty acids was markedly reduced in both treated and untreated seedlings. Chilling at 5°C resulted in losses of fresh weight and membrane lipids in leaves of both groups of plants. These losses were either reversible or irreversible, depending upon the duration of chilling and of pretreatment with paclobutrazol. Seedlings pretreated with 10 μg ml−1 paclobutrazol generally sustained less chilling injury than untreated controls, as judged by the extent of wilting, necrosis and desiccation. This correlated with reduced losses of leaf fresh Weight and membrane lipids.
Diurnal variations in the kinetics of delayed luminescence fromScenedesmus obtusiusculusafter exposure to various light and CO2regimes
Authors: Mellvig Staffan
Published: May 2006

Delayed luminescence was measured from samples of a synchronously growing cell culture of the unicellular green alga,Scenedesmus obtusiusculusChod., every second hour during the 24 h cell cycle under a 15/9 h lighi/dark regime. Both high (air + 2.5% CO2) and low (0.03% CO2) CO2conditions were used. Under high CO2conditions, while light excitation induces formation of a late (maximum reached after 10–60 s) transient peak in delayed luminescence in cells sampled after 10–16 h in the cell cycle. During most of the cell cycle low CO2conditions stimulate a late transient peak formation. Excitation with 700 nm light, but not with 680 nm light, induces a late transient peak in delayed luminescence under high CO2conditions. The transient peak is more or less pronounced depending on the cell stage. The variations might be due to a changing capacity for light‐induced state I/stale II transitions during the cell cycle. It is assumed that the formation of a late transient peak in delayed luminescence is due to ATP hydrolyzation and is thus favoured by a high ATP/NADPH ratio. Hydrolyzation of ATP affects the transthylakoidal ΔpH, which regulates the reverse electron flow to the plastoquinone‐pool and QA/QB, thus affecting the decay kinetics of the delayed luminescence.
Secondary dormancy in Avena fatua: Effect of temperature and after‐ripening
Authors: Symons Stephen J. , Simpson Graham M. , Adkins Stephen W.
Published: May 2006

To evaluate the effect of after‐ripening on secondary dormancy induction in pure genetic lines of Avena fatua L., seed samples were periodically removed from standard conditions of storage and the caryopses then subjected to anoxia. Anoxia did not induce secondary dormancy in SH430, a line characterized by no primary dormancy at harvest maturity; secondary dormancy was induced in caryopses of other lines that had been after‐ripened to over‐come primary dormancy ranging in duration from a few days (CS40, CS166) to several months (AN51, AN127). Germination response to low GA3 concentrations indicated that secondary dormancy in CS40 and CS166 was less intense than in AN51 and AN127. The longer the period of dry after‐ripening prior to anoxia treatment, the lower the intensity of secondary dormancy induced. After a period of dry after‐ripening, which was characteristic for each line, anoxia became an ineffective dormancy‐inducing treatment. Caryopses selected for their response to dormancy induction by anoxia were subjected to temperatures from 5 to 35°C to investigate the effect of low (5 to 18°C) and high (20 to 35°C) temperatures on both thermo‐ and secondary dormancy induction. SH430 was not responsive to any treatment, while CS40, CS166 and AN51 were induced into a thermo‐dormancy at temperatures above 20°C and CS166 and AN51 were induced into secondary dormancy by anoxia at temperatures from 5 to 35°C. The effect of anoxia on secondary dormancy induction in a range of pure genetic lines is discussed with reference to primary dormancy, after‐ripening and temperature.
Senescence in oat leaves: Changes in translatable mRNAs
Authors: Malik Nasir S. A.
Published: May 2006

Changes in translatable mRNA populations during the senescence of oat (Avena sativa L. cv. Victory) leaves were examined by analyzing the in vitro translation products of isolated RNA. Total RNA was isolated from oat leaves of 7‐day‐old seedlings, and also after these leaves were aged for different lengths of time under various conditions. Polypeptides from in vitro translations were separated by two‐dimensional gel electrophoresis to estimate any changes in translatable mRNA populations associated with senescence. Corresponding leaf samples were monitored for loss of chlorophyll as a measure of the extent of senescence. The aging of excised leaves in the light for 4 days resulted in the disappearance or substantial quantitative decrease of a number of mRNA species, while only five new translatable mRNA species were produced. Three of these mRNAs were unique to aging of leaves under light. Two of these mRNA species were also produced during the early stages of senescence in attached leaves of seedlings grown under light. The translatable mRNA populations of leaves aged for 4 days either on intact seedlings or detached and kept in the light in the presence of kinetin were very similar. Aging of excised leaves in the dark on water for 24 h resulted in very extensive changes in translatable mRNA populations. Over thirty polypeptides disappeared or were substantially reduced in quantity, while about an equal number appeared de novo or were substantially increased in quantity. Aging of these leaves for an additional 24 or 48 h resulted in only a few additional changes in translatable mRNAs. The presence of kinetin during aging of excised leaves in the dark inhibited few of the numerous changes in mRNAs that occured during the first 24 h, but did inhibit most of the changes that occured after 48 or 72 h of aging in the dark. When leaves were first aged in the dark and then returned to light, most of the initial changes in translatable mRNAs expression were reversed. Such changes in mRNAs thus appear to be light‐regulated and not necessarily associated with senescence.
Influence of the g‐force on the circumnutations of sunflower hypocotyls
Authors: Zachariassen Eli , Johnsson Anders , Brown Allan H. , Chapman David K. , Johnson‐Glebe Corey
Published: May 2006

Circumnutations of hypocotyls of sunflower (Helianthus annuus L. cv. Californicus) were studied under 1 g and 3 g conditions. Root mean square values of the hypocotyl deviation from the plumbline and period of the movements were determined from Calculations of the autocorrelation functions of the movements. The amplitude and the period of the circumnutations increased under 3 g as compared to 1 g. A transition from 3 to 1 g or vice versa also caused changes in period and amplitude of the movoments. The results are interpreted as a support for the idea that gravity influences the circumnutation parameters in this sunflower variety. A comparison is made with published results on the dwarf sunflower ev. Teddy Bear where the force influence is very small or negligible. Simulations of a model for circumnutations show movements which are in qualitative agreement with the experimental results, provided adaptation to g‐levels is included in the model. Finally, the results are discussed with the recent Spacelab‐experiment (SLI) as a background.