bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrate reductase in higher plants: A case study for transduction of environmental stimuli into control of catalytic activity
Authors: Kaiser W. M. , Weiner H. , Huber S. C.
Published: March 2003

In higher plants, cytosolic NAD(P)H‐nitrate reductase (NR) is rapidly modulated by environmental conditions such as light, CO2, or oxygen availability. In leaves, NR is activated by photosynthesis, reaching an activation state of 60–80%. In the dark, or after stomatal closure, leaf NR is inactivated down to 20 or 40% of its maximum activity. In roots, hypoxia or anoxia activate NR, whereas high oxygen supply inactivates NR. Spinach leaf NR is inactivated by phosphorylation of serine 543 and subsequent Mg2+‐dependent binding of 14‐3‐3 proteins at, or close to, this phosphorylation site. At least three different protein kinases (NR‐PK) have been identified in spinach leaves that are able to phosphorylate NR on serine 543. Two of them show up as calmodulin‐like domain protein kinases (CDPKs), and one as a SNF1‐like protein kinase. Dephosphorylation of serine 543 is catalyzed by a Mg2+‐dependent protein phosphatase and by a type 2A protein phosphatase (NR‐PP), which is regulated by a trimer/dimer interconversion. The NR‐PKs, NR‐PPs, and 14‐3‐3s are present even in NR‐depleted plant tissues. Artificial activation of NR in vivo is achieved by cellular acidification, by respiratory inhibitors, or by mannose feeding. As for anoxia, these treatments seem to act, at least in part, via cytosolic acidification, mediated by low cytosolic ATP levels. Activation is also achieved by ionophore‐induced release of divalent cations from the cytosol. In addition, cytosolic AMP and phosphate esters seem to regulate NR‐PK and NR‐PP activities, thereby adapting NR activity within minutes to the changing environment.
Further evidence for feedback regulation of gibberellin biosynthesis in pea
Authors: Ross John J. , MacKenzie‐Hose Alasdair K. , Davies Peter J. , Lester Diane R. , Twitchin Bruce , Reid James B.
Published: March 2003

In shoots of the garden pea (Pisum sativum L.), the main bioactive gibberellin (GA) is GA1, which is synthesised from GA20 by 3β‐hydroxylation. Gibberellin A20 is produced from GA19, as part of the process known as GA 20‐oxidation. Because these steps are thought to be negatively regulated by GA1, we compared the metabolism of labelled GA19 and GA20 in mutants deficient in GA1, with that observed in isogenic wild‐type (WT) plants. There was a large and specific increase in the 3β‐hydroxylation of labelled GA20 in the GA1‐deficient (dwarf) mutants, compared with the WT. Metabolism experiments did not provide convincing evidence for feedback regulation of 20‐oxidation, possibly because GA19 akppears to be metabolised rapidly, even in WT pea shoots. Both 3β‐hydroxylase and 20‐oxidase transcript levels were markedly higher in the mutants than in isogenic WT lines. The results sukpport previous suggestions that both biosynthetic steps are feedback‐regulated by GA1 in pea.
Regulation of the germination of Rhus coriaria, a post‐fire pioneer, by heat, ash, pH, water potential and ethylene
Authors: Ne'Eman Gidi , Henig‐Sever Nava , Eshel Amram
Published: March 2003

Germination of the post‐fire pioneer species Rhus coriaria, in Pinus halepensis forests on Mount Carmel, Israel, is restricted to the ash covered microsites under large burned pine trees, where the germination of other species is strongly inhibited. The aim of this study was to examine the effect of heat, ash cover, pH, water potential (Ψ) and ethylene on germination of R. coriaria seeds, in order to identify the causes of this unique germination pattern. Pre‐heating to 120–140°C for 15 min was essential for the induction of seed germination. Germination percentage was increased by ash cover of 1.2 and 2.4 kg m−2 (1 and 2 cm, respectively) but inhibited by ash cover of 6.0 kg m−2 (5 cm). Wet pine ash from a recently burned forest had pH of 10 and Ψ of −0.26 MPa. Under such conditions the germination of R. coriaria was reduced by ca 80%. On the other hand, germination was stimulated by 0.03–0.10 p.p.m. ethylene which was released by wet ash. The post‐fire germination of R. coriaria is regulated by the balance between the stimulating effects of fire heat and the ethylene released by the ash, and the inhibition caused by the high pH and the low Ψ caused by the ash. Its mode of dispersal by birds and these ecophysiological attributes direct germination of R. coriaria to preferred microsites under the burned canopies of large pine trees. These microsites are characterized by improved nutrition and low competition.
Intrinsic water use efficiency at the pollination stage as a parameter for drought tolerance selection in Phaseolus vulgaris
Authors: Pimentel C. , Laffray D. , Louguet P.
Published: March 2003

Genotype differences in gas exchange during ontogeny and water stress responses at the vegetative and pollination stages were evaluated in four lines of Phaseolus vulgaris L. In the cultivar Carioca, net photosynthetic rate (A) and stomatal conductance (gs) were lower at the vegetative stage (20 days after sowing [DAS]) and maximum at the pollination stage (39 DAS), followed by a decrease at the flowering stage (46 DAS) and a dramatic fall at the grain‐filling stage (60 DAS). Among the lines studied, the stomata of A320 closed faster than those of the other lines when water stress occurred at 20 or 39 DAS. The cultivar SC‐90298823 had greater stomatal conductance at 39 DAS and a higher photosynthetic level than the other lines. Stomata of Ouro negro remained partially open during the water stress at the pollination stage (39 DAS) and supported a positive net photosynthetic rate (A). Differences were also found between lines in intrinsic water use efficiency (IWUE) at 39 DAS, but not at 20 DAS. The possibility of using IWUE at the pollination stage is discussed, in view of its use as one of the parameters for a drought tolerance breeding program in bean lines.
Leaf and root control of stomatal closure during drying in soybean
Authors: Bunce James A.
Published: March 2003

The stomatal conductance of an illuminated 2.5 cm2 area of an intact soybean leaflet was the same whether the rest of the shoot was in light or darkness. This was true throughout soil drying cycles. Water potential of tissue immediately outside the illuminated area consistently decreased about 0.3 MPa upon illumination of the shoot. This erroneously suggested that stomatal conductance during soil drying did not respond to diurnal reductions in leaf water potential, but was controlled by root or soil water status. Tests showed that the water potential of tissue in the illuminated area did not change in the steady‐state upon illumination of the rest of the shoot. Water potentials of shaded sections of leaves were not different from predawn water potentials, and were higher than leaf xylem pressure potentials as determined with a pressure chamber. These steep local gradients of leaf water potential suggest that there is minimal interchange of water among xylem elements leading from roots to different sections of leaves. The relationship between stomatal conductance and leaf water potential was the same whether leaf water potential was reduced by soil drying, application of polyethylene glycol (PEG) to the root system, lowering root temperature, or leaf excision. In the root cooling experiment, there was no soil drying, and with leaf excision, there was no root drying. The similarity of stomatal responses to leaf water potential in all cases strongly suggests control of conductance by a signal produced by local leaf water potential rather than root or soil water status in these experiments.
Effect of chilling, heat shock, and vigor on the growth of cucumber (Cucumis sativus) radicles
Authors: Mangrich Mary E. , Saltveit Mikal E.
Published: March 2003

Chilling at 2.5°C reduced the subsequent growth of cucumber (Cucumis sativus L.) radicles at 25°C. The reduction in radicle growth was linear for 1–3 days of chilling at ≈10% per day of treatment, but then it increased in a non‐linear pattern until subsequent radicle growth was all but eliminated by 6 days of chilling. A heat shock of 40°C for 4–12 min increased chilling tolerance such that 4 days of chilling caused only a 36% decrease in radicle growth, compared to 66% for seedlings not heat shocked. Heat shocks were only able to protect that part of radicle growth that was in excess of the linear decrease in radicle growth projected from 0–3 days. There appear to be two effects of chilling on radicle growth. The first inhibition of subsequent growth was linear and was not affected by heat shocks. The second inhibition was much more severe; it appeared after 3 days of chilling and could be prevented by heat shock. Seeds classified with different levels of vigor (i.e., different initial rates of growth) did not respond significantly different to chilling stresses following heat‐shock treatments.
Mucilage strongly binds aluminum but does not prevent roots from aluminum injury in Zea mays
Authors: Feng Li Xiao , Ma Jian Feng , Hiradate Syuntaro , Matsumoto Hideaki
Published: March 2003

The possible role of mucilage in protecting roots from aluminum (Al) injury was investigated in Zea mays L. (cv. Golden Cross Bantam), focusing on binding of Al with mucilage and effects of mucilage on Al toxicity. Al was bound to mucilage after the treatment of roots with 10–50 μM Al for 1 h and 30 μM Al for 30, 60, 90 and 120 min. Using molecular sieve chromatography (Sephadex G‐100), Al was co‐eluted with a high molecular mass sugar and a low molecular mass sugar. The difficulty in desorbing Al from mucilage with organic acids confirmed the strong binding strength of Al by mucilage revealed by 27Al nuclear magnetic resonance (NMR). Al could not be desorbed completely by succinic, malic, oxalic and citric acid at a molar ratio of 1:1. It could only be completely removed by oxalic acid at a molar ratio of 20:1 (oxalate:Al). Bioassay experiments showed that cell viability and callose formation were unaffected by Al bound to mucilage. However, mucilage deprived roots had only 0.21–0.59 nmol apex−1 higher Al content than control roots after treatment with 30 μM Al for 1, 1.5 and 2 h. Moreover, inhibition of root elongation by 5 μM Al for 6, 12, 24 and 36 h was independent of the presence or absence of mucilage prior to the Al treatment. These results indicate that although mucilage affects the accumulation of Al by roots, it does not confer Al resistance to Z. mays root apices.
Kinetics of phosphate absorption by mycorrhizal and non‐mycorrhizal Scots pine seedlings
Authors: Van Tichelen K. K. , Colpaert J. V.
Published: March 2003

Kinetics of net phosphate (Pi) uptake was measured on intact ectomycorrhizal and non‐mycorrhizal Pinus sylvestris seedlings using a semihydroponic cultivation method. The depletion of Pi in a nutrient solution was assessed over a 160–0.2 μM Pi gradient. Growth of the pine seedlings was P limited and measurements were performed 7 and 9 weeks after inoculation. Three ectomycorrhizal fungi were studied: Paxillus involutus, Suillus bovinus and Thelephoraterrestris. Pi uptake was extremely fast in plants colonised by P. involutus. The Pi concentration dropped below 0.2 μM within 4–5 h. In plants colonised with S. bovinus this occurred in 5–6 h and in plants associated with T. terrestris 8 h were needed to run through the whole concentration range. Non‐mycorrhizal plants of similar size and nutrient status decreased Pi to a concentration between 1 and 2 μM in 18 h. Data were curve fitted to a two‐phase Michaelis‐Menten equation. The apparent kinetic constants, Km and Vmax, for the high affinity Pi uptake system of the pine roots could be estimated accurately. Vmax of this system was up to 7 times higher in pines associated with P. involutus than in non‐mycorrhizal seedlings. The intact extraradical mycelium greatly increased the absorption surface area of the roots (Vmax). Non‐mycorrhizal plants had a Km between 7.8 and 16.4 μM Pi. Plants mycorrhizal with P. involutus had Km values between 2.4 and 7.2, plants colonised with S. bovinus had a Km between 5.1 and 12.3, and seedlings associated with T. terrestris had a Km from 4.6 to 10.1 μM Pi. All 3 ectomycorrhizal fungi had a strong impact on the Pi absorption capacity of the pine seedlings. The results also demonstrated that there is substantial heterogeneity in kinetic parameters among the different mycorrhizal root systems.
Photosynthesis and its related physiological variables in the leaves of Brassica genotypes as influenced by sulphur fertilization
Authors: Ahmad Altaf , Abdin M. Z.
Published: March 2003

In the present investigation, we examined the effect of sulphur fertilization on photosynthesis (Pn) and its related physiological variables in the leaves of field grown Brassica genotypes (Brassica juncea [L.] Czern. and Coss. cv. Pusa Jai Kisan and Brassica campestris L. cv. Pusa Gold) over a whole growing season. Sulphur fertilization significantly (P<0.05) increased the Pn rate on leaf area basis at all the growth stages over −S treatment. The photosynthesis related variables such as soluble protein and Rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase) protein were significantly higher in the leaves of plants grown with +S treatment, when compared to −S treatment. Sulphur fertilization also improved the chlorophyll, N and S content in the leaves of +S treated plants over −S treatment. Leaf‐S content was linearly correlated with Pn rate, N‐content and Rubisco protein in the leaves of both genotypes. An interesting relationship between N‐content and Pn rate in the leaves of −S and +S treated plants was observed. In −S plants, the relationship between Pn rate and N‐content per unit area of fully matured leaves became non‐linear when leaf‐N exceeded 1.5 g m−2, while in +S plants the same remained linear. Rubisco protein was linearly related to Pn rate and leaf‐N content. The ratio of Rubisco/soluble protein was lesser in the leaves of −S treated plants than +S treated plants. The effect of sulphur fertilization on Pn is discussed in relation to improved nitrogen utilization efficiency of the plants that leads to incorporation of reduced‐N into the protein, especially in Rubisco protein rather than the non‐protein compounds.
Purification, characterization and antifungal properties of a lipid‐transfer protein from sunflower (Helianthus annuus) seeds
Authors: Regente Mariana C. , De La Canal Laura
Published: March 2003

An antifungal protein from Helianthus annuus L. seeds (Ha‐AP10) has been purified to homogeneity and characterized. Ha‐AP10 purification was performed by gel filtration, cation exchange chromatography and reverse phase HPLC. Its molecular mass was estimated to be 10 kDa and western blot analyses suggest that it has an extracellular location. The N‐terminal sequence of Ha‐AP10 showed strong homology to some plant lipid‐transfer proteins (LTPs). Antifungal tests have demonstrated that Ha‐AP10 exerts a fungistatic effect. It completely inhibits the germination of spores of the fungal pathogen Fusarium solani f. sp. eumartii at a concentration of 40 μg ml−1 and produces a 50% growth inhibition at 6.5 μg ml−1 (0.65 μM). These data place Ha‐AP10 among the most potent antifungal LTPs described so far.
Diurnal fluctuations of antioxidative systems in leaves of field‐grown beech trees (Fagus sylvatica): Responses to light and temperature
Authors: Peltzer Detlef , Polle Andrea
Published: March 2003

To test the hypothesis that antioxidant systems flexibly adjust to short‐term, diurnal fluctuations of ambient environmental conditions, ascorbate‐related systems were studied over several day/night cycles in mature sun‐acclimated leaves of field‐grown beech trees (Fagus sylvatica). Light‐dependent increases in the activities of ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate radical reductase (MDAR, EC 1.1.5.4) and glutathione reductase (GR, EC 1.6.4.2) were not observed. Lowest activities of APX and MDAR were found on hot, sunny days. A strong negative correlation occurred between APX activities and ambient temperatures suggesting that this enzyme was temperature‐ rather than light‐regulated. In contrast to the enzymatic defences, ascorbate levels increased by about 30% under bright sunlight suggesting that protection from excess light is mediated via the adjustment of metabolites. Under these conditions the apparent electron transport rate exceeded the capacity for assimilation and the dehydroascorbate pool increased twofold. Since dehydroascorbate reductase activities were hardly detected, MDAR activities seemed to be the major enzyme to keep ascorbate in its reduced state. However, MDAR appeared to be insufficient to maintain the redox balance of the ascorbate pool under high light intensities in the field.
Ultrastructure of the cuticle during growth of the grape berry (Vitis vinifera L.)
Authors: Casado Carolina G. , Heredia Antonio
Published: March 2003

The outer surface morphology and the ultrastructure of grape berries during growth were examined by electron microscopy. The cuticle began to form before anthesis as highly organized and tightly appressed cuticular ridges. During the period of rapid expansion, the cuticular material spread out over the grape berry. At the same time, an outer wax layer of about 0.5 μm was indentified. As growth proceeded, the cuticular material flattened out and eventually disappeared. At the final stage of growth, the berry had a smooth, continuous and homogeneous cuticle with a thickness of 3 μm.
Involvement of matrix NADP turnover in the oxidation of NAD+‐linked substrates by pea leaf mitochondria
Authors: Bykova Natalia V. , Møller Ian M.
Published: March 2003

The involvement of the internal rotenone‐insensitive NADPH dehydrogenase on the inner surface of the inner mitochondrial membrane [NDin(NADPH)] in the oxidation of strictly NAD+‐linked substrates by pea (Pisum sativum L.) leaf mitochondria was measured. As estimated by the inhibition caused by 5 μM diphenyleneiodonium (DPI) in the presence of rotenone to inhibit complex I, the activity of NDin(NADPH) during glycine oxidation (measured both as O2 uptake and as CO2 release) was 40–50 nmol mg−1 protein min−1. No significant activity of NDin(NADPH) could be detected during the oxidation of 2‐oxoglutarate, another strictly NAD+‐linked substrate; this was possibly due to its relatively low oxidation rate. Control experiments showed that, even at 125 μM, DPI had no effect on the activity of glycine decarboxylase complex (GDC) and lipoamide dehydrogenase. The relative activity of complex I, NDin(NADPH), and NDin(NADH) during glycine oxidation, estimated using rotenone and DPI, differed depending on the pyridine nucleotide supply in the mitochondrial matrix. This was shown by loading the mitochondria with NAD+ and NADP+, both of which were taken up by the organelle. We conclude that the involvement of NADP turnover during glycine oxidation is not due to the direct production of NADPH by GDC but is an indirect result of this process. It probably occurs via the interconversion of NADH to NADPH by the two non‐energy‐linked transhydrogenase activities recently identified in plant mitochondria.
The cytokinin 2‐isopentenyladenine causes partial reversion to skotomorphogenesis and induces formation of prolamellar bodies and protochlorophyllide657 in the lip1 mutant of pea
Authors: Seyedi Mahdi , Selstam Eva , Timko Michael P. , Sundqvist Christer
Published: March 2003

When grown in darkness the photomorphogenic lip1 mutant of pea (Pisum sativum L.) has a slender stem, expanded leaves, prolamellar body (PLB) lacking plastids with the size of chloroplasts and a low level of phytochrome A. The lack of PLBs in a dark‐grown material (lip1) created a possibility to further study the regulation of their formation in relation to plant development. Inclusion of a cytokinin, 2‐isopentenyladenine (2iP), in a medium supporting growth of the pea seedlings in darkness was found to reduce epicotyl length in the wild type. In lip1 the formation of a slender stem was inhibited and a short epicotyl developed. Furthermore, leaf expansion was inhibited, the plastid size reduced and the formation of PLBs induced. The PLB formation in lip1 was not accompanied by an increase in the amount of protochlorophyllide (Pchlide) or Pchilde oxidoreductase (POR). In the presence of 2iP the level of phytochrome A protein was increased in lip1 and the POR mRNA levels decreased in both lip1 and wild‐type plants. The chloroplast characteristic trans‐3‐hexadecenoate acyl group of phosphatidylglycerol, present in the plastids of dark‐grown lip1, was not influenced by 2iP. Thus, not all photomorphogenic processes reacted similarly in the lip1 mutant, but leaf expansion and plastid differentiation, including PLB formation, seemed to be regulated by the same signal transduction chain. Exogenously applied brassinolide could rescue neither dark‐ nor light‐grown defects of the lip1 mutant. Thus, cytokinins but not brassinolides seem to be involved in the regulation of certain characteristic traits of skotomorphogenesis in pea, including plastid development and PLB formation.
4‐Hydroxybenzyl alcohol accumulates in suspension‐cell cultures and inhibits somatic embryogenesis in carrot
Authors: Kobayashi Toshihiro , Higashi Katsumi , Kamada Hiroshi
Published: March 2003

Somatic embryogenesis in carrot (Daucus carota L.) is strongly inhibited by certain factors that accumulate in culture medium of high‐density cultures of embryogenic cells. We previously identified 4‐hydroxybenzyl alcohol (4HBA) as one of the inhibitory factors. In this study, we analyzed the accumulation pattern of 4HBA in the cultures of carrot suspension cells. When somatic embryogenesis was induced by culturing embryogenic cells in phytohormone‐free Murashige and Skoog medium at various initial cell densities, 4HBA accumulated in the culture medium. The concentration of 4HBA in high cell density cultures was higher than in low cell density cultures. The accumulation of 4HBA in high cell density cultures was rapid during the early days of culture. This rapid accumulation of 4HBA in high cell density cultures might result in the strong inhibition of somatic embryogenesis. The production of 4HBA decreased as the somatic embryos developed. In addition, embryogenic cells released larger amount of 4HBA into the culture medium compared with non‐embryogenic cells. These results suggest that the production of 4HBA is both related to embryogenic competence and developmentally regulated during somatic embryogenesis.
Limited carbohydrate availability as a potential cause of fruit abortion in Rubus chamaemorus
Authors: Jean Donald , Lapointe Line
Published: March 2003

Fruit abortion can be caused by a range of abiotic and biotic factors. To gain a better understanding of the causes of the high fruit abortion frequency in cloudberry (Rubus chamaemorus L.), we manipulated different sources of carbon, that is, leaves and rhizome. We also manipulated flower number to see if competition between floral ramets explained fruit abortion in cloudberry. Reducing the number of flowers had no impact on fruit abortion frequency. In fact, the species forms an extensive rhizome network with only a few ramets per clone and competition between floral ramets is unlikely. Ramet defoliation had limited impact on fruit abortion, but successful fruit development was affected by rhizome length. The longer the rhizome, the higher the chances to mature a fruit. These results suggest that current photoassimilate production by the reproductive ramet alone is insufficient to insure fruit development. Carbon can come from other ramets but distances are usually high between ramets. Fruit production might thus depend on the use of stored carbohydrates in the rhizome to balance insufficient photosynthetic contribution during fruit production.
Tolerance of coffee (Coffea spp.) seeds to ultra‐low temperature exposure in relation to calorimetric properties of tissue water, lipid composition, and cooling procedure
Authors: Dussert Stéphane , Chabrillange Nathalie , Rocquelin Gérard , Engelmann Florent , Lopez Marcel , Hamon Serge
Published: March 2003

The effect of exposure to ultra‐low temperature (liquid nitrogen, LN) on viability of seeds desiccated to various water contents was investigated in 9 coffee species. Three groups of species could be distinguished based on seed survival after LN exposure. In group 1 species, no seedling production could be obtained after LN exposure due to endosperm injury. In group 2 species, recovery was very low or nil after rapid cooling, and only moderate after slow cooling. In group 3 species, very high percentages of seedling development were observed after both rapid and slow cooling. A high interspecific variability for the high moisture freezing limit was observed within the species of groups 2 and 3, since it ranged from 0.14 to 0.26 g H2O g−1 dry weight. A very highly significant correlation was found for those species between the unfreezable water content, as determined from DSC analysis, and the high moisture freezing limit of their seeds. No significant correlation was found between seed lipid content, which varied from 9.8 to 34.6% dry weight, and survival after LN exposure. However, a negative relationship was found between seed unfreezable water content and lipid content. Interspecific differences in fatty acid composition of seed lipids resulted in a high variability in the percentage of unsaturated fatty acids, which ranged from 28.7 to 54.4% among the 9 species studied. For all species studied, a highly significant correlation was found between the percentage of unsaturated fatty acids and the percentage of seedling recovery after rapid or slow cooling.
Glyphosate selection of gene amplification in suspension cultures of 3 plant species
Authors: Widholm Jack M. , Chinnala A. R. , Ryu Jeom‐Ho , Song Hee‐Sook , Eggett Therese , Brotherton Jeffrey E.
Published: March 2003

Stepwise selection was carried out with increasing glyphosate concentrations to produce suspension cultures of Medicago sativa L. (alfalfa), Glycine max L. (Merr.) (soybean) and Nicotiana tabacum L. (tobacco) (two lines) that were at least 100‐fold more resistant than the original culture as measured by the I50. The selection process required from 8 to 11 transfers to fresh medium over a total period from 161 to 312 days. The alfalfa and soybean lines contained 62‐ and 21‐fold higher activity levels of the glyphosate target enzyme, 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSPS), respectively. The tobacco lines had EPSPS enzyme activity levels more than 800‐times higher than the original cultures. The EPSPS gene copy number and mRNA were increased in all of the lines as measured by southern and northern hybridization, respectively. Thus, as has been found before with most glyphosate‐resistant suspension cultures, the resistance is caused by high EPSPS enzyme activity due to EPSPS gene amplification. Alfalfa and soybean EPSPS gene amplification and the very high EPSPS enzyme activity increases found in the tobacco cultures have not been reported before. These studies show that EPSPS gene amplification can occur in many plant species to confer glyphosate tolerance.
Regulation of alternative oxidase activity during phosphate deficiency in bean roots (Phaseolus vulgaris)
Authors: Juszczuk Izabela M. , Wagner Anneke M. , Rychter Anna M.
Published: March 2003

Cyanide‐resistant respiration was studied in mitochondria isolated from the roots of bean plants (Phaseolus vulgaris L. cv. Złota Saxa) grown hydroponically up to 16 days on a phosphate‐sufficient (+P, control) or phosphate‐deficient (−P) medium. Western blotting indicated that the alternative oxidase (AOX) was present only in its reduced (active) form, both in phosphate‐sufficient and phosphate‐deficient roots, but in the latter, the amount of AOX protein was greater. Addition of pyruvate to the isolation, washing and reaction media made mitochondria from +P roots cyanide‐insensitive, similar to mitochondria from −P roots. The doubled activity of NAD‐malic enzyme (NAD‐ME) in −P compared with +P root mitochondria may suggest increased pyruvate production in −P mitochondria. Lower cytochrome c oxidase (COX) activity and no uncoupler effect on respiration indicated limited cytochrome chain activity in −P mitochondria. In −P mitochondria, the oxygen uptake decreased and the level of Q reduction increased from 60 to 80%. With no pyruvate present (AOX not fully activated), inhibition of the cytochrome pathway resulted in an increased level of the ratio of reduced ubiquinone (Qr) to total ubiquinone (Qt) (Qr/Qt) in +P mitochondria, but did not change Qr/Qt in −P mitochondria. When pyruvate was present, the kinetics for AOX were similar in mitochondria from −P and +P roots. It is suggested that AOX participation in −P respiration may provide an acclimation to phosphate deficiency. Stabilization of the ubiquinone reduction level by AOX might prevent the harmful effect of an increased formation of reactive oxygen species.
An aquatic perspective on the concepts of Ingestad relating plant nutrition to plant growth
Authors: Raven John A.
Published: March 2003

The Ingestad approach to the culture of higher terrestrial plants for physiological studies is discussed in relation to a number of resources, organisms and growth situations that were not part of the original design and rationale of Ingestad's methodology. The additional resource considered is photosynthetically active radiation, and difficulties of applying the Ingestad approach to this resource as well as to atmospheric CO2are considered. The relationship of the Ingestad approach to reductionist studies based on enzyme kinetic studies is then briefly considered. The organisms considered next are aquatic plants, including both micro‐ and macrophytes. The consideration of photosynthetic microorganisms leads to a comparison of the Ingestad approach with growth in batch, and in continuous (chemostat and turbidostat) cultures, and with studies on growth in synchronous cultures in which cyclic changes in cell composition in the cell growth and division cycle can be identified. The natural environmental conditions for these organisms are a natural extension of the light/dark synchronization of laboratory cultures, and the bloom (batch culture equivalent to new production) and of grazing and parasitism removing biomass and recycling nutrients (chemostat or turbidostat culture equivalent to recycled production) situations for phytoplankton. The overall conclusion is that, while the Ingestad approach is a useful mirror in which to examine other concepts of plant resource acquisition and manipulation, the Ingestad methodology seems to make assumptions about the intrinsic growth rate and composition of plants that cannot be independently verified.
Endophytic Neotyphodium lolii induced tolerance to Zn stress in Lolium perenne
Authors: Monnet Fabien , Vaillant Nathalie , Hitmi Adnane , Coudret Alain , Sallanon Huguette
Published: March 2003

The effect of Zn on growth, chlorophyll a fluorescence, net photosynthetic rate, gas exchange, water content and mineral concentrations (Zn, Mn and Mg) in ryegrass infected with or free from Neotyphodium lolii was studied by addition of ZnSO4 (0–20 mM) to the nutrient solution. Zn induced a decrease in growth of plants at 1, 5 and 10 mM and cessation of growth at 20 mM ZnSO4. From 1 to 10 mM, the decrease was less pronounced in the presence of the endophytic fungus than in its absence. The growth limitation was due to an accumulation of Zn in leaves. From 8 to 15 days, the presence of the fungus in the plant led to a limitation of the Zn concentration in the leaves (24–32% lower with N. lolii than without). This restriction of Zn concentrations in leaves also had a beneficial effect on photosystem II (PSII) activities, net photosynthetic rate and internal CO2 concentration. Particularly at 1 and 5 mM, the quantum yield of electron flow throughout PSII was greater in the presence of the fungus than in its absence and at 5 and 10 mM, the internal CO2 concentration was maintained at a normal level. Compared with the endophyte‐free ryegrass, the symbiotic plants showed higher values of total dry weight and tiller number, indicating a tolerance to environmental Zn stress.
Catalase gene expression in response to auxin‐mediated developmental signals
Authors: Guan Lingqiang M. , Scandalios John G.
Published: March 2003

The effect of auxin on maize catalase gene expression was examined at several different developmental stages during embryo and seedling development. All three catalase genes and their respective proteins were induced by both natural and synthetic auxin in immature embryos. Total catalase (CAT) activity increased dramatically in response to high concentrations of auxin, with CAT‐2, which is not normally expressed at this stage, being the isozyme most responsible for the increase. Cat1 transcript accumulated to high levels at 2–8 h after auxin treatment, while Cat2 and Cat3 transcripts increased dramatically, but only after 12 h. In CAT‐2 null mutant lines, the CAT‐1 isozyme compensated for the missing CAT‐2 activity and was the major isozyme responsible for the observed increase in total CAT activity. Auxin treatment mimics the germination process (i.e. induces germination) in immature embryos. Thus, the observed early induction of CAT‐1 and the later increase of CAT‐2 during the germination process may be due, in part, to changes in auxin content. In germinating embryos, auxin also induces total CAT activity and Cat transcript accumulation, although to a lesser extent. Auxin also induces Cat1 transcript accumulation in young leaves. The involvement of ROS in the auxin response is discussed.
Breakage of Pseudotsuga menziesii seed dormancy by cold treatment as related to changes in seed ABA sensitivity and ABA levels
Authors: Corbineau Françoise , Bianco Jacqueline , Garello Ginette , Côme Daniel
Published: March 2003

The main aims of the present work were to investigate whether a chilling treatment which breaks dormancy of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) seeds induces changes in the sensitivity of seeds to exogenous ABA or in ABA levels in the embryo and the megagametophyte, and whether these changes are related to the breaking of dormancy. Dormant seeds germinated very slowly within a narrow range of temperatures (20–30°C), the thermal optimum being approximately 25°C. The seeds were also very sensitive to oxygen deprivation. Treatment of dormant seeds at 5°C improved further germination, and resulted in a widening of the temperature range within which germination occurred and in better germination in low oxygen concentrations. In dry dormant seeds the embryo contained about one‐third of the ABA in the megagametophyte. ABA content of both organs increased during the first 4 weeks of chilling. It then decreased sharply in the megagametophyte to the level in the embryo after 7–15 weeks of chilling. At 15°C, a temperature at which dormancy was expressed, the ABA level increased in the embryo and the megagametophyte of dormant unchilled seeds whereas it decreased in the organs of chilled seeds. The longer the chilling treatment, the faster the decrease in ABA after the transfer of seeds from 5°C to higher temperatures, and the decrease was faster at 25 than at 15°C. These results suggest that the breaking of dormancy by cold was associated with a lower capacity of ABA biosynthesis and/or a higher ABA catabolism in the seeds subsequently placed at 15 or 25°C. Moreover, the chilling treatment resulted in a progressive decrease in the sensitivity of seeds to exogenous ABA. However, seeds remained more sensitive to ABA at 15 than at 25°C. The possible involvement of ABA synthesis and of responsiveness of seeds to ABA in the breaking of dormancy by cold treatment is discussed.
Molecular cloning of a functional protein phosphatase 2C (FsPP2C2) with unusual features and synergistically up‐regulated by ABA and calcium in dormant seeds of Fagus sylvatica
Authors: Lorenzo Oscar , Nicolás Carlos , Nicolás Gregorio , Rodríguez Dolores
Published: March 2003

Phosphorylation/dephosphorylation of proteins is a general mechanism of hormonal signal transduction, including ABA, and serine/threonine protein phosphatases 2C (PP2C, EC 3.1.3.16) have been suggested to play an important role in this process. By means of differential reverse transcriptase‐polymerase chain reaction (RT‐PCR) and further screening of a cDNA library made from mRNA of ABA‐treated Fagus sylvatica L. seeds, a full‐length cDNA clone (FsPP2C2) encoding a putative PP2C was obtained. Comparison to the databases revealed high homology to plant PP2C and most features of these enzymes, but unusual characteristics were found within the catalytic domain and the N‐terminal region of the amino acid sequence. The coding region of FsPP2C2 was expressed in Escherichia coli as histidine tag fusion protein and shows Mg2+‐dependent in vitro phosphatase activity. Transcription of the FsPP2C2 gene is low during seeds stratification at 4°C or under gibberellic acid (GA3) treatment and clearly increases when seeds are treated with ABA and calcium (Ca2+) together, while the addition of calcium chelators (EGTA or TMB‐8) decreases its expression. Furthermore, FsPP2C2 is only expressed in ABA‐treated tissues, preferentially in seeds, which suggests that this PP2C is specifically induced by ABA in dormant seeds, in a Ca2+‐dependent manner, and also in other ABA‐treated tissues.
Differential responses of Brassica napus and Petunia hybrida to leaf protoplast isolation stress
Authors: Watanabe Masami , Suzuki Kumiko , Kawasaki Hiroshi , Watanabe Yukio
Published: March 2003

Changes in the response to abiotic stress during the isolation of leaf protoplasts were compared between a recalcitrant species of Brassica napus and regenerating species of Petunia hybrida. Initially, levels of soluble free putrescine (put), spermidine (spd) and spermine (spm) in leaves and protoplasts were determined. The sum of these three polyamines increased in petunia and B. napus leaf protoplasts by 1.6‐fold and 1.1‐fold, respectively. The soluble free fraction of spd and spm decreased in B. napus but not in petunia protoplasts. During the isolation of leaf protoplasts from B. napus, the ratio of soluble free put to the total PAs almost doubled, but that of spd and spm declined significantly. Petunia leaf protoplasts treated with cyclohexylamine (CHA), an inhibitor of spermidine synthase, accumulated ammonia and soluble putrescine, but lost the soluble spermidine. The soluble polyamine levels of CHA‐treated petunia leaf protoplasts corresponded with those in B. napus. Leaves were subjected to abiotic stress during the isolation of protoplasts, namely wounding and osmotic stress which changed soluble free polyamine levels in B. napus and petunia, respectively. Both B. napus and petunia leaf protoplasts showed an increase in ammonia, but total free amino acid content and activation of proteases were only enhanced in B. napus leaf protoplasts. These results suggest that in B. napus wounding initiated senescence of leaf protoplasts during their isolation, leading to a constant production of ethylene early in the culture.
Isolation of mannose 6‐phosphate reductase cDNA, changes in enzyme activity and mannitol content in broomrape (Orobanche ramosa) parasitic on tomato roots
Authors: Delavault Philippe , Simier Philippe , Thoiron Séverine , Véronési Christophe , Fer André , Thalouarn Patrick
Published: March 2003

We are interested in developing a control strategy efficient at the early stages of subterranean development of Orobanche in the inhibition of mannose 6‐phosphate reductase (M6PR, EC 1.1.1.224), the key enzyme of mannitol production in the parasite. We examined M6PR gene expression during pre‐conditioning, germination, procaulome growth, underground shoot development and emergence of Orobanche ramosa L. attached to tomato roots, the enzyme activity at each of the above stages and the level of stored mannitol in the parasite. A 1120‐pb length cDNA isolated by 3′ and 5′RACE was identified as a M6PR sequence by cDNA expression in E. coli and M6PR activity measurement. Only one M6PR gene was detected in O. ramosa following southern blot analysis. M6PR expression, analysed by RT‐PCR, was constant from the pre‐conditioned seed to the emergence of broomrape, i.e. M6PR expression is constitutive in Orobanche. M6PR activity was also detected in pre‐conditioned seeds and attachment to tomato roots resulted in a two‐fold increase in enzyme activity during tubercle enlargement and crown root formation. Hexose and mannitol accumulation was strongly enhanced in the attached parasite, with accumulation primarily in the shoot. These results support the prospect of utilizing M6PR inhibitors as early applied herbicides to control this parasite in the early stages of its development.
Drought stress affects chloroplast lipid metabolism in rape (Brassica napus) leaves
Authors: Benhassaine‐Kesri Ghouziel , Aid Fatiha , Demandre Chantal , Kader Jean‐Claude , Mazliak Paul
Published: March 2003

Rape (Brassica napus L. var. Bienvenue) is a 16:3 plant which contains predominantly prokaryotic species of monogalactosyldiacylglycerol i.e. sn‐1 C18, sn‐2 C16 (C18/C16 MGDG). Rape plants were exposed to a restricted water supply for 12 days. Under drought conditions, considerable changes in lipid metabolism were observed. Drought stress provoked a decline in leaf polar lipids, which is mainly due to a decrease in MGDG content. Determination of molecular species in phosphatidylcholine (PC) and MGDG indicated that the prokaryotic molecular species of MGDG (C18/C16) decreased after drought stress while the eukaryotic molecular species (C18/C18) remained stable. Drought stress had different effects on two key enzymes of PC and MGDG synthesis. The in vitro activity of MGDG synthase (EC. 2.4.1.46) was reduced in drought stressed plants whereas cholinephosphotransferase (EC. 2.7.8.2) activity was not affected. Altogether these results suggest that the prokaryotic pathway leading to MGDG synthesis was strongly affected by drought stress while the eukaryotic pathway was not. It was also observed that the molecular species of leaf PC became more saturated in drought stressed plants. This could be due to a specific decrease in oleate desaturase activity.
Polyamine research in plants – a changing perspective
Authors: Kakkar Raj K. , Sawhney Vipen K.
Published: March 2003

Our understanding of the precise role(s) of polyamines (PAs) in various plant developmental and morphogenetic processes has advanced considerably by the ability to manipulate PA biosynthetic pathways using polyamine biosynthesis inhibitors, PA‐ mutants and by adopting various transgenic strategies. The cDNA for almost every biosynthesis pathway enzyme has been isolated and cloned in a number of systems. This review briefly summarizes our current understanding of the genetic control of PA metabolism in different model plant systems.
Surface morphology, leaf and cuticle thickness of four dwarf shrubs from a sub‐Arctic heath following long‐term exposure to enhanced levels of UV‐B
Authors: Semerdjieva S. I. , Phoenix G. K. , Hares D. , Gwynn‐Jones D. , Callaghan T. V. , Sheffield E.
Published: March 2003

In 1991 a field experiment was established in subarctic heathland at Abisko (68°35′N, 18°82′E), northern Sweden, to investigate the effects of enhanced UV‐B (280–315 nm) radiation, simulating 15% ozone depletion, on plants in their natural environment. Leaves of the four dominant dwarf shrubs, the deciduous Vaccinium myrtillus L. and V. uliginosum L. and the evergreen V. vitis‐idaea L. and Empetrum hermaphroditum Hagerup were examined after 7 years of UV‐B treatment. SEM and ESEM were used to visualize surface features and to determine trichome density. Multiphoton laser scanning microscopy showed that UV‐B absorbing compounds were localized in the trichomes of all species. Trichomes varied in size, number and distribution between the species. Enhanced UV‐B reduced adaxial trichome density significantly (by approximately 25%) in only one species, V. uliginosum. This effect could be of importance for the UV‐B absorbing potential of the adaxial epidermis of V. uliginosum. Epicuticular wax structures were found only on the abaxial surface of V. uliginosum and were unaffected by enhanced UV‐B. The cuticular surfaces of all other species were smooth and featureless. Leaf thickness, adaxial and abaxial cuticle thickness varied between the species although there was no apparent effect of enhanced UV‐B. It is concluded that long‐term enhancement of UV‐B has an effect on adaxial trichome density in V. uliginosum, but that there is no general effect on leaf morphology of the other species.
Fluoride inhibits root water transport and affects leaf expansion and gas exchange in aspen (Populus tremuloides) seedlings
Authors: Kamaluddin Mohammed , Zwiazek Janusz J.
Published: March 2003

The effects of sodium fluoride (0.3, 5 and 10 mM NaF) on root hydraulic conductivity, and gas exchange processes were examined in aspen (Populus tremuloides Michx.) seedlings grown in solution culture. A long‐term exposure of roots to NaF significantly decreased root hydraulic conductivity (Lp) and stomatal conductance ( gs). Root absorbed NaF significantly affected electrolyte leakage in leaf tissues and substantially restricted leaf expansion. NaF did not significantly affect leaf chlorophyll contents but decreased net photosynthesis (Pn). A short‐term exposure of excised roots to 5 mM NaF and KF significantly decreased root water flow (Qv) with a concomitant decline in root respiration and reduced gs when applied through intact roots or excised stems. The same molar concentration of NaCl also decreased Qv and gs in intact seedlings, but to a lesser extent than NaF or KF, and did not significantly affect root respiration. The results suggest that fluoride metabolically inhibited Qv or Lp, probably by affecting water channel activity. We suggest that the metabolic inhibition of Lp by root‐absorbed fluoride affected gas exchange and leaf expansion in aspen seedlings.
The control of proline consumption by abscisic acid during osmotic stress recovery of canola leaf discs
Authors: Trotel‐Aziz Patricia , Niogret Marie‐Françoise , Deleu Carole , Bouchereau Alain , Aziz Aziz , Larher François Robert
Published: March 2003

Some aspects of the function of abscisic acid (ABA) in the control of proline (PRO) metabolism in canola leaf discs (CLD) subjected in vitro to consecutive hyper‐osmotic (stress) and hypo‐osmotic (recovery) treatments have been investigated. PRO accumulation in response to stress conditions relies on both stimulation of its synthesis via enhancement of transcription of the gene and activity of Δ1‐pyrroline‐5‐carboxylate synthetase (P5CS) and inhibition of its degradation via inactivation of PRO dehydrogenase (PDH). These changes were partly reversed under recovery conditions. Thus both PDH mRNA and PDH activity increased while P5CS mRNA decreased. Surprisingly P5CS activity remained high even after a 20‐h period of rehydration. Exogenously supplied ABA at recovery inhibited net PRO consumption and this could be associated with downregulation of PDH gene expression and PDH activity. Under these conditions ABA hardly upregulated P5CS gene expression while P5CS activity first transiently decreased and then reached a value close to that found under stressing conditions. Experiments with CLD supplied with either methionine sulphoximine or gabaculine, brought preliminary evidence for a significant synthesis of PRO from glutamate during recovery that replenished the proline pool(s) and provoked a negative effect on the net rate of PRO consumption. Consequently, it is suggested that the availability of both PRO precursors and ABA could be determinant in the control of the amount of residual PRO present in CLD after the period of recovery. This level also seemed to depend on the amount of P5CS transcripts induced under stress conditions. However, the results obtained with turgid leaf discs treated with ABA indicate that the ABA status of the tissues, necessary for inducing the proline response, is not sufficient to determine their PRO content because it remained relatively low despite the stimulation of P5CS expression and P5CS activity.