bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidative damage and defense mechanisms in primary leaves of Phaseolus vulgaris as a result of root assimilation of toxic amounts of copper
Authors: Weckx Jolanda E. J. , Clijsters Herman M. M.
Published: May 2006

We studied the sequence of several metabolic reactions, representative for oxidative damage and protection, in primary leaves of Phaseolus vulgaris (cv. Limburgse vroege) as a function of root assimilation of a toxic sublethal Cu concentration (630 μM). A transient increase of products of membrane peroxidation was observed in the primary leaves during the period of Cu uptake. This rise was mainly due to the oxidizing properties of copper itself and not to a stimulation of the lipoxygenase (EC 1.13.11.12) activity. In our experimental conditions, membrane lipid peroxidation and K+‐leakage were not directly related; during at least three days after Cu application to the roots, when products of lipid peroxidation were already detected in the leaf, permeability of the cytoplasmic membrane for K+ was improved. However, Cu stimulated the capacity of catalase (EC 1.11.1.6) and ascorbate peroxidase (EC 1.11.1.11). These enzymes protect the tissue against oxidative stress since at least the hydrogen peroxide content was significantly reduced. Superoxide dismutase (EC 1.15.1.1) was not involved in this defense mechanism.
Early degradation of photosynthetic membranes in carob and sunflower cotyledons
Authors: La Rocca Nicoletta , Barbato Roberto , Casadoro Giorgio , Rascio Nicoletta
Published: May 2006

The assimilatory activity of cotyledons can play an essential role in the survival of seedlings with a slow and delayed development of primary leaves. Changes in the photosynthetic activity of the cotyledon, from the onset of greening through senescence, were studied in two such plants, carob and sunflower, in order to determine its efficiency and duration, also in connection with the achievement of assimilatory autonomy by the plantlet. Chlorophyll analyses showed that the cotyledon's chloroplasts reached maximal greening in plantlets with a pair of expanded leaves. In contrast, the cotyledon's photosynthetic activity, measured as the rate of oxygen release, started to decrease early, before expansion of primary leaves. The decrease was due to the inactivation of a number of photosystem II (PSII) units, as revealed by immunodetection of breackdown products of the reaction centre's D1 and D2 thylakoid proteins. No signals of PSII alteration were noticed in the primary leaf chloroplasts that differentiated under the same environmental conditions. The damage to the cotyledon PSII, occurring in a non‐photoinhibitory situation, might be due to a slower rate of turnover of D1 polypeptide than in the leaf thylakoids. The differential turnover of this protein in cotyledons and in leaves might represent an organ‐specific regulation of the photosynthetic activity. The peculiarity of the cotyledon thylakoids make these organs useful objects for studying the metabolic cycle of both D1 and D2 proteins in vivo, under non‐photoinhibiting conditions.
Proteolysis in the quiescent seed
Authors: Duarte Isabel , Ricardo Cándido P. P. , Duque‐Magalhäes Maria C.
Published: May 2006

The importance of the proteolytic system of the quiescent seed in regard to mobilization of storage protein was assessed by identification of proteases already present at this stage. Extracts of quiescent cotyledons of white lupin (Lupinus albus) submitted to 45 h autolysis in vitro displayed a higher degree of protein degradation than that observed in vivo after two days of seed imbibition. Differences in the susceptibility to proteolysis were verified by densitometric analysis of the polypeptides after electrophoretic separation. The pH dependence of the proteolytic activities and the responses to specific protease inhibitors showed that the proteolytic systems vary from quiescent to 1 ‐ to 3‐day‐imbibed cotyledons. By labelling an endogenous globulin with 125I a sensitive radiometric assay allowed the identification of both an acidic and a neutral proteolytic system in the quiescent cotyledon. Within the quiescent seed there already exists a high potential for initiating proteolysis, so that the requirement for proteolysis by specific endopeptidases synthesized de novo upon imbibition only applies to part of the reserve proteins.
Function, structure and regulation of cyanobacterial and chloroplast ATP synthase
Authors: van Walraven Hendrika S. , Bakels Ronald H. A.
Published: May 2006

The proton‐translocating ATP synthase from chloroplasts and cyanobacteria forms ATP upon photosynthetic electron transport by using the proton gradient across the thylakoid membrane. Both enzymes contain nine different subunits and from the similarity in gene organisation and the high degree of amino acid sequence homology of the subunits it appears that these ATP synthases might have a common ancestor. Both enzymes need to be activated by membrane energisation in order to perform catalytic activity but, in contrast to the chloroplast ATP synthase, that from the studied cyanobacteria (with the exception of Spirulina platensis) shows no effect of the redox state on activation. Functionally, the cyanobacterial enzyme corresponds to the reduced form of the chloroplast ATP synthase. In the chloroplast enzyme a stretch of 9 amino acids, including two cysteines in the γ‐subunit, is involved in this redox effect and this stretch is absent in cyanobacteria. With γ‐mutants from the cyanobacterium Synechocystis 6803 the role of this stretch is studied. When active, both the cyanobacterial and the reduced chloroplast ATP synthase transport 4 protons per ATP synthesised and hydrolysed. This ratio may depend on the environment of the enzyme such as protein and lipid composition and pH.
The oxidative burst in plant defense: Function and signal transduction
Authors: Low P. S. , Merida J. R.
Published: May 2006

The rapid production and accumulation of active oxygen species (AOS), the oxidative burst, has been shown to occur in a variety of plant/pathogen systems. In particular, two species, hydrogen peroxide (H2O2) and the superoxide radical anion O2− have received considerable attention. H2O2 and O2−, while acting directly as antimicrobial agents, may also serve as second messengers or catalysts in plants to activate a more diverse set of defense responses. Some of the better studied downstream responses promoted by AOS are (1) the cross‐linking of cell wall proteins, (2) the induction of defense‐related genes, (3) the stimulation of phytoalexin biosynthesis and (4) promotion of the hypersensitive response (HR).

A useful model for studying the oxidative burst in plants is the neutrophil NADPH ox‐idase complex, the primary source of AOS production in mammals. Several of the subunits of the neutrophil NADPH oxidase complex have been immunologically identified in plants. Furthermore, many of the components known to be involved in the signal transduction pathway in neutrophils have also been found to play a role in the oxidative burst in plants. Just as various ligands activate the oxidase complex in neutrophils, several ligands (elicitors or pathogens) also lead to induction of the oxidative burst in plant cells. The similarities between the neutrophil and plant oxidative bursts will be elaborated in this review.

Following stimulation with elicitors, different signal transduction pathways are activated in plants, depending on the source of elicitor used. While the identities and chronologies of the major intermediates in these pathways remain largely unknown, there is strong evidence at least for participation of phospholipases, H+/K+ exchange, Ca2+ influxes, protein kinases and phosphatases, and GTP binding proteins. In an effort to integrate these various signaling events into a single scheme, we have constructed a hypothetical model that proposes how different elicitors might induce the oxidative burst in the same cell by different pathways.
Abscisic acid inhibits shoot elongation of Scirpus mucronatus
Authors: Lee Tse‐Min , Shieh Yuh‐Jang , Chou Chang‐Hung
Published: May 2006

The relationships between free ABA levels and shoot elongation were investigated in shoots of Scirpus mucronatus L. Under submergence, shoot elongation increased but free ABA levels decreased. The extent of the increase in length and the decrease in free ABA in submerged shoots increased with the increase of water depth. When the shoots were transferred to air after 12 days of submergence, they ceased to elongate and the free ABA levels recovered to the values of air‐grown shoots. ABA, at concentrations from 1 μM to 1 mM, inhibited the submergence‐induced shoot elongation. In ambient air, fluridone, an inhibitor of ABA biosynthesis, at 7 μM decreased the free ABA levels in shoots but increased shoot elongation. The effects could be reversed by 10 μM ABA. These results indicate that ABA is an internal inhibitor of shoot growth in Scirpus.
Effects of root zone temperature on aluminium toxicity in two cultivars of spring wheat with different resistance to aluminium
Authors: Strid Håkan
Published: May 2006

Manifestations of aluminium (Al) toxicity in two cultivars of wheat (Triticum aestivum L. cvs Kadett [relatively Al‐resistant] and WW 20299 [relatively Al‐sensitive]) were investigated at two root zone temperatures (RZT) that may occur in the field. The plants were grown for 9 days at 10 or 25°C RZT. Mineral nutrients other than CaSO4 were supplied daily in exponentially increasing amounts to meet the demand of the plants. Al was added as Al2(SO4)3 at the beginning of the culture period at concentrations ranging from 0 to 100 μM. pH was kept constant at 4.1. Experimental data were analysed for interactions between Al and RZT on a fresh weight basis by the nonlinear Weibull function. Cultivar Kadett, when grown at 25°C RZT, was more resistant to Al than when grown at 10°C RZT. Cultivar WW 20299 was equally sensitive to Al at 10 and 25°C RZT but generally more sensitive to Al than cv. Kadett. It is suggested that cv. Kadett, in contrast to cv. WW 20299, possesses a mechanism for Al resistance that is less effective at 10°C than at 25°C RZT and therefore may be metabolically dependent. In roots, the concentrations of K, P, Mg and Ca were not negatively affected by Al or by RZT. In shoots of both cultivars the concentrations of Ca and Mg became comparatively low when the plants were treated with Al or at low RZT, the effect being larger for Ca than for Mg. At 10°C RZT under Al stress, the Ca concentrations in shoots approached the critical concentration where growth may be inhibited. As no Al was detected in the shoots, it is suggested that Al in the roots inhibits shoot growth by reducing transport of Ca from roots to shoots.
Ascorbate peroxidase activity, not the mRNA level, is enhanced in salt‐stressed Raphanus sativus plants
Authors: Lopez Felicie , Vansuyt Gerard , Casse‐Delbart Francine , Fourcroy Pierre
Published: May 2006

The effect of salt on ascorbate peroxidase (EC 1.11.1.11) activity and mRNA level in radish (Raphanus sativus L. cv. Fakir) was investigated. cDNA encoding a radish ascorbate peroxidase was obtained and sequenced. Sequence data analysis showed that the coding region was well conserved among higher plants. The radish cDNA was used as a probe to measure the steady‐state level of ascorbate peroxidase mRNA in plants subjected to salt stress (100 mM NaCl). The levels of transcripts encoding ascorbate peroxidase were almost identical in control or salt‐grown radish plants in both leaves and roots. The activity of soluble ascorbate peroxidase was enhanced by the salt treatment in both leaves and roots. The salt‐induced increase in ascorbate peroxidase activity requires days to become significant and can be considered as a late response. The increase in activity, but not in mRNA level, suggests that the salt‐induced ascorbate peroxidase expression is probably the consequence of post‐transcriptional events.
Development of seed coat‐imposed dormancy during seed maturation in Cynoglossum officinale
Authors: Stabell E. , Upadhyaya M. K. , Ellis B. E.
Published: May 2006

The relationship between seed phenolics and appearance of seed coat–imposed dormancy during seed development in Cynoglossum officinale L. was studied. Up to 24 days after anthesis, seeds failed to germinate upon imbibition in Petri dishes at 25°C. At 44 days after anthesis, seeds were fully germinable; removal of seed coats did not improve their germination or O2 uptake. At 72 days after anthesis, mature seeds at the base of the cyme did not germinate unless their coats were removed. Removal of seed coat also stimulated O2 uptake at this harvest date. The methanol‐soluble phenolic content of the seeds increased during the early stages of seed development, in both the seed coat and the embryo. As seed development continued, the methanol‐soluble phenolic content of the embryo stabilized, but that of the seed coat declined. This decline was associated with an increase in the thioglycolic acid–soluble phenolics, presumably lignins, in the seed coat. These results suggest that polymerization of methanol–soluble phenolics into lignins in the seed coat during later stages of seed development renders the seed coat of C. officinale impermeable to 03, and thus keeps the seed dormant.
Apoplastic pH in corn root gravitropism: A laser scanning confocal microscopy measurement
Authors: Taylor Douglas P. , Slattery James , Leopold A. Carl
Published: May 2006

The ability to measure the pH of the apoplast in situ is of special interest as a test of the cell wall acidification theory. Optical sectioning of living seedlings of corn roots using the laser scanning confocal microscope (LSCM) permits us to make pH measurements in living tissue. The pH of the apoplast of corn roots was measured by this method after infiltration with CI‐NERF, a pH‐sensitive dye, along with Texas Red Dextran 3000, a pH‐insensitive dye, as an internal standard. In the elongation zone of corn roots, the mean apoplastic pH was 4.9. Upon gravitropic stimulation, the pH on the convex side of actively bending roots was 4.5. The lowering of the apoplastic pH by 0.4 units appears to be sufficient to account for the increased growth on that side. This technique provides site‐specific evidence for the acid growth theory of cell elongation. The LSCM permits measurements of the pH of living tissues, and has a sensitivity of approximately 0.2 pH units.
Induction of chitinases and β‐l,3‐glucanases in Rhizoctonia solani‐infected rice plants: Isolation of an infection‐related chitinase cDNA clone
Authors: Anuratha Coimbatore S. , Zen Kuo‐Chang , Cole Kunwei Chen , Mew Tom , Muthukrishnan Subbaratnam
Published: May 2006

Extracts from several rice cultivars (Oryza sativa L. cvs IR58, 74586 and SC33) infected with the sheath blight pathogen Rhizoctonia solani, were analyzed to determine the isozyme distribution of chitinases (EC 3.2.1.14) and β‐l,3‐glucanases (EC 3.2.1.39). Upon infection by the fungal pathogen, two chitinases of 28 and 35 kDa and two β‐l,3‐glucanases of 30 and 32 kDa were shown to be induced in all cultivars. They resolved into multiple isozymes under nondenaturing electrophoretic conditions. Wounding, but not bacterial infection, resulted in the induction of these hydrolytic enzymes. Even though fungal infection resulted in induction of chitinases and β‐glucanases in all cultivars, some cultivars that were moderately resistant to R. solani appeared to have higher levels of specific isozymes. A chitinase cDNA clone was identified by screening a library, prepared from RNA isolated from R. solani‐infected rice plants, with an antibody to a bean chitinase. This cDNA encoded a 35‐kDa chitinase which was significantly different in amino acid sequence from other rice chitinases described so far. Northern blot analysis of RNA from infected rice plants indicated that transcripts corresponding to this chitinase gene were induced upon fungal infection.
Field evaluation of water transport in grape berries during water deficits
Authors: Greenspan Mark D. , Schultz Hans R. , Matthews Mark A.
Published: May 2006

The net flow in vascular and transpirational components of the grape berry water budget was evaluated during water deficits imposed at different stages of fruit development. Diurnal fluctuations in berry diameter were measured on field‐grown grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) by using electronic displacement transducers. Water deficits were imposed by withholding irrigation, and water potentials of mid‐shoot leaves, basal stem xylem and clusters were determined with a pressure chamber. The relative net flows through pedicel xylem and phloem and through berry transpiration were estimated pre‐veraison and post‐veraison. The xylem functioned nearly exclusively in providing net inflow pre‐veraison, while the phloem was clearly dominant post‐veraison. Accordingly, the amplitude of diurnal contraction was markedly smaller post‐veraison than pre‐veraison. The amplitude of diurnal contraction increased dramatically with decreasing plant water status pre‐veraison, yet exhibited little sensitivity to low vine water status post‐veraison. Measurements of the difference in water potential between clusters and source stems did not provide evidence of a gradient that would elicit significant water movement from the cluster to the stem at any time of the day. This was true for both irrigated and non‐irrigated vines, although the non‐irrigated vines exhibited a smaller gradient favoring inflow throughout much of the day. The gradient for xylem water transport to the cluster was considerably smaller post‐veraison than pre‐veraison. The results showed that berry transpiration functioned as the primary pathway for water loss both pre‐ and post‐veraison.
Opposite effects of fusicoccin and IAA on putrescine synthesis of rice coleop tiles
Authors: Lee Tse‐Min , Lin Yaw‐Hnei
Published: May 2006

Changes in polyamine biosynthesis and elongation of etiolated rice coleoptiles (Oryza sativa L. cv. Taichung Native 1) in response to fusicoccin (FC) and indoleacetic acid (IAA) were investigated. FC stimulated coleoptile elongation at concentrations higher than 1 μM but caused a decrease in the levels of free putrescine, spermidine and sper‐mine, as well as in the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and S‐adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50). The extent to which FC caused these effects was dependent on its concentration. Treatment with 100 μM IAA also induced coleoptile elongation and resulted in a decrease in free spermidine/sper‐mine and SAMDC activity. However, treatment with IAA resulted in an increase in free putrescine levels and ADC activity. The extent of coleoptile elongation and putrescine accumulation also depended on IAA concentration. α‐Difluoromethylarginine (DFMA), an irreversible inhibitor of ADC. but not α‐difluoromethylornithine (DFMO). an irreversible inhibitor of ODC (EC 4.1.1.17), inhibited the LAA‐stimulated coleoptile elongation and putrescine accumulation. Addition of putrescine could not reverse the effect of DFMA.
Genome and plastome effects on photosynthesis parameters in Oenothera species of differential low‐temperature tolerance
Authors: Dauborn Babette , Brüggemann Wolfgang
Published: May 2006

The influence of the plastid genome (plastome) on the temperature dependence of chlorophyll fluorescence parameters was studied in four Oenothera species from climatically different habitats. Equipped with their natural plastome, the species could be arranged with respect to their low‐temperature tolerance in the order Oe‘villosa’ (plastome I) =Oe argillicola (V) > Oe. grandiflora (III) > Oe elata ssp. hookeri (J). Exchanging the naturally occurring plastome with those from other species did not result in changes of the photosynthetic performance of the genotypes, except for decreasing pigment contents and photosynthesis rates (on area basis) in Oe. elata ssp. hookeri with plastome III. Furthermore, plastome exchange in Oe. elata ssp. hookeri and in Oe. grandiflora did not affect kinetic properties of purified ribulose‐l,5‐bis‐phosphate carboxylase/oxygenase (EC 4,1.1.39), indicating that the gene for the large subunit of this enzyme has remained conserved during plastome evolution in Oenothera. It is concluded that the evolution of the plastome in North American Oenothera spp. did not influence the temperature adaptation of the photosynthetic apparatus, but that the latter is governed by effects residing in the nuclear genome.
Lipid peroxidation and peroxide‐scavenging in soybean seeds during aging
Authors: Sung J. M.
Published: May 2006

The possible role of lipid peroxidation in seed deterioration was investigated during natural aging and accelerated aging of seeds of edible soybean (Glycine max [L], Merr. cv. Kaohsiung Selection No. 1). Natural aging was achieved by sealing the seeds in aluminum foil bags coated with polyethylene and storing the seeds at room temperature for 3 to 12 months. Accelerated aging was obtained by incubating the seeds at 45°C and close to 100% relative humidity for 3 to 12 days, after which the seeds were air dried to their original moisture level (8%). The results indicate that both natural and accelerated aging enhanced lipid peroxidation, as germination was depressed. Aging also inhibited the activity of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase. The changes in germination and physiological activities, expressed as a function of aging duration, were somewhat similar in the two aging treatments.
Temporal, spatial and hormonal regulation of the S‐adenosylmethionine synthetase gene in petunia
Authors: Izhaki Anat , Shosevov Oded , Weiss David
Published: May 2006

Gibberellic acid (GA3) promotes corolla elongation and pigmentation in petunia flowers. We have previously shown that G.A3 induces pigmentation by activating specific genes of the anthocyanin biosynthetic pathway. The aim of the present work was to examine whether GA3 induces also the expression of genes from other metabolic pathways in petunia corollas that may be associated with growth. Recently we reported the cloning of the petunia sam gene coding for S‐adenosylmethionine synthetase (SAM‐S). In the present work we show that sam expression is induced by GA3 in both corollas and stems. The expression of the gene was correlated with corolla elongation. GA3 and the cylokinin, N‐6‐benzyladenine (BA) promoted corolla growth and sam expression, whereas abscisic acid (ABA) inhibited corolla elongation and repressed sam mRNA accumulation. An analysis of sam expression in stems indicated a high level in young, elongating internodes and a very low level in the mature, non‐elongating stem zone. The results of the present study show that the effect of GA3 on gene expression in the corolla of petunia, is not restricted to the anthocyanin biosynthetic pathway, they also suggest a possible role for sam in GA3‐induced corolla and stem elongation.
Phytochrome control of short‐day‐induced bud set in black cottonwood
Authors: Howe Glenn T. , Gardner Gary , Hackett Wesley P. , Furnier Glenn R.
Published: May 2006

In trees and other woody perennial plants, short days (SDs) typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud and bud dormancy. Phytochrome control of SD‐induced bud set was investigated in two northern clones of black cottonwood (Populus trichocarpa Torr. & Gray) by using night breaks with red light (R) and far‐red light (FR). For both clones (BC‐1 and BC‐2), SD‐induced bud set was prevented when R night breaks as short as 2 min were given in the middle of the night. When night breaks with 2 min of R were immediately followed by 2 min of FR, substantial reversibility of bud set was observed for BC‐1 but not for BC‐2. By comparing the effects of the R night breaks on bud set and the length of specific internodes, we determined that the R night breaks influenced internode elongation in two opposing ways. First, the addition of a R night break to the SD treatment prevented the cessation of internode elongation that is associated with bud set. Those internodes that would not have elongated under SDs (and would have been found within the terminal bud) elongated in the R treatment. Second, the R night breaks decreased internode length relative to the long‐day (LD) control. In contrast to the clonal differences in reversibility that we observed for bud set, the decrease in internode length (i.e. the second effect of R) was R/FR reversible in both clones. Based on these results, we conclude that internode elongation is influenced by two distinct types of phytochrome‐mediated response. The first response is a typical response to photpperiod, whereas the second response is a typical “end‐of‐day” response to light quality. Our results demonstrate that SD‐induced bud set in black cottonwood is controlled by phytochrome but that clonal differences have an important influence on the R/FR reversibility of this response. The availability of an experimental system in which SD‐induced bud set is R/FR reversible will be valuable for studying the physiological genetics of photoperiodism in trees.
Changes in malondialdehyde content and in superoxide dismutase, catalase and glutathione reductase activities in sunflower seeds as related to deterioration during accelerated aging
Authors: Bailly Christophe , Benamar Abdelilah , Corbineau Françoise , Come Daniel
Published: May 2006

Sunflower (Helianthus annuus L.) seeds progressively lost their ability to germinate at 25°C, the optimal temperature for germination, after accelerated aging was carried out at 45°C (a temperature too high to permit germination) in water or at 76 or 100% relative humidity (RH). The deleterious effects of the high‐temperature treatment increased with increasing seed moisture content. Incubation of seeds at 45°C in water resulted in electrolyte leakage, which indicated a loss of membrane integrity. A relationship between leakage and loss of seed viability could not be assumed, since no increase in electrolyte efflux occurred after aging al 100% RH. Accelerated aging induced accumulation of malondialdehyde, suggesting that seed deterioration was associated with lipid peroxidation. However, there was no direct relationship between lipid peroxidation and deterioration in membrane integrity. Loss of seed viability was also associated with a decrease in superoxide dismutase, catalase and glutathione reductase activities. Finally, the results obtained suggest that sunflower seed deterioration during accelerated aging is closely related to a decrease in the activities of detoxifying enzymes and to lipid peroxidation.
Cadmium and copper uptake and distribution in Mediterranean tree seedlings
Authors: Arduini Iduna , Godbold Douglas L. , Onnis Antonino
Published: May 2006

Copper and cadmium uptake and distribution in 2‐week‐old seedlings of stone pine (Pinus pinea L.), maritime pine (Pinus pinaster Ait.) and ash (Fraxinus angustifolia Vahl.) were investigated. Seedlings were grown in culture solution at increasing concentrations of CuSO4 (0.012–5 μM) and CdSO4 (0.0–5 μM). All species accumulated copper in a larger amount than cadmium. Translocation to the shoot was strongly restricted for both metals, though higher cadmium mobility within the plant could be evidenced. A strong relationship between root content and growth inhibition was detected in the roots in response to copper but not to cadmium treatments. Among species P pinea seemed to be more tolerant to cadmium, whereas F. angustifolia was highly sensitive to both cadmium and copper. X–ray microanalysis of root tip sections showed that copper and cadmium only accumulated in the root tips of F. angustifolia. copper mostly in the cell walls of the cortex layer, cadmium in the inner compartments of the cortex cells. It is suggested that in the two Pinus species the well developed root cap plays a protecting role against metal uptake at the root–tip zone.
Salt‐induced inhibition of phosphorus transport in lettuce plants
Authors: Martinez Vicente , Bernstein Nirit , Läuchli André
Published: May 2006

Experiments with labeled phosphorus (32P) were carried out to study the effect of NaCl (80 mM) on transport of inorganic phosphorus (P1) in the salt sensitive lettuce plant (Lactuca sativa L. cv. Black‐seeded Simpson). The concentration of P1 used in all experiments was 0.1 mM. Salinity inhibited 32P uptake by the roots as well as translocation of 32P1 from root to shoot. When the plants were exposed for 3 h to a nutrient solution containing 32P, 80 mM NaCl reduced 32P, translocation from root to shoot by 21%. This inhibition increased to 85% during a subsequent 3‐h period in unlabeled solution.‐ The concentration of 32P in leaves increased with decreasing leaf age regardless of the salinity level and leaf size. Indirect evidence supports the proposal that NaCl inhibits the retranslocation of P1 from old to young leaves. It is hypothesized that high levels of NaCl decrease the mobility of P1 stored in vacuoles and, as a result, inhibit export from this storage compartment to other parts of the plant.
Azide‐stimulated oxygen consumption by the green alga Selenastrum minutum
Authors: Lynnes Jaret A. , Weger Harold G.
Published: May 2006

Dark O2 consumption by the green alga Selenastrum minutum was sensitive to inhibition by the cytochrome pathway respiration inhibitor cyanide in the absence of an alternative oxidase inhibitor, consistent with previous work that suggested that this alga lacks alternative oxidase capacity. In contrast, addition of low concentrations of the cytochrome pathway inhibitor azide (50–750 μM) resulted in a stimulation of dark O2 consumption, while higher concentrations of azide (1–2 mM) partially inhibited O2 consumption. Measurements of changes in cellular levels of pyruvate, malate and pyridine nucleotides upon cyanide addition were consistent with the absence of alternative oxidase capacity, and suggested that cyanide inhibition of O2 consumption was not due to nonspecific effects of cyanide. Addition of salicylhydroxamic acid (SHAM) also resulted in an increase in the rate of O2 consumption. Both azide‐ and SHAM‐stimulated O2 consumption were sensitive to inhibition by 50 mM ascorbate or by cyanide. However, the ubiquinone analogs chloroquine and quinacrine specifically inhibited azide‐stimulated O2 consumption, with only minor effects on SHAM‐stimulated O2 consumption. These results suggest that azide‐stimulated O2 consumption was not mediated by the previously characterized SHAM‐stimulated oxidase, and are consistent with the possibility that azide‐stimulated O2 consumption is mediated by a plasma membrane redox system.
Gene expression under water deficit in loblolly pine (Pinus taeda): Isolation and characterization of cDNA clones
Authors: Chang Shujun , Puryear Jeffrey D. , Dias M. A. Dilip L. , Funkhouser Edward A. , Newton Ronald J. , Cairney John
Published: May 2006

Poly(A+) RNA was extracted from roots of loblolly pine (Pinus taeda L.) seedlings subjected to gradual and prolonged water deficit. This RNA was used to construct a cDNA library. A number of cDNA clones were isolated whose expression was induced by water deficit. Four of these cDNA clones, designated pLP2, pLP3, pLP4 and pLP5* were characterized further. Each of these pine genes has unique characteristics either in sequence or pattern of expression. The protein encoded by pLP2 shows 91% identity to S‐adenosylmethionine synthetase from a range of plants. The protein encoded by pLP3 is similar to a tomato protein induced by water deficit and during fruit ripening, but the pine protein possesses a unique 34‐amino‐acid region near the amino terminal. The LP4 protein is similar to stellacyanin, a copper‐binding protein in the Japanese lacquer tree, but possesses a proline/serine‐rich carboxy terminus not found in other plants. Clone pLP5 encodes a novel glycine‐rich protein with similarity to both silk fibroin and the rat chondroitin core protein, but the putative pine protein is distinct from previously characterized glycine‐rich proteins. Transcript levels of the four genes rose under moderate water deficit stress and then declined as stress became severe (1 month without water), with the exception of pLP5 mRNA, which remained at elevated levels even under severe stress. The possible roles of the encoded proteins in Cell wall reinforcement are discussed.
Stage‐specific nitrogen metabolism in developing carrot somatic embryos
Authors: Joy Richard W. , Mclntyre Deane D. , Vogel Hans J. , Thorpe Trevor A.
Published: May 2006

The physiology of individual somatic embryo developmental stages otDaucus carota L. was examined by in vivo nuclear magnetic resonance (NMR) spectroscopy, amino acid analysis and 14C‐labeling. 15N NMR spectroscopy was used to examine the uptake and incorporation of 15N isotopically labeled inorganic nitrogen sources. NMR spectra of proembryogenic masses (PEMs) contained resonances for histidine, amino sugars, glutamine, arginine, urea, alanine. α‐amino nitrogen, serine, aliphatic amines and several unknowns. Similar resonances were found in various embryo developmental stages. However, resonances for arginine and aliphatic amines peaked during globular and torpedo stages and substantially decreased in germinating stage embryos. The dominant resonances observed in non‐embryogenic cells and germinating embryos were glutamine and α‐amino nitrogen. Amino acid analysis of the various embryo stages showed that glutamate, glutamine and arginine were the major contributors to the soluble amino acid profiles. During development, glutamate and glutamine continued to increase in concentration whereas arginine and its related metabolites (i.e. ornithine and y‐aminobutyric acid [GABA]) were biphasic; increasing in globular and torpedo stage embryos and decreasing in germinating embryos. Carbon‐14 labeling indicated that labeled glutamine pools in non‐embryogenic and germinating embryos were greatest compared to other embryo stages, whereas labeled GABA pools were greatest in globular and torpedo stage embryos. Taken together, these data indicate that the physiology of each embryo developmental stage is distinct. They also suggest that during somatic embryo development, a switch takes place in metabolism whereby the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway is predominant in non‐embryogenic cells and germinating stage embryos. Furthermore, during early to mid‐embryo development (PEMs, globular and torpedo stage embryos), metabolism utilizing the omithine cycle is enhanced and predominant.
Sugar uptake into strawberry fruit is stimulated by abscisic acid and indoleacetic acid
Authors: Ofosu‐Anim John , Kanayama Yoshinori , Yamaki Shohei
Published: May 2006

Changes in sugar uptake into strawberry fruits with maturation and the hormonal effect on uptake mechanisms, though important to fruit development, are not known. Therefore, the kinetics of sugar uptake into strawberry (Fragaria x ananassa Duch cv. Nyoho) fruit tissue and the effects of abscisic acid (ABA) and indoleacetic acid (LAA) on the mechanism of uptake were investigated at 25 and 35 days after pollination (DAP). Uptake of 14C‐sugar was measured over the concentration range of 2 to 30 mM. Uptake kinetics showed a biphasic response to increasing external concentration of 14C‐sugars, and indicated the presence of P‐chlorormercuribenzenesulfonic acid (PCMBS)‐sensitive and PCMBS‐insensitive uptake. The Km value for each sugar was in the range of 10 to 20 mM. Stage of development had no effect on Km. but Vmax for glucose decreased with maturation. Further, sucrose was not taken up through a PC‐MBS‐sensitive transport at 35 DAP. ABA, especially 10 μM, at 25 DAP stimulated uptake of all sugars, mostly through enhanced PCMBS‐insensitive uptake but not PC‐MBS‐sensitive uptake. In contrast to ABA, stimulation of sugar uptake by IAA was most effective at 1 μM. The PCMBS‐insensitive uptake of each sugar was also stimulated by IAA. Further, the PCMBS‐sensitive uptake of glucose was enhanced. The developmental change of PCMBS‐sensitive sugar uptake and the effect of ABA and IAA on uptake mechanism in this study are considered to be important in influencing the development and enlargement of fruits.
Light and oxygen stress in Spirulina platensis (cyanobacteria) grown outdoors in tubular reactors
Authors: Vonshak Avigad , Torzillo Giuseppe , Accolla Paola , Tomaselli Luisa
Published: May 2006

As the effects of light and oxygen stress in algae on mass culture has not been intensively studied, we investigated them in Spirulina platensis under outdoor conditions in controlled tubular reactors where the respective roles of each stress can be distinguished. It was observed that exposure of this cyanobacterium at two oxygen concentrations (ca 20 and 53 mg 1−1) caused very little change in the ratio between variable and maximum fluorescence (Fv/Fm) during the day even when the culture was grown at higher oxygen concentration (about 7% lower in the evening than in the morning). Vice‐versa, when the photochemical efficiency of PSII (photon yield, Φc) was measured, a reduction of about 20% was observed. Neither the Fv/Fm ratio nor the Φc of the culture grown at the lower oxygen concentration changed significantly during the day. The daily productivity of the culture exposed to the higher oxygen concentration was reduced by about 20%. Laboratory cultures bubbled with air or pure oxygen under continuous light showed a similar response; i.e., a smaller decrease in Fv/Fm (17%) than in the Φc (56%) after 4 h. After 32 h of culture in pure oxygen, a total lysis of the cells occurred. Our results support the hypothesis that photoinhibition and photooxidation, two traditionally linked terms, although often closely associated under similar environmental conditions, may comprise two types of stress with different sites of inhibition.
Ionic processes underlying the decrease in osmotic potential of Chara L‐cell fragments in dilute electrolyte solutions
Authors: Kiyosawa Keitaro
Published: May 2006

Movements of ions are considered to be governed by the electroneutrality rule. Therefore, a cation moving across the cell membrane into the cell either passively or actively should move together with its counterion, an anion, in equal amounts of charge or in exchange for another cation inside the cell. This means that the net influx of the cation in question should be affected by the permeability of its counterion and/or another cation inside the cell. To examine osmotic and ionic regulation in Chara cells, cell fragments of Chara having a lower osmotic pressure than normal (L‐cell fragments) were prepared. The L‐cell fragments were individually put into various dilute electrolyte solutions and their osmotic potentials were measured with a turgor balance. Concentrations of K+, Na+, Ca2+, Mg2+, Cl−, NO−3. and SO2−4. in the external electrolyte solutions in which L‐cells had been incubated were also analysed by ion chromatography. The results showed that in 0.5 mM KCL + 0.1 mM CaCl2 solution, Chara L‐cell fragments absorbed K+ and Cl− to maintain electroneutrality and then regained their osmotic potential very rapidly. When the anion was Cl, the cation absorbed at the highest rate was K+ On the other hand, when the cation was K, the anion absorbed at the highest rate was Cl, Other ions Ca2+, SO2−4 and NO−3 showed much less permeability than K+ and Cl −for the Chara plasma membrane. The conclusion from these findings was that due to the constraint of electroneutral transport, the uptake rate of a salt into L‐cells is limited by the permeability of the least permeable ion.
A role for nitrogen reserves in forage regrowth and stress tolerance
Authors: Volenec J. J. , Ourry A. , Joern B. C.
Published: May 2006

Carbohydrate accumulation and utilization during shoot regrowth after defoliation and winter has been studied extensively in most species used as forage. However, recent work suggests that N reserves found in vegetative tissues also are important for defoliation tolerance and winter hardiness. Results suggest that these N reserves constitute an alternative N source used when N2 fixation and/or mineral N uptake are reduced. 15N labelling experiments indicate that a large proportion of herbage N is derived from N reserves mobilized from stem bases or roots to developing leaves and shoots. Amino acids and specific proteins (i.e. vegetative storage proteins, VSPs) are deposited in roots and stem bases and, in the case of VSPs, are degraded rapidly after defoliation. Identification and characterization of VSPs will increase our understanding of the role N reserves play in stress tolerance and may lead to innovative approaches for improving forage persistence and productivity.
Interactive effects of Ca2+ and NaCl salinity on the ionic relations and proline accumulation in the primary root tip of Sorghum bicolor
Authors: Colmer Timothy D. , Fan Teresa W.‐M. , Higashi Richard M. , Läuchli André
Published: May 2006

The effects of supplemental Ca2+ supply and NaCl salinity on the ionic relations and levels of proline and other amino acids in the primary root of Sorghum bicolor (cv. Hegari) seedlings were investigated. Two days of exposure to 150 mM NaCl resulted in a 50‐fold increase in the proline level in the 0–10 mm root tips of seedlings supplied with 5.0 mM Ca2+, but only a 4‐fold increase in seedlings with 0.5 mM Ca2+. In contrast to the high levels of proline in the root tip, proline accumulation was only modest in the expanded tissues of the root. The enhancement of proline accumulation in the root tip of salinized seedlings with the Ca2+ supplement may be related to their more favorable tissue K to Na ratio. Thus, elevated Ca2+ may mitigate the NaCl‐induced inhibition of S. bicolor root growth via the maintenance of net K to Na selectivity and the enhancement of proline accumulation in the root tip.
Effect of root perturbation and excision on nitrate influx and efflux in barley (Hordeum vulgare) seedlings
Authors: Aslam Muhammad , Travis Robert L. , Rains D. William , Huffaker Ray C.
Published: May 2006

The effects of perturbation and excision on net NO‐3, uptake, influx and efflux in roots of 8‐day‐old barley (Hordeum vulgare L.) seedlings induced with NO‐3 or NO‐2 were determined. Perturbation was simulated by mechanically striking the intact roots with a glass rod. Perturbation or excision of roots and subsequent division into small segments had little effect on NO‐3 influx, but briefly inhibited net uptake which recovered within a few min. While in perturbed roots net uptake rates recovered to the same level as in control roots, full recovery did not occur in excised roots. Inhibition of net uptake was due to stimulation of NO‐3 efflux. The recovery time and level of inhibition of net NO‐3 uptake and/or stimulation of efflux were a function of extent of perturbation, or the number of segments following excision, and root NO‐3 concentration. NO‐3 efflux was further stimulated when roots were perturbed after cytoplasmic NO‐3 had been depleted, indicating that both the plasmalemma and tonoplast may be affected. In excised roots both NO‐3 influx and efflux decreased with age due to depletion of energy sources. The results indicate that root perturbation and excision had no effect on NO‐3 influx but inhibited net uptake by stimulating efflux.
A soluble auxin‐binding protein from mung bean hypocotyls has indole‐3‐acetaldehyde reductase activity
Authors: Sugaya Sumiko , Sakai Shingo
Published: May 2006

To clarify the roles of auxin‐binding proteins (ABPs) in the action of auxin, soluble auxin‐binding proteins were isolated from an extract of etiolated mung bean hypocotyls by affinity chromatography on 2,4‐dichlorophenoxyacetic acid (2,4‐D)‐linked Sepharose 4B. A 39‐kDa polypeptide was retained on the affinity column and eluted with a solution containing IAA or 2,4‐D, but not with a solution containing benzoic acid. The protein was then purified by several column‐chromatographic steps. The apparent molecular mass of the protein was estimated to be 77 kDa by gel filtration and 39 kDa by SDS‐PAGE. We designated this protein ABP39. The partial amino acid sequences of ABP39, obtained after chemical cleavage by CNBr, revealed high homology with alcohol dehydrogenase (ADH; EC 1.2.1.1). While the ABP39 was not capable of oxidizing ethanol, it did catalyze the reduction of indole‐3‐acetaldehyde (IAAld) to indole‐3‐ethanol (IEt) with an apparent Km of 22 μM. The IAAld reductase (EC 1.2.3.1) is specific for NADPH as a cofactor. The ABP39 also catalyzed the reduction of other aldehydes, such as acetaldehyde, benzaldehyde, phenylacetaldehyde and propionealdehyde. Indole‐3‐aldehyde was a poor substrate. The enzyme activity was inhibited by both indole‐3‐acetic acid and 2,4‐D in a competitive manner. Therefore, the enzyme is considered to be retained on the affinity column by recognition of auxin structure.
Characterisation of the H+‐ATPase in plasma membranes isolated from the green alga Chlamydomonas reinhardtii
Authors: Norling Birgitta , Nurani Ghasem , Franzén Lars‐Gunnar
Published: May 2006

Plasma membranes from the green alga Chlamydomonas reinhardtii were purified by differential centrifugation and two‐phase partitioning in an aqueous polymer system. The isolated plasma membranes were virtually free from contaminating chloroplasts, mitochondria, endoplasmic reticulum and Golgi membranes as shown by marker enzyme and pigment analysis. The isolated plasma membranes exhibited vanadate sensitive ATPase activity, indicating the presence of a P‐type ATPase. This was verified by using antibodies against P‐type ATPase from Arabidopsis, which crossreacted with a protein of 109 kDa. The ATPase activity was inhibited to more than 90% by vanadate (Ki= 0.9 μM) but not affected by inhibitors specific for F‐ or V‐type ATPases. demonstrating the purity of the plasma membranes. Mg‐ATP was the substrate, and the rate of ATP‐hydrolysis followed simple Michaelis‐Menten kinetics giving a Km= 0.46 mM. Free Mg2+ stimulated the activity, K1/2= 0.68 mM. Maximal activity was obtained at pH 8. The ATPase activity was latent but stimulated 10 to 20‐fold in the presence of detergents. This indicates that the isolated plasma membrane vesicles were tightly sealed and mostly right‐side‐out, making the ATPase inaccessible to the hydrophilic substrate ATP. In the presence of the Brij 58, the isolated plasma membranes performed ATP dependent H+‐pumping as shown by the optical pH probe acridine orange. H+‐pumping was dependent on the presence of valinomycin and K+ ions and completely abolished by vanadate. Addition of Brij 58 has been shown to produce 100% sealed inside‐out vesicles of plant plasma membranes (Johansson et al. 1995, Plant J. 7: 165–173) and this was also the case for plasma membranes from the green alga Chlamydomonas reinhardtii.
The expansion of maize root‐cap mucilage during hydration. 2. Observations on soil‐grown roots by cryo‐scanning electron microscopy
Authors: McCully M. E. , Sealey L. J.
Published: May 2006

Expansion of root‐cap mucilage during hydration was followed by cryo‐scanning analytical microscopy of soil‐grown roots of diploperennis and Zea mays. Roots examined directly from the soil have no expanded mucilage. Their condensed, unexpanded mucilage is in three domains, periplasmic, intercellular and peripheral to the cap tissue. Carbon concentration is the same in the three domains. During hydration there is no change in carbon concentration as the condensed mucilage moves through these three domains; however there is a sharp drop at the periphery where a gel phase transition occurs. The rate of expansion of the mucilage blob around the root tip is limited by the rate of this gel phase transition.