bluuebunny/crossref_metadata_2025 huggingface dataset:
The modulating effects of pH and benzyladenine on the Ca2+– and Mg2+‐ATPases in the plasmalemma of wheat root cells
Authors: Kuiper Daan , Sommarin Marianne , Kylin Anders
Published: May 2006

Plant cells frequently and rapidly have to respond to environmental changes for survival. Regulation of transport and other energy‐requiring processes in the plasmalemma of root cells is therefore one important aspect of the ecological adaptation of plants. Wheat (Triticum aestivum L. cv. Drabant) was grown hydroponically, with or without 50 nM benzyladenine in the medium, and plasma membranes from root cells of 8‐day‐old plants were prepared by aqueous polymer two‐phase partitioning. The influence of Ca2+ and Mg2+ on the plasmalemma ATPase activities was investigated. The presence of benzyladenine during growth increased the ATPase activity, that dependent upon Ca2+ more than that elicited by Mg2+. As a general characteristic, ATP was the preferred substrate, but all nucleotide tri‐ and diphosphates could be accepted with activities in plasma membranes from control plants of 7‐36% (Mg2+) and 40‐86% (Ca2+) and in plasma membranes from benzyladenine‐treated plants of 12‐47% (Mg2+) and 53‐102% (Ca2+) as compared with activities obtained with ATP. Nucleotidemonophosphates were not hydrolyzed by the preparations. In preparations from benzyladenine‐treated plants one peak of Ca2+‐ATPase at pH 5.2–5.6, with a tail from pH 6 and upwards, and one peak of Mg2+‐ATPase at pH 6.0–6.5 were observed in the presence of EDTA in the assay media. In preparations from control plants, the addition of EDTA to the assays resulted in a wide optimum between pH 6 and 7 for Mg2+‐ATPase and low Ca2+‐ATPase activity with no influence of pH in the range 4.5 to 8. Analysis of the pH dependence in the presence of both Ca2+ and Mg2+ indicates that the control plants mainly contain Mg2+‐ATPase corresponding to the proton pump. Preparations from benzyladenine‐treated wheat roots show, in addition, activation by Ca2+, which, in the slightly alkaline pH range may correspond to a Ca2+‐extruding (Ca2++ Mg2+)‐ATPase. In the acidic range, the responses are more complicated: the Mg2+‐ATPase is inhibited by vanadate, while the Ca2+‐ATPase is insensitive, and benzyladenine added during growth influences the interaction between Ca2+ and Mg2+ in a way that parallels the effect of high salt medium.
Cell cycle and cell differentiation in lentil roots grown on a slowly rotating clinostat
Authors: Legué Valérie , Driss‐Ecole Dominique , Perbal Gérald
Published: May 2006

Root growth was studied for seedlings of lentil (Lens culinaris L. cv. Verte du Puy) grown for 27 h either on a slowly rotating clinostat (0.9 rev. min−1) of vertically (controls). Horizontal clinorotation was employed, so that the longitudinal axis of the root was parallel to the axis of the rotation. Morphological (root length and orientation) and cellular (cell proliferation and cell elongation) parameters were studied. The cell cycle was also analysed by flow cytometry. Root length deviation of the roots from the initial orientation was observed on the clinostat; this deviation could be due to spontaneous oscillation. Cell elongation of the clinostat‐rotated roots occurred closer to the tip than in the vertical roots, but the mitotic index was not modified. Clinorotation did not change the frequencies of the G1, S and G2 phases of the cell cycle. These results were compared to those obtained during the D1 mission on Spacelab, 1985. The effects of microgravity on root orientation and mitotic index were not simulated by clinorotation.
Histological study of initiation and development in vitro of adventitious roots in minicuttings of apple rootstocks of M 26 and EMLA 9
Authors: Zhou Junyan , Wu Hong , Collet G. F.
Published: May 2006

Apple rootstocks M 26 and EMLA 9 ‘COST’ shoots propagated in vitro were used for the histological study of initiation and development of adventitious roots after a brief induction pretreatment. The results show that there are differences in mode and timing of initiation and development of adventitious roots between the two varieties. In M 26, adventitious roots were directly initiated from the derivatives of the cambium, some of which were immediately transformed into meristemoids in situ 36 h after pretreatment. Subsequently, meristemoids differentiated into root primordia. Development of adventitious roots were completed when they emerged at the surface of stem bases 10 days after pretreatment. In EMLA 9, before the meristemoids formed, internal cell files were formed by continuous divisions of cambial cells. The cells were regularly arranged in files external to the cambium. On the fourth day after pretreatment, some cells in the outermost layers of these files became meristematic, started to divide and turned into meristemoids, which differentiated into root primordia. The cells of the files between the root primordium and the cambium were transformed into vascular tissues which connected the vascular systems of the adventitious roots and stems.
A metabolic connection between nitrogenase activity and the synthesis of ureides in nodulated soybean
Authors: Atkins Craig A. , Fernando Milanthi , Hunt Stephen , Layzell David B.
Published: May 2006

Application of allopurinol (AP; 1H‐pyrazolo‐[3,5‐d]pyrimidine‐4‐o1) to intact nodulated roots of ureide‐forming legumes causes rapid inhibition of NAD:xanthine dehydrogenase (XDH: EC 1.2.1.37), cessation of ureide synthesis and, subsequently, severe nitrogen deficiency (Atkins et al. 1988. Plant Physiology 88: 1229–1234). Nitrogen deficiency is a result of inhibited nitrogenase (EC 1.7.99.2) activity. Using an open gas exchange system to measure H2 and CO2 evolution, short term effects of AP application were examined in a Hup− soybean symbiosis [Glycine max (L.) Merr. cv. Harosoy: USDA 16]. The onset of inhibition of nitrogenase was detected after ca 2 h exposure of the roots to AP. At the same time xanthine began to accumulate and ureide levels declined in nodules as a result of inhibition of XDH. The decline in H2 evolution following AP application was not due to altered electron allocation between N2 and H+ by nitrogenease but was coincident with increased gaseous diffusive resistance of nodules and a decline in intracellular oxygen concentration. A possible scheme for the intermediary metabolism of soybean nodules which might account for a direct connection between nitrogenase activity and ureide synthesis is proposed. The suggested mechanism envisages coupling production of reducing power by cytosolic enzymes of purine oxidation to synthesis of dicarboxylic acid substrates (malate and succinate) required for bacteroid respiration.
Influence of calcium chloride and benzyladenine on lipoxygenase of Vigna unguiculata leaf discs during senescence
Authors: Swamy P. M. , Suguna P.
Published: May 2006

Cowpea (Vigna unguiculata L.) leaf discs incubated in the dark in CaCl2 and benzyladenine maintained higher levels of chlorophyll and protein than controls. The CaCl2 or benzyladenine treatments reduced lipoxygenase activity, and the effect of these compounds in combination was additive. HPLC analysis of the product profile of lipoxygenase activity with arachidonic acid as a substrate showed a single peak comigrating with standard 15‐hydroperoxyeicosatetraenoic acid. There appears to be a strong temporal correlation between the CaCl2+ benzyladenine delay of senescence and lipoxygenase activity.
Denitrification in lucerne nodules and bacteroids supplied with nitrate
Authors: Arrese‐Igor C. , Royuela M. , Aparicio‐Tejo P. M.
Published: May 2006

Nodulated lucerne plants (Medicago sativa L. cv. Aragón) were supplied with 20 mM nitrate. Anaerobically isolated bacteroids of Rhizobium meliloti from these plants were able to denitrify after 48 h treatment. R. meliloti bacteroids behave as total denitrifiers, reducing nitrate to dinitrogen: when acetylene was omitted from the assay medium very little nitrous oxide was recovered. The onset of denitrification activity was coincident with the induction of nitrite reductase activity (EC 1.7.99.3) whereas nitrate reductase activity (EC 1.7.99.4) was constitutive. Whole nodules from plants receiving several doses of nitrate were assayed, in a nitrate‐free medium, to monitor denitrification activity dependent on nitrate within the nodules. Denitrification activity was detected after 2 days of 20 mM nitrate supply or after 3 days in the presence of 10 or 5 mM nitrate. These results are discussed in relation to current controversy about nitrate entry into the infection region of nodules. It is concluded that this process occurs more rapidly than suggested in recent research.
Identification of a single‐copy gene encoding a Type I chlorophyll a/b‐binding polypeptide of photosystem I in Arabidopsis thaliana
Authors: Jensen Poul E. , Kristensen Michael , Hoff Tine , Lehmbeck Jan , Stummann Bjarne M. , Henningsen Knud W.
Published: May 2006

We have isolated and sequenced cDNA and genomic clones from Arabidopsis thaliana which specify a 241 residue protein with 84% sequence identity to a photosystem I Type I chlorophyll a/b‐binding (CAB) protein from tomato. The open reading frame is interrupted by three introns which are found at equivalent positions as the corresponding introns in the tomato gene. Comparison to the amino acid sequence of other CAB proteins confirms that all CAB proteins share two regions of very high similarity. However, near the N‐terminus and between the conserved regions this light‐harvesting complex I (LHCI) protein, as other LHCI proteins from other plant species, has sequence motifs which appear to be PSI‐specific. Restriction analysis of genomic DNA shows that the Arabidopsis protein is encoded by a single‐copy gene.
Inorganic carbon transport across cell compartments of the halotolerant alga Dunaliella salina
Authors: Ramazanov Ziyadin , Cárdenas Jacobo
Published: May 2006

The inorganic carbon (Ci) accumulation and the intracellular location of carbonic anhydrase (CA, EC 4.2.1.1) in the halotolerant unicellular alga Dunaliella salina have been investigated. The rate of HCO3 ‐dependent O2 evolution was determined by growth conditions. Algae grown under high CO2 conditions (5% CO2 in air, v/v; high Ci cells) had a very low affinity for HCO3− at pH 7.0 and 8.2, whereas algae grown under low CO2 conditions (0.03% CO2 in air; low Ci cells) showed a high affinity for HCO3− at both pH values and were sensitive to Dextran‐bound sulfonamide (DBS), an inhibitor of extracellular CA. The photosynthetic rate or HCO4− dependent O2 evolution was always higher at pH 7.0 than at pH 8.2. Ethoxyzolamide (EZ), an inhibitor of total (extacellular plus intracellular) CA activity, strongly inhibited photosynthesis at both pH values. During adaptation from high to low CO2 conditions CA activity increased in chloroplasts in a process dependent on the novo protein synthesis. Carbonic anhydrase activity was found in the supernatant and pellet fractions of chloroplast homogenates. The rate of photosynthesis of chloroplasts from low Ci cells was higher at pH 7.0 than at pH 8.2. The alkalinization of the growth medium, which took place only in the presence of Ci, was partially inhibited by DBS and completely by EZ. We suggest that in D. salina CO2 is the general form of Ci transported across the plasma membrane and the chloroplast envelope and that bicarbonate enters the cell mainly, although not entirely, by an ‘indirect’ mechanism after dehydration to CO2.
Exopolygalacturonase protein accumulates late in peach fruit ripening
Authors: Downs Christopher G. , Brady Colin J. , Gooley Andrew
Published: May 2006

Two exo‐acting polygalacturonase enzymes (exoPG, EC 3.2.1.67) increase in activity as peach (Prunu persica L. Batsch cvs Coronet and Flavorcrest) fruits ripen. By examining populations of fruit, we show that the increase in activity occurs late in ripening when the fruit are very soft (below 2 kgf). The more abundant form of the enzyme, exoPG 2, was extensively purified and analyzed for its amino acid content and N‐terminal amino acid sequence. ExoPG 2 is a polypeptide of M, 66 000 and has a substantial excess of basic over acidic amino acids. Polyclonal antisera to exoPG 2 were raised in mice. The antisera inhibited the enzyme activity and recognized a Mr 66 000 polypeptide in Western blots. Western blot analyses of extracts of fruit ranked for softness revealed a Mr 66 000 polypeptide only in the softest fruit (less than 2.5 kgf). We conclude that the increased in exopolygalacturonase activity that occurs in very soft fruit is due to an increase in the amount of enzyme protein.
Ascorbate peroxidase – a hydrogen peroxide‐scavenging enzyme in plants
Authors: Asada Kozi
Published: May 2006

Ascorbate peroxidase is a hydrogen peroxide‐scavenging enzyme that is specific to plants and algae and is indispensable to protect chloroplasts and other cell constituents from damage by hydrogen peroxide and hydroxyl radicals produced from it. In this review, first, the participation of ascorbate peroxidase in the scavenging of hydrogen peroxide in chloroplasts is briefly described. Subsequently, the phylogenic distribution of ascorbate peroxidase in relation to other hydrogen peroxide‐scavenging peroxidases using glutathione, NADH and cytochrome c is summarized. Chloroplastic and cytosolic isozymes of ascorbate peroxidase have been found, and show some differences in enzymatic properties. The basic properties of ascorbate peroxidases, however, are very different from those of the guaiacol peroxidases so far isolated from plant tissues. Amino acid sequence and other molecular properties indicate that ascorbate peroxidase resembles cytochrome c peroxidase from fungi rather than guaiacol peroxidase from plants, and it is proposed that the plant and yeast hydrogen peroxide‐scavenging peroxidases have the same ancestor.
Root nodule development: origin, function and regulation of nodulin genes
Authors: Verma D. P. S. , Hu C.‐A. , Zhang M.
Published: May 2006

The symbiotic root nodule, an organ formed on leguminous plants, is a product of successful interactions between the host plant and the soil bacteria, Rhizobium spp. Plant hormones play an important role in the genesis of this organ. The hormonal balance appears to be modulated by the signals produced by bacteria. Many host genes induced during nodule organogenesis and the symbiotic state have been identified and characterized from several legumes. These genes encode nodule‐specific proteins (nodulins) which perform diverse functions in root nodule development and metabolism. Formation of a subcellular compartment housing the bacteria is essential to sustain the symbiotic state, and several nodulins are involved in maintaining the integrity and function of this compartment. The bacteroid enclosed in the perbacteroid membrane behaves as an ‘organelle,’completely dependent on the host for all its requirements for carbon, nitrogen and other essential elements. Thus it seems likely that the nodulins in the peribacteroid membrane perform specific transport functions. While the function of a few other nodulins is known (e.g. nodulin‐100, nodulin‐35), a group of uncharacterized nodulins exists in soybean root nodules. These nodulins share structural similarities and seem to have been derived from a common ancestor. Induction of nodulin genes occurs prior to and independent of nitrogen fixation, and thus is a prelude to symbiosis. Although some of the early nodulin genes are induced prior to or during infection, induction of late nodulins requires endocytotic release of bacteria.
Electrophoretic separation and characterization of pea protoplasts
Authors: Koonen F. , Jacobsen H.‐J.
Published: May 2006

A carrier‐free electrophoresis system was developed to separate protoplasts according to their zeta‐potential and to study their behaviour in subsequent cell culture. Apex protoplasts from young cotyledon‐free pea embryos (Pisum sativum L. cv. Belman), including primordia, were analysed with respect to their electrophoretic mobility, viability, cell size, cell division capacity, chlorophyll content, and expression of a 50 kDa protein involved in early somatic embryogenesis. Protoplasts fractionated on the basis of their electrophoretic mobility were viable and able to divide and form microcallus in cell culture. Cell culture procedures were modified in order to handle low numbers of protoplasts (50–2000 per fraction). Electrophoretic separation revealed distinct classes of protoplasts, differing in all parameters tested except cell size. Therefore, a connection between zeta potential and other physiological parameters can be proposed.
Electrostimulated regeneration of plantlets from protoplasts derived from cell suspensions of barley (Hordeum vulgare)
Authors: Mordhorst Andreas P. , Lörz Horst
Published: May 2006

For transformation and somatic hybridisation of barley (Hordeum vulgare L.), it is necessary to develop an efficient and reliable system for routne plant regeneration from protoplasts. Freshly‐isolated cell suspension‐derived protoplasts were treated with both rectangular and exponential electric pulses with the aim of increasing plating efficiency as well as to stimulate regenerative capacity. Suspensions were initiated from callus from immature embryos of barley (cv. Dissa). Increasing field strength, capicitance, or number of applied pulses resulted in a decreased protoplast viability and plating efficency. However, the regeneration of albino leaves and albino plantlets from electro‐treated protoplasts was stimulated in comparison with controls.
Evidence for early stages of somatic embryo development in a protoplast‐derived cell culture of Prunus avium
Authors: David Hélène , Domon Jean‐Marc , Savy Colette , Miannay Nicole , Sulmont Gérard , Dargent Robert , David Alain
Published: May 2006

In the genus Prunus, so far, somatic embryogenesis has not been reported either from cell suspensions or from their protoplast‐derived cells. Rhizogenic cell suspensions of Prunus avium L., initiated from adventitious roots developed from cotyledon‐derived callus of mature zygotic embryos, have been subcultured for more than one year without losing their morphogenic potential. A yield of 8 × 105 protoplasts ml−1 of packed cells with a viability of 98% has been routinely obtained. Optimum cell division frequency (around 2.5% at day 10 and 4–6% at day 15) occurs in agarose lenses, with Murashige and Skoog (1962. Physiol. Plant 15: 476–497)‐based medium supplemented with 5 μM naphthalene acetic acid, 1 μM benzyladenine and 0.25 μM zeatin. Colony formation has been achieved after 35 days with a plating efficiency of 3–4%. Cell suspensions have been initiated from protoplast‐derived callus. While the older cell cultures express a rhizogenic response, the younger ones contain early stages of somatic embryo development. Ultrastructural examination confirms the polarization of these structures.
Fusion of male‐sterile tobacco causes modifications of mtDNA leading to changes in floral morphology and restoration of fertility in cybrid plants
Authors: Kofer Waltraud , Glimelius Kristina , Bonnett Howard T.
Published: May 2006

Protoplasts from male‐sterile Nicotiana tabacum cultivars with cytoplasms of N. suaveolens, N. bigelovii and N. undulata were fused in different pairwise combinations. Cybrid plants were obtained and categorized according to their flower morphologies into groups as parental male‐sterile types, recombined biparentals, novel male‐steriles and male fertiles. Restriction enzyme analyses and DNA gel blot hybridizations of the mitochondrial DNA (mtDNA) of these cybrid plants revealed that all plants with parental male‐sterile morphologies had banding patterns identical to the parental patterns, whereas all cybrids with flower morphologies different from their parents had novel patterns. Several restriction fragments were found to be unique to the mtDNA of male‐fertile plants with perfectly restored stamen morphologies when compared to the mtDNA from cybrid plants with incomplete restoration. MtDNA gel blot hybridization analysis of fertile plants revealed that the probe for atpA hybridized to two restriction fragments, one from each parent. Further, fertile plants with complete stamen restoration lacked an expressed sequence in the 3’flanking region of atpA, in contrast to both male‐sterile parents.
Transgenic rice plants: Characterization of two generations of seed progeny
Authors: Lynch P. T. , Jones J. , Zhang H. , Rech E. L. , Eyles P. S. , Kothari S. L. , Blackhall N. W. , Cocking E. C. , Davey M. R.
Published: May 2006

Transgenic rice plants have been regenerated from kanamycin‐resistant callus of Oryza sativa (cv. Taipei 309) derived from protoplasts electroporated with pCaMVNEO carrying the neomycin phosphotransferase II (nptII) gene. Of 6 randomly selected plants, all contained the nptll gene, but only 2 plants expressed NPTII activity. The transgenic plants were significantly shorter, produced fewer tillers, took longer to flower and had reduced fertility compared to non‐transformed protoplastderived plants. Fifty‐six seeds collected from one transgenic plant expressing NPTII activity germinated on medium containing kanamycin sulphate to give 16 green, first seed generation (R1) plants. The latter could be divided into 3 groups: (i) Plants which set seed, had normal floret morphology and produced a total of 76 seeds; (ii) Plants which flowered, but which failed to set seed; (iii) Plants which failed to flower, were shorter and had significantly fewer tillers than plants of groups (i) and (ii). The nptII gene was present in all transgenic R1 plants, but only 8 plants expressed the gene. Phenotypic characteristics, observed in transgenic R1 plants were also seen in the transforned R2 plants. These included reduced stature, a longer vegetative phase and reduced fertility compared to non‐transformed plants.
Applications of an optimized monocot expression vector in studying transient gene expression and stable transformation of barley
Authors: Maas Christoph , Schell Jeff , Steinbiß Hans‐Henning
Published: May 2006

Protoplasts of a barley (Hordeum vulgare L. cv. Golden Promise) suspension cell line were used for PEG‐mediated gene transfer. Transient gene expression in barley protoplasts was studied using a chimeric CaMV 35S cat construct, which was only poorly expressed in barley cells. However, insertion of exon 1 and intron 1 of the maize Shrunken‐1 (Sh1) gene in the 5′‐untranslated leader of the construct strongly stimulated gene expression. By using the optimized chimeric cat construction the amount of CAT protein that was reached 19 hours after DNA uptake was 0.5% of total protein, which was calculated from western blot data.

As an alternative marker gene for expression studies, we also tested the firefly luciferase gene in barley protoplasts. Low level expression of chimeric CaMV 35S luciferase genes could be highly stimulated when Sh1 exon1 and intron1 were inserted in the 5′‐untranslated leader of the constructs. Enhanced luciferase gene expression by Shrunken‐1 intronic sequences enabled us to monitor gene integration events early after DNA uptake using a promoterless luciferase marker gene, which could only be expressed after integration behind an endogenous promoter.
Progress in plant protoplast research
Authors: Puite Klaas J.
Published: May 2006

During the past years plant regeneration from protoplasts was achieved for a number of important crops (maize, sorghum, rice, wheat, sugar beet). The use of embryogenic tissue for protoplast isolation greatly contributed to this success. There was also some progress in woody plant species and ornamentals. Fusion of protoplasts resulted in may fertile hybrid plants, especially in the Brassicaceae and Solanaceae. These somatic hybridization studies led to introduction of new agronomical traits from sexually incompatible species into the cultivar gene pool and to new nucleus‐organelle compositions. The limitations of somatic hybridization, mainly imposed by the taxonomic distance of the parents, and expressed as chromosome loss and reduced fertility, are more clearly recognized now. Asymmetric hybridization with irradiated donor protoplasts resulted in cybrids with new cytoplasmic traits (e. g. intraspecific fusions in Brassica), as well as in the transfer of only a few donor choromosomes (e. g. intrageneric fusions in Nicotiana). Most intrageneric fusions, however, resulted only in a limited elimination of donor chromosomes (e. g. in Lycopersicon), and polyploidization occurred (e. g. in Nicotiana). Also some success on protoplast transformation was obtained in both monocots and dicots. Fertile transgenic rice plants (Japonica, Indica) were produced after direct gene transfer into protoplasts derived from embryogenic cell suspensions. Particle gun experiments using embryogenic cell suspension of maize resulted in fertile transgenic plants. Transformation of citrus and lettuce by direct gene transfer was also reported.
Purification and properties of a lytic enzyme from the cell wall of Chlorella ellipsoidea C‐87
Authors: Araki Naoko , Takeda Hiroshi
Published: May 2006

Cell wall lytic activity was detected in the culture medium and cell wall of 1AM Chlorella ellipsoidea C‐87. The enzymes of both fractions had their highest activity at pH 5. The lytic activity bound to the cell wall consisted of a polysaccharide releasing enzyme, an exo‐type enzyme releasing disaccharide, and glucosidase; but only the polysaccharide releasing enzyme was solubilized by lithium chloride. A polysaccharide releasing enzyme with a molecular weight around 40 kDa was isolated from the culture medium. Hemicellulose is degraded by the polysaccharide releasing enzyme, and the rigid wall by the exo‐type enzyme.
Nitrate assimilatory properties of barley grown under long‐term N limitation: Effects of local nitrate supply in split‐root cultures
Authors: Öhlén Elisabeth , Larsson Carl‐Magnus
Published: May 2006

The effect of nitrate availability on characteristics of the nitrate assimilatory system was investigated in N‐limited barley (Hordeum valgare L. cv. Golf), grown with the seminal root system split into initially equal‐sized halves. The cultures were continuously supplied with nitrate‐N at a relative addition rate (RA) of 0.09 day−1, which resulted in relative growth rates (RG) that were ca 85% of those observed under surplus nitrate nutrition. The total N addition was divided between the subroots in ratios of 100:0, 80:20, 70:30, 60:40, and 50:50. For comparison, standard cultures were grown at RAs ranging from 0.03 to 0.18 day−1. Initially, biomass and N partitioning to the subroots responded strongly and proportionally to the nitrate distribution ratio. After 12‐14 days no further effect was observed. The Vmax for net nitrate uptake and in vitro nitrate reductase (NR) activity were measured in acclimated plants, i.e., after > 14 days under a certain nitrate regime. In subroots fed from 20 to 100% of the total N addition, Vmax for net nitrate uptake increased slightly, whereas NR activity was unaffected. Uptake and NR activities were insignificant in the 0%‐subroot. Uneven nitrate supply to individual subroots had negligible effect on the whole‐plant ability for nitrate uptake, and the relative Vmax (unit N taken up per unit N in whole plant tissue and time) remained about 7‐fold in excess of the demand set by growth. Balancing nitrate concentrations (the resulting external nitrate concentrations at a certain RA) generally ranged between 2 and 10 μM at growth‐limiting RA, both when predicted from uptake kinetics and when actually measured. When comparing split root and standard cultures when acclimated, it appears that uptake and NR activities in roots respond more strongly to over‐all nitrate availability than to nitrate availability to individual subroots.
Stomatal responses to light in the facultative Crassulacean acid metabolism species, Portulacaria afra
Authors: Lee David M. , Assmann Sarah M.
Published: May 2006

Guard cell responses to light are mediated by guard cell chlorophyll and by a specific blue light photoreceptor. Gas exchange and epidermal peel techniques were employed to investigate these responses in the facultative Crassulacean acid metabolism (CAM) species, Portulacaria afra (L.) Jacq. In P. afra individuals performing C3 metabolism, red light stimulated an increase in leaf conductance in intact leaves and stomatal opening in isolated epidermal peels, indicating the presence in guard cells of the chlorophyll‐mediated response to light. Under a background of continuous red illumination, conductance exhibited transient increases following pulses of blue but not red light, indicating that the specific stomatal response to blue light was also operative. In contrast, in CAM individuals, conductance in gas exchange experiments and stomatal opening in epidermal peel experiments were not stimulated by red light. In CAM plants, conductance did not increase following blue light pulses administered over a range of temperatures, vapor pressure differences (VPD), ambient CO2 concentrations and background red light intensities. These results indicate that P. afra does possess typical guard cell responses to light when performing C3 metabolism. The metabolic pathways mediating these responses are either lost or inhibited when CAM is induced.
Effect of light and its interaction with nitrate and ammonium ions in seed germination of Caesulia axillaris
Authors: Singh Bharat , Amritphale Dilip
Published: May 2006

Seeds of Caesulia axillaris Roxb. displayed an absolute light requirement for germination throughout the period of dry storage at 28°C. The seeds were found to show a gradual increase in percent germination with storage time ‐ reaching a maximum value between 8‐14 months and then a sharp decline. Percent water uptake and photosensitivity were at maximum after a 5‐day imbibition period in the dark in both seedlots studied. Seedlot I, which was only marginally responsive to far‐red light, showed a nearly complete red‐far‐red reversal effect in contrast to seedlot II. The latter also displayed a considerable promotion of germination in far‐red light. Interestingly, a noticeable degree of heterogeneity, besides the one observed in both seedlots with reference to red light, was found to exist in seedlot II for far‐red light. Exogenous application of nitrate and ammonium, at the levels occurring in soil during seed germination/seedling emergence phase of the plant in nature, promoted a considerable proportion of high Ø‐requiring seeds to germinate under irradiation conditions establishing low Ø‐value. The probable ecological implication of this reponse has been discussed. Little correlation was found between the requirement for an exogenous supply of nitrate and the endogenous nitrate level in the seeds in their response to far‐red light.
Recovery of photosynthesis and phtosystem II fluorescence in Chlamydomonas reinhardtii after exposure to three levels of high light
Authors: Falk Stefan , Samuelsson Göran
Published: May 2006

Recovery from 60 min of photoinhibitory treatment at photosynthetic photon flux densities of 500, 1400 and 2200 μMmol m−2 s− was followed in cells of the green alga Chlamydomonas reinhardtii grown at 125 μMmol m−2 s−1. These light treatments represent photoregulation, moderate photoinhibition and strong photoinhibition, respectively. Treatment in photoregulatory light resulted in an increased maximal rate of oxygen evolution (Pmax) and an increased quantum yield (Φ), but a 15% decrease in Fv/FM. Treatment at moderately photoinhibitory light resulted in a 30% decrease in Fv/FM and an approximately equal decrease in Φ. Recovery in dim light restored Fv/FM within 15 and 45 min after high light treatment at 500 and 1400 μMmol m−2 s−1, respectively. Convexity (Θ), a measure of the extent of co‐limitation between PS II turnover and whole‐chain electron transport, and Φ approached, but did not reach the control level during recovery after exposure to 1400 μMmol m−2 s−1, whereas Pmax increased above the control. Treatment at 2200 μMmol m−2 s−1 resulted in a strong reduction of the modeled parameters Φ, Θ and Pmax. Subsequent recovery was initially rapid but the rate decreased, and a complete recovery was not reached within 120 min. Based on the results, it is hypothesized that exposure to high light results in two phenomena. The first, expressed at all three light intensities, involves redistribution within the different aspects of PS II heterogeneity rather than a photoinhibitory destruction of PS II reaction centers. The second, most strongly expressed at 2200 μmol m−2 s−1, is a physical damage to PS II shown as an almost total loss of PS IIα and PS II QB‐reducing centers. Thus recovery displayed two phase, the first was rapid and the only visible phase in algae exposed to 500 and 1400 μmol m−2 s−1. The second phase was slow and visible only in the later part of recovery in cells exposed to 2200 μmol m−2 s−1.
Relationships between nitrogen fixation and growth in Robinia pseudoacacia seedlings: A functional growth‐analysis approach using 15N
Authors: Johnsen Kurt H. , Bongarten Bruce C.
Published: May 2006

The effects of NO3− fertilization on N2 fixation and growth of black locust (Robinia pseudoacacia L.) seedlings were examined by growth analyses. Seedlings were grown under low (0.25 mM) and high (2.00 mM) NO3− provided with each watering. In one experiment, seedlings were given NO3− with enriched levels of 15N (11.03%) to identify N accumulation from soil and atmospheric sources. Curves describing accretion of total dry weight and N were fit as functions of accumulated photosynthetically active radiation (PAR). Relative growth rates (RGR) and nitrogen productivities (NP) were derived from these curves and examined as functions of seedling size and/or internal N concentration. Early in the experiments seedlings receiving the higher amount of NO3− grew faster, acquired more N, had greater internal nitrogen concentrations (N1) and had higher NP than seedlings receiving the lower amounts. Seedlings receiving higher N also acquired most of their N from NO3−, whereas those receiving lower N acquired most from N2 fixation. Later in the experiments, no differences in growth rae, N1 or NP were observed. Furthermore, midway through the experiments seedlings receiving the higher amounts of NO3− began to acquire the majority of N from N2 fixation. At the end of the two experiments, seedlings given higher NO3− were 16 and 78% larger in dry weight. Differences in size were due to growth differences that occurred only during the first half of the experiments. During this period, the faster growth of seedlings given higher NO3− was attributed to greater access to utilizable N and lower energy costs associated with the acquisition and/or utilization of NO3−, relative to N2. Unlike the situation in non‐N2‐fixing plants, differences in available soil N had no influence on biomass allocation to roots, stems or leaves in black locust. When soil N became limiting, N2 fixation capacity increased, rather than root mass, to acquire more N.
Phytotoxicity of cadmium ions on germinating seedlings of mung bean (Phaseolus vulgaris): Involvement of lipid peroxides in chlorphyll degradation
Authors: Somashekaraiah B. V. , Padmaja K. , Prasad A. R. K.
Published: May 2006

Germinating seedlings of mung bean (Phaseolus vulgaris L. cv. K‐16) were treated with different concentrations of cadmium acetate (10, 50 and 100 μM). Cd2+ lowered the chlorophyll and heme levels. The level of lipid peroxides were higher on day 3 than on day 6. However, Cd2+ treatment significantly enhanced the level of lipid peroxides. Similarly, a dose‐dependent induction of lipoxygenase (EC 1.13.11.12) activity was observed with Cd2+ treatment. Further, the activities of antioxidant enzymes such as superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) were decreased. Our results suggest that lipoxygenase‐mediated accumulation of lipid peroxides on the one hand and inhibition of free radical scavenging enzymes like superoxide dismutase and catalase on the other caused a pronounced reduction in the chlorophyll and heme levels of the seedlings. The experiments conducted on the effect of Cd2+ on dark‐grown seedlings did not conform with the result of light‐grown seedlings. Though chlorophyll and heme levels decreased in a dose‐dependent manner, no accumulation of lipid peroxides was observed, suggesting that the inhibition of chlorophyll synthesis by Cd2+ is achieved both by reaction with constituent biosynthetic enzymes as well as peroxide‐mediated degradation.
Regulation of the photosynthetic capacity of primary bean leaves by the red:far‐red ratio and photosynthetic photon flux density of incident light
Authors: Barreiro Roberto , Guiamét Juan J. , Beltrano José , Montaldi Edgardo R.
Published: May 2006

The main objective of the present work was to examine the effects of the red:far‐red ratio (R:FR) prevailing during leaf development on the photosynthetic capacity of mature leaves. Plants of Phaseolus vulgaris L. cv. Balin de Albenga were grown from time of emergence in a controlled environment room, 25 ± 3°C, 12‐h photoperiod, with different light treatments:a) high photosynthetic photon flux density (PPFD) = 800 μmol m−1 s−1+ high R:FR= 1.3;b) low PPFD= 300 μmol m−2 s−1+ high R:FR= 1.3; c) high PPFD=800 μmol m−2 s−1+ low R:FR= 0.7; d) low PPFD= 300 μmol m−2s−1+ low R:FR=0.7. With an R:FR ratio of 1.3, a decrease in irradiance during leaf growth reduced photosynthesis when measured at moderate to high PPFD; but when measured at low PPFD, leaves expanded under low irradiance actually had photosynthesis rates higher than those of leaves grown in high irradiance. A low R:FR ratio during development reduced the photosynthetic capacity of the leaves. In leaves expanded under R:FR = 0.7 and high irradiance photosynthesis was reduced by 42 to 89%, depending on the PPFD at which measurements were made, whereas for leaves developed at R:FR = 0.7 and low irradiance photosynthesis decreased by 21 to 24%, compared to leaves under R:FR = 1.3 and similar irradiance. The reduced photosynthetic capacity under R:FR = 0.7 and high irradiance. In natural environments, leaves may experience low R:FR conditions temporarily during their development, and this may affect their future photosynthetic capacity in full sunlight.
Reserve lipid accumulation and translocation of 14C in the photosynthetically active and senescent shoot parts of Dicranum elongatum
Authors: Hakala Kaija , Sewón Pirjo
Published: May 2006

Lipid metabolism of the subarctic moss Dicranum elongatum was studied by feeding the moss with 2‐14C‐acetate and, after extraction of the lipids, counting the 14C‐content of different lipid fractions immediately after feeding or after chase periods. Translocation of 14C after 14C‐feeding was studied with autoradiography. Both low temperature (+6°C) and drought (at +23°C) resulted in increased incorporation of 14C into the neutral lipid (NL) fraction and decreased incorporation of 14C into the glycolipid (GL) fraction of the green shoot part of the moss. The distribution of radioactivity between the NL classes suggests that diacylglycerols (1, 2‐DAG) and common triacylglycerols (cTAG) are turned into acetylenic triacylglycerols (aTAG), which are accumulated preferentially. The decrease in the radioactivity of the GL fraction was due to two unknown fractions, whereas 14C incorporation into the chloroplast membrane lipids, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG), was very low throughout the experiments. The phospho‐lipid (PL) fraction accounted for 48–63% of total lipid radioactivity at both low and high temperatures. 2‐14C‐acetate feeding to the senescent moss part resulted in vigorous 14C incorporation into the lipids, especially into the reserve TAGs. Electron microscopic examination showed the presence of plastids, which explains the capability of the senescent part of the moss for lipid synthesis. The fact that transport of 14C from 2‐14C‐acetate took place upwards and downwards in the moss shoot, together with the capability for lipid synthesis of the senescent moss part, supports the suggestion that the senescent moss part plays a role as an energy store.
Effects of cropping, nutrition and water supply on accumulation and distribution of biomass and nutrients for apple trees on‘M9’root systems
Authors: Buwalda J.G. , Lenz F.
Published: May 2006

The effects of cropping, nutrition and water supply on accumulation and distribution of biomass and nutrients for apple trees on‘M9’root systems were examined using trees growing in lysimeters. For 3‐year‐old ‘Golden Delicious’ trees, cropping significantly increased total biomass, although leaf and root biomass were reduced. For 3‐year‐old‘Golden Delicious', ‘Coxs Orange’ and ‘Gloster’ trees, cropping only in the third year reduced root biomass by 39 to 45%. Cropping did not affect water use by trees of any cultivar early in the season, but increased water use later in the season for ‘Gloster’ trees. For trees with fruit, total non‐structural carbohydrate (TNC) contents at the end of the season were highest in fruit (up to 1 400 g plant−1). For trees without fruit, TNC contents were generally highest in the roots (up to 110 g planr−1). Supplying trees with nutrient solution diluted to 10% of the standard composition increased the root biomass for ‘Golden Delicious’ trees only, but decreased biomass of above‐ground tissues for all cultivars. Reducing the nutrient supply decreased water and nutrient uptake, and reduced nutrient contents within vegetative parts of the tree more than within roots. For ‘Golden Delicious’ trees, restricting the water supply to 50% or 25% of that consumed by control trees significantly reduced above‐ground biomass, but root biomass was not significantly affected. The N, P and K. contents for the trees were also reduced by water stress, due to reduced contents within above‐ground organs. Water stress reduced the TNC and starch contents of all tissues, except the roots. These results are discussed in relation to the efficiency of root systems for water and nutrient uptake.
In vivo and in vitro effects of boron on the plasma membrane proton pump of sunflower roots
Authors: Roldán Marta , Belver Andrés , Rodríguez‐Rosales Pilar , Ferrol Nuria , Donaire Juan Pedro
Published: May 2006

The effect of boron excess and deficiency on H+ efflux from excised roots from sunflower (Heliarahus annuus L. cv. Enano) seedlings and on plasma membrane H+‐ATPase (EC 3.6.1.35) in isolated KI‐washed microsomes has been investigated. When seedlings were grown in media with toxic levels of H3BO3 (5 mM) or without added boron and exposed to light conditions, an inhibition of the capacity for external acidification by excised roots was observed as compared to roots from seedlings grown with optimal H3BO3 concentration (0.25 mM). Toxic and deficient boron conditions also inhibited the vanadate‐sensitive H+‐ATPase of microsomes isolated from the roots. The mechanism of boron toxicity was investigated in vitro with microsorne vesicles. A strong effect of boron on the vanadate‐sensitive, ATP‐dependent H+ transport was found, but the vanadate‐sensitive phospho‐bydrolase activity was not affected. These results suggest that boron could exert an effect on the plasma membrane properties, directly or indirectly regulating, proton transport.
Water stress induced changes in concentrations of proline and total soluble sugars in nodulated alfalfa (Medicago sativa) plants
Authors: Irigoyen J. J. , Einerich D. W. , Sánchez‐Díaz M.
Published: May 2006

Susceptibility of alfalfa (Medicago sativa L. cv. Aragón) nodules and leaves to water stress has been investigated. Nodule acetylene reduction activity (ARA), leaf CO2 exchange rate (CER) as well as soluble protein, proline and total soluble sugar (TSS) contents were determined during drought. Water status was estimated as water potential (Ψw) and Relative water content (RWC) of the respective tissues. Maximum rates of ARA required higher Ψw than CER. Nodules had lower RWC for a given Ψw than leaves. Water stress reduced soluble protein content in both tissues; however, the decline in soluble protein content was detected at greater Ψw in nodules than in leaves. Proline and TSS increased in leaves and nodules, and again the threshold Ψw triggering such accumulation was higher in nodule tissues. Oior results suggest that alfalfa nodules are more susceptible to water shortage than leaves. Effects of accumulated TSS and proline upon leaf and nodule physiology are discussed in relation to protein stability (proline), pH control (proline) and osmotic adjustment (proiine and TSS). The TSS accumulation induced by water stress suggests that substrate shortage would not be the primary effect of drought on nodule activity.
Degradation of membrane lipid components and antiovidanl levels in Hordeum vulgare exposed to long‐term fumigation with SO2
Authors: Navari‐Izzo. Flavia , Quartacci Mike F. , Izzo Riccardo , Pinzino Calogero
Published: May 2006

Hordeum vulgare L. (cv. Barberousse) seedlings were continuosly exposed to SO2 (40±5 and 117±20 ppb) for 48 days and compared to control plants exposed to charcoal‐filtered air. Glyco‐and phospolipid amounts were strongly affected by exposure to SO2:, and decreased with increasing SO2, fumigation. The chloroplast membranes of fumigated leaves were characterized by lower quantities of rnonogalacto‐syldiacylglycerol (MGDG) as well as of sulphoquinovosyldiacylglycerol (SQDG). Among the phospholipids a decrease in the phosphatidylglycerol (PG) content was observed, indicating that the chloroplast membranes are affected even by such low concentrations of SO2 as used here. As for the other phospholipids, phosphatidylcholine (PC) and phosphatidylinositol (PI) suffered a reduction and phosphatidylethano‐lairrine (PE) almost disappeared at the highest SO2, concentration, whereas phosphatidic acid (PA) followed the opposite trend. The fatty acids of both glyco‐ and phospholipids fell sharply upon fumigation without any decline in the degree of unsataration. In particuSar, neither linoleic nor linolenic acid showed any evident change in level, suggesting that no lipid peroxidation of polytmsaturated fatty acid tails occurred. Furthermore, the electron spin resonance (ESR) showed no differences in the free radical levels between control and fumigated leaves.

The level of malondialdehyde (MDA) decreased, while lipid‐soluble antioxidants, as well as superoxide dismutase (SOD; EC 1.15.1.1) and catalase (EC 1.11.1.6) activities increased with the increase in SO2 concentration, providing evidence that defence mechanisms against oxy‐radical action are activated by the plants at low levels of SO2,. Even if SO2, at low concentrations may not directly oxidize polyunsaturated fatty acids, it may act as a deesterifying factor on each component of both glyco‐ and phospholipids.
Effects of cadmium and lead on the accumulation of Ca2+ and K+ and on the influx and translocation of K+ in wheat of low and high K+ status
Authors: Trvedi Shailja , Erdei László
Published: May 2006

The effects of cadmium and lead on the internal concentrations of Ca2+ and K+, as well as on the uptake and translocation of K(86Rb+) were studied in winter wheat (Triticum aestivum L. a. MV‐8) grown hydroponically at 2 levels of K+ (100 uM and 10 mM). Cd2+ and Pb2+ were applied in the nutrient solution in the range of 0.3 to 1000 u.M. Growth was more severely inhibited by Cd2+ and in the high‐K+ plants as compared to Pbz+ and low‐K+ plants. Ions of both heavy metals accumulated in the roots and shoots, but the K+ status influenced their levels. Ca2+ accumulation was increased by low concentrations of Cd2+ mainly in low‐K+ shoots, whereas it was less influenced by Pb2+. The distribution of Cd2+ and Ca2+ in the plant and in the growth media indicated high selectivity for Cd2+ in the root uptake, while Ca2+ was preferred in the radial and/or xylem transport. Cd2+ strongly inhibited net K+ accumulation in high‐K+ plants but caused stimulation at low K+ supply. In contrast, the metabolis‐dependent influx of K+(86Rb+) was inhibited in low‐K+ plants, while the passive influx in high‐K+ plants was stimulated. Translocation of K+ from the roots to the shoots was inhibited by Cd2+ but less influenced in Pb2+‐treated plants. It is concluded that the effects of heavy metals depend upon the K+‐status of the plants.