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  • 11
    Electronic Resource
    Electronic Resource
    Photooxidative stress in plants (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 92 (1994), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The light-dependent generation of active oxygen species is termed photooxidative stress. This can occur in two ways: (1) the donation of energy or electrons directly to oxygen as a result of photosynthetic activity; (2) exposure of tissues to ultraviolet irradiation. The light-dependent destruction of catalase compounds the problem. Although generally detrimental to metabolism, superoxide and hydrogen peroxide may serve useful functions if rigorously controlled and compartmentalised. During photosynthesis the formation of active oxygen species is minimised by a number of complex and refined regulatory mechanisms. When produced, active oxygen species are eliminated rapidly by efficient antioxidative systems. The chloroplast is able to use the production and destruction of hydrogen peroxide to regulate the thermal dissipation of excess excitation energy. This is an intrinsic feature of the regulation of photosynthetic electron transport. Photoinhibition and photooxidation only usually occur when plants are exposed to stress. Active oxygen species are part of the alarm-signalling processes in plants. These serve to modify metabolism and gene expression so that the plant can respond to adverse environmental conditions, invading organisms and ultraviolet irradiation. The capacity of the antioxidative defense system is often increased at such times but if the response is not sufficient, radical production will exceed scavenging and ultimately lead to the disruption of metabolism. Oxidative damage arises in high light principally when the latter is in synergy with additional stress factors such as chilling temperatures or pollution. Environmental stress can modify the photooxidative processes in various ways ranging from direct involvement in light-induced free radical formation to the inhibition of metabolism that renders previously optimal light levels excessive. It is in just such situations that the capacity for the production of active oxygen species can exceed that for scavenging by the antioxidative defense systems. The advent of plant transformation, however, may have placed within our grasp the possibility of engineering greater stress tolerance in plants by enhancement of the antioxidative defence system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1994.tb03042.x
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  • 12
    Electronic Resource
    Electronic Resource
    Modulation of carbon and nitrogen metabolism, and of nitrate reductase, in untransformed and transformed Nicotiana plumbaginifolia during CO2 enrichment of plants grown in pots and in hydroponic culture (1997)
    Springer
    Planta 202 (1997), S. 510-521 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Carbon dioxide enrichment ; Carbon/nitrogen ratio ; Glutamine ; Nicotiana (C and N metabolism) ; Nitrate ; Nitrate reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Transformed plants of Nicotiana plumbaginifolia Viv. constitutively expressing nitrate reductase (35S-NR) or β-glucuronidase (35S-GUS) and untransformed controls were grown for two weeks in a CO2-enriched atmosphere. Whereas CO2 enrichment (1000 μl · l−1) resulted in an increase in the carbon (C) to nitrogen (N) ratio of both the tobacco lines grown in pots with vermiculite, the C/N ratio was only slightly modified when plants were grown in hydroponic culture in high CO2 compared to those grown in air. Constitutive nitrate reductase (NR) expression per se did not change the C/N ratio of the shoots or roots. Biomass accumulation was similar in both types of plant when hydroponic or pot-grown material, grown in air or high CO2, were compared. Shoot dry matter accumulation was primarily related to the presence of stored carbohydrate (starch and sucrose) in the leaves. In the pot-grown tobacco, growth at elevated CO2 levels caused a concomitant decrease in the N content of the leaves involving losses in NO− 3 and amino acid levels. In contrast, the N content and composition were similar in all plants grown in hydroponic culture. The 35S-NR plants grown in air had higher foliar maximum extractable NR activities and increased glutamine levels (on a chlorophyll or protein basis) than the untransformed controls. These increases were maintained following CO2 enrichment when the plants were grown in hydroponic culture, suggesting that an increased flux through nitrogen assimilation was possible in the 35S-NR plants. Under CO2 enrichment the NR activation state in the leaves was similar in all plants. When the 35S-NR plants were grown in pots, however, foliar NR activity and glutamine content fell in the 35S-NR transformants to levels similar to those of the untransformed controls. The differences in NR activity between untransformed and 35S-NR leaves were much less pronounced in the hydroponic than in the pot-grown material but the difference in total extractable NR activity was more marked following CO2 enrichment. Foliar NR message levels were decreased by CO2 enrichment in all growth conditions but this was much more pronounced in pot-grown material than in that grown hydroponically. Since β-glucuronidase (GUS) activity and message levels in 35S-GUS plants grown under the same conditions of CO2 enrichment (to test the effects of CO2 enrichment on the activity of the 35S promoter) were found to be constant, we conclude that NR message turnover was specifically accelerated in the 35S-NR plants as well as in the untransformed controls as a result of CO2 enrichment. The molecular and metabolic signals involved in increased NR message and protein turnover are not known but possible effectors include NO3 −, glutamine and asparagine. We conclude that plants grown in hydroponic culture have greater access to N than those grown in pots. Regardless of the culture method, CO2 enrichment has a direct effect on NR mRNA stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050156
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  • 13
    Electronic Resource
    Electronic Resource
    Changes in apoplastic antioxidants induced by powdery mildew attack in oat genotypes with race non-specific resistance (1999)
    Springer
    Planta 208 (1999), S. 444-452 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Antioxidant ; Avena (pathogen resistance) ; Blumeria ; Erysiphe ; Hydrogen peroxide ; Pathogen resistance (race non-specific)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Three oat (Avena sativa L.) lines which show differential responses to attack by the biotrophic fungal pathogen Blumeria graminis DC f. sp. avenae Marchal, which causes powdery mildew, were studied: Maldwyn shows the strongest resistance in adult plants; Selma shows greater susceptibility; while a Selma × Maldwyn hybrid, OM1387, has a similar degree of resistance to Maldwyn. Host responses to pathogen attack were complete 48 h after inoculation but largely accomplished within the first 24 h, the point when material was taken for enzyme and metabolic assays. In Maldwyn and OM1387 about 80% of attacked cells showed localized autofluorescent host-cell responses but this fell to less than 20% in Selma. A cytoplasmic marker enzyme, glucose 6-phosphate dehydrogenase, was used to determine contamination of the apoplastic extracts by cellular components. After correction for cytoplasmic contamination, up to 4% of the total foliar activities of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase activities were detected in the apoplast. The apoplast contained about 2% of the total foliar glutathione pool and dehydroascorbate, but not ascorbate, at values amounting to 10% of the total foliar ascorbate plus dehydroascorbate pool. Twenty-four hours after inoculation the foliar or apoplastic ascorbate pools were similar in inoculated and control leaves. Foliar catalase activity increased in both susceptible and resistant responses. Resistance correlated with increased total foliar glutathione, an increase in the ratio of reduced to oxidized glutathione and with decreased total activities of foliar ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050581
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  • 14
    Electronic Resource
    Electronic Resource
    Light-dependent reduction of dehydroascorbate and uptake of exogenous ascorbate by spinach chloroplasts (1983)
    Springer
    Planta 158 (1983), S. 442-450 
    Details
    ISSN: 1432-2048
    Keywords: Ascorbate uptake ; Chloroplast ; Dehydroascorbate reduction ; Glutathione dehydrogenase ; Glutathione metabolism ; Spinacia (ascorbate metabolism)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A reconstituted spinach chloroplast system containing thylakoids, stroma and 0.1 mM NADPH supported O2 evolution in the presence of oxidised glutathione (GSSG). The properties of the reaction were consistent with light-coupled GSSG-reductase activity involving H2O as eventual electron donor. The reconstituted system also supported dehydroascorbate-dependent O2 evolution in the presence of 0.6 mM reduced glutathione (GSH) and 0.1 mM NADPH with the concomitant production of ascorbate. The GSSG could replace GSH in which case the production of GSH preceded the accumulation of ascorbate. The data are consistent with the light-dependent reduction of dehydroascorbate using H2O as eventual electron donor via the sequence H2O→NADP→GSSG→dehydroascorbate. Approximately 30% of the GSH-dehydrogenase activity of spinach leaf protoplasts is localised in chloroplasts: this could not be attributed to contamination of chloroplasts by activity from the extrachloroplast compartment. Washed intact chloroplasts supported the uptake of ascorbate but the uptake mechanism had a very low affinity for ascorbate (Km approximately 20 mM). The rate of uptake of ascorbate was less than the rate of light-dependent reduction of dehydroascorbate and too slow to account for the rate of H2O2 reduction by washed intact chloroplasts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397738
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  • 15
    Electronic Resource
    Electronic Resource
    Compartmentation and fluxes of inorganic phosphate in photosynthetic cells (1984)
    Springer
    Planta 161 (1984), S. 525-530 
    Details
    ISSN: 1432-2048
    Keywords: Asparagus ; Inorganic phosphate ; Ion flux ; Photosynthesis ; Relaxation kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An analysis of the compartmentation and fluxes of inorganic phosphate in isolated cladophyll cells from Asparagus officinalis was made in parallel with an ultrastructural study. The elution pattern of labelled inorganic phosphate (which indicates that the asparagus cells are behaving as a system of three compartments in series) was used to quantify the fluxes between the vacuole, cytoplasm and free space. A relaxation time of 198 min was calculated for inorganic phosphate exchange between the vacuole and cytoplasm. It is, therefore, suggested that the vacuole serves to buffer the cytoplasmic inorganic phosphate concentration in the long term. However, in the short term, exchange with the vacuole will not appreciably affect the cytoplasmic inorganic phosphate concentration and thus the partitioning of photosynthetically fixed carbon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00407084
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  • 16
    Electronic Resource
    Electronic Resource
    Intercellular compartmentation of sucrose synthesis in leaves of Zea mays L. (1985)
    Springer
    Planta 164 (1985), S. 172-178 
    Details
    ISSN: 1432-2048
    Keywords: Fructose 1,6-bisphosphatase ; Sucrose phosphate synthetase ; Sucrose synthesis ; Zea (sucrose synthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The incorporation of 14C into sucrose and hexose phosphates during steady-state photosynthesis was examined in intact leaves of Zea mays L. plants. The compartmentation of sucrose synthesis between the bundle sheath and mesophyll cells was determined by the rapid fractionation of the mesophyll and comparison of the labelled sucrose in this compartment with that in a complete leaf after homogenisation. From these experiments it was concluded that the majority of sucrose synthesis occurred in the mesophyll cell type (almost 100% when the time-course of sucrose synthesis was extrapolated to the time of 14C-pulsing). The distribution of enzymes involved in sucrose synthesis between the two cell types indicated that sucrose-phosphate synthetase was predominantly located in the mesophyll, as was cytosolic (neutral) fructose-1,6-bisphosphatase activity. Stromal (alkaline) fructose-1,6-bisphosphatase activity was found almost exclusively in the bundle-sheath cells. No starch was found in the mesophyll tissue. These data indicate that in Zea mays starch and sucrose synthesis are spatially, separated with sucrose synthesis occurring in the mesophyll compartment and starch synthesis in the bundle sheath.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396079
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  • 17
    Electronic Resource
    Electronic Resource
    Effects of constitutive expression of nitrate reductase in transgenic Nicotiana plumbaginifolia L. in response to varying nitrogen supply (1995)
    Springer
    Planta 196 (1995), S. 288-294 
    Details
    ISSN: 1432-2048
    Keywords: Nicotiana ; Nitrate nutrition ; Nitrate reductase ; Photosynthesis ; Transgenic plant (tobacco)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transformed Nicotiana plumbaginifolia plants with constitutive expression of nitrate reductase (NR) activity were grown at different levels of nitrogen nutrition. The gradients in foliar NO 3 − content and maximum extractable NR activity observed with leaf order on the shoot, from base to apex, were much decreased as a result of N-deficiency in both the transformed plants and wild type controls grown under identical conditions. Constitutive expression of NR did not influence the foliar protein and chlorophyll contents under any circumstances. A reciprocal relationship between the observed maximal extractable NR activity of the leaves and their NO 3 − content was observed in plants grown in nitrogen replete conditions at low irradiance (170 μmol photons·m−2 ·s−1). This relationship disappeared at higher irradiance (450 μmol photons·m−2·S−1) because the maximal extractable NR activity in the leaves of the wild type plants in these conditions increased to a level that was similar to, or greater than that found in constitutive NR-expressors. Much more NO 3 − accumulated in the leaves of plants grown at 450 μmol photons·m−2·s−1 than in those grown at 170 μmol photons·m−2·s−1 in N-replete conditions. The foliar NO 3 − level and maximal NR activity decreased with the imposition of N-deficiency in all plant types such that after prolonged exposure to nitrogen depletion very little NO 3 − was found in the leaves and NR activity had decreased to almost zero. The activity of NR decreased under conditions of nitrogen deficiency. This regulation is multifactoral since there is no regulation of NR gene expression by NO 3 − in the constitutive NR-expressors. We conclude that the NR protein is specifically targetted for destruction under nitrogen deficiency. Consequently, constitutive expression of NR activity does not benefit the plant in terms of increased biomass production in conditions of limiting nitrogen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201387
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  • 18
    Electronic Resource
    Electronic Resource
    Short-term modulation of nitrate reductase activity by exogenous nitrate in Nicotiana plumbaginifolia and Zea mays leaves (1996)
    Springer
    Planta 199 (1996), S. 366-371 
    Details
    ISSN: 1432-2048
    Keywords: Nicotiana (nitrate reductase) ; Nitrate ; Nitrate reductase (activation state) ; Protein phosphorylation ; Transgenic plants ; Zea (nitrate reductase)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Maize (Zea mays L.) grown on low (0.8 mM) NO 3 - , as well as untransformed and transformed Nicotiana plumbaginifolia constitutively expressing nitrate reductase (NR), was used to study the effects of NO 3 - on the NR activation state. The NR activation state was determined from the relationship of total activity extracted in the presence of ethylenediaminetetracetic acid to that extracted in the presence of Mg2+. Light activation was observed in both maize and tobacco leaves. In the tobacco lines, NO 3 - did not influence the NR activation state. In excised maize leaves, no correlation was found between the foliar NO 3 - content and the NR activation state. Similarly, the NR activation state did not respond to NO 3 - . Since the NR activation state determined from the degree of Mg2+-induced inhibition of NR activity is considered to reflect the phosphorylation state of the NR protein, the protein phosphatase inhibitor microcystin LR was used to test the importance of protein phosphorylation in the NO 3 - -induced changes in NR activity. In-vivo inhibition of endogenous protein phosphatase activity by microcystin-LR decreased the level of NR activation in the light. This occurred to the same extent in the presence or absence of exogenous NO 3 - . We conclude that NO 3 - does not effect the NR activation state, as modulated by protein phosphorylation in either tobacco (a C3 species) or maize (a C4 species). The short-term regulation of NR therefore differs from the NO 3 - -mediated responses observed for phosphoenolpyruvate carboxylase and sucrose phosphate synthase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195728
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  • 19
    Electronic Resource
    Electronic Resource
    Light-dependent modulation of foliar glutathione synthesis and associated amino acid metabolism in poplar overexpressing γ-glutamylcysteine synthetase (1997)
    Springer
    Planta 202 (1997), S. 357-369 
    Details
    ISSN: 1432-2048
    Keywords: Key words: γ-Glutamylcysteine ; γ-Glutamylcysteine synthetase ; Glutathione ; Glycine ; Photorespiration ; Populus (transformed)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Glutathione (GSH), γ-glutamylcysteine (γ-EC) and major free amino acids were measured in darkened and illuminated leaves from untransformed poplars (Populus tremula × P. alba) and poplars expressing Escherichia coli genes for γ-glutamylcysteine synthetase (γ-ECS; EC 3.2.3.3) and glutathione reductase (GR; EC 1.6.4.2). In poplars overexpressing γ-ECS, foliar γ-EC contents and GSH contents were markedly enhanced compared to poplars lacking the bacterial gene for the enzyme. However, the quantitative relationship between the foliar pools of γ-EC and GSH in these transformants was markedly dependent on light. In the dark, GSH content was relatively low and γ-EC content high, the latter being higher than the foliar GSH contents of untransformed poplars in all conditions. Hence, this transformation appears to elevate γ-EC from the ranks of a trace metabolite to one of major quantitative importance. On illumination, however, γ-EC content decreased fourfold whereas GSH content doubled. Glutathione was also higher in the light in untransformed poplars and in those overexpressing GR. In these plants, γ-EC was negligible in the light but increased in the dark. Cysteine content was little affected by light in any of the poplar types. No light-dependent changes in the extractable activities of γ-ECS, glutathione synthetase (EC 3.2.3.2) or GR were observed. In contrast, both the activation state and the maximum extractable activity of nitrate reductase (EC 1.6.6.1) were increased by illumination. In all poplar types, glutamate and aspartate were the major amino acids. The most marked light-induced increases in individual amino acids were observed in the glutamine, asparagine, serine and glycine pools. Illumination of leaves from poplars overexpressing γ-ECS at elevated CO2 or low O2 largely abolished the inverse light-dependent changes in γ-EC and GSH. Low O2 did not affect foliar contents of cysteine or glutamate but prevented the light-induced increase in the glycine pool. It is concluded that light-dependent glycine formation through the photorespiratory pathway is required to support maximal rates of GSH synthesis, particularly under conditions where the capacity for γ-EC synthesis is augmented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050138
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  • 20
    Electronic Resource
    Electronic Resource
    Modification of thiol contents in poplars (Populus tremula × P. alba) overexpressing enzymes involved in glutathione synthesis (1997)
    Springer
    Planta 203 (1997), S. 362-372 
    Details
    ISSN: 1432-2048
    Keywords: Key words:γ-Glutamylcysteine synthetase ; Glutathione synthesis ; Glutathione synthetase ; Transgenic poplar ; Populus (glutathione synthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The hybrid poplar (Populus tremula × P.␣alba) was transformed to express the Escherichia coli gene for γ-glutamylcysteine synthetase (EC 6.3.2.2: γ-ECS) in the cytosol. Four transformed lines of poplar were obtained. These were phenotypically indistinguishable from untransformed poplars. Three lines, ggs28 (Noctor et al. 1996, Plant Physiol 112: 1071–1078), ggs11 and ggs5 possessed high levels of bacterial gene transcripts. Line ggs17 had lower transcript levels. Antisera were prepared against bacterial γ-ECS and bacterial glutathione synthetase (EC 6.3.2.3: GS). Using the antiserum prepared against the purified His-tagged E.␣coliγ-ECS, lines ggs28, ggs11 and ggs5 were shown to possess abundant quantities of the bacterial protein, whereas ggs17 contained lower amounts. The antiserum prepared against the purified His-tagged E. coli GS was also effective in screening poplars transformed with the E.␣coli gene coding for this enzyme. Immunoblots of leaf extracts from poplars overexpressing GS using this antibody revealed two bands. The extractable foliar γ-ECS activities of the γ-ECS transformants were in quantitative agreement with the protein levels. Lines ggs28, ggs11 and ggs5 had approximately 30-fold higher γ-ECS activity than untransformed poplars, whereas in ggs17 this activity was only augmented about 3-fold. The lines strongly overexpressing γ-ECS, ggs28, ggs11 and ggs5, contained enhanced foliar levels of cysteine (up to 2-fold), γ-glutamylcysteine (5- to 20-fold) and glutathione (2- to 4-fold). Foliar thiol contents in ggs17 were no different to those of untransformed plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050202
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