Storage carbohydrate production and overwintering strategy in a winter-green tussock grass on South Georgia (Sub Antarctic)

Summary Water-soluble and ethanol-soluble carbohydrates were extracted from leaves, shoots, roots, rhizomes and flowers ofParodiochloa flabellata (Lam.) Rasp. (=Poa flabellata (Lam.) Hook f.) throughout a growing season. Very high levels of soluble carbohydrates were found in the shoot, comprising up to 71% of the shoot dry weight. There was no significant storage in the rhizome. It is suggested that the production of storage fructans with a degree of polymerization greater than 14, rather than oligosaccharides or starch, may be related to the cold environment. Relationships between the onset of senescence and levels of fructans suggest that recovery of sugars from dying tissue is high. The sugar reserves together with preformation of the flowers should ensure production of seed however poor the summer or long the winter might be. The high levels of fructans may partly inhibit growth but may also offer some degree of freezing resistance.     

Activity and quantity of ribulose bisphosphate carboxylase-and phosphoenolpyruvate carboxylase-protein in two Crassulacean acid metabolism plants in relation to leaf age,nitrogen nutrition,and point in time during a day/night cycle

Activity of ribulose 1,5-bisphosphate (RuBP) carboxylase in leaf extracts of the constitutive Crassulacean acid metabolism (CAM) plant Kalanchoe pinnata (Lam.) Pers. decreased with increasing leaf age, whereas the activity of phosphoenolpyruvate (PEP) carboxylase increased. Changes in enzyme activities were associated with changes in the amount of enzyme proteins as determined by immunochemical analysis, sucrose density gradient centrifugation, and SDS gel electrophoresis of leaf extracts. Young developing leaves of plants which received high amounts of NO ₃ ^- during growth contained about 30% of the total soluble protein in the form of RuBP carboxylase; this value declined to about 17% in mature leaves. The level of PEP carboxylase in young leaves of plants at high NO ₃ ^- was an estimated 1% of the total soluble protein and increased to approximately 10% in mature leaves, which showed maximum capacity for dark CO₂ fixation. The growth of plants at low levels of NO ₃ ^- decreased the content of soluble protein per unit leaf area as well as the extractable activity and the percentage contribution of both RUBP carboxylase and PEP carboxylase to total soluble leaf protein. There was no definite change in the ratio of RuBP carboxylase to PEP carboxylase activity with a varying supply of NO ₃ ^- during growth. It has been suggested (e.g., Planta 144, 143–151, 1978) that a rhythmic pattern of synthesis and degradation of PEP carboxylase protein is involved in the regulation of -carboxylation during a day/night cycle in CAM. No such changes in the quantity of PEP carboxylase protein were observed in the leaves of Kalanchoe pinnata (Lam.) Pers. or in the leaves of the inducible CAM plant Mesembryanthemum crystallinum L.Abbreviations CAM Crassulacean acid metabolism - RuBP ribulose 1,5-bisphosphate - PEP phosphoenolpyruvate - G-6-P glucose-6-phosphate     

Decomposition of tree leaf litters grown under elevated CO2: Effect of litter quality

Ash (Fraxinus excelsior L.), birch (Betula pubescens Ehrh.), sycamore (Acer pseudoplatanus L.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) leaf litters were monitored for decomposition rates and nutrient release in a laboratory microcosm experiment. Litters were derived from solar domes where plants had been exposed to two different CO₂ regimes: ambient (350 L L^-1 CO₂) and enriched (600 L L^-1 CO₂).Elevated CO₂ significantly affected some of the major litter quality parameters, with lower N, higher lignin concentrations and higher ratios of C/N and lignin/N for litters derived from enriched CO₂. Respiration rates of the deciduous species were significantly decreased for litters grown under elevated CO₂, and reductions in mass loss at the end of the experiment were generally observed in litters derived from the 600 ppm CO₂ treatment. Nutrient mineralization, dissolved organic carbon, and pH in microcosm leachates did not differ significantly between the two CO₂ treatments for any of the species studied. Litter quality parameters were examined for correlations with cumulative respiration and decomposition rates: N concentration, C/N and lignin/N ratios showed the highest correlations, with differences between litter types. The results indicate that higher C storage will occur in soil as a consequence of litter quality changes resulting from higher atmospheric concentrations of CO₂.Abbreviations CHO soluble carbohydrates - DOC dissolved organic carbon - HCel holocellulose - WTREM weight remaining     

Role of other plant organs in gibberellic acid-induced delay of leaf senescence in alstroemeria cut flowers

Chlorophyll loss in leaves of cut flowers of alstroemeria (Alstroemeria pelegrina L. cv. Westland) was rapid in darkness and counteracted by irradiation and treatment of the flowers with gibberellic acid (GA₃). The mechanism of the effect of GA₃ under dark conditions was investigated. The content of various carbohydrates in the leaves under dark conditions rapidly decreased; this was not influenced by treatment with GA_3. indicating that the loss of carbohydrates in the leaves did not induce the loss of chlorophyll. Placing the cut flowers in various solutions of organic and inorganic nutrients exhibited no significant effect on the retention of chlorophyll in leaves of dark-senescing flowers. The total nitrogen content in leaves of dark-senescing cut flowers decreased with time. Leaves of GA₃-treated flowers retained more nitrogen. In contrast, the buds of GA₃-treated flowers retained less nitrogen during senescence in the dark than control buds. To investigate whether GA₃ affects export of assimilates from the leaf to various parts of control and GA₃-treated flowers, we labelled one leaf with radioactive carbon dioxide. ¹⁴C-assimilates accumulated preferentially in the flowers, in which the relative specific activity of the youngest floral buds was highest. No significant differences were observed in the distribution of ¹⁴C-labelled compounds between the buds of control and GA₃-treated flowers. To establish the importance of source-sink relations for the loss of leaf chlorophyll we removed the flower buds (i. e. the strongest sink) from the cut flowers. This removal only slightly delayed chlorophyll loss as compared to the large delay caused by GA₃-treatment. In addition, detached leaf tips exhibited chlorophyll loss in the dark, which was delayed by GA₃-treatment in a fashion comparable with that in flowers. Together these data demonstrate that interactions of the leaves with other plant organs are not essential for chlorophyll loss during senescence in the dark. Additionally, we have found no evidence that GA₃ delays the loss of chlorophyll by affecting the transport of nutrients within the cut flowers.     

Effects of base cation fertilization on the nutrient status,free amino acids and some carbon fractions of the leaves of sugar maple (Acer saccharum Marsh.)

A study was conducted in the Lower Laurentians of southern Quebec to test the hypothesis that base cation fertilization would improve the nutrient status of declining sugar maples (Acer saccharum Marsh.) and alter the partitioning of leaf C and N. Six 40×40 m plots were delineated in an 80 year old stand of sugar maple. Three plots received a mixture of fertilizer and liming materials (500 kg ha^–1 of K₂SO₄, 250 kg ha^–1 of CaCO₃ and 250 kg ha^–1 of CaMg(CO₂)₂) in the spring of 1989. Leaves from mid crown of dominant or co-dominant maples were sampled monthly during the 1990 growing season. Trees were cored in 1992 to measure their response in diameter growth. Fertilization increased diameter growth and foliar K concentration of trees but reduced foliar Ca concentration. Fertilization resulted in lower starch concentrations and higher ratios of soluble sugars to starch in June and September, and in higher free amino acid concentrations but lower ratio of total non-structural carbohydrates to free amino acids in September. Leaf proline concentration was correlated with leaf starch concentration (r=0.39). The results suggest that amelioration of K deficiencies in sugar maple through fertilization with a mixture of base cations can increase tree growth and affect the seasonal dynamics of foliar C and N pools.Abbreviations FAA free amino acids - TNC total non-structural carbohydrates     

Response of photosynthesis and respiration of resurrection plants to desiccation and rehydration

Using non-invasive techniques (CO₂ gas exchange, light scattering, light absorption, chlorophyll fluorescence, chlorophyll luminescence), we have analysed the response of respiration and photosynthesis to dehydration and rehydration of leaves of the resurrection plants Craterostigma plantagineum Hochst., Ramonda mykoni Reichb. and Ceterach officinarum Lam. et DC. and of the drought-sensitive mesophyte spinach (Spinacia oleracea L.). The following observations were made: (i) The rate of water loss during wilting of detached leaves of drought-tolerant resurrection plants was similar to that for leaves of the sensitive mesophyte, spinach. Leaves of Mediterranean xerophytes lost water much more slowly. (ii) Below a residual water content of about 20%, leaves of spinach did not recover turgor on rewatering, whereas leaves of the resurrection plants did. (iii) Respiration was less sensitive to the loss of water during wilting in the resurrection plants than in spinach. (iv) The sensitivity of photosynthesis to dehydration was similar in spinach and the resurrection plants. Up to a water loss of 50% from the leaves, photosynthesis was limited by stomatal closure, not by inhibition of reactions of the photosynthetic apparatus. Photosynthesis was inhibited and stomates reopened when loss of water became excessive. (v) After the leaves had lost 80% of their water or more, the light-dependent reactions of photosynthetic membranes were further inhibited by rewatering in spinach; they recovered in the resurrection plants. (vi) In desiccated leaves of the resurrection plants, slow rehydration reactivated mitochondrial gas exchange faster than photosynthetic membrane reactions. Photosynthetic carbon assimilation recovered only slowly.     

Photosynthesis and assimilate transport in potato with top-roll disorder caused by the aphid Macrosiphum euphorbiae

In pot experiments in a glasshouse, top-roll symptoms were induced on potato plants after infestation with the aphid Macrosiphum euphorbiae. Leaves showing symptoms accumulated carbohydrates and tuber yields of affected plants were decreased by 44% compared with controls. Leaves grown after killing the aphids had a normal appearance and sugar contents. Infestation with aphids primarily inhibited carbohydrate transport in the stem and the accumulation of ¹⁴C-labelled assimilate in the vascular bundles of the leaves. It is suggested that photosynthesis is inhibited by impaired phloem transport and subsequent accumulation of carbohydrates in the leaves and not by direct mechanical damage caused by the feeding aphid.     

LEACHING OF METABOLITES FROM FOLIAGE AND SUBSEQUENT REABSORPTION AND REDISTRIBUTION OF THE LEACHATE IN PLANTS

Inorganic and organic metabolites, including carbohydrates, amino acids, and organic acids, may be leached from the foliage of 125 diverse plant species by the action of rain, dew, and mist. Ca⁴⁵, P³², and Sr⁸⁹ absorbed by roots, and C¹⁴ absorbed as C¹⁴O₂ by foliage were leached from squash leaves and were subsequently reabsorbed by the roots and translocated to the aboveground parts of several plant species. This phenomenon of nutrient recycling is apparently a widespread natural phenomenon and has implications in plant nutrition. Bean plants were grown through 1 complete generation on the leachates from squash leaves. Leaching and reabsorption of the leachates are important in the distribution of fallout products, in the stimulation and suppression of plants beneath the spread of other plants, in plant competition, and in the development of plant associations.     

Effects of elevated CO2 on feeding preference and performance of the gypsy moth (Lymantria dispar) larvae

Multiple‐choice assays were conducted in the laboratory to examine the effect of CO₂‐induced changes in leaf quality on growth, nutritional indices and preferences of the gypsy moth (Lymantria dispar) larvae. The tested tree species, one‐year‐old aspen (Populus pseudo‐simonii Kitag.), two‐year‐old birch (Betula platyphylla) and three‐year‐old oak (Quercus mongolica Fisch.) were transplanted to open‐top chambers at ambient or elevated CO₂ (650 ppm) concentrations in May 2005. The present study was conducted in 2006. Leaves from the upper and lower crowns of each tree species were sampled and analysed, respectively. On both measurement dates (24 July 2006 and 16 August 2006), there were significant CO₂ effects on levels of condensed tannin, starch, nitrogen and C : N ratio. But only on the latter date, were the concentrations of total phenolics, soluble sugar, carbon and total non‐structural carbohydrates significantly affected by elevated CO₂. Leaf dry weight content and specific leaf weight were almost completely unaffected by CO₂ enrichment. Gypsy moth larvae exhibited a clear selectivity for tested leaf types (leaves from the upper and lower crowns of each tree species) even in their early instar stage, with the upper leaves of P. pseudo‐simonii being the most preferable and the lower leaves of Q. mongolica being the least preferred. The changes in leaf quality significantly reduced larval growth and altered partial indices of insect performance (e.g., relative growth rate and relative consumption rate). However, at least in this short‐term choice feeding assay (13 days), the CO₂‐induced changes in leaf quality had no significant effects on food preference behaviour of the gypsy moth larvae, neither within the limited range of host plants nor within the leaves at different canopy heights of the same tree species.     

The effect of Albugo Candida (white blister rust) on the photosynthetic and carbohydrate metabolism of leaves of Arabidopsis thaliana

Albugo candida (pers.) O. Kuntze (white blister rust) is a biotrophic fungus which infects cruciferous plants including Arabidopsis thaliana (L) Heynh. We report the effect of this pathogen on the photosynthetic and carbohydrate metabolism of A. thaliana. As infection progressed A. Candida caused a reduction in the rate of photosynthesis when measured at either ambient or saturating concentrations of CO₂. These data suggested that both chlorophyll and Rubisco were lost from regions of infected leaves, and measurements of chlorophyll, Rubisco content and activity supported these observations. The reduction in the rate of photosynthesis was not caused by closure of stomata as transpiration was unaffected by the disease. Infected leaves accumulated both soluble carbohydrates and starch. The activities of sucrose-phosphate synthase, sucrose synthase and ADP glucose pyrophosphorylase did not change in response to infection. However, the activities of both the wall-bound and soluble acid invertases were higher in infected leaves than in controls; a new soluble invertase isoform with a pl of 5-1 appeared in infected leaves. The possible origin of the increase in wall-bound and soluble invertase activities and its effect on the carbohydrate and photosynthetic metabolism of the leaf are discussed.     

Carbohydrate and Proline Contents in Leaves, Roots, and Apices of Salt-Tolerant and Salt-Sensitive Wheat Cultivars1

Intra-specific variations in nonstructural carbohydrates and free proline were determined in leaves, apices, roots, and maturing seeds of two salt-tolerant cultivars (CR and Kharchia-65) and one salt-sensitive cv. Ghods of spring wheat (Triticum aestivum L.) grown in sand culture at various levels of salinity (0, 100, 200, and 300 mM NaCl and CaCl₂ at 5 : 1 molar ratio) under controlled environmental conditions. The levels of leaf, apex, and root ethanol-soluble carbohydrates, fructans, starch, and proline increased in line with elevating level of salinity in all three cultivars under investigation. The contents of proline, soluble and insoluble carbohydrates in the apex increased to levels exceeding those in the leaves and roots. Soluble carbohydrate content of salt-sensitive cv. Ghods was higher in the leaves, apices, and roots and lower in the maturing seeds than in the other cultivars at all levels of salinity except at 300 mM. The results show considerable variation in the amount of soluble, insoluble sugars, and proline among plant tissues and wheat genotypes in response to salinity. Higher soluble carbohydrates and fructan in leaves, roots and maturing seeds of stressed plants indicate that their accumulation may help plant to tolerate salinity. Salt-sensitive cv. Ghods accumulated less soluble sugars in the maturing seeds and higher soluble sugars in the apices, which might be used as an indicator in screening wheat genotypes for salinity tolerance.     

Physiological and photosynthetic plasticity in the amphibious, freshwater plant, Littorella uniflora, during the transition from aquatic to dry terrestrial environments

The physiological and photosynthetic responses of Littorella uniflora (L.) Ascherson, an amphibious macrophyte of isoetid life form, to rapid and prolonged emersion onto dry land, was studied at a reservoir. Water relations were little affected in the short term, but declining water potential and turgor pressure indicated water stress after flowering. High leaf lacunal CO₂ concentrations suggested continued CO₂ uptake from sediments. In contrast, a switch from Crassulacean acid metabolism (CAM) to C₃ photosynthesis was indicated by much lower levels of ΔH⁺ (down minus dusk titratable acidity) and phosphoenolpyruvate carboxylase (PEPC) activity in new terrestrial leaves, 7–8‐fold higher activity of ribulose bisphosphate carboxylase oxygenase (Rubisco), and increased chlorophyll and soluble protein contents. Accumulated nitrate and amino acid pools were depleted, whereas storage of carbohydrates as soluble sugars, fructan and starch increased. Plant carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) declined, perhaps reflecting changes in C fixation processes, N metabolism, and source C and N. In leaves of plants grown half‐emersed for an extended period, contrasting activities of PEPC and Rubisco were found in submersed and emersed portions. Overall, L. uniflora showed considerable phenotypic plasticity, yet seemed to remain poised for re‐submersion; these characteristics could be adaptive in the unpredictable water margin habitat.     

Contrasting Effects of Carbon Dioxide and Irradiance on the Acclimation of Photosynthesis in Developing Soybean Leaves

Leaves developed at high irradiance (I) often have higher photosynthetic capacity than those developed at low I, while leaves developed at elevated CO₂ concentration [CO₂] often have reduced photosynthetic capacity compared with leaves developed at lower [CO₂]. Because both high I and elevated [CO₂] stimulate photosynthesis of developing leaves, their contrasting effects on photosynthetic capacity at maturity suggest that the extra photosynthate may be utilized differently depending on whether I or [CO₂] stimulates photosynthesis. These experiments were designed to test whether relationships between photosynthetic income and the net accumulation of soluble protein in developing leaves, or relationships between soluble protein and photosynthetic capacity at full expansion differed depending on whether I or [CO₂] was varied during leaf development. Soybean plants were grown initially with a photosynthetic photon flux density (PPFD) of 950 µmol m^–2 s^–1 and 350 µmol [CO₂] mol^–1, then exposed to [CO₂] ranging from 135 to 1400 µmol mol^–1 for the last 3 d of expansion of third trifoliolate leaves. These results were compared with experiments in which I was varied at a constant [CO₂] of 350 µmol mol^–1 over the same developmental period. Increases in area and dry mass over the 3 d were determined along with daily photosynthesis and respiration. Photosynthetic CO₂ exchange characteristics and soluble protein content of leaves were determined at the end of the treatment periods. The increase in leaflet mass was about 28 % of the dry mass income from photosynthesis minus respiration, regardless of whether [CO₂] or I was varied, except that very low I or [CO₂] increased this percentage. Leaflet soluble protein per unit of area at full expansion had the same positive linear relationship to photosynthetic income whether [CO₂] or I was varied. For variation in I, photosynthetic capacity varied directly with soluble protein per unit area. This was not the case for variation in [CO₂]. Increasing [CO₂] reduced photosynthetic capacity per unit of soluble protein by up to a factor of 2.5, and photosynthetic capacity exhibited an optimum with respect to growth [CO₂]. Thus CO₂ did not alter the relationship between photosynthetic income and the utilization of photosynthate in the net accumulation of soluble protein, but did alter the relationship between soluble protein content and photosynthetic characteristics in this species.     

Carbohydrate Metabolism and Translocation in Healthy and Cocoa Swollen Shoot Virus-Infected Cocoa Plants

Analyses of cocoa swollen shoot virus-infected and healthy cocoa (Theobroma cacao L.) plant tissues were made to determine the effect of virus infection on the metabolism and transport of carbohydrates in affected plants. Starch, sucrose and reducing sugars were found to accumulate in infected tissues. Translocation of photosynthates (mainly as sucrose) to the stem and root system, as estimated by the overnight loss of carbohydrates from the leaves and by ¹⁴CO₂ tracer experiments, was as efficient in the infected plants as in the healthy. Infected plants showed a higher diurnal turnover of carbohydrates in their leaves and, on unit leaf area basis, higher levels of ¹⁴C-labelled assimilates suggesting that they have a greater photosynthetic capacity than the healthy plants. The rate of respiration, as determined by the proportions of organic acids, amino acids and other intermediary metabolites formed from translocated ¹⁴C-labelled sugars, was generally higher in infected than in healthy plants. It is concluded from available data showing the presence in infected tissues of mineral nutrients, protein N and amino acids at the same concentrations as in healthy plants, and from the relatively high rates of photosynthesis and respiration that a high rate of metabolic activity is maintained in the host-virus system. Some factors possibly contributing to the stunted growth of infected plants are discussed in the light of these findings.     

Nitrogen availability and susceptibility of tomato leaves to Botrytis cinerea

The aim of this study was to investigate the effect of nitrogen availability on susceptibility of tomato leaves to the fungal pathogen Botrytis cinerea. Plants with varying nitrogen availability were grown by adding N daily in exponentially increasing amounts to a nutrient solution at different rates. Leaves of plants grown at low nitrogen availability had a high leaf C/N ratio (21 g g^-1) and were about 2.5 times more susceptible to primary lesion formation by B. cinerea compared to plant grown at high nitrogen availability, which had a low leaf C/N ratio (11 g g^-1). Leaf C/N ratio accounted for 95% of variation in susceptibility. This relationship between C/N ratio and susceptibility persisted when plants were grown with exponential P addition and optimal N supply, and was thus independent of plant growth rate or related factors. We could not explain the effect of nitrogen availability by variation in the most obvious N-based resistance compound α-tomatine because more susceptible leaves with a high C/N ratio contained more α-tomatine. These leaves also contained more soluble carbohydrates. The level of soluble carbohydrates correlated positively with susceptibility, independent of the growth method. We therefore suggest that the effect of N availability on susceptibility must be explained by variation in levels of soluble carbohydrates and speculate about the role of these carbohydrates in the infection process. This revised version was published online in June 2006 with corrections to the Cover Date.     

Pathogenesis of barley leaves by Helminthosporium teres II: Carbohydrate involvement

Conidia of Helminthosporium teres had negligible difference in germination and germ tube length between the decolorized and non-decolorized host leaves. Appressoria, penetration and colonization were less on decolorized host leaves, but addition of exogenous nutrients stimulated these stages. Leached conidia had reduced germination on decolorized host leaves, while appressoria formation, penetration and colonization were negligible. The addition of nutrients in the external environment, however, enabled some of the leached conidia to penetrate and colonize. Stimulation by the exogenous nutrients in decreasing order were: sucrose > glucose > yeast extract > leaf leachates. Optimum levels for various nutrients tested were 2% (w/v) each of sucrose and glucose, and 0.1% (w/v) yeast extract. Higher concentrations inhibited these stages of infection. Leached conidia and decolorized leaves had smaller amounts of carbohydrates than non-leached conidia and non-decolorized leaves, respectively. Depletion of host carbohydrates reduced appressoria formation, penetration and colonization and loss of carbohydrates from spores reduced germination.     

Effects of soil phosphorus and Glomus intraradices on growth,nonstructural carbohydrates,and photosynthetic activity of Citrus aurantium

Sour orange (Citrus aurantium L.) grown in low-P (9–12 ppm) and high-P (420 ppm) soil inoculated with or without Glomus intraradices (G.i.), were evaluated for biomass, carbohydrates, ribulose bisphosphate carboxylase (RuBPCase), phosphoenolpyruvate carboxylase (PEPCase) activity, leaf ¹⁴CO₂ incorporation, and other physiological parameters. Growth of plants in the low-P, noninoculated soil was lowest, with total dry biomass reduced up to half of the low-P, inoculum treatment. Total nonstructural carbohydrates were 40% lower in leaves of plants in the low-P, noninoculated soil, compared with the other treatments. Inoculation of the low-P soil enhanced leaf ¹⁴CO₂ incorporation by 67%, total chlorophyll content by 28%, and RuBPCase activity by 42%, compared with low-P, noninoculated treatment. Improved P-use efficiency by G.i. in low-P soil was comparable to high-P nutrition in improving leaf ¹⁴CO₂ incorporation and concentration of major leaf photosynthetic products that include starch and sucrose. Leaf PEPCase activity in the low-P, noninoculated treatment, however, was at least threefold higher than the other treatments, suggesting a possible alteration in organic acid metabolism in sour orange leaves as a result of P deficiency.     

Response of antioxidant enzymes to transfer from elevated carbon dioxide to air and ozone fumigation, in the leaves and roots of wild‐type and a catalase‐deficient mutant of barley

A catalase-deficient mutant (RPr 79/4) and the wild-type (cv. Maris Mink) barley (Hordeum vulgare L.) counterpart, were grown for 3 weeks in high CO₂ (0.7%) and then transferred to air and ozone (120 nl 1^?1) in the light and shade for a period of 4 days. Leaves and roots were analysed for catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and glutathione reductase (GR, EC 1.6.4.2) activities. CAT activity in the leaves of the RPr 79/4 catalase-deficient mutant was around 5-10% of that determined in Maris Mink, but in the roots, both genotypes contained approximately the same levels of activity. CAT activity in Maris Mink increased in the leaves after transferring plants from 0.7% CO₂ to air or ozone, reaching a maximum of 5-fold, after 4 days in shade and ozone. For the catalase-deficient mutant, only small increases in CAT activity were observed in light/air and light/ozone treatments. In the roots, CAT activity decreased consistently in both genotypes, after plants were transferred from 0.7% CO₂. The total soluble SOD activity in the leaves and roots of both genotypes increased after plants were transferred from 0.7% CO₂. The analysis of SOD isolated from leaves following non-denaturing PAGE, revealed the presence of up to eight SOD isoenzymes classified as Mn-SOD or Cu/Zn-SODs; Fe-SOD was not detected. Significant changes in Mn- and Cu/Zn-SOD isoenzymes were observed; however, they could not account for the increase in total SOD activity. In leaves, GR activity also increased in Maris Mink and RPr 79/4, following transfer from 0.7% CO₂; however, no constant pattern could be established, while in roots, GR activity was reduced after 4 days of the treatments. The data suggest that elevated CO₂ decreases oxidative stress in barley leaves and that soluble CAT and SOD activities increased rapidly after plants were transferred from elevated CO₂, irrespective of the treatment (light, shade, air or ozone).     

Effect of Grapevine Leafroll on the Photosynthesis of Field Grown Grapevine Plants (Vitis vinifera L. cv. Lagrein)

We have studied the effect of grapevine leafroll infection on some features of the thylakoids from field grown grapevine (Vitis vinifera L.) leaves. Changes in photosynthetic pigments, soluble proteins, ribulose‐1,5‐bisphosphate carboxylase (RuBP), nitrate reductase, photosynthetic activities and thylakoid membrane proteins were investigated. The level of total chlorophyll (Chl) and carotenoids were reduced in virus‐infected leaves. Similar results were also observed for soluble proteins and RuBP case activity. The in vivo nitrate reductase activity was significantly reduced in infected leaves. Virus infection considerably decreased leaf net photosynthetic rate (P_n), stomatal conductance (g_s) and transpiration rate (E) in grapevine leaves. When various photosynthetic activities were followed in isolated thylakoids, virus infection caused marked inhibition of whole chain and photosystem (PS) II activity while the inhibition of PSI activity was only marginal. The artificial exogenous electron donors, diphenyl carbazide and hydroxylamine (NH₂OH) significantly restored the loss of PSII activity in infected leaves. The same results were obtained when F_v/F_m was evaluated by Chl fluorescence measurements. The marked loss of PSII activity in infected leaves could be due to the loss of 47, 43, 33, 28–25, 23 and 17 kDa polypeptides. It is concluded that virus infection inactivates the donor side of PSII. This conclusion was confirmed by immunological studies showing that the content of the 33 kDa protein of the water‐splitting complex was diminished significantly in infected leaves.     

Effect of CO2 enrichment on non-structural carbohydrates in leaves, stems and ears of spring wheat

Field-grown spring wheat (Triticum aestivum L. cv. Dragon) was exposed to ambient and elevated CO₂ concentrations (1.5 and 2 times ambient) in open-top chambers. Contents of non-structural carbohydrates were analysed enzymatically in leaves, stems and ears six times during the growing season. The impact of elevated CO₂ on wheat carbohydrates was non-significant in most harvests. However, differences in the carbohydrate contents due to elevated CO₂ were found in all plant compartments. Before anthesis, at growth stage (GS) 30 (the stem is 1 cm to the shoot apex), the plants grown in elevated CO₂ contained significantly more water soluble carbohydrates (WSC), fructans, starch and total non-structural carbohydrates (TNC) in the leaves in comparison with the plants grown in ambient CO₂. It is hypothesised that the plants from the treatments with elevated CO₂ were sink-limited at GS30. After anthesis, the leaf WSC and TNC contents of the plants from elevated CO₂ started to decline earlier than those of the plants from ambient CO₂. This may indicate that the leaves of plants grown in the chambers with elevated CO₂ senesced earlier. Elevated CO₂ accelerated grain development: 2 weeks after anthesis, the plants grown in elevated CO₂ contained significantly more starch and significantly less fructans in the ears compared to the plants grown in ambient CO₂. Elevated CO₂ had no effect on ear starch and TNC contents at the final harvest. Increasing the CO₂ concentration from 360 to 520 μmol mol^?1 had a larger effect on wheat non-structural carbohydrates than the further increase from 520 to 680 μmol mol^?1. The results are discussed in relation to the effects of elevated CO₂ on yield and yield components.