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Adjustment of diurnal starch turnover to short days: depletion of sugar during the night leads to a temporary inhibition of carbohydrate utilization, accumulation of sugars and post-translational activation of ADP-glucose pyrophosphorylase in the followin
No full textA larger proportion of the fixed carbon is retained as starch in the leaf in short days, providing a larger store to support metabolism and carbon export during the long night. The mechanisms that facilitate this adjustment of the sink-source balance are unknown. Starchless pgm mutants were analysed to discover responses that are triggered when diurnal starch turnover is disturbed. Sugars accumulated to high levels during the day, and fell to very low levels by the middle of the night. Sugars rose rapidly in the roots and rosette after illumination, and decreased later in the light period. Global transcript profiling revealed only small differences between pgm and Col0 at the end of the day but large differences at the end of the night, when pgm resembled Col0 after a 4-6 h prolongation of the night and many genes required for biosynthesis and growth were repressed [Plant J. 37 (2004) 914]. It is concluded that transient sugar depletion at the end of the night inhibits carbon utilization at the start of the ensuing light period. A second set of experiments investigated the stimulation of starch synthesis in response to short days in wild-type Col0. In short days, sugars were very low in the roots and rosette at the end of the dark period, and after illumination accumulated rapidly in both organs to levels that were higher than in long days. The response resembles pgm, except that carbohydrate accumulated in the leaf as starch instead of sugars. A similar response was found after transfer from long to short days. Inclusion of sugar in the rooting medium attenuated the stimulation of starch synthesis. Post-translational activation of ADP-glucose pyrophosphorylase (AGPase) was increased in pgm, and in Col0 in short days. It is concluded that starch synthesis is stimulated in short day conditions because sugar depletion at the end of the night triggers a temporary inhibition of growth and carbohydrate utilization in the first part of the light period, leading to transient accumulation of sugar and activation of AGPase
Effect of Brestan on Saccharomyces cerevisiae during continuous cultivation
No full textAn increase in Brestan concentration in nutrient media decreased the content of protein, phosphor-us, total ribonucleic acid, activity of pyruvate carboxylase and isocitrate lyase in cells of Saccharomyces cerevisiae parent strain and respiratory deficient (RD) mutant while the trehalose content increased. The respiration quotient value for the RD mutant was higher than for the parent strain. The RD mutant lacked cytochrome aa(3); cytochrome c and b contents were lower than those of the parent strain
Atrazine in groundwater of Vojvodina Province
No full textThe objective of this study was to investigate concentrations of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), deethylatrazine (DEA) (2-amino-4-chloro-6-isopropylamino-1,3,5-triazine), deisopropylatrazine (DIA) (2-amino-4-chloro-6-ethylamino-1,3,5-triazine) and deethyldeisopropylatrazine (DEIA) (6-chloro-2,4-diamino-1,3,5-triazine) in groundwaters of Vojvodina Province. A study was conducted during April 2001. Some 110 samples of groundwater were taken from near surface aquifers. The water samples were first passed through a disk containing solid matrix coated with a chemically bonded C-18 organic phase. The disk was then eluted with supercritical carbon dioxide to remove compounds from the sorbent. Finally the extract was injected into capillary gas chromatograph. Average concentrations were 0.198 mug L-1 for atrazine, 0.116 mug L-1 for DEA, 0.043 mug L-1 for DIA and 0.077 mug L-1 for DEIA
Photosynthesis, chlorophyll fluorescence, and water relations in young sugar beet plants as affected by sulfur supply
No full textThe effect of different concentrations of sulfur (1 and 3 mM) and interruption of sulfur (S) supply for 25 days on the photosynthesis and leaf water relations in young sugar beet plants (Beta vulgaris L.) was studied in water culture, under greenhouse conditions. Interruption of S-supply significantly reduced the content of sulfur, chlorophylls a + b and carotenoids, leaf area, density of stomatal and epidermal cells, transpiration rate and leaf water potential, while it increased the free proline content and stomatal diffusion resistance. An increase in S concentration in the nutrient medium from 1 to 3 mM did not significantly affect the tested parameters, except for an increase in leaf S content and a decrease of leaf water potential. Sulfur deficiency caused a pronounced decrease of the rate and quantum yield of photosynthetic oxygen evolution under non-photorespiratory conditions. This was partly the result of the diminished photochemical efficiency of photosystem II reaction centers. Less efficient excitation of PSII reaction centers is most probably the consequence of higher thermal energy dissipation in the reaction centers of S-starved plants. These data support that S nutrition is one of the factors regulating plant photosynthesis
Effects of nitrogen nutrition on photosynthesis in Cd-treated sunflower plants
No full textIncreased nitrogen supply stimulates plant growth and photosynthesis. Since it was shown that heavy metals may cause deficiencies of essential nutrients in plants the potential reversal of cadmium toxicity by increased N nutrition was investigated. The effects on photosynthesis of low Cd (0, 0.5, 2 or 5 mmol m(-3)) combined with three N treatments (2, 7.5 or 10 mol m(-3)) were examined in young sunflower plants. Chlorophyll fluorescence quenching parameters were determined at ambient CO2 and at 100 or 800 mu mol quanta m(-2) s(-1). The vitality index (R-fd) decreased approx. three-times in response to 5 mmol m(-3) Cd, at 2 and 10 mol m(-3) N. The maximum photochemical efficiency of PSII reaction centres (F-v/F-m) was not influenced by Cd or N treatment. The highest Cd concentration decreased quantum efficiency of PSII electron transport (Phi(II)) by 30 %, at 2 and 10 mol m(-3) N, mostly due to increased closure of PSII reaction centres (q(p)). Photosynthetic oxygen evolution rates at saturating CO2 were decreased in plants treated with 5 mmol m(-3) Cd, at all N concentrations. The results indicate that Cd treatment affected the ribulose-1,5-bisphosphate (RuBP) regeneration capacity of the Calvin cycle more than other processes. At the same time, the amounts of soluble and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein increased with Cd treatment. Decreased photosynthesis, but substantially increased Rubisco content, in sunflower leaves under Cd stress indicate that a significant amount of Rubisco protein is not active in photosynthesis and could have another function. It is shown that optimal nitrogen nutrition decreases the inhibitory effects of Cd in young sunflower plants
Acclimation to long-term water deficit in the leaves of two sunflower hybrids: photosynthesis, electron transport and carbon metabolism
No full textThe influence of long-term water deficit on photosynthesis, electron transport and carbon metabolism of sunflower leaves has been examined. Water deficit was imposed from flower bud formation up to the stage of full flowering in the field on two sunflower hybrids with different drought tolerance. CO2 assimilation and stomatal conductance of the intact leaves, determined at atmospheric CO2 and full sunlight (1500-2000 mu mol quanta m(-2) s(-1)), decreased with water deficit, Maximum quantum efficiency of PSII (F-v/F-m) and relative quantum yield of PSII (Phi(II)) determined under similar experimental conditions, did not change significantly in severely stressed leaves. The strong inhibition of the plateau region of the light response curve, determined at high CO2 (5%) in water-deficient sunflower leaves, indicates that photosynthesis is also limited by non-stomatal factors. The decreased slope and the plateau of the CO2 response curves show that the capacity of carboxylation and RuBP regeneration decreased in severely stressed intact leaves. Rubisco specific activity decreased in severely stressed leaves, but Rubisco content increased under prolonged drought. The increase of Rubisco content was significantly higher in leaves of the drought-tolerant sunflower hybrid indicating that a higher Rubisco content could be one factor in conferring better acclimation and higher drought tolerance
Effect of excess lead on sunflower growth and photosynthesis
No full textThe effect of different lead (Pb) concentrations in the nutrient solution on the growth, Pb and chlorophyll a+b content, chlorophyll fluorescence and quenching parameters in the leaves of young sunflower (Helianthus annuas L.) plants was studied. The content of ph in the analyzed plant parts increased following the increase in Pb content in the nutrient medium. This increase was expressed to a higher extent in the roots than in the stems and leaves. In the presence of high concentration of ph in the leaf area, the dry mass and the height of plants were reduced. Lead treatment of sunflower plants led to a pronounced reduction of chlorophyll (a+b) content, accompanied by much smaller decrease of photosynthetic O-2 evaluation rate and PSII efficiency at low light intensity. Hence, Pb effect did not result in the destruction of the photosynthetic apparatus, but in its reduction. The highest Pb concentration in the nutrient solution induced, however, at saturating photon flux density (PFD) a decrease in photochemical quenching and in the efficiency of PSII electron transport and significantly affected nonphotochemical fluorescence quenching, indicating an increase in proton gradient across the thylakoid membrane and a decrease of photophosphorylation
Boron as limiting factor in photosynthesis and growth of sunflower plants in relation to phosphate supply
No full textThe effect of varied boron supply (0, 0.5, 1, 25 and 100 mu M) in the nutrient solution containing different phosphate concentrations on nutrient utilization, plant growth and photosynthesis was studied in young sunflower (Helianthus annuus L.) plants, Boron deficiency decreased the dry matter yield of plants, leaf area and chlorophyll content in the leaves. The decrease was significantly higher in the presence of sub-(0.1 mM) and supra-optimal phosphate concentrations (3 mM) in the nutrient solution. Boron deficiency appreciably decreased photosynthetic oxygen evolution per unit leaf area and proton gradient across the thylakoid membrane, but it did not influence photochemical and electron transport efficiency of photosystem two. The diminished rate of photosynthesis in boron-deficient sunflower leaves could be correlated to the reduction in chlorophyll content, electron transport to CO2 and photophosphorylation. In P-deficient plants nonphotochemical chlorophyll fluorescence quenching increased with baron concentration, implying an increase in the proton gradient, and confirming the role for boron in maintaining the integrity of thylakoid membranes