Amount Of Ribulose Research Articles

Effects of nitrogen nutrition on the relationships between the levels of rbcS and rbcL mRNAs and the amount of ribulose 1·5‐bisphosphate carboxylase/oxygenase synthesized in the eighth leaves of rice from emergence through senescence

ABSTRACTSoon after the emergence of the eighth leaf blades, rice plants were grown with two (1 and 4 mm) levels of nitrogen (N) supply, and the relationships between the levels of rbcS and rbcL mRNAs, the amount of ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) synthesized and the N influx were examined in the eighth leaf blades from emergence through senescence. The levels of both rbcS and rbcL mRNAs, the amount of Rubisco synthesized and the N influx were greater for the 4 mm N treatment than for the 1 mm N treatment throughout the experiment. The amount of Rubisco synthesized was well correlated with the levels of both mRNAs during leaf expansion, but not after the completion of leaf expansion in both N treatments. The ratio of the amount of Rubisco synthesized to the levels of both mRNAs dramatically declined after full expansion. On the other hand, the amount of Rubisco synthesized was well correlated with the N influx in both N treatments. These results indicate that the N influx, namely, N availability, rather than the levels of rbcS and rbcL mRNAs, is more closely related to the amount of Rubisco synthesized in the leaf blade of rice throughout the lifespan of a leaf.

Enhanced photosynthesis and growth of transgenic plants that express ictB, a gene involved in HCO3− accumulation in cyanobacteria

Transgenic Arabidopsis thaliana and Nicotiana tabacum plants that express ictB, a gene involved in HCO3- accumulation within the cyanobacterium Synechococcus sp. PCC 7942, exhibited significantly faster photosynthetic rates than the wild-types under limiting but not under saturating CO2 concentrations. Under conditions of low relative humidity, growth of the transgenic A. thaliana plants was considerably faster than the wild-type. This enhancement of growth was not observed under humid conditions. There was no difference in the amount of ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) detected in the wild-types and their respective transgenic plants. Following activation in vitro, the activities of RubisCO from either low- or high-humidity-grown transgenic plants were similar to those observed in the wild-types. In contrast, the in vivo RubisCO activity, i.e. without prior activation, in plants grown under low humidity was considerably higher in ictB-expressing plants than in their wild-types. The CO2 compensation point in the transgenic plants that express ictB was lower than in the wild-types, suggesting that the concentration of CO2 in close proximity to RubisCO was higher. This may explain the higher activation level of RubisCO and enhanced photosynthetic activities and growth in the transgenic plants. These data indicated a potential use of ictB for the stimulation of crop yield.

Changes in the turnover of Rubisco and levels of mRNAs of rbcL and rbcS in rice leaves from emergence to senescence

AbstractChanges in the amount of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4·1·1·39) synthesized and degraded and the levels of rbcL and rbcS mRNAs were examined in the eighth leaf blades of rice from emergence to senescence. Synthesis of Rubisco was very active during leaf expansion, became quite low at the time of full expansion and then declined further during senescence. The changes in the levels of rbcL and rbcS mRNAs co‐ordinated approximately with those in the amount of Rubisco synthesized. Thus, it is suggested that the amount of Rubisco synthesized is determined primarily by the levels of rbcL and rbcS mRNAs during the life span of the leaves. Degradation of Rubisco started just before the time of full expansion and became far more active than its synthesis during senescence. Since the synthesis of Rubisco during senescence scarcely contributed to its amount, it can be concluded that the degradation of Rubisco is the major determinant for the amount of Rubisco in senescent leaves. The decline in the level of rbcL mRNA occurred much earlier in the developmental stage and proceeded at a much faster rate than that of rbcL DNA, indicating that the level of rbcL DNA is not a major determinant for the level of rbcL mRNA in senescent leaves of rice.

Effects of CO2 and sugars on photosynthesis and composition of avocado leaves grown in vitro

The effects of micropropagation conditions on avocado (Persea americana Mill.) have been measured in leaves and plants cultured in vitro. The consequences of the type and concentration of sugar in the medium and of carbon dioxide concentration in the atmosphere on the rates of photosynthesis and amounts of ribulose 1,5-biphosphate carboxylase-oxygenase (EC 4.1.1.39; Rubisco) and total soluble protein (TSP) were measured. At the highest sucrose supply (87.6 mM), Rubisco content was substantially decreased in leaves, and even more when elevated CO2 (1 000 μmol·mol−1) was supplied. Maximum photosynthetic rate (Pmax) was significantly decreased when plants developed in high sucrose and elevated CO2. However, Rubisco concentration was significantly greater when glucose was supplied at the same molar concentration or when the concentration of sucrose was small (14.6 mM), and no differences were observed due to the CO2 concentration in the air in these treatments. The ratio of Rubisco to total soluble protein (Rubisco/TSP) was dramatically decreased in plants grown in the highest concentration of sucrose and with elevated CO2. Leaf area and ratio of leaf fresh weight/(stem + root) fresh weight, were greater in plants grown with CO2 enriched air. However, upon transplanting, survival was poorer in plants grown on low sucrose/high CO2 compared to those grown on high sucrose/high CO2.

Changes in Activities of Enzymes of Carbon Metabolism in Leaves during Exposure of Plants to Low Temperature

The aim of this study was to determine the response of photosynthetic carbon metabolism in spinach and bean to low temperature. (a) Exposure of warm-grown spinach and bean plants to 10 degrees C for 10 days resulted in increases in the total activities of a number of enzymes, including ribulose 1,5-bisphosphate carboxylase (Rubisco), stromal fructose 1,6 bisphosphatase (Fru 1,6-P(2)ase), sedoheptulose 1,7-bisphosphatase (Sed 1,7-P(2)ase), and the cytosolic Fru 1,6-P(2)ase. In spinach, but not bean, there was an increase in the total activity of sucrose-phosphate synthase. (b) The CO(2)-saturated rates of photosynthesis for the cold-acclimated spinach plants were 68% greater at 10 degrees C than those for warm-acclimated plants, whereas in bean, rates of photosynthesis at 10 degrees C were very low after exposure to low temperature. (c) When spinach leaf discs were transferred from 27 to 10 degrees C, the stromal Fru 1,6-P(2)ase and NADP-malate dehydrogenase were almost fully activated within 8 minutes, and Rubisco reached 90% of full activation within 15 minutes of transfer. An initial restriction of Calvin cycle fluxes was evident as an increase in the amounts of ribulose 1,5-bisphosphate, glycerate-3-phosphate, Fru 1,6-P(2), and Sed 1,7-P(2). In bean, activation of stromal Fru 1,6-P(2)ase was weak, whereas the activation state of Rubisco decreased during the first few minutes after transfer to low temperature. However, NADP-malate dehydrogenase became almost fully activated, showing that no loss of the capacity for reductive activation occurred. (d) Temperature compensation in spinach evidently involves increases in the capacities of a range of enzymes, achieved in the short term by an increase in activation state, whereas long-term acclimation is achieved by an increase in the maximum activities of enzymes. The inability of bean to activate fully certain Calvin cycle enzymes and sucrose-phosphate synthase, or to increase nonphotochemical quenching of chlorophyll fluorescence at 10 degrees C, may be factors contributing to its poor performance at low temperature.

Rubisco Activity in Guard Cells Compared with the Solute Requirement for Stomatal Opening

We investigated whether the reductive pentose phosphate path in guard cells of Pisum sativum had the capacity to contribute significantly to the production of osmotica during stomatal opening in the light. Amounts of ribulose 1,5-bisphophate carboxylase/oxygenase (Rubisco) were determined by the [(14)C]carboxyarabinitol bisphosphate assay. A guard cell contained about 1.2 and a mesophyll cell about 324 picograms of the enzyme; the ratio was 1:270. The specific activities of Rubisco in guard cells and in mesophyll cells were equal; there was no indication of a specific inhibitor of Rubisco in guard cells. Rubisco activity was 115 femtomol per guard-cell protoplast and hour. This value was different from zero with a probability of 0.99. After exposure of guard-cell protoplasts to (14)CO(2) for 2 seconds in the light, about one-half of the radioactivity was in phosphorylated compounds and <10% in malate. Guard cells in epidermal strips produced a different labelling pattern; in the light, <10% of the label was in phosphorylated compounds and about 60% in malate. The rate of solute accumulation in intact guard cells was estimated to have been 900 femto-osmol per cell and hour. If Rubisco operated at full capacity in guard cells, and hexoses were produced as osmotica, solutes could be supplied at a rate of 19 femto-osmol per cell and hour, which would constitute 2% of the estimated requirement. The capacity of guard-cell Rubisco to meet the solute requirement for stomatal opening in leaves of Pisum sativum is insignificant.

Seasonal variation in the photosynthetic capacity of a willow (Salix cv. Aquatica gigantea) canopy. 1 Changes in the activity and amount of ribulose 1,5-bisphosphate carboxylase-oxygenase and the content of nitrogen and chlorophyll at different levels in the canopy

The role of ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco) in the regulation of photosynthesis in the field was assessed by following changes in the amount and activity of Rubisco and in the amounts of chlorophyll and total nitrogen in a willow (Salix cv. Aquatica gigantea) canopy during two growing seasons. An additional aim of this study was to determine how nitrogen is partitioned in the canopy and whether Rubisco and chlorophyll serve as sources of nitrogen. During both growing seasons, the total activity and the amount of Rubisco were high in young, sun-exposed leaves and decreased as the leaves aged and became shaded. In 1985, the specific activity was low (on average 0.8 micromol mm(-1) mg(-1) Rubisco protein) compared with the values obtained in 1986 (on average 1.8 micromol min(-1) mg(-1) Rubisco protein). These differences in the specific activity of Rubisco between the two years might be associated with changes in partitioning of nitrogen. During the cool summer of 1985, about 20% of the total nitrogen was partitioned to Rubisco compared with about 13% during the warm summer of 1986. Rubisco comprised a high proportion (about 60%) of the total soluble protein throughout the 1985 growing season, whereas during the 1986 growing season, the proportion of Rubisco in the total soluble protein fraction was lower and decreased markedly as the leaves became shaded. Chlorophyll did not serve as a source of nitrogen in the canopy. On the contrary, the proportion of total nitrogen in chlorophyll increased with time, which indicates acclimation of the thylakoid membranes to decreasing irradiance. The degree of activation of Rubisco in samples collected in 1986 was high in young, sun-exposed leaves, which suggests that in these leaves, Rubisco may limit the rate of CO(2) uptake. In the shaded leaves of the lower canopy, the degree of activation of Rubisco was low, which indicates that in these leaves, photosynthesis is limited by factors other than Rubisco.

Changes in Photosynthesis and Other Chloroplast Traits in Lanceolate Leaflet Isoline of Soybean

Lanceolate leaflet soybean (Glycine max L. Merrill) has been known to photosynthesize more CO(2) per unit leaf area than normal leaflet soybean. The exact reason for this increase in photosynthetic rate is still unclear. The present study was undertaken to investigate the leaf photosynthetic rate and other physiological traits in relation to chloroplast of lanceolate leaflet soybean. Ontogenic changes in apparent photosynthesis (AP) were related primarily to variations in the amount of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area, and only secondarily to difference in specific activity of the said enzyme. Moreover, lanceolate leaflet consistently maintained a higher leaf AP, higher Rubisco activity, and more chloroplasts per unit leaf area basis than did normal leaflet soybean throughout leaf ontogeny. However, lanceolate soybean tended to have lower AP and Rubisco activity on a chloroplast basis. The superiority of leaf AP and other leaf physiological traits, expressed on a leaf area basis, in lanceolate leaflet soybean is associated with a corresponding increase in chloroplast number.

Correlation of Activity and Amount of Ribulose 1,5-bisphosphate Carboxylase with Chloroplast Stroma Crystals in Water-Stressed Willow Leaves

Vapaavuori, E. M. 1986. Correlation of activity and amount of ribulose 1,5-fti.sphosphate carboxylase with chloroplast stroma crystals in water-stressed willow leaves.—J. exp. Bot. 37: 89 98. Changes in the activity and amount of ribulose 1,5-bisphosphate (RuBP) carboxylase (E.C. 4.1.1.39) were studied in well-watered plants of Salix 'aquatica gigantea' and in similar plants during three different water stress treatments and after rewatering. The chloroplast ultrastructure of these plants was examined by electron microscopy. The amounts of crystallized protein in the chloroplast stroma were assessed according to the area of crystal structure seen in the thin sections. RuBP carboxylase activity decreased with decreasing leaf water potentials but recovered upon rewatering, except when leaves had been exposed to severe water stress. The percentage of total chloroplast area made up of crystal inclusions decreased with decreasing leaf water potentials. After rewatering, the crystals either disappeared or the amount decreased markedly. Both RuBP carboxylase activity and the area of crystal inclusions increased initially with increased extractable RuBP carboxylase protein but decreased with further increases above 6700-7000 fig RuBP carboxylase protein mg-1 chlorophyll. In well-watered and water-stressed plants the activity of RuBP carboxylase, based on amount of chlorophyll, increased with an increasing amount of crystal inclusions in the chloroplast stroma. In rewatered plants no such correlation was observed, and the low percentage of crystal inclusions in the chloroplast area was independent of RuBP carboxylase activity. Key words-Chloroplast stroma crystals, ribulose 1,5-btsphosphate carboxylase, Salix, water stress. Correspondence to: The Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki, Finland.

Measurement and Preservation of the in Vivo Activation of Ribulose 1,5-Bisphosphate Carboxylase in Leaf Extracts

Photosynthetic carbon fixation is regulated in the chloroplast by the amount of ribulose 1,5-bisphosphate carboxylase which is activated. The activated carboxylase was preserved in detached leaves (barley, maize, soybean, spinach, wheat) for 90 min when stored on ice. With leaf extracts stored at 2 degrees C, the amount of activated enzyme, representing that originally in the leaf, as well as the fully activated enzyme, formed by incubation of leaf extracts with Mg(2+) and bicarbonate, both slowly declined in activity. However, for each activity this decline was proportional such that the ratio (percent activation) appeared constant. No change was observed in activation of the enzyme during the brief time of leaf homogenization. Optimal conditions (Mg(2+), incubation time) for measurement of leaf activation of ribulose bisphosphate carboxylase vary depending on the plant.3-Phosphonoproprionate, a positive effector of the purified ribulose bisphosphate carboxylase and a metabolically inert analog of 2-phosphoglycolate, was used to examine what metabolic effectors might do to enzyme activation during leaf homogenization and preparation of the extract at 2 degrees C. Activation under these conditions was not altered by 3-phosphonoproprionate. When 3-phosphonoproprionate was brushed on attached leaves or taken up by the transpiration stream of detached leaves, a considerable increase in activation of the carboxylase was measured.