Ribulose Diphosphate Carboxylase Activity Research Articles

The complex stress of waterlogging and high temperature accelerated maize leaf senescence and decreased photosynthetic performance at different growth stages

AbstractThe greenhouse effect caused by global warming was becoming more and more obvious, resulting in increased frequency of high temperature and high humidity, which significantly affected maize productivity. However, it was poorly understood how the interactions of high temperature and high humidity affected leaf senescence, photosynthetic performance and yield of summer maize. Three stress treatments including (a) high temperature stress (T), (b) waterlogging stress (W) and (c) complex stress (T‐W) were set at the third leaf stage (V3), the sixth leaf stage (V6) and the tasselling stage (VT) in 2019–2020 to explore the influence mechanism of complex stress. Each stress treatment period lasted 6 days. Non‐stressed plants served as control. Yield, antioxidant enzyme activity, photosynthetic characteristics, and dry matter accumulation were determined. Our study found that the activity of antioxidant enzymes was significantly decreased, while malonyldialdehyde (MDA) accumulation was increased under each stress treatment. As a result, the photosynthetic characteristics were impaired, manifested in a significant decrease in net photosynthetic rate (Pn), enzyme activities of phosphoenolpyruvate carboxylase (PEPCase) and ribulose diphosphate carboxylase (RUBPCase). The decrease in photosynthetic intensity affected by each stress treatment led to a significant decrease in total dry matter accumulation and grain yield. The most significant effects of waterlogging and combined stresses on yield occurred at the V3 stage, followed by the V6 and VT stages. However, the most significant effects of high temperature occurred at the VT stage, followed by the V6 and V3 stages. Moreover, the compound stress exacerbated damage to leaf senescence and photosynthetic properties of summer maize compared to the single stress of high temperature or waterlogging.

Sink-source relationship of potato plants and its role involved in the reduction of tuber yield in continuous cropping system

The Yellow River irrigation area in middle Gansu Province is one of the main production bases for processing potato and potato tuber seeds in China. However, continuous potato cropping (CPC), resulting from intensive cultivation, has been affecting the sound development of the potato industry. A long-term field experiment was carried out in order to reveal the mechanisms of CPC obstacles. Five treatments, with different years of continuous potato cropping, were designed marking as 0-5 a, 0 a was maize-potato rotation, used as the control (CK). The present study focused on how to change in sink size and sink activity as well as source activity of potato plants under CPC conditions, especially their roles involved in the reduction of tuber yield. There were no significant differences in tuber yield under short-term CPC (1-2 a) compared with CK, however, significant decline by 28.6%-32.8% occurred under long-term CPC (3-5 a), which was mainly derived from the decline in fresh mass of each tuber. Compared with CK, long-term CPC significantly decreased sink size by 38.4%-53.0%. In addition, long-term CPC not only postponed the potato development progress, by postponing the formation and development of potato tubers, but reduced dry matter accumulation in tubers as well. Long-term CPC significantly decreased source activity, showing that plant height, branch numbers per main stem, chlorophyll content, and dry-matter content of leaf were significantly lower than those of CK, besides, morphological development of root system was also restrained. Compared with CK, root vigor, ribulose diphosphate carboxylase (RuBP Case) and sucrose phosphate synthase (SPS) activities of leaves under long-term CPC significantly decreased by 28.6%-63.1%, 52.6%-64.6% and 26.3%-53.4%, respectively. Long-term CPC caused signi-ficant decline in production capability of source, consequently, reduced the production of assimilation product by a large margin, and contributed to the deficiency in translocation amount of assimilates into tuber during post-anthesis, which finally led to the reduction in tuber yield. In conclusion, the unbalance of sink-source relationship of potato plants was the main cause for CPC obstacles in the Yellow River irrigation area in middle Gansu Province.

Potassium Internal Use Efficiency Relative to Growth Vigor, Potassium Distribution, and Carbohydrate Allocation in Rice Genotypes

Potassium (K) deficiency in soils is widespread and has become one of the most nutritional limiting factors for increasing rice yield in China and Asia. Improving K use efficiency by exploiting genetic potential largely depends on understanding physiological and genetic mechanisms underlying K efficiency in lowland rice. In this study, the K internal use efficiency (KIUE) at low K supply relative to K accumulation and distribution, tillering and grain filling rates, dry matter accumulation and allocation were examined under field conditions. The relative K concentrations in upper and lower leaves at booting and grain filling stages decreased with decreasing K internal use efficiency among the rice genotypes, indicating that K-efficient genotypes had greater K translocation ability than the K-inefficient genotypes at low K. The KIUE in biomass production at seedling and tillering stages was closely and positively correlated with the KIUE in grain production at the harvest stage. Significant positive correlations were noted between the KIUE at low K and the relative dry matter yield at the tillering stage and the harvest index among the rice genotypes. The K-efficient genotypes had a greater relative tillering rate during the tillering stage and a greater relative grain filling rate at the late grain filling stage, as compared with the inefficient genotypes. The relative net photosynthetic rate in the upper, and especially in the lower leaves was much lower in the K-inefficient genotypes than in the efficient ones at the grain filling stage, which may partly be due to the fact that the efficient genotype could maintain greater stomatal conductance and ribulose diphosphate carboxylase (RuBPcase) activity in functioning leaves under low K. The results indicate that (i) the K internal use efficiency could be an important index for measuring rice tolerance to low K stress, and (ii) K internal use efficiency is closely associated with efficient translocation and distribution of both K and carbohydrate within rice plants.

Compartmental modelling of photorespiration and carbon metabolism of water stressed leaves

Abstract Carbon fluxes in photosynthesis and photorespiration of water stressed leaves have been analysed in a steady state model based on the ribulose diphosphate carboxylase (RuDP carboxylase) and RuDP oxygenase enzyme activities and the CO2 and O2 concentrations in the leaf. Agreement between predicted and observed photorespiration (Lawlor & Fock, 1975) and C flux in the glycollate pathway is good over much of the range of water stress, but not at severe stress. An alternative source of respiratory CO2 is suggested to explain the discrepancy. The model suggests that resistance to CO2 fixation is mainly in the carboxylation reactions, not in CO2 transport. Using the steady state model, the kinetics of 14C incorporation into photosynthetic and photorespiratory intermediates are simulated. The predicted rate of 14C incorporation is faster than observed and delay terms in the model are used to simulate the slow rates of mixing and metabolic reactions. Inactive pools of glycine and serine are suggested to explain the observed specific activities of glycine and serine. Three models of carbon flux between the glycollate pathway, the photosynthetic carbon reduction cycle and sucrose synthesis are considered. The most satisfactory simulation is for glycollate pathway carbon feeding into the PCR cycle pool of 3-phosphoglyceric acid which provides the carbon for sucrose synthesis. Simulation of the specific activity of CO2 released in photorespiration suggests that a source of unlabelled carbon may contribute to photorespiration.

Photosynthesis, chlorophyll content and ribulose diphosphate carboxylase activity in relation to yield in wheat genotypes

SummaryPhotosynthetic rates, chlorophyll content and activity of ribulose 1,5-diphosphate carboxylase (RuDPC) were determined for 18 genotypes of wheat (Triticum aestivum L.) in pot culture. Measurements were made at various growth stages. Correlation studies between physiological characteristics and seed yield were made at each stage separately.Genotypic variations were observed at different growth and developmental stages in photosynthetic rates (1·8–2·7-fold), chlorophyll contents (1·2-fold) and enzyme activities (2-fold). Chlorophyll content and enzymic activity increased in plant leaves with advancing age while apparent rates of photosynthesis decreased.RuDPC activity in flag leaf at anthesis showed significant positive correlation with grain yield (r = 0·55). Other attributes did not show significant association with grain yield.

Effect of Glycidate, an Inhibitor of Glycolate Synthesis in Leaves, on the Activity of Some Enzymes of the Glycolate Pathway

Under conditions where glycolate synthesis was inhibited at least 50% in tobacco (Nicotiana tabacum L.) leaf discs treated with glycidate (2,3-epoxypropionate), the ribulose diphosphate carboxylase activity in extracts and the inhibition of the activity by 100% oxygen were unaffected by the glycidate treatment. [1-(14)C]Glycidate was readily taken into leaf discs and was bound to leaf proteins, but the binding occurred preferentially with proteins of molecular weight lower than ribulose diphosphate carboxylase. Glycidate added to the isolated enzyme did not inhibit ribulose diphosphate carboxylase activity or affect its inhibition by 100% O(2). Thus, glycidate did not inhibit glycolate synthesis by a direct effect on ribulose diphosphate carboxylase/oxygenase.NADH-glyoxylate reductase and phosphoglycolate phosphatase activities were also unaffected in extracts of leaf discs supplied with glycidate, but NADPH-glyoxylate reductase was inhibited about 35% in such extracts. Addition of 10 mm glycidate to isolated NADPH-glyoxylate reductase inhibited the activity about 25% after 15 minutes of reaction.The small inhibition of NADPH-glyoxylate reductase by glycidate may help to explain the increase in glyoxylate concentration found in glycidate-treated leaf discs. Increasing the glyoxylate pool size in leaf discs has been shown to effectively block glycolate synthesis and photorespiration and increase net photosynthesis. Thus, the similar effects brought about by glycidate in leaf discs can be attributed to indirect effects of metabolic regulation.

Light versus Dark Carbon Metabolism in Cherry Tomato Fruits

The photosynthetic properties of the internal and peripheral tissues of the cherry tomato fruit (Lycopersicum esculentum var. cerasiforme Dun A. Gray) were investigated. Whole fruit and their isolated tissues evolve large amounts of CO(2) in darkness. In the light, this evolution decreases but nevertheless remains a net evolution; 3-(3,4-dichlorophenyl)-1,1-dimethylurea abolishes the effects of light.Incorporation of (14)CO(2) by leaves and fruit tissues demonstrates that the outer region of the fruit has the highest photosynthetic efficiency on a chlorophyll basis; the internal fruit tissue, richer in chlorophyll, has a much lower efficiency. The identification of intermediates following short term incubations with (14)CO(2) shows that in darkness the fruit accumulates the majority of label in malate. In the light, leaf tissue exhibits a pattern of incorporation characteristic of C-3 metabolism, whereas fruit tissue exhibits a decreased labeling of malate with a concomitant appearance of label in Calvin cycle intermediates. This is in agreement with the levels and types of carboxylating activities demonstrated in vitro; especially noteworthy is the very low ribulose diphosphate carboxylase activity in the internal fruit tissue.The photosynthetic potential, phosphoenolpyruvate carboxylase activity, and quantities of malate accumulated by fruit tissues are parallel to their chlorophyll content during growth and maturation.

Water Relations and Physiological Activity of Potatoes1

Abstract The effects of water stress on internal water potential components and specific physiological processes were investigated in field grown potatoes (Solanum tuberosum L. cv. Viking). Leaf water potential (ψleaf) as estimated by the pressure chamber, was not directly related to soil water potential (ψsoil) until a specific minimum ψsoil was attained. Subsequently ψleaf did not increase in response to increases in ψsoil. Water stress affected physiological processes such as stomatal resistance, photosynthesis and enzyme activity. A decline in ψleaf was apparently responsible for increased stomatal resistance and decreases in photosynthetic rates. The activities of ribulose diphosphate carboxylase and phosphoenolpyruvate carboxylase decreased as ψleaf declined. The relationship between water stress and physiological processes and the inability of ψleaf to respond to increases in ψsoil after a maximum stress may partially explain the extreme sensitivity of potatoes to even mild water stress.

Changing Ribulose Diphosphate Carboxylase/Oxygenase Activity in Ripening Tomato Fruit

Tomato fruit (Lycopersicum esculentum Mill) from green, pink, and red stages were assayed for changes in the activity of ribulose diphosphate carboxylase and oxygenase, phosphoenolpyruvate carboxylase, changes in the levels of glycolate and respiratory gas exchange. The ribulose diphosphate carboxylase activity decreased as the fruit ripened. By comparison, the ribulose diphosphate oxygenase activity increased during the transition from the green to the pink stage, and declined afterward. The changes in the endogenous glycolate levels and the respiratory gas exchange, as observed at different stages of ripening, resembled the changes in the ribulose diphosphate oxygenase activity. The utilization of glycolate in further metabolic activity may result in the formation of peroxidases required for the onset of ripening.

Some effects of nitrogen-starvation on nitrogen and carbohydrate metabolism inAnkistrodesmus braunii

Enzymic activities have been measured in cell-free extracts from nitrogen-starved cultures ofAnkistrodesmus braunii. During ten hours of nitrogenstarvation the activities of the enzymes nitrite reductase (E.C.1.6.6.4), glutamic dehydrogenase (E.C.1.4.1.4), glutamine synthetase (E.C.6.3.1.2) and urea amidolyase (E.C.3.5.1.5) were derepressed while the activities of the enzymes malate dehydrogenase (E.C.1.1.1.37) and hexokinase (E.C.2.7.1.1) remained more or less unchanged. In contrast, the photosynthetic capacity of the nitrogen-starved cultures declined rapidly and accompanying this decline were losses in the activities of ribulose diphosphate carboxylase (E.C.4.1.1.39) and triose phosphate-NADP-dehydrogenase (E.C.1.2.1.13).

Mechanism of Plant Growth Stimulation by Naphthenic Acid

Potassium naphthenate, 20 mm, was applied to the foliage of 14-day-old plants of bush bean, Phaseolus vulgaris L, cv Top Crop, maize, Zea mays L, cv Golden Bantam, spring wheat, Triticum vulgare Vill., cv Neepawa, and a 2 mm solution to 21-day-old plants of sugar beet, Beta vulgaris L, cv CS-43. Seven days after application, the activities of ribulose diphosphate carboxylase and phosphoenolpyruvic carboxylase in leaves of naphthenate-treated bean and maize were greater than in the leaves of untreated plants. The increase in activity of the carboxylases in treated spring wheat lacked statistical significance. At the same time after treatment, the CO(2) compensation point of bean was smaller than that of control plants, as was the average CO(2) compensation point of sugar beet measured at intervals up to 21 days after spraying. Respiratory rates of embryos of bean seeds soaked for 12, 24, and 48 hours in 43.5 mum K naphthenate were greater than those of seeds soaked in water. Ascorbate oxidase activity in bean leaves, determined 7, 14, and 21 days after K naphthenate application, was also stimulated. Foliar application of 10 mm cyclohexanecarboxylic acid to bean was followed in 7 and 14 days by a greater activity of catalase than in control plants. Higher activity of the enzyme, measured 6, 7, 12, and 14 days after spraying, also resulted from K naphthenate application. The results indicate that the higher rates of photosynthesis in naphthenate-treated plants may be due in part to increased rates of CO(2) fixation, and that greater photosynthetic efficiency, together with a more plentiful supply of ATP arising from increased electron flow in respiration, is involved in the greater growth of plants to which naphthenate has been applied.

Differential Localization of Fraction I Protein between Chloroplast Types

The soluble proteins of C(3) and C(4) mesophyll chloroplasts and C(4) bundle sheath extracts have been analyzed by gel electrophoresis for fraction I protein. Gel scans of soluble protein from C(4) bundle sheath extracts and C(3) mesophyll chloroplasts showed typical fraction I protein peaks that could be identified by ribulose diphosphate carboxylase activity. No such peak was observed for C(4) mesophyll chloroplasts, which also lacked both large and small subunits of ribulose diphosphate carboxylase on sodium dodecyl sulfate gels. The absence of fraction I protein in these chloroplasts was reflected in the soluble protein to chlorophyll ratios, which were roughly 3-fold lower than the ratio obtained for C(3) chloroplasts. The carboxylating enzyme in C(4) mesophyll cells, phosphoenolpyruvate carboxylase, was found to be a major protein in the cytoplasm of C(4) mesophyll protoplasts, and had higher mobility than fraction I protein.

Relationship between leaf development, carboxylase enzyme activities and photorespiration in the C4-plant Portulaca oleracea L.

Ribulose diphosphate (RuDP) and (PEP) phosphoenolpyruvate carboxylase enzyme activities were studied in young, mature, and senescent Portulaca oleracea leaves. While the absolute amount of both the C3 (RuDP) and C4 (PEP) carboxylase is less in senescent leaves than in mature leaves, RuDP carboxylase activity is reduced to a lesser degree. In senescent leaves, PEP carboxylase activity equals 10% of that in mature tissue, but RuDP carboxylase is 27% of that in mature leaves. The same ontogenetic series was also used to determine photorespiration rates and responses to several gas treatments. Young and mature leaves were unaffected by changes in the light regime or oxygen concentrations, and exhibited typical C4-plant light/dark (14)CO2 evolution ratios. Senescent leaves, on the other hand, have photorespiration ratios similar to C3-plants. In addition, senescent leaves were affected by minus CO2, 100% O2 and N2 in a manner expected of C3-plants, but not C4-plants. These results are discussed in terms of a relative increase in activity of the C3 cycle in later developmental stages in this plant.

A mutant strain of Scenedesmus obliquus deficient in ribulose diphosphate carboxylase, cytochrome f and Photosystem II activity

The partial reactions of photosynthesis shown by strain F208, a non-photosynthetic mutant strain of Scenedesmus obliquus, have been compared with those performed by other mutant strains which lacked; Photosystem II activity (strains 11 and F131), cytochrome f (strain 50), P-700 and cytochrome f (strain F119), and P-700 (strains F139 and 199). In this respect the properties of strain F208 were those that would be expected if Photosystem II activity and cytochrome f were not present in this strain. Examination of the composition of strain F208 has shown the absence of cytochrome f in both the soluble and the membrane-bound form. The considerably lower level of plastoquinone compared to that found in the wild type is characteristic of the strains which lack Photosystem II activities. Fraction 1 protein could not be detected in extracts of strain F208 by sedimentation velocity experiments in the ultracentrifuge, and only 7% of the wild type ribulose diphosphate carboxylase activity was found after chromatography of these extracts on DEAE-cellulose. The properties of strain F208 are compared with those of the ac-20 and cr-1 strains of Chlamydomonas rheinhardi, both of which have a deficiency of ribulose diphosphate carboxylase which is considered to result from a deficiency of chloroplast ribosomes. Strain F208 resembles these strains in its abnormal chloroplast ultrastructure and its decreased levels of the RNA forms derived from the chloroplast ribosomes when compared with the wild type. Chloroplast fragments isolated from strains of S. obliquus which lacked cytochrome f (strains 50 and F208) were able to use diaminodurene and ascorbate as an electron donor to Photosystem I. Since this reaction was inhibited by mercuric salts it would appear that plastocyanin, but not cytochrome f, was involved in this electron transfer.

Factors affecting interconversion between kinetic forms of ribulose diphosphate carboxylase-oxygenase from spinach

Ribulose diphosphate carboxylase was found to exist in two distinct kinetic forms in spinach leaf extracts. One form displayed an apparent K m for CO 2 in excess of 200 μ m and is likely to be the form purified and studied by many previous workers. However, if leaf extracts were prepared in the presence of Mg 2+ and atmospheric levels of CO 2, the recently described high-affinity form was obtained. It had a K m for CO 2 of about 20 μ m, was quite stable even at 25 °C, and its properties were consistent with it being the form which operates in photosynthesis in vivo. Mg 2+ was also able to convert the high- K m (CO 2) form to the low- K m (CO 2) form when it was added to an extract which had been prepared in its absence. Mg 2+ was more effective in causing this conversion if bicarbonate was added as well. This activating effect of bicarbonate is a probable cause of previously reported apparent homotropic effects of bicarbonate on ribulose diphosphate carboxylase activity. It is possible that the apparently high- K m (CO 2) form is not intrinsically active and appears to have activity only by virtue of the low- K m (CO 2) form produced by contact with Mg 2+ and bicarbonate (or CO 2) during the course of the assay. Extracts prepared with ribose 5-phosphate in the absence of Mg 2+ also showed low- K m (CO 2) carboxylase activity initially, but the presence of this sugar phosphate was deleterious during storage at 25 °C, where it promoted conversion to the apparently high- K m (CO 2) form. Effects on the affinity of ribulose diphosphate carboxylase for CO 2 were paralleled by effects on the activity of the associated ribulose diphosphate oxygenase. Treatments which produced the low- K m (CO 2) form of the carboxylase also resulted in high oxygenase activity, and it is possible that the apparently high- K m (CO 2) form of the carboxylase has little, if any, oxygenase activity associated with it. The carboxylase and oxygenase activities of the low- K m (CO 2) form showed broad and quite similar responses to pH variation, and the oxygenase had a K m for O 2 of 0.22 m m. The stability of the low- K m (CO 2) form in the presence of Mg 2+ and bicarbonate was quite sufficient for it to be partially purified by Sepharose chromatography. The significance of the low- K m (CO 2) form is discussed with respect to activation of photosynthesis by Mg 2+.

Blue light-induced formation of phosphoenolpyruvate carboxylase in colorless <italic>Chlorella</italic> mutant cells

The activities of NAD-malic dehydrogenase, aspartate aminotransferase, phosphoenolpyruvate carboxylase and NADP-malic enzyme in colorless mutant cells of Chlorella vulgaris (Mutant No. 125) decreased during starvation (in phosphate buffer in darkness). The most pronounced decrease was observed in phosphoenolpyruvate carboxylase activity. A trace of ribulose diphosphate carboxylase activity detected in the growing cells disappeared on starvation and no activity of pyruvate carboxylase was detected in these mutant cells. Blue light (462 or 465 nm) enhanced phosphoenolpyruvate carboxylase activity in the starved cells about 2-fold, while the activities of aspartate aminotransferase and NADP-malic enzyme were slightly lowered by the blue light. Red light (mainly 600–650 nm) brought about a slight decrease in all the enzyme activities tested. Cycloheximide (5 μ/ml) completely abolished the enhancing effect of blue light on phosphoenolpyruvate carboxylase activity, indicating that the short wavelength light specifically increased the de novo synthesis of this enzyme.

Ribulose diphosphate carboxylase/oxygenase. IV. Regulation by phosphate esters

The stimulation or inhibition of ribulose diphosphate oxygenase by a variety of compounds is compared with the reported effects on these compounds on the ribulose diphosphate carboxylase activity. A possible transition state analog of ribulose diphosphate, 2-carboxyribitol 1, 5-diphosphate, at a molar ratio of inhibitor to enzyme of 10 to 1, irreversibly inactivates the oxygenase and carboxylase activities. This is consistent with the hypothesis that there may be a single active site for both the carboxylase and oxygenase activities. Several compounds of the reductive pentose photosynthetic carbon cycle act as effectors of the ribulose diphosphate oxygenase in a manner complementary to their reported effect upon the carboxylase. Ribose 5-phosphate inhibits the oxygenase with an apparent Ki of 1.8 mM, but it is reported to activate the carboxylase; fructose 6-phosphate and glucose 6-phosphate act similarly but are less effective than ribose 5-phosphate. Fructose 1. 6-diphosphate stimulates the oxygenase at low magnesium ion concentrations. The stimulatory effect of 6-phosphogluconate on the oxygenase is associated with a 3-fold reduction of the Km (Mg2+). ATP inhibits the oxygenase but has been reported to stimulate the carboxylase; pyrophosphate acts in an opposite manner. From these results it appears that the ratio of carboxylase to oxygenase activity may be a variable factor with predictable subsequent alteration in the ratio between photosynthetic CO2 fixation and photorespiration.

Ribulose diphosphate carboxylase/oxygenase. III. Isolation and properties

Similarities in properties of ribulose diphosphate carboxylase and oxygenase activities further substantiate the hypothesis that the same protein catalyzes both reactions. The Km (ribulose diphosphate) is 0.33 mM for the ribulose diphosphate oxygenase, when assayed in air with an oxygen electrode. Maximum activity is obtained with 10 to 35 mM MgCl2. Higher MgCl2 concentrations are inhibitory, but they shift the pH optimum from 9.3 or 9.4 to 8.7 or 9.0. MnCl2 is an effective cofactor of the oxygenase and some activity is obtained with CoCl2. Both the ribulose diphosphate carboxylase and oxygenase activity of the purified protein from spinach leaves are slowly inactivated by storage at 0 degrees and reactivated in 10 min at 50 degrees, provided both 25 mM MgCl2 and 1 mM dithiothreitol are present. The sulfhydryl groups of the enzyme which react rapidly with 5,5'-dithiobis(2-nitrobenzoic acid) are approximately 4 at pH 7.8 and 11 at pH 9.4. At both pH values ribulose diphosphate prevents two of these sulfhydryl groups from reacting with this reagent. About 50% inhibition of the oxygenase activity at pH 9.0 occurs with 50 mM bicarbonate in the presence of 3 mM ribulose diphosphate, and from variations in these parameters the inhibition is attributed to the CO2 species. The purified enzyme of acrylamide gels prevented the reduction of nitroblue tetrazolium in the presence of the superoxide radical, but the enzyme in solution did not react as a superoxide dismutase.

Serological comparison of ribulose-1,5-diphosphate carboxylase from Euglena gracilis, chlorella fusca and several blue-green algae

An antiserum prepared to the ribulose-1,5-diphosphate carboxylase (RuDPCase) of Euglena gracilis has been tested by double immuno-diffusion against the pure homologous enzyme and against extracts from E. gracilis, Chlorella fusca and four species of blue-green algae. Single precipitin bands were formed in all cases. partial immunological identity was established between the E. gracilis and C. fusca enzymes. The precipitin bands produced by the blue-green algae were all mutually identical but only partially identical with both eukaryotic algal enzymes. The enzymatic activities of the RuDPCase purified from E. gracilis and C. fusca were inhibited by the antiserum to the Euglena enzyme, the same inhibition—antibody titre relationship occurring. The antiserum also inhibited ribulose diphosphate carboxylase activity in all blue-green algal extracts tested.

Ribulose Diphosphate Carboxylase Synthesis in Euglena

The transfer of dark-grown cultures of Euglena gracilis Klebs strain Z regreening in the light back into darkness resulted in a dramatic increase in ribulose diphosphate carboxylase activity. On a culture volume basis activity increased 4-fold over a 24-hour dark period, although on a protein basis activity declined because of rapid cell division. Mixed assays with light- and dark-growing cell extracts provided no evidence for the removal of an inhibitor of ribulose diphosphate carboxylase upon transferring regreening cells back to darkness. Although ribulose diphosphate carboxylase activity increased over a 24-hour dark period, there was no concomitant increase in the potential of the cells for photosynthetic carbon dioxide fixation.Higher light intensities than the optimum for ribulose diphosphate carboxylase synthesis during regreening resulted in a greater relative rate of synthesis on transfer to darkness so that the maximum activity of ribulose diphosphate carboxylase reached in the dark was constant, regardless of light intensity during regreening. A tentative hypothesis to explain these results is that the synthesis of the large and small subunits of ribulose diphosphate carboxylase occur at different stages of cell development, light being necessary for the synthesis of the large subunit and also for regulating the synthesis of the small subunit.