Bisphosphate Carboxylase Activity Research Articles

Photosynthetic responses of sugar beet and Nicotiana benthamiana Domin. infected with beet curly top virus

This study examined photosynthesis and assimilate partitioning in sugar beet (Beta vulgaris L.) and Nicotiana benthamiana Domin. plants systemically infected with either the Logan or CFH strains of beet curly top virus (BCTV). Leaves of both susceptible (Z-10) and resistant (9BB6090) beet varieties exhibited an accumulation of sucrose, as much as 10-fold greater than controls, and 38-fold higher than that seen in infected N. benthamiana per dm2leaf area. [U-14C]-sucrose uptake experiments showed a decline in the export of this sugar, particularly from young leaves of the Z-10 variety. This directly confirms that BCTV impairs phloem transport in sugar beet leaves, and can cause excessive retention of sucrose. Starch levels were also elevated, but remained substantially lower than sucrose levels. Anatomical changes included increases in mesophyll cell size, indicating high cell turgor pressure due to the elevated sugar content. There was an associated 20–50% reduction in photosynthetic rates compared to mock-inoculated plants, and a decrease in ribulose 1,5 bisphosphate carboxylase activity and protein levels. Similar reductions in the activity of cytoplasmic and chloroplastic fructose 1,6, bisphosphatase were consistent with a possible down-regulation of genes encoding key photosynthetic enzymes initiated by the buildup of sugars. BCTV-infected plants may therefore constitute a useful naturally occurring system for investigating end-product control of carbon assimilation

Photoinhibition of photophosphorylation, adenosine triphosphate content, and glyceraldehyde-3-phosphate dehydrogenase (NADP+) following high-irradiance desiccation of Selaginella lepidophylla

Selaginella lepidophylla (Hook, and Grev.) Spring, a poikilohydrous desert pteridophyte, curls dramatically during desiccation. As part of a larger study of potential photoinhibition in this resurrection plant, the hypothesis that stem curling may ameliorate high-irradiance reduction of light-activated enzyme activities, noncyclic photophosphorylation, and adenosine triphosphate content was tested under laboratory conditions. Plants restrained from curling during desiccation at a constant irradiance of 2000 μmol ∙ m−2 ∙ s−1 when rehydrated had significantly decreased glyceraldehyde-3-phosphate dehydrogenase (NADP+) enzyme activity, noncyclic photophosphorylation, and adenosine triphosphate content relative to plants that were allowed to curl naturally under the same conditions. Ribulose bisphosphate carboxylase and malate dehydrogenase enzyme activities were not significantly affected by the restraint treatment. These results demonstrate that stem curling during desiccation limits bright-light damage that could otherwise decrease photophosphorylation capacity, adenosine triphosphate content, and light-activated carbon assimilation enzyme activity when the plants are next wetted. In addition, examination of the adenosine phosphate contents of desiccated, 24-h dark hydrated, and 24-h 500 μmol ∙ m−2 ∙ s−1 irradiance hydrated Selaginella lepidophylla plants revealed that adenosine triphosphate pools were not conserved during desiccation and that during hydration in the light, adenosine triphosphate content increases substantially as a result of both oxidative and photophosphorylation. Key words: Selaginella lepidophylla, photoinhibition, desiccation tolerance, photophosphorylation, adenosine phosphate.

Protection and enhancement of ribulose 1,5 bisphosphate carboxylase activity by exogenous proteins

When assayed in vitro, the activity of the photosynthetic enzyme ribulose 1,5 bisphosphate carboxylase oxygenase is both enhanced and protected from spontaneous decay by exogenous proteins such as hemoglobin, serum albumin, and aldolase. Other proteins and amino acids tested are either ineffective (lysozyme, ferritin, lysine, and cysteine) or afford only partial protection (catalase, glycine, and phenylalanine). Protective proteins do not bind to, or exchange disulfides with, ribulose 1.5 bisphosphate carboxylase/oxygenase. Since their effect can be mimicked by reductively treated detergents such as Triton X-100, it appears that proteins protect from decay by quenching the spontaneous oxidative degradation and inhibiting surface adsorption which could lead to enzyme unfolding. Release of adsorbed molecules from the container surface is likely to be the cause of carboxylase activity enhancement.

Chemoautotrophic metabolism of intracellular gill bacteria in the marine bivalve Spisula subtruncata (da Costa)

Spisula substruncata, a mactrid bivalve living in well-oxygenated sublittoral sandy bottoms, contains two types of intracellular bacteria in its gills. Chemoautotrophic metabolism of these bacteria was tested in different ways. Homogenates of gill tissues showed a slight ribulose — 1.5 — bisphosphate carboxylase activity. Fixation of 14C-labelled bicarbonate in S. subtruncata was higher than in Venus gallina, a clam without bacteria living in the same environment. Other experiments were performed with and without two reduced compounds (sodium thiosulphate and ammonium chloride) at different incubation times (45 to 300 min). With the two compounds, the levels of fixed carbon per g of gill tissue increased significantly after 60 min incubation. A possible ammonia utilization by gill bacteria is demonstrated and may be explained by the fact that the most abundant dissolved reduced compound available for chemoautotrophs is ammonia. The values obtained in this association were lower than those recorded for other bivalves with bacterial cells in their gills. These low values may be explained by the relatively small number of the two types of bacteria observed in the gills of S. subtruncata.

Thermostability of the Photosynthetic System of the Thermoacidophilic AlgaCyanidium caldariumin Continuous Culture

Ford, T. W. 1986. Thermostability of the photosynthetic system of the thermoacidophilic alga Cyanidium caldarium in continuous culture.—J. exp. Bot. 37: 1698 1707. Cyanidium caldarium, when exposed to gradual increases in temperature in continuous culture, exhibits a growth temperature maximum of 55 °C. This correlates with the thermostability of the membrane-located photosynthetic electron transport system but not with in vivo ribulose-1,5 bisphosphate (RUBP) carboxylase activity, which retained full activity after 1 h at 60 °C. Pigment content and phycocyanin : chlorophyll a ratios were relatively constant at growth temperatures up to 50 °C, but both declined in cells cultured at 55 °C. Some modification of the photosynthetic system of the alga, in response to growth temperature, was detected with both oxygen evolution and RUBP carboxylase activity showing improved thermostability in cells grown at 50 °C or 55 C compared with those cultured at lower temperatures. However, this enhanced thermostability was at the expense of total pigment content and overall photosynthetic capacity which were considerably reduced in high temperature cells, as was the temperature spectrum for efficient RUBP carboxylase operation. The contributions of membrane and macromolecular components of the cell to the imposition of optimum

Effects of Nitrate Application on Amaranthus powellii Wats.

Optimal allocation of leaf nitrogen maximizes daily CO(2) assimilation for a given leaf nitrogen concentration. According to the hypothesis of optimization, this condition occurs when the partial derivative of assimilation rate with respect to leaf nitrogen concentration is constant. This hypothesis predicts a linear increase of assimilation rate with leaf nitrogen concentration under constant conditions. Plants of Amaranthus powellii Wats. were grown at 1, 5, 10, or 45 millimolar nitrate to obtain leaves with different nitrogen concentrations. Assimilation rate at 340 microbar CO(2)/bar, stomatal conductance, CO(2)- and light-saturated net photosynthetic rate, the initial slope of the CO(2) response of photosynthesis, ribulose-1,5'-bisphosphate carboxylase activity, and phosphoenolpyruvate carboxylase activity were linearly related to estimated or actual leaf nitrogen concentration. The data are consistent with the optimal use of leaf nitrogen. This hypothesis and the hypothesis of optimal stomatal conductance were combined to determine the relationship between conductance and leaf nitrogen concentration. The slope of conductance versus leaf nitrogen concentration was not significantly different than the slope predicted by the combination of the two hypotheses. Stomatal conductance was linearly related to leaf nitrogen in the field and the slope decreased with lower xylem pressure potentials in a manner consistent with the hypotheses. Finally, apparent maximum stomatal aperture of isolated abaxial epidermal strips was linearly related to leaf nitrogen suggesting stomatal conductance and assimilation rate are controlled in parallel by leaf nitrogen concentration or some factor correlated with leaf nitrogen.

Glycollate Excretion by N2-fixing Cyanobacteria Treated With Photorespiratory Inhibitors

Summary We have examined the effects of various inhibitors of glycollate metabolism on glycollate excretion, photosynthetic CO2 assimilation and N2 fixation by cyanobacteria. α-HPMS (α-hydroxy-α(2-pyridyl)-methane sulphonate) increased the rate of glycollate excretion by Anabaena cylindrica considerably, but also inhibited net CO2 photoassimilation and N2 fixation. α-HPMS inhibted glycollate dehydrogenase in A. cylindrica extracts but did not affect ribulose bisphosphate carboxylase or phosphoglycollate phosphatase activities. Diamox (5 acetamido-1,3,5-thiadizaole-S-sulphonamide) also stimulated glycollate excretion, inhibited CO2 fixation and caused a low inhibition of N2 fixation. INH (isonicotinic acid hydrazide) enhanced glycollate excretion by A. cylindrica, suggesting the metabolism of glycollate via the glycineserine pathway, but again inhibited CO2 fixation and N2 fixation. Glyoxylate also stimulated glycollate excretion by A. cylindrica, Anabaena variabilis and Nostoc muscorum. The data are discussed in terms of the specificity of glycollate metabolism inhibitors in cyanobacteria and the regulation of glycollate metabolism in these organisms.

Limited photosynthetic plasticity in Sedum pulchellum Michx.

Carbon dioxide exchange pattern, carboxylating enzyme specific activity and titratable acidity were measureed for field collected individuals of Sedum pulchellum Michx., a winter annual of xeric cedar glade communities in central Tennessee. Evidence of a weak-CAM mode of photosynthesis was found on 4 of 27 sampling dates during a three year period. Three of these dates occurred during 1978, the driest study season, and nocturnal CO2 uptake contributed a maximum of 10% of the plants daily CO2 uptake. Weak CAM in the field was associated with elevated phosphoenol-pyruvate (PEP) carboxylase activity and, to a lesser degree, with decreased ribulose bisphosphate (RuBP) carboxylase activity. In contrast, carboxylating enzyme specific activities of the sympatric, obligate CAM species Opuntia compressa, a dominant perennial of the cedar glades, were highly stable.Weak CAM was also induced in S. pulchellum upon water stress in the laboratory. Again, weak CAM was associated with elevated PEP carboxylase and decreased RuBP carboxylase activities and represented a relatively minor CO2 uptake contribution. The potential ecological significance of this limited photosynthetic flexibility in S. puchellum is not obvious but it may play an important role in successful yearly reproduction in this annual species at a time when water stress is frequent.

The Effects of Cyanide and Azide on the Photoreduction of 3-Phosphoglycerate and Oxaloacetate by Wild Type and Two Reductive Pentose Phosphate Cycle Mutants of Chlamydomonas reinhardtii

3-Phosphoglycerate- and oxaloacetate-dependent O(2) photoevolution by permeabilized cell preparations (Pressates), prepared from wild type (Wt) and two reductive pentose phosphate cycle mutants of Chlamydomonas reinhardtii showed different sensitivities to the inhibitors sodium cyanide and sodium azide. NaCN (1.5 millimolar) severely inhibits both CO(2)- and 3-phosphoglycerate-dependent O(2) photoevolution by the Wt Pressate, but does not inhibit 3-phosphoglycerate-dependent O(2) photoevolution by Pressates prepared from the mutants rcl-u-1-10-6C (which lacks ribulose, 1-5, bisphosphate carboxylase activity) and F60 (which lacks phosphoribulokinase activity). NaN(3) (0.5 millimolar) inhibits 3-phosphoglycerate-dependent O(2) photoevolution by the rcl-u-1-10-6C Pressate more severely than in the Pressates prepared from F60 and Wt. A higher concentration of NaN(3) (2.0 millimolar) severely inhibited oxaloacetate-dependent O(2) photoevolution by the rcl-u-1-10-6C, but not by the F60 Pressate. O(2) exchange-dependent upon methyl viologen was not strongly inhibited by 2 millimolar NaN(3) in either of the mutant Pressates. The data suggests that the mutational lesions which resulted in decreased ribulose-1,5-bisphosphate carboxylase and phosphoribulokinase activities effected changes in other photosynthetic reactions, either by direct interactions between component proteins or by causing changes in substrate or cofactor availability to the partial reactions.

Ribulose-1,5-bisphosphate Carboxylase Synthesis in Detached Cytokinin-treated Pumpkin Cotyledons

Summary The stimulatory role of the cytokinin, 6-benzylaminopurine, in the development of ribulose-1,5bisphosphate carboxylase activity is studied in detached pumpkin cotyledons in both light and dark experiments. The measurement of enzyme activity by means of monospecific antiserum to ribulosebisphosphate carboxylase from Euglena gracilis shows that benzylaminopurine activates enzyme synthesis in the dark. Illumination causes further increase in the rate of enzyme synthesis. Chloramphenicol (200 mg/1) immediately blocks the increase in ribulosebisphosphate carboxylase activity. Cycloheximide (10 mg/1) does not prevent for