Ribulose Bisphosphate Carboxylase Activity Research Articles

Exogenous trehalose differently improves photosynthetic carbon assimilation capacities in maize and wheat under heat stress

ABSTRACT High temperature inhibits the growth and development of maize (Zea mays L.) and wheat (Triticum aestivum L.) seedlings. The current study attempts to elucidate the underlying mechanisms of exogenous trehalose for the improvement of maize and wheat responses to heat stress. Results show that, in maize seedlings, exogenously-supplied trehalose was able to effectively elevate the capacity of photosynthetic carbon assimilation and improve the carbohydrate content via up-regulating the transcript levels of key enzymes including phosphoenol pyruvate carboxylase (PEPC), NADP-malate dehydrogenase (NADP-MDH), NADP-malic enzyme (NADP-ME), pyruvate phosphate dikinase (PPDK) and Ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit. Besides, it was also able to improve C4 pathway enzyme activities, including PEPC, NADP-MDH, NADP-ME and Ribulose-1,5-bisphosphate carboxylase (RUBPCase). In wheat seedlings, exogenously-supplied trehalose promoted photosynthetic carbon assimilation by elevating the activity of RUBPCase. These results show that exogenous trehalose improved photosynthetic carbon assimilation capacities in maize and wheat seedlings under heat stress through different mechanisms.

A Transcriptomic Approach to Understanding the Combined Impacts of Supra-Optimal Temperatures and CO2 Revealed Different Responses in the Polyploid Coffea arabica and Its Diploid Progenitor C. canephora.

Understanding the effect of extreme temperatures and elevated air (CO2) is crucial for mitigating the impacts of the coffee industry. In this work, leaf transcriptomic changes were evaluated in the diploid C. canephora and its polyploid C. arabica, grown at 25 °C and at two supra-optimal temperatures (37 °C, 42 °C), under ambient (aCO2) or elevated air CO2 (eCO2). Both species expressed fewer genes as temperature rose, although a high number of differentially expressed genes (DEGs) were observed, especially at 42 °C. An enrichment analysis revealed that the two species reacted differently to the high temperatures but with an overall up-regulation of the photosynthetic machinery until 37 °C. Although eCO2 helped to release stress, 42 °C had a severe impact on both species. A total of 667 photosynthetic and biochemical related-DEGs were altered with high temperatures and eCO2, which may be used as key probe genes in future studies. This was mostly felt in C. arabica, where genes related to ribulose-bisphosphate carboxylase (RuBisCO) activity, chlorophyll a-b binding, and the reaction centres of photosystems I and II were down-regulated, especially under 42°C, regardless of CO2. Transcriptomic changes showed that both species were strongly affected by the highest temperature, although they can endure higher temperatures (37 °C) than previously assumed.

Improving boll capsule wall, subtending leaves anatomy and photosynthetic capacity can increase seed cotton yield under limited drip irrigation systems

Drought stress is considered to be the main source of yield reduction around the world. Improving plant performance under stressful environments by understanding growth and physio-biochemical responses are important. However, the detail mechanism of how boll capsule wall and subtending leaves anatomy, physio-biochemical characteristics and key enzymes i.e. Ribulose-1,5-bisphosphate carboxylase (RUBPC) and phosphoenolpyruvate carboxylase (PEPC) affect cotton (Gossypium hirsutum L.) yield have not yet been reported. To cover this knowledge gap, a two-year field experiment evaluated three drip irrigation rates [W1 (4800 m³ ha−1), W2 (3840 m³ ha−1) and W3 (2880 m³ ha−1)] effects on cotton main stem leaves, boll subtending leaves, capsule wall anatomy, biomass accumulation, RUBPC and PEPC activity. Compared with W1, W2 had 10.4–15.7 %, 8.3–24.6 %, 4.4–22.7 % and 5.0–15.3 % higher boll subtending leaf net photosynthetic rate, chlorophyll content, RUBP and PEPC activity at 21–42 days after anthesis. The palisade tissue thickness at 35 DAA (days after anthesis) and the ratio of palisade tissue to sponge tissue (p/s) of boll subtending leaf during 21–49 DAA were 7.7 % and 3.6–10.2 % higher for W2 over W1. Under W2treatment,improvements in these attributes significantly prolonged biomass accumulation rate (T, 6.9 d and 22.1 d) of main stem leaves and boll subtending leaf resulted in the maximum growth rate of seed cotton weight (Vx, 0.195 g d-1). Conclusively, higher photosynthetic capacity of the boll subtending leaves during 21–42 DAA and thicker capsule wall are the main drivers for achieving higher seed cotton weight under limited drip irrigation systems in arid region.

Study on Carbon Sequestration Capacity of Typical Crops in Northern China

The carbon sequestration potential of different crops in their mature period in Northern China was analyzed in order to promote the selection of green species. Carbon dioxide infrared gas detection, three-dimensional fluorescence, fixed carbon enzyme activity analysis and other methods were used to test the carbon sequestration capacity of nine representative mature crops in the Beijing area. Results show that the carbon sequestration capacity of the nine crops was: corn > sorghum > wheat > tomato > cucumber > cabbage > celery > eggplant > pepper. Among them, the carbon sequestration capacity of corn and sorghum which are C4 crops was stronger than that of other crops. Meanwhile, the three-dimensional fluorescence spectra of corn were closer to sorghum, and there were significant differences in the characteristics of the three-dimensional fluorescence spectra of C3 crops. Based on the analysis of the activity of the fixed carbon enzyme—Phosphoenolpyruvate Carboxylase (PEP) carboxylase and Ribulose-1, 5-Bisphosphate (RuBP) Carboxylase of these plants show that the carbon sequestration capacity of C4 crops was much larger than C3 crops because of its higher PEP carboxylase activity. The carbon sequestration capacity of C3 crops was positively correlated with the activity of RuBP carboxylase in addition to cabbage. Therefore, the carbon sequestration capacity of crops can be measured by using the portable carbon dioxide infrared analyzer.

High plant density inhibits vegetative branching in cotton by altering hormone contents and photosynthetic production

Manual removal of vegetative branches (VB) is a traditional cultural practice widely adopted in Chinese cotton production, but the increasing labor cost in the country has reduced its cost-effectiveness. It is well known that high plant density inhibits the VB growth of cotton and can be a potential alternative to the traditional practice, but the underlying mechanisms are poorly understood. This study mainly aimed to determine how the VB growth of cotton could be inhibited by increasing plant density. Cotton was planted on 76-cm row widths at low (3 plants m−2), moderate (6 plants m−2) and high (9 plants m−2) plant densities. The VB growth and development, as well as the underlying agronomic, physiological and molecular events were examined. The high plant density decreased the number of VB by 67.3% and the ratio of VB biomass to total biomass by 95.0% at 125 days after seeding (DAS) compared with the low plant density. The net photosynthetic (Pn) rate, chlorophyll content and ribulose-1, 5-bisphosphate (RuBP) carboxylase activity in VB leaves were considerably decreased under high plant density, followed by reduced soluble sugar and starch contents, suggesting a suppressed photosynthetic production in the leaves. This decreased photosynthesis resulting from reduced RuBP carboxylase activity and chlorophyll content was one of the reasons for the poor VB growth under high plant density. High plant density increased the auxin (IAA) content and promoted auxin polar transport by increasing the expression of the auxin biosynthesis gene, GhYUC5 and auxin polar transport gene, GhPIN1. It also increased the content of cytokinins (CKs) by increasing the expression of the CKs biosynthesis gene, GhIPT3 in the main-stem tips, and decreasing the IAA and CKs contents as well as auxin polar transport by reducing the expression of GhYUC5, GhPIN1, GhPIN5 and GhIPT3 in the VB tips. The GhPhyB gene was down-regulated by high plant density, but the strigolactones (SLs) content was increased by up-regulating the SL receptor gene, GhD14 in the VB tips. The decreased IAA, CKs, GA and BR contents plus the increased content of SLs due to differential expression of hormone-related genes in the VB tips was another reason for the inhibition of vegetative branching. Although high plant density did not increase seedcotton yield, it improved the fiber quality by decreasing the number of VB-sourced bolls. Our results suggested that high plant density can be a substitute for the traditional plant pruning.

Effects of nitrogen application and supplemental irrigation on canopy temperature and photosynthetic characteristics in winter wheat

AbstractNitrogen (N) application and irrigation to winter wheat may decrease leaf temperature and enhance photosynthesis: as a result, more photosynthates will be allocated to the grains, resulting in higher grain yields. To investigate this hypothesis, a 2-year field study was conducted with three levels of N fertilizer application (no fertilizer, N0; 240 kg N/ha, N1; 360 kg N/ha, N2) and two different water regimes (rainfed with no irrigation, R; irrigation at the over-wintering, stem elongation and grain filling stages, W). The results show that both N application and supplemental irrigation significantly increased grain yield with increases in both grain number/m2 and the 1000-grain weight, viz., WN2>WN1>WN0>RN2>RN1>RN0. In addition, application of N under both water regimes significantly increased flag leaf area, above-ground biomass and single stem productivity and decreased leaf temperature, which led to an increase in net photosynthesis rates and ribulose bisphosphate (RuBP) carboxylase activity. Moreover, analysis of the chlorophyll α fluorescence transient showed that N fertilizer application and supplemental irrigation significantly increased electron donor and acceptor performance of the photosystem II reaction centre.

Drought-inhibited ribulose-1,5-bisphosphate carboxylase activity is mediated through increased release of ethylene and changes in the ratio of polyamines in pakchoi

To study the mechanisms of drought inhibiting photosynthesis and the role of PAs and ethylene, the photosynthetic rate (Pn), the maximal photochemical efficiency of PSII (Fv/Fm), the intercellular CO2 concentration (Ci), photorespiratory rate (Pr), the amount of chlorophyll (chl), antioxidant enzyme activity, ethylene levels, RuBPC (ribulose-1,5-bisphosphate carboxylase) activity and endogenous polyamine levels of pakchoi were examined, and an inhibitor of S-adenosylmethionine decarboxylase (SAMDC) and an inhibitor of ethylene synthesis and spermidine (Spd) were used to induce the change of endogenous polyamine levels. The results show that drought induced a decrease in Pn and RuBPC activity, an increase in the intercellular CO2 concentration (Ci), but no change in the actual photochemical efficiency of PSII (ΦPSII), and chlorophyll content. In addition, drought caused an increase in the free putrescine (fPut), the ethylene levels, a decrease in the Spd and spermine (Spm) levels, and the PAs/fPut ratio in the leaves. The exogenous application of Spd and amino oxiacetic acid (AOAA, an inhibitor of ethylene synthesis) markedly reversed these drought-induced effects on polyamine, ethylene, Pn, the PAs/fPut ratio and RuBPCase activity in leaves. Methylglyoxal-bis(guanylhydrazone) (MGBG), an inhibitor of SAMDC resulting in the inability of activated cells to synthesize Spd and Spm, exacerbates the negative effects induced by drought. These results suggest that the decrease in Pn is at least partially attributed to the decrease of RuBPC activity under drought stress and that drought inhibits RuBPC activity by decreasing the ratio of PAs/fPut and increasing the release of ethylene.

Abscisic acid as a factor in regulation of photosynthetic carbon metabolism of pea seedlings

The influence of abscisic acid (ABA) on carbon metabolism and the activity of ribulosebisphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylases in 8-day-old pea seedlings was investigated. It was endeavoured to correlate the changes observed in metabolic processes with the endogenous ABA level. In plants treated with ABA incorporation of labeled carbon into sucrose, glucose, fructose and sugar phosphates was depressed, while <sup>14</sup>C incorporation into starch, ribulose and malic acid was enhanced. The activity of RuBP carboxylase was considerably lowered, whereas that of PEP carboxylase was slightly increased. It is considered that inhibition of photosynthesis due to the action of ABA is caused to a great extent by the obstruction of the C-3 pathway and reduced activity of RuBP carboxylase, whereas (β-carboxylation was not blocked.

Diallel Analysis of Photosynthetic Traits in Maize

ABSTRACTCapability to intercept and utilize sunlight is important in maize (Zea mays L.) for its growth and dry matter accumulation. Little research has been conducted on the combining ability of maize physiological traits related to photosynthesis, such as light saturation point (LSP), light compensation point (LCP), apparent quantum efficiency (AQE), maximum photosynthesis (Pmax), total protein content (PRO), and activity of phosphoenolpyruvate carboxylase (PEPC) and ribulosebisphosphate carboxylase (RuBPC). The five photosynthesis‐related traits and two key enzymes were examined for their combining abilities using a six‐parent diallel design. The objectives were to (i) evaluate general combining ability (GCA) and maternal (MAT) effects of the six maize lines and specific combining ability (SCA) and nonmaternal (NMAT) effects for crosses and (ii) determine if GCA effects were different among three maize heterotic groups. Results revealed that the additive gene effects were more important than nonadditive effects for LSP, LCP, Pmax, PRO, PEPC, and RuBPC. Maternal effects for LCP, PRO, and RuBPC were significant and positive for some lines, which could be used as female parents in hybrid development. Information on means of parental lines, combining ability, and heterosis values suggested that RUBPC, PEPC, and PRO might be the key traits that make the Suwan 1 heterotic group different from the Reid and non‐Reid groups and should be explored fully in future hybrid maize breeding programs.

Impeded Carbohydrate Metabolism in Rice Plants under Submergence Stress

The detrimental effects of submergence on physiological performances of some rice varieties with special references to carbohydrate metabolisms and their allied enzymes during post-flowering stages have been documented and clarified in the present investigation. It was found that photosynthetic rate and concomitant translocation of sugars into the panicles were both related to the yield. The detrimental effects of the complete submergence were recorded in generation of sucrose, starch, sucrose phosphate synthase and phosphorylase activity in the developing panicles of the plants as compared to those under normal or control (i.e. non-submerged) condition. The accumulation of starch was significantly lower in plants under submergence and that was correlated with ADP-glucose pyrophosphorylase activity. Photosynthetic rate was most affected under submergence in varying days of post-flowering and was also related to the down regulation of Ribulose bisphosphate carboxylase activity. However, under normal or control condition, there recorded a steady maintenance of photosynthetic rate at the post-flowering stages and significantly higher values of Ribulose bisphosphate carboxylase activity. Still, photosynthetic rate of the plants under both control and submerged conditions had hardly any significant correlation with sugar accumulation and other enzymes of carbohydrate metabolism like invertase with grain yield. Finally, plants under submergence suffered significant loss of yield by poor grain filling which was related to impeded carbohydrate metabolism in the tissues. It is evident that loss of yield under submergence is attributed both by lower sink size or sink capacity (number of panicles, in this case) as well as subdued carbohydrate metabolism in plants and its subsequent partitioning into the grains.

Hydrogen sulphide enhances photosynthesis through promoting chloroplast biogenesis, photosynthetic enzyme expression, and thiol redox modification in Spinacia oleracea seedlings

Hydrogen sulphide (H2S) is emerging as a potential messenger molecule involved in modulation of physiological processes in animals and plants. In this report, the role of H2S in modulating photosynthesis of Spinacia oleracea seedlings was investigated. The main results are as follows. (i) NaHS, a donor of H2S, was found to increase the chlorophyll content in leaves. (ii) Seedlings treated with different concentrations of NaHS for 30 d exhibited a significant increase in seedling growth, soluble protein content, and photosynthesis in a dose-dependent manner, with 100 μM NaHS being the optimal concentration. (iii) The number of grana lamellae stacking into the functional chloroplasts was also markedly increased by treatment with the optimal NaHS concentration. (iv) The light saturation point (Lsp), maximum net photosynthetic rate (Pmax), carboxylation efficiency (CE), and maximal photochemical efficiency of photosystem II (Fv/Fm) reached their maximal values, whereas the light compensation point (Lcp) and dark respiration (Rd) decreased significantly under the optimal NaHS concentration. (v) The activity of ribulose-1,5-bisphosphate carboxylase (RuBISCO) and the protein expression of the RuBISCO large subunit (RuBISCO LSU) were also significantly enhanced by NaHS. (vi) The total thiol content, glutathione and cysteine levels, internal concentration of H2S, and O-acetylserine(thiol)lyase and L-cysteine desulphydrase activities were increased to some extent, suggesting that NaHS also induced the activity of thiol redox modification. (vii) Further studies using quantitative real-time PCR showed that the gene encoding the RuBISCO large subunit (RBCL), small subunit (RBCS), ferredoxin thioredoxin reductase (FTR), ferredoxin (FRX), thioredoxin m (TRX-m), thioredoxin f (TRX-f), NADP-malate dehydrogenase (NADP-MDH), and O-acetylserine(thiol)lyase (OAS) were up-regulated, but genes encoding serine acetyltransferase (SERAT), glycolate oxidase (GYX), and cytochrome oxidase (CCO) were down-regulated after exposure to the optimal concentration of H2S. These findings suggest that increases in RuBISCO activity and the function of thiol redox modification may underlie the amelioration of photosynthesis and that H2S plays an important role in plant photosynthesis regulation by modulating the expression of genes involved in photosynthesis and thiol redox modification.

Developmental pattern in the formation of various multienzyme complexes associated with Benson-Calvin cycle in cotton leaves

An electrophoretically homogeneous preparation of a multienzyme complex with a mol wt of 520 ± 20 kD was isolated from 15- to 25-day-old cotton (Gossypium hirsutum L.) leaves uniform in their age and position on the shoot (3rd to 4th leaves from the top when the plants possessed 5–6 true leaves). When cotton leaves were sampled at the stage of budding and flowering, two complexes with mol wts of 520 ± 20 kD and 480 ± 15 kD were isolated. Comparative enzymatic studies of these complexes revealed developmental changes in activities of ribose phosphate isomerase, phosphoribulokinase, and ribulose-bisphosphate carboxylase. The multienzyme complexes were almost identical in activity of ribose phosphate isomerase. Activities of phosphoribulokinase and ribulose-bisphosphate carboxylase for various multienzyme complexes showed variations between 14 and 17% in the presence of ribose-5-phospate + ATP as a substrate, but the differences were smaller (6–7%) in the presence of specific substrates of these enzymes. The formation of multienzyme Benson-Calvin cycle complexes, featuring different properties at various stages of plant development, is presumably related to the increased demand in assimilates for epigenetic processes during formation of generative organs.

Cinnamic acid-inhibited ribulose-1,5-bisphosphate carboxylase activity is mediated through decreased spermine and changes in the ratio of polyamines in cowpea

This study investigated the effects of cinnamic acid (CA) on ribulose-1,5-bisphosphate carboxylase (RuBPC) activity and the endogenous polyamine levels of cowpea leaves. The results show that 0.1 mM CA treatment decreased photosynthetic rate ( P n) and RuBPC activity, but it did not affect the maximal photochemical efficiency of PSII ( F v/ F m), the actual photochemical efficiency of PSII ( ΦPSII), intercellular CO 2 concentration ( C i), and relative chlorophyll content. These suggest that the decrease in P n is at least partially attributed to a lowered RuBPC activity. In addition, 0.1 mM CA treatment increased the putrescine (Put) level, but decreased spermidine (Spd) and spermine (Spm) levels, thereby reducing the (Spd+Spm)/Put (PAs) ratio in the leaves. The exogenous application of 1 mM Spd markedly reversed these CA-induced effects for polyamine and partially restored the PAs ratio and RuBPC activity in leaves. Methylglyoxal-bis (guanylhydrazone) (MGBG), which is an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), results in the inability of activated cells to synthesize Spd and exacerbates the negative effects induced by CA. The exogenous application of 1 mM d-arginine ( d-Arg), which is an inhibitor of Put biosynthesis, decreased the levels of Put, but increased the PAs ratio and RuBPC activity in leaves. These results suggest that 0.1 mM CA inhibits RuBPC activity by decreasing the levels of endogenous free and perchloric acid soluble (PS) conjugated Spm, as well as the PAs ratio.

Ribulose bisphosphate carboxylase activity and a Calvin cycle gene cluster in Sulfobacillus species

The Calvin-Benson-Bassham (CBB) cycle has been extensively studied in proteobacteria, cyanobacteria, algae and plants, but hardly at all in Gram-positive bacteria. Some characteristics of ribulose bisphosphate carboxylase/oxygenase (RuBisCO) and a cluster of potential CBB cycle genes in a Gram-positive bacterium are described in this study with two species of Sulfobacillus (Gram-positive, facultatively autotrophic, mineral sulfide-oxidizing acidophiles). In contrast to the Gram-negative, iron-oxidizing acidophile Acidithiobacillus ferrooxidans, Sulfobacillus thermosulfidooxidans grew poorly autotrophically unless the CO(2) concentration was enhanced over that in air. However, the RuBisCO of each organism showed similar affinities for CO(2) and for ribulose 1,5-bisphosphate, and similar apparent derepression of activity under CO(2) limitation. The red-type, form I RuBisCO of Sulfobacillus acidophilus was confirmed as closely related to that of the anoxygenic phototroph Oscillochloris trichoides. Eight genes potentially involved in the CBB cycle in S. acidophilus were clustered in the order cbbA, cbbP, cbbE, cbbL, cbbS, cbbX, cbbG and cbbT.

Effect of water deficit on photosynthetic and other physiological responses in grapevine (Vitis vinifera L. cv. Riesling) plants

The grapevine (Vitis vinifera L. cv. Riesling) plants subjected to water deficit were studied for changes in relative water content (RWC), leaf dry mass, contents of chlorophyll (Chl), total leaf proteins, free amino acids, and proline, and activities of ribulose-1,5-bisphosphate carboxylase (RuBPC), nitrate reductase (NR), and protease. In water-stressed plants RWC, leaf dry matter, Chl content, net photosynthetic rate (P N), and RuBPC and NR activities were significantly decreased. The total leaf protein content also declined with increase in the accumulation of free amino acids. Concurrently, the protease activity in the tissues was also increased. A significant two-fold increase in proline content was recorded.

Photosynthesis of Eucalyptus globulus with Mycosphaerella leaf disease

Mycosphaerella leaf disease (MLD) is a major cause of foliage damage in Eucalyptus globulus plantations. Our study is the first to describe the physiological effects of MLD on E. globulus leaves. It involved measurements on both field and potted plants. Changes in photosynthetic parameters in response to MLD were quantified in a study using gas exchange techniques. There was a negative linear relationship between light-saturated photosynthesis (A(max)) and leaf-level damage from MLD. Reductions in A(max) were proportionally greater than might be expected from the reduction in green leaf area as a result of the disease, indicating that asymptomatic tissue also was affected by MLD. The reductions in A(max) were not related to increases in stomatal resistance, but were a result of reduced activity of ribulose bisphosphate carboxylase (Rubisco) and changes in the capacity for ribulose bisphosphate (RuBP) regeneration. Changes in mesophyll resistance to CO2 were also implicated. The effect of MLD was similar at different sites and irrespective of tree-level infection, suggesting a general leaf-level response of E. globulus to MLD.

Photosynthetic responses of radish (Raphanus sativus var. longipinnatus) plants to infection by turnip mosaic virus

Plant growth, chlorophyll (Chl) content, photosynthetic gas exchange, ribulose-1,5-bisphosphate carboxylase (RuBPCO) enzyme activity, and Chl fluorescence in radish (Raphanus sativus var. longipinnatus) plants were examined after turnip mosaic virus (TuMV) infection. Plant fresh mass, dry mass, Chl content, net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), and RuBPCO activity were significantly lower in infected plants after 5 weeks of virus infection as compared to healthy plants. The 5-week virus infection did not induce significant differences in intercellular CO2 concentration (Ci, photochemical efficiency of photosystem 2, PS2 (Fv/Fm), excitation capture efficiency of open PS2 reaction centres (Fv'/Fm'), effective quantum efficiency of photosystem 2 (ΔF/Fm'), and photochemical quenching (qP), but non-photochemical quenching (qN) and alternative electron sink (AES) were significantly enhanced. Thus the decreased plant biomass of TuMV-infected plants might be associated with the decreased photosynthetic activity mainly due to reduced RuBPCO activity.

Low-night temperature (LNT) induced changes of photosynthesis in grapevine ( Vitis vinifera L.) plants

Changes of leaf pigments, ribulose-1,5-bisphosphate carboxylase (RuBPC) and photosynthetic efficiency were examined in grapevine ( Vitis vinifera L.) plants grown under ambient irradiation (maximum daily PAR = 1500 μmol m −2 s −1) for 7 days to low night temperature (LNT) of 5 °C (daily from 18:00 to 06:00). The contents of chlorophyll (Chl) and carotenoids (Car) per fresh mass were lower in LNT leaves than in control leaves. The contents of α + β carotene and lutein-5,6-epoxide remained unaffected, but the de-epoxidation state involving the components of xanthophyll cycle increased. RuBPC activity and soluble proteins were also significantly reduced in LNT leaves. In isolated thylakoids, a marked inhibition of whole chain (PS I + PS II) and PS II activity were observed in LNT leaves. Smaller inhibition of PS I activity was observed in LNT leaves. The artificial exogenous electron donors, MnCl 2, DPC and NH 2OH did not restored the loss of PS II activity in LNT leaves. The same results were obtained when F v/ F m was evaluated by Chl fluorescence measurements. The marked loss of PS II activity in LNT leaves was due to the marked loss of D1 protein which was determined by immunological studies.

Activation of Rubisco controls CO2 assimilation in light: a perspective on its discovery

CO(2) fixation during photosynthesis is regulated by the activity of ribulose bisphosphate carboxylase (Rubisco). This conclusion became more apparent to me after CO(2)-fixation experiments using isolated spinach chloroplasts and protoplasts, purified Rubisco enzyme, and intact leaves. Ribulose bisphosphate (RuBP) pools and activation of Rubisco were measured and compared to (14)CO(2) fixation in light. The rates of (14)CO (2) assimilation best followed the changes in Rubisco activation under moderate to high light intensities. RuBP pool sizes regulated (14) (2) assimilation only in very high CO(2) levels, low light and in darkness. Activation of Rubisco involves two separate processes: carbamylation of the protein and removal of inhibitors blocking carbamylation or blocking RuBP binding to carbamylated sites before reaction with CO(2) or O(2).

New Thermophilic Methanotrophs of the Genus Methylocaldum

Two pure cultures of obligate methanotrophs, strains H-11 and 0-12, growing in the temperature range from 30 to 61 degrees C with an optimum at 55 degrees C were isolated from samples of silage and manure. Based on the results of analysis of the 16S rRNA genes, membrane-bound methane monooxygenase, and phenotypic properties, the isolates were assigned to the genus Methylocaldum. Significant temperature-dependent variations in morphology and phospholipid and fatty acid composition were revealed. Both strains assimilated methane carbon via the ribulose monophosphate, serine, and ribulose bisphosphate pathways. The activity of hexulose phosphate synthase was independent of the cultivation temperature; however, the activities of hydroxypyruvate reductase and ribulose bisphosphate carboxylase were higher in cells grown at 55 degrees C that in cells grown at 37 degrees C, indicating the important roles of the serine and ribulose bisphosphate pathways in the thermoadaptation of the strains under study. NH4+ assimilation occurred through reductive amination of alpha-ketoglutarate and via the glutamate cycle. The relationship between the physiological-biochemical peculiarities of the isolates and their thermophilic nature is discussed.