Gene nomenclature recommendations for green photosynthetic bacteria and heliobacteria

Recommendations are given for naming of genes coding for reaction center, antenna and electron transport proteins in green photosynthetic bacteria and heliobacteria     

Evolution of heliobacteria: Implications for photosynthetic reaction center complexes

The evolutionary position of the heliobacteria, a group of green photosynthetic bacteria with a photosynthetic apparatus functionally resembling Photosystem I of plants and cyanobacteria, has been investigated with respect to the evolutionary relationship to Gram-positive bacteria and cyanobacteria. On the basis of 16S rRNA sequence analysis, the heliobacteria appear to be most closely related to Gram-positive bacteria, but also an evolutionary link to cyanobacteria is evident. Interestingly, a 46-residue domain including the putative sixth membrane-spanning region of the heliobacterial reaction center protein shows rather strong similarity (33% identity and 72% similarity) to a region including the sixth membrane-spanning region of the CP47 protein, a chlorophyll-binding core antenna polypeptide of Photosystem II. The N-terminal half of the heliobacterial reaction center polypeptide shows a moderate sequence similarity (22% identity over 232 residues) with the CP47 protein, which is significantly more than the similarity with the Photosystem I core polypeptides in this region. An evolutionary model for photosynthetic reaction center complexes is discussed, in which an ancestral homodimeric reaction center protein (possibly resembling the heliobacterial reaction center protein) with 11 membrane-spanning regions per polypeptide has diverged to give rise to core of Photosystem I, Photosystem II, and of the photosynthetic apparatus in green, purple, and heliobacteria.     

Nitrogen fixation and nitrogen metabolism in heliobacteria

Three species of anoxygenic phototrophic heliobacteria, Heliobacterium chlorum, Heliobacterium gestii, and Heliobacillus mobilis, were studied for comparative nitrogen-fixing abilities and regulation of nitrogenase. Significant nitrogenase activity (acetylene reduction) was detected in all species grown photoheterotrophically on N₂, although cells of H. mobilis consistently had higher nitrogenase activity than did cells of either H. chlorum or H. gestii. Nitrogen-fixing cultures of all three species of heliobacteria were subject to switch-off of nitrogenase activity by ammonia; glutamine also served to switch-off nitrogenase activity but only in cells of H. mobilis and H. gestii. Placing photosynthetically grown heliobacterial cultures in darkness also served to switch-off nitrogenase activity. Dark-mediated switch-off was complete in lactate-grown heliobacteria but in pyruvate-grown cells substantial rates of nitrogenase activity continued in darkness. In all heliobacteria examined ammonia was assimilated primarily through the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway although significant levels of alanine dehydrogenase were present in extracts of cells of H. gestii, but not in the other species. The results suggest that heliobacteria, like phototrophic purple bacteria, are active N₂-fixing bacteria and that despite their gram-positive phylogenetic roots, heliobacteria retain the capacity to control nitrogenase activity by a switch-off type of mechanism. Because of their ability to fix N₂ both photosynthetically and in darkness, it is possible that heliobacteria are significant contributors of fixed nitrogen in their paddy soil habitat.     

Chemotrophic growth of heliobacteria in darkness

Abstract Conditions are described that support anaerobic dark chemotrophic growth of heliobacteria. Growth was pyruvate-dependent and was best in well-buffered pyruvate media supplemented with yeast extract. Heliobacterial cells grown in darkness synthesized bacteriochlorophyll g and carotenoids and fermented pyruvate to acidic products, CO₂, and in some cases, H₂. All recognized species of heliobacteria as well as several newly isolated strains were capable of dark anaerobic growth, suggesting that this growth mode may be ecologically important for survival of these organisms in their soil habitat.     

A stable carbon isotope study of dissolved inorganic carbon cycling in a softwater lake

The dissolved inorganic carbon (DIC) cycle in a softwater lake was studied using natural variations of the stable isotopes of carbon,¹²C and¹³C. During summer stratification there was a progressive decrease in epilimnion DIC concentration with a concomitant increase in ¹³C_DIC), due to preferential uptake of¹²C by phytoplankton and a change in the dominant CO₂ source from inflow andin situ oxidation to invasion from the atmosphere. There was an increase in hypolimnion DIC concentration throughout summer with a concomitant general decrease in ¹³C_DIC from oxidation of the isotopically light particulate organic carbon that sank down through the thermocline from the epilimnion.Mass balance calculations of DI¹²C and DI¹³C in the epilimnion for the summer (June 23–September 25) yield a mean rate of net conversion of DIC to organic carbon (C_org) of 430 ± 150 moles d^-1 (6.5 ± 1.8 m moles m^-2 d^-1. Net CO₂ invasion from the atmosphere was 420 ± 120 moles d^-1 (6.2 ± 1.8 m moles m^-2 d^-1) with an exchange coefficient of 0.6 ± 0.3m d^-1. These results imply that at least for the summer months the phytoplankton obtained about 90% of their carbon from atmosphere CO₂. About 50% of CO₂ invasion and conversion to C_org for the summer occurred during a two week interval in mid-summer.DIC concentration increased in the hypolimnion at a rate of 350 ± 70 moles DIC d^-1 during summer stratification. The amount of DIC added to the hypolimnion was equivalent to 75 ± 20% of net conversion of DIC to C_org in the euphotic zone over spring and summer implying rapid degradation of POC in the hypolimnion. The ¹³C of DIC added to the deep water (-22.) was too heavy to have been derived from oxidation of particulate organic carbon alone. About 20% of the added DIC must have diffused from hypolimnetic sediments where relatively heavy CO₂ (-7) was produced by a combination of POC oxidation and as a by-product of methanogenesis.     

Modelling the importance of sediment bacterial carbon for profundal macroinvertebrates along a lake nutrient gradient

In dimictic, temperate lakes little is known about the quantitative importance of trophic coupling between pelagic and profundal communities. Although it is a generally accepted paradigm that profundal secondary production is dependent on autochthonous pelagic production (primarily diatoms), the importance of interactions between phytodetrital inputs, sediment bacteria, and macroinvertebrates are still not well understood. In this study, we used theoretical models to estimate macroinvertebrate carbon requirement (production + respiration) and bacterial production for lakes of different trophic categories. Comparisons of estimates show that the importance of bacterial production as a carbon source for benthic macroinvertebrates is inversely related to lake trophic state. Assuming that infauna assimilates 50% of ingested bacterial carbon, this food source could account for between 47% (oligotrophic lakes) and 2% (hypertrophic lakes) of their carbon demand. These calculations indicate that bacterial carbon should not be an important C-resource for profundal macroinvertebrates of eutrophic and hypertrophic lakes.     

Characteristics of photosynthetic carbon metabolism of spikelets in rice

In lemmas and paleae of rice, the amount of pyruvate, Pi dikinase (PPDK) protein increased dramatically 6 d after anthesis and this change was consistent with that in the activity of PPDK. Since lemmas and paleae at this stage also showed high activities of the other marker enzymes of C4 pathway including phosphot enolpyruvate carboxylase (Imaizumi et al. (1990) Plant Cell Physiol 31: 835–843), photosynthetic carbon metabolism with lemmas at this stage were characterized. In a 14C pulse-12C chase study by photosynthetic CO2 fixation, about 35% and 25% of 14C fixed in lemmas were incorporated initially into 3-phosphoglycerate (3-PGA) and C4 acids, respectively. This suggests that lemmas participate mainly in C3-type photosynthetic metabolism, but that lemmas may also participate in the metabolism of C4 acids to some extent. To clarify this possibility, large amounts of 14C-labeled C4 acids were synthesized in vivo by a light-enhanced dark CO2 fixation (LED) method and the fate of 14C in C4 acids in the light was investigated. The percentage distribution of 14C in C-4 position of malate was about 90% and 83% after 10 s of photosynthetic 14CO2 fixation and 110 s of LED, respectively. Some of the 14C incorporated into C4 acids was transferred into 3-PGA and sugar phosphates. The possibility of direct fixation of CO2 by phosphot enolpyruvate carboxylase and metabolic pathway of CO2 released by decarboxylation of malate produced were discussed.     

Relationship between photosynthetic and respiratory carbon metabolism in freshwater phytoplankton

Measurements of algal carbon metabolism in the light and the dark were conducted in (1) short-term (3-h) light and dark incubations, (2) a diel (24-h) experiment, and (3) a longer-term (4-d) carbon accumulation experiment to examine the relationship between photosynthetic rates, photosynthetic carbon metabolism in the light, and respiration and carbon metabolism in the ensuing dark period in natural assemblages of freshwater phytoplankton. High rates of photosynthesis and polysaccharide synthesis in the light were followed by high rates of respiration and polysaccharide utilization in the dark. Polysaccharide was the major respiratory substrate in the dark, and small molecular weight metabolites, lipids, and protein were less important sources of metabolic energy. The protein pool accumulated carbon during dark incubations, but more slowly than during active photosynthesis in the light. Because the intracellular macromolecular pools turn over at very different rates (polysaccharide > protein and lipid), patterns of short-term photosynthetic carbon metabolism are not necessarily indicative of the biochemical composition of the phytoplankton.     

Effects of temperature on the regulation of photosynthetic carbon assimilation in leaves of maize and barley

The aim of this work was to examine the effect of temperature in the range 5 to 30 ° C upon the regulation of photosynthetic carbon assimilation in leaves of the C₄ plant maize (Zea mays L.) and the C₃ plant barley (Hordeum vulgare L.). Measurements of the CO₂-assimilation rate in relation to the temperature were made at high (735 bar) and low (143 bar) intercellular CO₂ pressure in barley and in air in maize. The results show that, as the temperature was decreased, (i) in barley, pools of phosphorylated metabolites, particularly hexose-phosphate, ribulose 1,5-bisphosphate and fructose 1,6-bisphosphate, increased in high and low CO₂; (ii) in maize, pools of glycerate 3-phosphate, triose-phosphate, pyruvate and phosphoenolpyruvate decreased, reflecting their role in, and dependence on, intercellular transport processes, while pools of hexose-phosphate, ribulose 1,5-bis phosphate and fructose 1,6-bisphosphate remained approximately constant; (iii) the redox state of the primary electron acceptor of photosystem II (Q_A) increased slightly in barley, but rose abruptly below 12° C in maize. Non-photochemical quenching of chlorophyll fluorescence increased slightly in barley and increased to high values below 20 ° C in maize. The data from barley are consistent with the development of a limitation by phosphate status at low temperatures in high CO₂, and indicate an increasing regulatory importance for regeneration of ribulose 1,5-bisphosphate within the Calvin cycle at low temperatures in low CO₂. The data from maize do not show that any steps of the C₄ cycle are particularly cold-sensitive, but do indicate that a restriction in electron transport occurs at low temperature. In both plants the data indicate that regulation of product synthesis results in the maintenance of pools of Calvin-cycle intermediates at low temperatures.Abbreviations Glc6P glucose-6-phosphate - Fru6P fructase-6-phosphate - Frul,6bisP fructose-1,6-bisphosphate - PGA glycerate-3-phosphate - p _i intercellular partial pressure of CO₂ - RuBP ribulose-1,5-bisphosphate - triose-P sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate We thank the Agricultural and Food Research Council, UK (Research grant PG50/67) and the Science and Engineering Research Council, UK for financial support. C.A.L. was supported by the British Council, by the Conselho Nacional de Desenvolvimento Cientiflco e Tecnologico (CNPq), Brazil and by an Overseas Research Student Award. We also thank Mark Stitt (Bayreuth, FRG) and Debbie Rees for helpful discussions.     

13C-NMR study of lactate metabolism in Propionibacterium freudenreichii subsp. shermanii

The adaptation to osmotic stress in Propionibacterium freudenreichii subsp. shermanii was investigated by using natural-abundance ¹³C nuclear magnetic resonance spectroscopy. Cells incubated either in a standard laboratory medium or in a medium designed to simulate the physicochemical conditions of Swiss-type cheese were found to accumulate different levels of osmotic-stress-protectant molecules. Proline, betaine, trehalose and glutamate were found simultaneously. Moreover, two types of polysaccharides were in evidence in this strain. Lactate catabolism was not mainly directed towards cell growth requirements and organic acid production but also towards biosynthesis of osmolytes requested for adaptation in a cheese environment. The possible involvement of such type of metabolite accumulation in the main cheese-ripening bacteria in Swiss-type cheeses is discussed.     

植物的光合作用与光合氮、碳代谢的耦联及调节

概述了光合作用反应与CO2同化和NO^-3/NO^-2还原的耦联关系,提出了应该从氮,碳代谢整合角度讨论作动和光合作用,以便根据生产目的,调节作物的氮,碳代谢,实现农业生产的高产,优质。     

水杨酸对植物光合作用影响的研究进展

水杨酸作为一种信号分子,对植物呼吸代谢、种子萌发、成花诱导、衰老及抗逆等生理过程都有调节作用,近年来有关水杨酸对植物光合作用影响的研究取得了很大进展。水杨酸能够调节植物叶片气孔运动、光合色素含量、光合机构性能、光合碳同化酶活性等各方面,其效果因浓度、植物种类、环境条件等不同而表现出差异。该文就近年来国内外有关水杨酸对植物光合作用的影响(主要从植物叶片气孔运动、光合色素含量、光合机构性能和光合碳同化酶活性等方面)研究进展进行综述。     

The importance and place of the photosynthetic carbon sequestration in the organic branch of its global cycle

Results of comparative analysis of turnover times and the capacity of major global pools of organic carbon are presented; the place of photosynthetic carbon sequestration is defined; concept of its catalytic role in the regulation of the organic branch of the global carbon cycle is ground. Concept of reservoir-flux model of photosynthetic carbon sequestration and of the net photosynthetic production at the territory of Northern Eurasia is suggested.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 81–89.Original Russian Text Copyright © 2005 by Voronin, Black.     

Interaction of flooding with carbon metabolism of forest trees

Waterlogging and flooding cause oxygen deprivation in the root system of trees. Since oxygen is essentially for mitochondrial respiration, this process cannot be maintained under anoxic conditions and must be replaced by other pathways. For the roots it is therefore a matter of survival to switch from respiration to alcoholic fermentation. Due to the low efficiency of this process to yield energy equivalents (ATP), energy and carbon metabolism of trees are usually strongly affected by oxygen deprivation, even if a rapid switch from respiration to fermentation is achieved. The roots can compensate for the low energy yield of fermentation either (1) by decreasing the demand for energy by a reduction of energy-dependent processes such as root growth and/or nutrient uptake, or (2) by consuming more carbohydrates per unit time in order to generate sufficient energy equivalents. In the leaves of trees, flooding and waterlogging cause a decline in the rates of photosynthesis and transpiration, as well as in stomatal conductance. It is assumed that, due to reduced phloem transport, soluble sugars and starch accumulate in the leaves of flooded trees, thereby negatively affecting the sugar supply of the roots. Thus, root growth and survival is negatively affected by both changes in root internal carbon metabolism and impaired carbon allocation to the roots by phloem transport. In addition, accumulation of toxic products of fermentation in the roots, such as acetaldehyde, can further impair root metabolism. A main feature of tolerance against flooding and waterlogging of trees seems to be the steady supply of carbohydrates to the roots in order to maintain alcoholic fermentation; in addition, roots of tolerant trees seem to avoid accumulation of fermentation-derived ethanol and acetaldehyde. From studies with flooding tolerant and non-tolerant tree species, it is hypothesized that (1) the transport of ethanol produced in the roots under hypoxic conditions into the leaves via the transpiration stream, (2) its conversion into acetyl-CoA in the leaves, and (3) its use in the plant's general metabolism, are mechanisms of flooding tolerance of trees.     

Contribution of photosynthetic sulphur bacteria to primary production in Lake Vechten

The role of photosynthetic sulphur bacteria as primary producers in monomictic Lake Vechten (The Netherlands) is described. Lake Vechten has a surface area of 4.7 ha, a maximum depth of 11.9 m and a mean depth of 6 m.Bacterial populations, appearing at the boundary layer of the oxidative and reductive zone from early June till late October, were composed of cyanobacteria, Chromatiaceae and green and brown coloured Chlorobiaceae. Predominating genera were Synechococcus, Chloronema, Chromatium and Thiopedia. The photosynthetic sulphur bacteria accounted for a primary production rate of 13.6–106.1 mg C.m^–2 day^–1, which corresponded to 3.9–17.5% of total daily productivity in the pelagial zone. The percentage of photosynthetic bacterial production of total annual planktonic primary production calculated for the entire pelagial zone, taking into account compensation for decreasing volume of lower strata, was 3.6% (i.e. 127 against a total production of 3 510 kg C.lake^–1yr^–1).     

Physiology of pyruvate metabolism in Lactococcus lactis

Lactococcus lactis, a homofermentative lactic acid bacterium, has been studied extensively over several decades to obtain sometimes conflicting concepts relating to the growth behaviour. In this review some of the data will be examined with respect to pyruvate metabolism. It will be demonstrated that the metabolic transformation of pyruvate can be predicted if the growth-limiting constraints are adequately established. In general lactate remains the major product under conditions in which sugar metabolism via a homolactic fermentation can satisfy the energy requirements necessary to assimilate anabolic substrates from the medium. In contrast, alternative pathways are involved when this energy supply becomes limiting or when the normal pathways can no longer maintain balanced carbon flux. Pyruvate occupies an important position within the metabolic network of L. lactis and the control of pyruvate distribution within the various pathways is subject to co-ordinated regulation by both gene expression mechanisms and allosteric modulation of enzyme activity.     

Regulation of photosynthetic carbon metabolism during phosphate limitation of photosynthesis in isolated spinach chloroplasts

Intact chloroplasts isolated from spinach were illuminated in the absence of inorganic phosphate (Pi) or with optimum concentrations of Pi added to the reaction medium. In the absence of Pi photosynthesis declined after the first 1–2 min and was less than 10% of the maximum rate after 5 min. Export from the chloroplast was inhibited, with up to 60% of the ¹⁴C fixed being retained in the chloroplast, compared to less than 20% in the presence of Pi. Despite the decreased export, chloroplasts depleted of Pi had lower levels of triose phosphate while the percentage of total phosphate in 3-phosphoglycerate was increased. Chloroplast ATP declined during Pi depletion and reached dark levels after 3–4 min in the light without added Pi. At this point, stromal Pi concentration was 0.2 mM, which would be limiting to ATP synthesis. Addition of Pi resulted in a rapid burst of oxygen evolution which was not initially accompanied by net CO₂ fixation. There was a large decrease in 3-phosphoglycerate and hexose plus pentose monophosphates in the chloroplast stroma and a lesser decrease in fructose-1,6-bisphosphate. Stromal levels of triose phosphate, ribulose-1,5-bisphosphate and ATP increased after resupply of Pi. There was an increased export of ¹⁴-labelled compounds into the medium, mostly as triose phosphate. Light activation of both fructose-1,6-bisphosphatase and ribulose-1,5-bisphosphate carboxylase was decreased in the absence of Pi but increased following Pi addition.It is concluded that limitation of Pi supply to isolated chloroplasts reduced stromal Pi to the point where it limits ATP synthesis. The resulting decrease in ATP inhibits reduction of 3-phosphoglycerate to triose phosphate via mass action effects on 3-phosphoglycerate kinase. The lack of Pi in the medium also inhibits export of triose phosphate from the chloroplast via the phosphate transporter. Other sites of inhibition of photosynthesis during Pi limitation may be located in the regeneratige phase of the reductive pentose phosphate pathway.Abbreviations FBP Fructose-1,6-bisphosphate - FBPase Fructose-1,6-bisphosphatase - MP Hexose plus pentose monophosphates - PGA 3-phosphoglycerate - Pi inorganic orthophosphate - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase - TP Triose Phosphate     

湛江5种红树林树种光合作用特性及光合固碳能力研究

应用Li-6400便携式光合作用测定系统,对湛江市特呈岛5种红树林树种的净光合速率日变化和光合作用—光响应曲线进行了测定,探讨了各树种的光合作用特性以及主要影响因子并评估其固碳能力大小。结果表明:在自然光照条件下,秋茄和红海榄叶片净光合速率(Pn)的日变化曲线呈单峰型,白骨壤、木榄和桐花树为双峰型,光合"午休"现象明显,而且峰值分别出现在10:00和14:00左右。其中,白骨壤和木榄的光合午休主要由气孔限制因素引起,桐花树主要由非气孔限制因素引起。通径分析表明,光合有效辐射(PAR)是影响白骨壤和桐花树叶片Pn的主要决策因子,而叶面大气蒸汽压亏缺(VPD)是主要限制因子;影响秋茄和红海榄叶片Pn的主要决策因子是气孔导度(Gs),主要限制因子是叶温(Tl);影响木榄叶片Pn的主要决策因子是气孔导度(Gs)。基于叶片净光合作用速率的各树种日净固碳量存在显著性差异(P0.01),秋茄的日净固碳量最大(13.83 g·m-2·d-1),其次为白骨壤和桐花树(9.48和8.24 g·m-2·d-1),木榄和红海榄的较小(6.72和6.30 g·m-2·d-1)。5种红树林树种的光补偿点(LCP)介于28.3~137.0μmol·m-2·s-1之间,显示了阳生植物的特性。光饱和点(LSP)介于169.3~1189.3μmol·m-2·s-1之间,桐花树最大,红海榄最小。5种红树林树种的表观量子效率(AQY)存在极显著差异(P0.01),白骨壤最高为0.064 mol·mol-1,木榄最低,仅为0.005 mol·mol-1。5种红树林植物叶片的光响应参数与日净固碳量的关联度大小顺序为最大净光合速率(Pmax)、LSP-LCP、AQY、LSP、LCP。