共查询到20条相似文献,搜索用时 15 毫秒
1.
The source of glycolate in photorespiration and its control, a particularly active and controversial research topic in the
1970s, was resolved in large part by several discoveries and observations described here. George Bowes discovered that the
key carboxylation enzyme Rubisco (ribulosebisphosphate carboxylase/oxygenase) is competitively inhibited by O 2 and that O 2 substitutes for CO 2 in the initial `dark' reaction of photosynthesis to yield glycolate-P, the substrate for photorespiration. William Laing
derived an equation from basic enzyme kinetics that describes the CO 2, O 2, and temperature dependence of photosynthesis, photorespiration, and the CO 2 compensation point in C 3 plants. Jerome Servaites established that photosynthesis cannot be increased by inhibiting the photorespiratory pathway prior
to the release of photorespiratory CO 2, and Douglas Jordan discovered substantial natural variation in the Rubisco oxygenase/carboxylase ratio. A mutant Arabidopsis plant with defective glycolate-P phosphatase, isolated by Chris Somerville, definitively established the role of O 2 and Rubisco in providing photorespiratory glycolate. Selection techniques to isolate photorespiration-deficient plants were
devised by Jack Widholm and by Somerville, but no plants with reduced photorespiration were found. Somerville's approach,
directed mutagenesis of Arabidopsis plants, was subsequently successful in the isolation of numerous other classes of mutants and revolutionized the science
of plant biology.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
The extent of photorespiration, the inhibition of apparent photosynthesis (APS) by 21% O 2, and the leaf anatomical and ultrastructural features of the naturally occurring C 3–C 4 intermediate species in the diverse Panicum, Moricandia, and Flaveria genera are between those features of representative C 3 and C 4 plants. The greatest differences between the photosynthetic/photorespiratory CO 2 exchange characteristics of the C 3–C 4 intermediates and C 3 plants occur for the parameters which are measured at low pCO 2 (i.e., the CO 2 compensation concentration and rates of CO 2 evolution into CO 2-free air in the light). The rates of APS by the intermediate species at atmospheric pCO 2 are similar to those of C 3 plants.The mechanisms which are responsible for reducing photorespiration in the C 3–C 4 intermediate species are poorly understood, but two proposals have been advanced. One emphasizes the importance of limited C 4 photosynthesis which reduces O 2 fixation by ribulose 1,5-bisphosphate carboxylase/oxygenase, and, thus, reduces photorespiration by a CO 2-concentrating mechanism, while the other emphasizes the importance of the internal recycling of photorespiratory CO 2 evolved from the chloroplast/mitochondrion-containing bundle-sheath cells. There is no evidence from recent studies that limited C 4 photosynthesis is responsible for reducing photorespiration in the intermediate Panicum and Moricandia species. However, preliminary results suggest that some, but not all, of the intermediate Flaveria species may possess a limited C 4 cycle. The importance of a chlorophyllous bundle-sheath layer in the leaves of intermediate Panicum and Moricandia species in a mechanism based on the recycling of photorespiratory CO 2 is uncertain.Therefore, although they have yet to be clearly delineated, different strategies appear to exist in the C 3–C 4 intermediate group to reduce photorespiration. Of major importance is the finding that some mechanism(s) other than Crassulacean acid metabolism or C 4 photosynthesis has (have) evolved in at least the majority of these terrestrial intermediate species to reduce the seemingly wasteful metabolic process of photorespiration.Abbreviations APS
apparent (net) photosynthesis
- CAM
Crassulacean acid metabolism
- CE
carboxylation efficiency
- T
CO 2 compensation concentration
- IRGA
infrared gas analysis
- P i
orthophosphate
- PEP
phosphoenolpyruvate
- RuBP
ribulose 1,5-bisphosphate
Published as Paper No. 7383, Journal Series, Nebraska Agricultural Experiment Station. 相似文献
3.
15N-labelled (amino group) asparagine (Asn), glutamate (Glu), alanine (Ala), aspartate (Asp) and serine (Ser) were used to study the metabolic role and the participation of each compound in the photorespiratory N cycle of Pisum sativum L. leaves. Asparagine was utilised as a nitrogen source by either deamidation or transamination, Glu was converted to Gln through NH 3 assimilation and was a major amino donor for transamination, and Ala was utilised by transamination to a range of amino acids. Transamination also provided a pathway for Asp utilisation, although Asp was also used as a substrate for Asn synthesis. In the photorespiratory synthesis of glycine (Gly), Ser, Ala, Glu and Asn acted as sources of amino-N, contributing, in the order given, 38, 28, 23, and 7% of the N for glycine synthesis; Asp provided less than 4% of the amino-N in glycine. Calculations based on the incorporation of 15N into Gly indicated that about 60% (Ser), 20% (Ala), 12% (Glu) and 11% (Asn) of the N metabolised from each amino acid was utilised in the photorespiratory nitrogen cycle.Abbreviations Ala
alamine
- Asn
asparagine
- Asp
aspartate
- Glu
glutamate
- MOA
methoxylamine
- Ser
serine 相似文献
4.
High CO 2 concentrations stimulate net photosynthesis by increasing CO 2 substrate availability for Rubisco, simultaneously suppressing photorespiration. Previously, we reported that silencing the chloroplast vesiculation ( cv) gene in rice increased source fitness, through the maintenance of chloroplast stability and the expression of photorespiration-associated genes. Because high atmospheric CO 2 conditions diminished photorespiration, we tested whether CV silencing might be a viable strategy to improve the effects of high CO 2 on grain yield and N assimilation in rice. Under elevated CO 2, OsCV expression was induced, and OsCV was targeted to peroxisomes where it facilitated the removal of OsPEX11-1 from the peroxisome and delivered it to the vacuole for degradation. This process correlated well with the reduction in the number of peroxisomes, the decreased catalase activity and the increased H 2O 2 content in wild-type plants under elevated CO 2. At elevated CO 2, CV-silenced rice plants maintained peroxisome proliferation and photorespiration and displayed higher N assimilation than wild-type plants. This was supported by higher activity of enzymes involved in NO 3− and NH 4+ assimilation and higher total and seed protein contents. Co-immunoprecipitation of OsCV-interacting proteins suggested that, similar to its role in chloroplast protein turnover, OsCV acted as a scaffold, binding peroxisomal proteins. 相似文献
5.
Mesophyll protoplasts and bundle sheath cells were prepared by enzymatic digestion of leaves of Alternanthera tenella, a C 3-C 4 intermediate species. The intercellular distribution of selected photosynthetic, photorespiratory and respiratory (mitochondrial) enzymes in these meso-phyll and bundle sheath cells was studied. The activity levels of photosynthetic enzymes such as PEP carboxylase (EC 4.1.1.31) or NAD-malic enzyme (EC 1.1.1.39) and photorespiratory enzymes such as glycolate oxidase (EC 1.1.3.1) or NADH-hydroxypyruvate reductase (EC 1.1.1.29) were similar in the two cell types. The activity levels of mitochondrial TCA cycle enzymes such as citrate synthase (EC 4.1.3.7) or fumarase (EC 4.2.1.2) were 2- to 3-fold higher in bundle sheath cells. On the other hand, the activity levels of mitochondrial photorespiratory enzymes, namely glycine decarboxylase (EC 2.1.2.10) and serine hydroxymethyltransferase (EC 2.1.2.1), were 6-9-fold higher in bundle sheath cells than in mesophyll protoplasts. Such preferential localization of mitochondria enriched with the glycine-decarboxylating system in the inner bundle sheath cells would result in efficient refixa-tion of CO 2 from not only photorespiration but also dark respiration before its exit from the leaf. We propose that predominant localization of mitochondria specialized in glycine decarboxylation in bundle sheath cells may form the basis of reduced photorespiration in this C 3-C 4 intermediate species. 相似文献
6.
A mutant of Hordeum vulgare L. (LaPr 85/84) deficient in serine: glyoxylate aminotransferase (EC 2.6.1.45) activity has been isolated. The plant also lacks serine: pyruvate aminotransferase and asparagine: glyoxylate aminotransferase activities. Genetic analysis of the mutation strongly indicates that these three activities are all carried on the same enzyme protein. The mutant is incapable of normal rates of photosynthesis in air but can be maintained at 0.7% CO 2. The rate of photosynthesis cannot be restored by supplying hydroxypyruvate, glycerate, glutamate or ammonium sulphate through the xylem stream. This photorespiratory mutant demonstrates convincingly that photorespiration still occurs under conditions in which photosynthesis becomes insensitive to oxygen levels. Two major peaks and one minor peak of serine: glyoxylate aminotransferase activity can be separated in extracts of leaves of wild-type barley by diethylaminoethyl-sephacel chromatography. All three peaks are missing from the mutant, LaPr 85/84. The mutant showed the expected rate (50%) of ammonia release during photorespiration but produced CO 2 at twice the wild-type rate when it was fed [ 14C]glyoxylate. The large accumulation of serine detected in the mutant under photorespiratory conditions shows the importance of the enzyme activity in vivo. The effect of the mutation on transient changes in chlorophyll a fluorescence initiated by changing the atmospheric CO 2 concentration are presented and the role of the enzyme activity under nonphotorespiratory conditions is discussed.Abbreviations DEAE
diethylaminoethyl
- PFR
photon fluence rate
- SGAT
serine:glyoxylate aminotransferase 相似文献
7.
Three allelic mutants of Arabidopsis thaliana which lack mitochondrial serine transhydroxymethylase activity due to a recessive nuclear mutation have been characterized. The mutants were shown to be deficient both in glycine decarboxylation and in the conversion of glycine to serine. Glycine accumulated as an end product of photosynthesis in the mutants, largely at the expense of serine, starch, and sucrose formation. The mutants photorespired CO 2 at low rates in the light, but this evolution of photorespiratory CO 2 was abolished by provision of exogenous NH 3. Exogenous NH 3 was required by the mutants for continued synthesis of glycine under photorespiratory conditions. These and related results with wild-type Arabidopsis suggested that glycine decarboxylation is the sole site of photorespiratory CO 2 release in wild-type plants but that depletion of the amino donors required for glyoxylate amination may lead to CO 2 release from direct decarboxylation of glyoxylate. Photosynthetic CO 2 fixation was inhibited in the mutants under atmospheric conditions which promote photorespiration but could be partially restored by exogenous NH 3. The magnitude of the NH 3 stimulation of photosynthesis indicated that the increase was due to the suppression of glyoxylate decarboxylation. The normal growth of the mutants under nonphotorespiratory atmospheric conditions indicates that mitochondrial serine transhydroxymethylase is not required in C 3 plants for any function unrelated to photorespiration. 相似文献
8.
Effect of phosphorus deficiency on photosynthetic and respiratory CO 2 exchanges were analysed in primary leaves of 2-week-old bean ( Phaseolus vulgaris L. cv. Golden Saxa) plants under non-photorespiratory (2 % O 2) and photorespiratory (21 % O 2) conditions. Low P decreased maximum net photosynthetic rate (P Nmax) and increased the time necessary to reach it. In the leaves of P-deficient plants the relative decrease of P Nmax at 2 % O 2 was larger than at 21 % O 2. The results suggested the influence of photorespiration in the cellular turnover of phosphates. 相似文献
9.
C i, intercellular CO 2 concentration Fv/ Fm, quantum efficiency of excitation capture by open photosystem II centresFBPase, fructose-1,6-bisphosphataseGAPDH, glyceraldehyde-3-phosphate dehydrogenaseGDC, glycine decarboxylaseGS-2, chloroplastic glutamine synthetaseHPR, hydroxypyruvate reductasePFD, photon flux density ΦCO 2, quantum efficiency of CO 2 assimilation ΦPSII, quantum efficiency of photosystem II electron transport ψ, water potential qN, non-photochemical chlorophyll a fluorescence quenching qP, photochemical chlorophyll a fluorescence quenchingRuBP, ribulose-1,5-bisphosphateRubisco, ribulose-1,5-bisphosphate carboxylase-oxygenaseSBPase, sedoheptulose-1,7-bisphosphataseSGAT, serine : glyoxylate aminotransferaseThe significance of photorespiration in drought-stressed plants was studied by withholding water from wild-type barley ( Hordeum vulgare L.) and from heterozygous mutants with reduced activities of chloroplastic glutamine synthetase (GS-2), glycine decarboxylase (GDC) or serine : glyoxylate aminotransferase (SGAT). Well-watered plants of all four genotypes had identical rates of photosynthesis. Under moderate drought stress (leaf water potentials between –1 and –2 MPa), photosynthesis was lower in the mutants than in the wild type, indicating that photorespiration was increased under these conditions. Analysis of chlorophyll a fluorescence revealed that, in the GDC and SGAT mutants, the lower rates of photosynthesis coincided with a decreased quantum efficiency of photosystem II and increased non-photochemical dissipation of excitation energy. Correspondingly, the de-epoxidation state of xanthophyll-cycle carotenoids was increased several-fold in the drought-stressed GDC and SGAT mutants compared with the wild type. Accumulation of glycine in the GDC mutant was further evidence for increased photorespiration in drought-stressed barley. The effect of drought on the photorespiratory enzymes was determined by immunological detection of protein abundance. While the contents of GS-2 and P- and H-protein of the GDC complex remained unchanged as drought stress developed, the content of NADH-dependent hydroxypyruvate reductase increased. Enzymes of the Benson–Calvin cycle, on the other hand, were either not affected (ribulose-1,5-bisphosphate carboxylase-oxygenase and plastidic fructose-1,6-bisphosphatase) or declined (sedoheptulose- 1,7-bisphosphatase and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase). These data demonstrate that photorespiration was enhanced during drought stress in barley and that the control exerted by photorespiratory enzymes on the rate of photosynthetic electron transport and CO 2 fixation was increased. 相似文献
10.
Glutamine synthetase (GS) localized in the chloroplasts, GS2, is a key enzyme in the assimilation of ammonia (NH 3) produced from the photorespiration pathway in angiosperms, but it is absent from some coniferous species belonging to Pinaceae such as Pinus. We examined whether the absence of GS2 is common in conifers (Pinidae) and also addressed the question of whether assimilation efficiency of photorespiratory NH 3 differs between conifers that may potentially lack GS2 and angiosperms. Search of the expressed sequence tag database of Cryptomeria japonica, a conifer in Cupressaceae, and immunoblotting analyses of leaf GS proteins of 13 species from all family members in Pinidae revealed that all tested conifers exhibited only GS1 isoforms. We compared leaf NH 3 compensation point (γ NH3) and the increments in leaf ammonium content per unit photorespiratory activity (NH 3 leakiness), i.e. inverse measures of the assimilation efficiency, between conifers ( C. japonica and Pinus densiflora) and angiosperms ( Phaseolus vulgaris and two Populus species). Both γ NH3 and NH 3 leakiness were higher in the two conifers than in the three angiosperms tested. Thus, we concluded that the absence of GS2 is common in conifers, and assimilation efficiency of photorespiratory NH 3 is intrinsically lower in conifer leaves than in angiosperm leaves. These results imply that acquisition of GS2 in land plants is an adaptive mechanism for efficient NH 3 assimilation under photorespiratory environments. 相似文献
11.
The effects of added glycine hydroxamate on the photosynthetic incorporation of 14CO 2 into metabolites by isolated mesophyll cells of spinach ( Spinacia oleracea L.) was investigated under conditions favorable to photorespiratory (PR) metabolism (0.04% CO 2 and 20% O 2) and under conditions leading to nonphotorespiratory (NPR) metabolism (0.2% CO 2 and 2.7% O 2). Glycine hydroxamate (GH) is a competitive inhibitor of the photorespiratory conversion of glycine to serine, CO 2 and NH 4+. During PR fixation, addition of the inhibitor increased glycine and decreased glutamine labeling. In contrast, labeling of glycine decreased under NPR conditions. This suggests that when the rate of glycolate synthesis is slow, the primary route of glycine synthesis is through serine rather than from glycolate. GH addition increased serine labeling under PR conditions but not under NPR conditions. This increase in serine labeling at a time when glycine to serine conversion is partially blocked by the inhibitor may be due to serine accumulation via the “reverse” flow of photorespiration from 3-P-glycerate to hydroxypyruvate when glycine levels are high. GH increased glyoxylate and decreased glycolate labeling. These observations are discussed with respect to possible glyoxylate feedback inhibition of photorespiration. 相似文献
12.
Previous studies have indicated that the rate of photorespiration in C 4 plants is low or negligible. In this study, wild-type and mutant leaves of the C 4 plant Amaranthus edulis were treated with the glutamine synthetase inhibitor, phosphinothricin and the glycine decarboxylase inhibitor, aminoacetonitrile, at different concentrations of CO 2. The time course of ammonia accumulation in leaves of the wild type was compared with a mutant lacking phosphoenolpyruvate carboxylase activity (EC 4.1.1.31), and with three different mutants that accumulated glycine. The increase in the concentration of ammonia in the leaves, stimulated by the treatments was used as a measurement of the rate of photorespiration in C 4 plants. The application of glutamine and glycine maintained the rate of photorespiratory ammonia production for a longer period in the wild type, and increased the rate in a mutant lacking phosphoenolpyruvate carboxylase suggesting that there was a lack of amino donors in these plants. The calculated rate of photorespiration in Amaranthus edulis wild-type leaves when the supply of amino donors was enough to maintain the photorespiratory nitrogen flow, accounted for approximately 6% of the total net photosynthetic CO 2 assimilation rate. In a mutant lacking phosphoenolpyruvate carboxylase, however, this rate increased to 48%, when glutamine was fed to the leaf, a value higher than that found in some C 3 plants. In mutants of Amaranthus edulis that accumulated glycine, the rate of photorespiration was reduced to 3% of the total net CO 2 assimilation rate. The rate of ammonia produced during photorespiration was 60% of the total produced by all metabolic reactions in the leaves. The data suggests that photorespiration is an active process in C 4 plants, which can play an important role in photosynthetic metabolism in these plants. 相似文献
13.
In C 4 plants, photorespiration is decreased relative to C 3 plants. However, it remains unclear how much photorespiratory capacity C 4 leaf tissues actually have. We thoroughly investigated the quantitative distribution of photorespiratory organelles and the immunogold localization of the P protein of glycine decarboxylase (GDC) in mesophyll (M) and bundle sheath (BS) cells of various C 4 grass species. Specific differences occurred in the proportions of mitochondria and peroxisomes in the BS cells (relative to the M cells) in photosynthetic tissues surrounding a vein: lower in the NADP-malic enzyme (NADP-ME) species having poorly formed grana in the BS chloroplasts, and higher in the NAD-malic enzyme (NAD-ME) and phosphoenolpyruvate carboxykinase (PCK) species having well developed grana. In all C 4 species, GDC was localized mainly in the BS mitochondria. When the total amounts of GDC in the BS mitochondria per unit leaf width were estimated from the immunogold labeling density and the quantity of mitochondria, the BSs of NADP-ME species contained less GDC than those of NAD-ME or PCK species. This trend was also verified by immunoblot analysis of leaf soluble protein. There was a high positive correlation between the degree of granal development (granal index) in the BS chloroplasts and the total amount of GDC in the BS mitochondria. The variations in the structural and biochemical features involved in photorespiration found among C 4 species might reflect differences in the O 2/CO 2 partial pressure and in the potential photorespiratory capacity of the BS cells.Abbreviations BS Bundle sheath - GDC Glycine decarboxylase - M Mesophyll - NAD-ME NAD-malic enzyme - NADP-ME NADP-malic enzyme - PCK Phosphoenolpyruvate carboxykinase 相似文献
14.
Photorespiratory metabolism is essential for plants to maintain functional photosynthesis in an oxygen‐containing environment. Because the oxygenation reaction of Rubisco is followed by the loss of previously fixed carbon, photorespiration is often considered a wasteful process and considerable efforts are aimed at minimizing the negative impact of photorespiration on the plant’s carbon uptake. However, the photorespiratory pathway has also many positive aspects, as it is well integrated within other metabolic processes, such as nitrogen assimilation and C 1 metabolism, and it is important for maintaining the redox balance of the plant. The overall effect of photorespiratory carbon loss on the net CO 2 fixation of the plant is also strongly influenced by the physiology of the leaf related to CO 2 diffusion. This review outlines the distinction between Rubisco oxygenation and photorespiratory CO 2 release as a basis to evaluate the costs and benefits of photorespiration. 相似文献
15.
Nitrogen‐13 (t 1/2 9.97 m), a radioactive isotope of nitrogen, offers unique opportunities to explore plant nitrogen utilization over short time periods. Here we describe a method for administering 13N as gaseous 13NH 3 to intact leaves of Nicotiana tabacum L. (cv Samsun), and measuring the labelled amino acids using radio high‐performance liquid chromatography (HPLC) on tissue extract. We used this method to study the effects of defence induction on plant nitrogen utilization by applying treatments of methyl jasmonate (MeJA), a potent defence elicitor. MeJA caused a significant increase relative to controls in key [ 13N]amino acids, including serine, glycine and alanine by 4 h post‐treatment, yet had no effect on 13NH 3 incorporation, a process that is primarily under the control of the glutamine synthatase/glutamate synthase pathway (GS/GOGAT) in cellular photorespiration. We suggest that the reconfiguration of nitrogen metabolism may reflect induction of non‐photorespiratory sources of nitrogen to better serve the plant's defences. 相似文献
16.
It is well established that the plastidic isoform of glutamine synthetase (GS 2) is the enzyme in charge of photorespiratory ammonium reassimilation in plants. The metabolic events associated to photorespiratory NH 4+ accumulation were analyzed in a Lotus japonicus photorespiratory mutant lacking GS 2. The mutant plants accumulated high levels of NH 4+ when photorespiration was active, followed by a sudden drop in the levels of this compound. In this paper it was examined the possible existence of enzymatic pathways alternative to GS 2 that could account for this decline in the photorespiratory ammonium. Induction of genes encoding for cytosolic glutamine synthetase (GS 1), glutamate dehydrogenase (GDH) and asparagine synthetase (ASN) was observed in the mutant in correspondence with the diminishment of NH 4+. Measurements of gene expression, polypeptide levels, enzyme activity and metabolite levels were carried out in leaf samples from WT and mutant plants after different periods of time under active photorespiratory conditions. In the case of asparagine synthetase it was not possible to determine enzyme activity and polypeptide content; however, an increased asparagine content in parallel with the induction of ASN gene expression was detected in the mutant plants. This increase in asparagine levels took place concomitantly with an increase in glutamine due to the induction of cytosolic GS 1 in the mutant, thus revealing a major role of cytosolic GS 1 in the reassimilation and detoxification of photorespiratory NH 4+ when the plastidic GS 2 isoform is lacking. Moreover, a diminishment in glutamate levels was observed, that may be explained by the induction of NAD(H)-dependent GDH activity. 相似文献
17.
The pattern of photorespiratory ammonia (PR–NH 3) formation and its modulation by exogenous bicarbonate or glycine were investigated in C 3–C 4 intermediates of Alternanthera ( A. ficoides and A. tenella) and Parthenium hysterophorus in comparison to those of C 3 or C 4 species. The average rates of PR–NH 3 accumulation in leaves of the intermediates were slightly less than (about 25% reduced) those in C 3 species, and were further low in C 4 plants (40% of that in C 3). The levels of PR–NH 3 in leaf discs decreased markedly when exogenous bicarbonate was present in the incubation medium. The inhibitory effect of bicarbonate on PR–NH 3 accumulation was pronounced in C 3 plants, very low in C 4 species and was moderate in the C 3–C 4 intermediates. Glycine, an intermediate of photorespiratory metabolism, raised the levels of PR–NH 3 in leaves of not only C 4 but also C 3–C 4 intermediates, bringing the rates close to those of C 3 species. The rate of mitochondrial glycine decarboxylation in darkness in C 3–C 4 intermediates was partially reduced (about 80% of that in C 3 species), corresponding to the activity-levels of glycine decarboxylase and serine hydroxymethyltransferase in leaves. The intermediates had a remarkable capacity of reassimilating photorespiratory CO 2 in vivo, as indicated by the apparent refixation of about 85% of the CO 2 released from exogenous glycine in the light. We suggest that the reduced photorespiration in the C 3–C 4 intermediate species of Alternanthera and Parthenium is due to both a limitation in the extent of glycine production/decarboxylation and an efficient refixation/recycling of internal CO 2.Abbreviations GDC
glycine decarboxylase
- GS
glutamine synthetase
- GOGAT
glutamate-oxoglutarate aminotransferase
- -HPMS
-hydroxy-2-pyridinemethanesulfonic acid
- INH
isonicotinyl hydrazide
- MSO
L-methionine sulfoximine
- PR–NH 3
photorespiratory-ammonia
- SHMT
serine hydroxymethyltransferase 相似文献
18.
The afterglow (AG) luminescence is a delayed chlorophyll fluorescence emitted by the photosystem II that seems to reflect the level of assimilatory potential (NADPH+ATP) in chloroplast. In this work, the thermoluminescence (TL) emissions corresponding to the AG band were investigated in plants of the WT and the Ljgln2‐2 photorespiratory mutant from Lotus japonicus grown under either photorespiratory (air) or non‐photorespiratory (high concentration of CO 2) conditions. TL glow curves obtained after two flashes induced the strongest overall TL emissions, which could be decomposed in two components: B band (t max = 27–29°C) and AG band (t max = 44–45°C). Under photorespiratory conditions, WT plants showed a ratio of 1.17 between the intensity of the AG and B bands (I AG/I B). This ratio increased considerably under non‐photorespiratory conditions (2.12). In contrast, mutant Ljgln2‐2 plants grown under both conditions showed a high I AG/I B ratio, similar to that of WT plants grown under non‐photorespiratory conditions. In addition, high temperature thermoluminescence (HTL) emissions associated to lipid peroxidation were also recorded. WT and Ljgln2‐2 mutant plants grown under photorespiratory conditions showed both a significant HTL band, which increased significantly under non‐photorespiratory conditions. The results of this work indicate that changes in the amplitude of I AG/I B ratio could be used as an in vivo indicator of alteration in the level of photorespiratory metabolism in L. japonicus chloroplasts. Moreover, the HTL results suggest that photorespiration plays some role in the protection of the chloroplast against lipid peroxidation. 相似文献
19.
Net photosynthesis in the submersed angiosperms Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royal was inhibited by 21% O 2, but the degree of inhibition was greater for plants in the high than in the low photorespiratory state. Increasing the CO 2 concentration from 50 through 2,500 l l -1 decreased the O 2 inhibition of the high-photorespiration plants in a competitive manner, but it had no effect on the O 2 inhibition of plants in the low photorespiratory state. Carbonic-anhydrase activity increased by almost threefold with the induction of the low photorespiratory state. Ethoxyzolamide, an inhibitor of carbonic anhydrase, reduced the net photosynthesis of low-photorespiration Myriophyllum and Hydrilla plants by 40%, but their dark respiration was unaffected. This ethoxyzolamide inhibition of net photosynthesis exhibited a competitive response to CO 2 concentration, resulting in a decrease in the apparent affinity of photosynthesis for CO 2. The net photosynthesis of plants in the high photorespiratory state was inhibited only slightly by ethoxyzolamide, and this inhibition was independent of the CO 2 level. Ethoxyzolamide treatment caused an increase in the O 2 inhibition of net photosynthesis of plants in the low photorespiratory state. Ethoxyzolamide increased the low CO 2 compensation points of low-photorespiration Myriophyllum and Hydrilla, but the values for the high-photorespiration plants were unchanged. In comparison, the CO 2 compensation points of the terrestrial plants Sorghum bicolor (C 4), Moricandia arvensis (C 3-C 4 intermediate) and Nicotiana tabacum (C 3) were unaltered by ethoxyzolamide treatment. These data indicate that the low photorespiratory state in Myriophyllum and Hydrilla is repressed by ethoxyzolamide treatment, thus implicating carbonic anhydrase as a component of the photorespiration-reducing mechanism in these plants. The competitive interaction of CO 2 with ethoxyzolamide provides evidence that the low photorespiratory state in submersed angiosperms is the result of some type or types of CO 2 concentrating mechanism. In Myriophyllum it may be via bicarbonate utilization, but in Hydrilla it probably takes the form of an inducible C 4-type system.Abbreviations PEP
phosphoenolpyruvate
- RuBP
ribulose bisphosphate 相似文献
20.
The submersed angiosperms Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royal exhibited different photosynthetic pulse-chase labeling patterns. In Hydrilla, over 50% of the 14C was initially in malate and aspartate, but the fate of the malate depended upon the photorespiratory state of the plant. In low photorespiration Hydrilla, malate label decreased rapidly during an unlabeled chase, whereas labeling of sucrose and starch increased. In contrast, for high photorespiration Hydrilla, malate labeling continued to increase during a 2-hour chase. Thus, malate formation occurs in both photorespiratory states, but reduced photorespiration results when this malate is utilized in the light. Unlike Hydrilla, in low photorespiration Myriophyllum, 14C incorporation was via the Calvin cycle, and less than 10% was in C 4 acids. Ethoxyzolamide, a carbonic anhydrase inhibitor and a repressor of the low photorespiratory state, increased the label in glycolate, glycine, and serine of Myriophyllum. Isonicotinic acid hydrazide increased glycine labeling of low photorespiration Myriophyllum from 14 to 25%, and from 12 to 48% with high photorespiration plants. Similar trends were observed with Hydrilla. Increasing O2 increased the per cent [14C]glycine and the O2 inhibition of photosynthesis in Myriophyllum. In low photorespiration Myriophyllum, glycine labeling and O2 inhibition of photosynthesis were independent of the CO2 level, but in high photorespiration plants the O2 inhibition was competitively decreased by CO2. Thus, in low but not high photorespiration plants, glycine labeling and O2 inhibition appeared to be uncoupled from the external [O2]/[CO2] ratio. These data indicate that the low photorespiratory states of Hydrilla and Myriophyllum are mediated by different mechanisms, the former being C4-like, while the latter resembles that of low CO2-grown algae. Both may require carbonic anhydrase to enhance the use of inorganic carbon for reducing photorespiration. 相似文献
|