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1.
The effect of Mg2+ during the isolation of chlorophyll-protein complexes was studied in two moss species (Pleurozium schreberi and Ceratodon purpureus) and New Zealand spinach (Tetragonia expansa). When 2 mM MgCl2 was included in all the extraction and separation phases, the proportions of chlorophyll-protein complex I. were very small in all plants studied. The withdrawal of Mg2+ considerably increased the proportions of CP I. The most pronounced increase in the chlorophyll present as CP I was found when Mg2+ was withdrawn from the gel, and this also increased the mobility of the CP II complex and free pigment zone. Exclusion of Mg2+ from the running buffer had very little effect. Although Mg2+ had little effect on the relative amount of chlorophyll in CP II, the withdrawal of Mg2+ from all the extraction and separation phases caused formation of polymers of CP II. In the mosses, the formation of polymers of CP II seemed to be more obvious in the species with large grana. Absence of Mg2+ from all the extraction and separation phases sometimes also produced a polymer of CP I.  相似文献   

2.
The effects of the addition and withdrawal of gibberellic acid (GA3) and Ca2+ on enzyme synthesis and secretion by barley (Hordeum vulgare L. cv. Himalaya) aleurone layers were studied. Incubation of layers in GA3 plus Ca2+ affects the total amount of secreted α-amylase (EC 3.2.1.1) and acid phosphatase (EC 3.1.3.2) by promoting the appearance of different isoenzymic forms of these enzymes. The release of α-amylase isoenzymes 1–4 in response to GA3 plus Ca2+ has a lag of 6 h. When layers are incubated in GA3 alone for 6 h prior to the addition of Ca2+, isoenzymes 1–4 appear in the medium after only 30 min. When the addition of Ca2+ to layers pretreated in GA3 is delayed beyond 12 h, its effectiveness in stimulating the synthesis and release of isoenzymes 3 and 4 is diminished. After 35 h of preincubation in GA3, addition of Ca2+ will not stimulate synthesis of α-amylase isoenzymes 3 and 4. Aleurone layers preincubated for 6 h in GA3 will respond to Ca2+ when the GA3 is withdrawn from the incubation medium by producing α-amylase isoenzymes 1–4. The converse is not the case, however, since layers preincubated in Ca2+ for 6 h will not produce all isoenzymes of α-amylase when subsequently incubated in GA3. The Ca2+-stimulated release of α-amylase from GA3 pre-treated layers is dependent on the time of incubation in Ca2+ and the concentration of the ion. The response to Ca2+ is temperature-dependent, and other divalent cations such as Mg2+ cannot substitute for Ca2+. We conclude that Ca2+ influences α-amylase release by influencing events at the biochemical level.  相似文献   

3.
Mammalian cells contain a pool of iron that is not strongly bound to proteins, which can be detected with fluorescent chelating probes. The cellular ligands of this biologically important “chelatable”, “labile” or “transit” iron are not known. Proposed ligands are problematic, because they are saturated by magnesium under cellular conditions and/or because they are not “safe”, i.e. they allow iron to catalyse hydroxyl radical formation. Among small cellular molecules, certain inositol phosphates (InsPs) excel at complexing Fe3+ in such a “safe” manner in vitro. However, we previously calculated that the most abundant InsP, inositol hexakisphosphate, cannot interact with Fe3+ in the presence of cellular concentrations of Mg2+. In this work, we study the metal complexation behaviour of inositol 1,2,3-trisphosphate [Ins(1,2,3)P 3], a cellular constituent of unknown function and the simplest InsP to display high-affinity, “safe”, iron complexation. We report thermodynamic constants for the interaction of Ins(1,2,3)P 3 with Na+, K+, Mg2+, Ca2+, Cu2+, Fe2+ and Fe3+. Our calculations indicate that Ins(1,2,3)P 3 can be expected to complex all available Fe3+ in a quantitative, 1:1 reaction, both in cytosol/nucleus and in acidic compartments, in which an important labile iron subpool is thought to exist. In addition, we calculate that the fluorescent iron probe calcein would strip Fe3+ from Ins(1,2,3)P 3 under cellular conditions, and hence labile iron detected using this probe may include iron bound to Ins(1,2,3)P 3. Therefore Ins(1,2,3)P 3 is the first viable proposal for a transit iron ligand. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

4.
The inositol phosphates are ubiquitous metabolites in eukaryotes, of which the most abundant are inositol hexakisphosphate (InsP 6) and inositol 1,3,4,5,6-pentakisphosphate [Ins(1,3,4,5,6)P 5)]. These two compounds, poorly understood functionally, have complicated complexation and solid formation behaviours with multivalent cations. For InsP 6, we have previously described this chemistry and its biological implications (Veiga et al. in J Inorg Biochem 100:1800, 2006; Torres et al. in J Inorg Biochem 99:828, 2005). We now cover similar ground for Ins(1,3,4,5,6)P 5, describing its interactions in solution with Na+, K+, Mg2+, Ca2+, Cu2+, Fe2+ and Fe3+, and its solid-formation equilibria with Ca2+ and Mg2+. Ins(1,3,4,5,6)P 5 forms soluble complexes of 1:1 stoichiometry with all multivalent cations studied. The affinity for Fe3+ is similar to that of InsP 6 and inositol 1,2,3-trisphosphate, indicating that the 1,2,3-trisphosphate motif, which Ins(1,3,4,5,6)P 5 lacks, is not absolutely necessary for high-affinity Fe3+ complexation by inositol phosphates, even if it is necessary for their prevention of the Fenton reaction. With excess Ca2+ and Mg2+, Ins(1,3,4,5,6)P 5 also forms the polymetallic complexes [M4(H2L)] [where L is fully deprotonated Ins(1,3,4,5,6)P 5]. However, unlike InsP 6, Ins(1,3,4,5,6)P 5 is predicted not to be fully associated with Mg2+ under simulated cytosolic/nuclear conditions. The neutral Mg2+ and Ca2+ complexes have significant windows of solubility, but they precipitate as [Mg4(H2L)]·23H2O or [Ca4(H2L)]·16H2O whenever they exceed 135 and 56 μM in concentration, respectively. Nonetheless, the low stability of the [M4(H2L)] complexes means that the 1:1 species contribute to the overall solubility of Ins(1,3,4,5,6)P 5 even under significant Mg2+ or Ca2+ excesses. We summarize the solubility behaviour of Ins(1,3,4,5,6)P 5 in straightforward plots.  相似文献   

5.
孟令博  赵曼  亢燕  祁智 《西北植物学报》2021,41(10):1681-1690
以羊草幼苗为研究对象,通过调整全营养培养基(CK,0.05 mmol/L Fe2+、0.015 mmol/L Zn2+)中铁或者锌含量设置0、10倍、20倍Fe2+(Zn2+)浓度处理Fe0(Zn0)、Fe10(Zn10)、Fe20(Zn20),以及在高铁培养基中单独添加0.15 mmol/L Zn2+或同时添加10 mmol/L Ca2+、5 mmol/L Mg2+、20 mmol/L K+处理,测定培养6 d后幼苗生长指标和矿质元素含量、以及高铁(Fe20)处理下幼苗根中抗氧化指标和相关基因表达量,探究不同浓度Fe2+、Zn2+对羊草幼苗生长、矿质元素吸收积累及抗氧化指标、基因表达的影响。结果表明:(1)缺锌(Zn0)显著抑制羊草幼苗鲜重的增加和Zn元素的积累,但促进Fe、Mg元素的积累;高浓度锌(Zn10、Zn20)显著促进幼苗叶片生长和Zn元素的积累;缺铁(Fe0)显著抑制幼苗的根长、鲜重和Fe元素的积累,促进Mg、Zn元素的积累;高浓度铁(Fe10、Fe20)显著抑制羊草幼苗根叶生长、根毛发育和Ca、Zn、Mg、K元素的积累。(2)增加Zn2+和Ca2+、Mg2+、K+浓度无法恢复高铁胁迫对幼苗生长的抑制作用。(3)高浓度铁(Fe20)处理羊草幼苗48 h后,根部过氧化物酶、超氧化物歧化酶、过氧化氢酶、抗坏血酸过氧化物酶、谷胱甘肽还原酶活性和丙二醛、抗坏血酸、还原型谷胱甘肽含量显著升高;烟酰胺合成酶基因、过氧化物酶基因表达量显著下调,植物类萌发素蛋白基因表达量显著上调。研究发现,羊草幼苗生长发育和矿质元素积累对环境中Zn2+浓度变化不敏感,却受到环境中高浓度Fe2+的显著抑制,并造成严重的氧化胁迫伤害,这种伤害无法在添加Zn2+或同时添加Ca2+、Mg2+、K+的条件下恢复。  相似文献   

6.
The soluble fraction of a cell-free system from immature seeds of Phaseolus vulgaris L. converts gibberellin A20 (GA20) to GA1 and GA5. It does however not metabolize GA1 and GA29 to GA5, showing that in this system GA20 is converted directly to GA5. The steps from GA20 to GA1 (3-hydroxylation) and from GA20 to GA5 (2 double-bond formation) require oxygen, Fe2+ and -ketoglutarate, and are stimulated by ascorbate. The enzymes catalyzing these conversions bate. The enzymes catalyzing these conversions have properties similar to those of GA oxidases found in Cucurbita maxima and Pisum sativum.Abbreviations GAn gibberellin An - HPLC high-performance liquid chromatography - GC-MS combined gas chromatography-mass spectrometry - TLC thin-layer chromatography - TMSi/TMSi trimethylsilyl ether/trimethylsilyl ester Graduate student, University of Tokyo  相似文献   

7.
Cell-free systems were prepared from germinating seed and seedlings of Phaseolus coccineus. Gibberellin A4 (GA4)-metabolising activity was detected in vitro using preparations from roots, shoots and cotyledons of germinating seed, but only up to 24 h after imbibition. Cell-free preparations from cotyledons converted [3H]GA4 to GA1, GA34, GA4-glucosyl ester and a putative O-glucoside of GA34, and, in addition converted [3H]GA1 to GA8. Preparations from embryo tissues contained 2-hydroxylase activity, converting [3H]GA4 to GA34 and [3H]GA1 to GA8.The presence of GA-metabolising enzymes was also indicated by in-vivo feeds of [3H]GA4 to epicotyls of intact 4-d-old seedlings, which resulted in the accumulation of GA1, GA8, GA3-3-O-glucoside, GA4-glucosyl ester, GA8-2-O-glucoside and a putative O-glucoside of GA34. Gibberellin A1 was the first metabolite detected, 15 min after application of [3H]GA4, but after 24 h most of the label was associated with GA8-2-O-glucoside. Over 90% of the recovered radioactivity was found in the shoot. Within the shoot, movement was preferentially acropetal, and was not dependent upon metabolism of the applied [3H]GA4.Abbreviations DEAE diethylaminoethyl - GAn gibberellin An - GPC gel permeation chromatography - HPLC-RC high performance liquid chromatography-radio counting - S-1 1000·g supernatant - UDP uridine 5-diphosphate  相似文献   

8.
Jajoo  Anjana  Bharti  Sudhakar 《Photosynthetica》2000,37(4):529-535
Cations such as Mg2+ regulate spillover of absorbed excitation energy mainly in favour of photosystem (PS) 2. Effect of low concentration (<10 mM) of the monovalent cation Na+ on chlorophyll (Chl) a fluorescence was completely overridden by divalent cation Mg2+ (5 mM). Based on Chl a fluorescence yield and 77 K emission measurements, we revealed the role and effectiveness of anions (Cl-, SO4 2-, PO4 3-) in lowering the Mg2+-induced PS2 fluorescence. The higher the valency of the anion, the lesser was the expression of Mg2+ effect. Anions may thus overcome Mg2+ effects up to certain extent in a valency dependent manner, thereby diverting more energy to PS1 even in the presence of MgCl2. They may do so by reversing Mg2+-induced changes.  相似文献   

9.
The GA-signal transduction pathways downstream to the Gα protein in rice seedling root were investigated using in-gel kinase assay and in vitro protein phosphorylation techniques with a Gα protein defective mutant, d1. A 50-kDa protein kinase was detected downstream to Gα protein in the membrane fraction of rice seedling roots using an in-gel kinase assay with histone III-S as a substrate. The activity of a 50-kDa protein kinase increased in the wild-type rice by gibberellin (GA3) treatment, but did not change in the d1 mutant. This protein kinase activity was inhibited by the Ca2+ chelator ethyleneglycol-bis-(beta-aminoethylether)-N,N,N 1,N 1-tetraacetic acid (EGTA), protein kinase inhibitors, staurosporine and H7, and calmodulin antagonist, trifluoperazine, suggesting that the 50-kDa protein kinase is a putative plant Ca2+-dependent protein kinase (CDPK). The activity of the 50-kDa putative CDPK reached its highest level at 3 h after GA3 treatment and then gradually declined with time. In order to identify the endogenous substrate for 50-kDa putative CDPK, two-dimensional polyacrylamide gel electrophoresis followed by in vitro protein phosphorylation was carried out. The phosphorylation activity of an endogenous protein PP30, identified as an unknown protein having molecular weight 30 kDa and isoelectric point 5.8 was increased in the wild-type rice by GA3 treatment, compared with the d1 mutant. The addition of GA3 treated membrane fraction, which predominantly represent a 50-kDa putative CDPK further increased the phosphorylation of PP30. Almost similar to GA3 treatment, phosphorylation activity of PP30 was also increased by the treatment with cholera toxin in the wild-type rice but not in d1 mutant. These results suggest that the 50-kDa putative CDPK and an unknown protein, PP30 promoted by GA3 treatment are G-protein mediated in rice seedling roots.  相似文献   

10.
Paramecium tetraurelia responds to extracellular GTP (≥ 10 nm) with repeated episodes of prolonged backward swimming. These backward swimming events cause repulsion from the stimulus and are the behavioral consequence of an oscillating membrane depolarization. Ion substitution experiments showed that either Mg2+ or Na+ could support these responses in wild-type cells, with increasing concentrations of either cation increasing the extent of backward swimming. Applying GTP to cells under voltage clamp elicited oscillating inward currents with a periodicity similar to that of the membrane-potential and behavioral responses. These currents were also Mg2+- and Na+-dependent, suggesting that GTP acts through Mg2+-specific (I Mg) and Na+-specific (I Na) conductances that have been described previously in Paramecium. This suggestion is strengthened by the finding that Mg2+ failed to support normal behavioral or electrophysiological responses to GTP in a mutant that specifically lacks I Mg (``eccentric'), while Na+ failed to support GTP responses in ``fast-2,' a mutant that specifically lacks I Na. Both mutants responded normally to GTP if the alternative cation was provided. As I Mg and I Na are both Ca2+-dependent currents, the characteristic GTP behavior could result from oscillations in intracellular Ca2+ concentration. Indeed, applying GTP to cells in the absence of either Mg2+ or Na+ revealed a minor inward current with a periodicity similar to that of the depolarizations. This current persisted when known voltage-dependent Ca2+ currents were blocked pharmacologically or genetically, which implies that it may represent the activation of a novel purinergic-receptor–coupled Ca2+ conductance. Received: 28 October 1996/Revised: 24 December 1996  相似文献   

11.
Cell-free extracts capable of converting [14C]-labeled gibberellins (GAs) were prepared from spinach (Spinacia oleracea L.) leaves. [14C]-labeled GAs, prepared enzymically from [14C]mevalonic acid, were incubated with these extracts, and products were identified by gas chromatography-mass spectrometry. The following pathway was found to operate in extracts from spinach leaves grown under long day (LD) conditions: GA12 → GA53 → GA44 → GA19 → GA20. The pH optima for the enzymic conversions of [14C]GA53, [14C]GA44 and [14C]GA19 were approximately 7.0, 8.0, and 6.5, respectively. These three enzyme activities required Fe2+, α-ketoglutarate and O2 for activity, and ascorbate stimulated the conversion of [14C]GA53 and [14C]GA19. Extracts from plants given LD or short days (SD) were examined, and enzymic activities were measured as a function of exposure to LD, as well as to darkness following 8 LD. The results indicate that the activities of the enzymes oxidizing GA53 and GA19 are increased in LD and decreased in SD or darkness, but that the enzyme activity oxidizing GA44 remains high irrespective of light or dark treatment. This photoperiodic control of enzyme activity is not due to the presence of an inhibitor in plants grown in SD. These observations offer an explanation for the higher GA20 content of spinach plants in LD than in SD.  相似文献   

12.
Russell L. Jones 《Planta》1980,150(1):70-81
Changes in the level of the endoplasmicreticulum (ER) marker enzyme cytochrome-c reductase (EC 1.6.2.1) were followed with time of imbibition of de-embryonated half-seeds of barley (Hordeum vulgare L.) and the subsequent incubation of their aleurone layers in gibberellic acid (GA3) and H2O. During imbibition there is an increase in the level of cytochrome-c-reductase activity and in the amount of 280-nm absorbance associated with this enzyme. When aleurone layers are incubated for a further 42 h in water, there is a doubling of the cytochrome-c-reductase activity. In GA3, the activity of cytochrome-c reductase reaches a maximum at 24 h of incubation and thereafter falls to below 70% of its level at the beginning of the incubation period. Changes in the cytochrome-c-reductase activity correlate with changes in the fine structure of the aleurone cell. The ER isolated in low Mg2+ from aleurone layers incubated in buffer for up to 18 h has buoyant density of 1.13–1.14 g cc-1 while that from layers incubated in GA3 for 7.5–18 h has a density of 1.11–1.12 g cc-1. The -amylase (EC3.2.1.1) isolated with the organelle fraction by Sepharose gel filtration is associated with the ER on isopycnic and rate-zonal density gradients, and its activity can be enhanced by Triton X-100. The soluble -amylase fraction from Separose-4B columns, on the other hand, is not Triton-activated but is acid-labile. Acid phosphatase (EC3.1.3.2) is distributed in at least three peaks on isopycnic gradients. In low Mg2+ the second peak of activity has a density of 1.12 g cc-1 in GA3-treated tissue and 1.13–1.14 g cc-1 in H2O-treated tissue. With high-Mg2+ buffers, this peak of phosphatase activity disappears. Acid-phosphatase activity is not enhanced by Triton X-100 nor is it acid-labile.Abbreviations EDTA ethylenediaminetetraacetic acid - ER endoplasmic reticulum - GA gibberellin - GA3 gibberellic acid  相似文献   

13.
Two Sites of Hormonal Action during Germination of Chenopodium album Seeds   总被引:3,自引:0,他引:3  
During the overall germination process in the light-requiring seeds of Chenopodium album L. two sites of hormonal action can be distinguished. The start of visible growth is induced in darkness by the gibberellins 4 and 7 (GA4+7) or by ethylene. Added cytokinins are inactive although 8-14C-kinetin shows rapid penetration into the seed and rapid turnover. The induction of growth by GA4+7 and the uptake of 8-methylene-14C-GA3 are enhanced at lower pH values. Prolonged incubation in darkness results in a decreased responsiveness of the seeds towards GA4+7 and ethylene. A second site of hormonal action is located during the progress of growth inside the covering structures. ABA inhibits radicle growth, while GA4+7, GA3, kinetin, zeatin and ethylene reduce the inhibition.  相似文献   

14.
Chlorophyll loss in leaves of cut flowers of alstroemeria (Alstroemeria pelegrina L. cv. Westland) was rapid in darkness and counteracted by irradiation and treatment of the flowers with gibberellic acid (GA3). The mechanism of the effect of GA3 under dark conditions was investigated. The content of various carbohydrates in the leaves under dark conditions rapidly decreased; this was not influenced by treatment with GA3. indicating that the loss of carbohydrates in the leaves did not induce the loss of chlorophyll. Placing the cut flowers in various solutions of organic and inorganic nutrients exhibited no significant effect on the retention of chlorophyll in leaves of dark-senescing flowers. The total nitrogen content in leaves of dark-senescing cut flowers decreased with time. Leaves of GA3-treated flowers retained more nitrogen. In contrast, the buds of GA3-treated flowers retained less nitrogen during senescence in the dark than control buds. To investigate whether GA3 affects export of assimilates from the leaf to various parts of control and GA3-treated flowers, we labelled one leaf with radioactive carbon dioxide. 14C-assimilates accumulated preferentially in the flowers, in which the relative specific activity of the youngest floral buds was highest. No significant differences were observed in the distribution of 14C-labelled compounds between the buds of control and GA3-treated flowers. To establish the importance of source-sink relations for the loss of leaf chlorophyll we removed the flower buds (i. e. the strongest sink) from the cut flowers. This removal only slightly delayed chlorophyll loss as compared to the large delay caused by GA3-treatment. In addition, detached leaf tips exhibited chlorophyll loss in the dark, which was delayed by GA3-treatment in a fashion comparable with that in flowers. Together these data demonstrate that interactions of the leaves with other plant organs are not essential for chlorophyll loss during senescence in the dark. Additionally, we have found no evidence that GA3 delays the loss of chlorophyll by affecting the transport of nutrients within the cut flowers.  相似文献   

15.
The endogenous gibberellins (GAs) from shoots of the GA-insensitive mutant,gai, ofArabidopsis thaliana were analyzed and compared with the GAs from the Landsberg erecta (Ler) line. Twenty GAs were identified in Ler plants by full-scan gas chromatography-mass spectrometry (GC-MS) and Kovats retention indices (KRI's). These GAs are members of the early-13-hydroxylation pathway (GA53, GA44, GA19, GA17, GA20, GA1, GA29, and GA8), the non-3,13-hydroxylation pathway (GA12, GA15, GA24, GA25, GA9, and GA51), and the early-3-hydroxylation pathway (GA37, GA27, GA36, GA13, GA4, and GA34). The same GAs, except GA53, GA44, GA37, and GA29 were detected in thegai mutant by the same methods. In addition, extracts fromgai plants contained GA41 and GA71. Both lines also contained several unknown GAs. In Ler plants these were mainly hydroxy-GA12 derivatives, whereas in thegai mutant hydroxy-GA24, hydroxy-GA25, and hydroxy-GA9 compounds were detected. Quantification of seven GAs by GC-selected ion monitoring (SIM), using internal standards, and comparisons of the ion intensities in the SIM chromatograms of the other thirteen GAs, demonstrated that thegai mutant had reduced levels of all C20-dicarboxylic acids (GA53, GA44, GA19, GA12, GA15, GA24, GA37, GA27, and GA36). In contrast,gai plants had increased levels of C20-tricarboxylic acid GAs (GA17, GA25, and GA41) and of all C19-GAs (GA20, GA1, GA8, GA9, GA51, GA4, GA34, and GA71) except GA29. The 3β-hydroxylated GAs, GA1 and GA4, and their respective 2β-hydroxylated derivatives, GA8 and GA34, were the most abundant GAs found in shoots of thegai mutant. Thus, thegai mutation inArabidopsis results in a phenotype that resembles GA-deficient mutants, is insensitive to both applied and endogenous GAs, and contains low levels of C20-dicarboxylic acid GAs and high levels of C19-GAs. This indicates that theGAI gene controls a step beyond the synthesis of an active GA. Thegai mutant is presumably a GA-receptor mutant or a mutant with a block in the transduction pathway between the receptor and stem elongation. We thank Dr. L.N. Mander, Australian National University, Canberra, for providing [2H]gibberellins, Dr. B.O. Phinney, University of California, Los Angeles, USA for [13C]GA8, and Dr. D.A. Gage, MSU-NIH Mass Spectrometry Facility (grant No. DRR00480), for advice with mass spectrometry. This work was supported by a fellowship from the Spanish Ministry of Agriculture (I.N.I.A.) to M.T., by the U.S. Department of Energy under Contract DE-ACO2-76ERO-1338, and by U.S. Department of Agriculture grant No. 88-37261-3434 to J.A.D.Z.  相似文献   

16.
The effect of NaCl in the culture medium on growth, photosynthesis and cell content of chlorophyll, K+, Na+, Ca2+ and Mg2+ in Euglena gracilis was studied. O2 production, quantum yield of photosystem II (PSII), the non-photochemical quenching of chlorophyll fluorescence (qN) and the chlorophyll alb ratio all diminished by 0.2 M NaCl. Respiration and chlorophyll a and b increased, whereas the photochemical quenching (qp) of chlorophyll fluorescence was not affected by 0.2 M NaCl. Salt stress also induced an increase in cell volume and in K+ and Na+ concentrations, but decreased the concentrations of Ca2+ and Mg2+. Except for a protective effect on O2 production, additional Ca2+ in the culture medium did not attenuate the salt effect on the parameters measured. The addition of HCO3? restored the PSII quantum yield of O2 production in cells grown in high salt. Salt stress promoted a decrease in the apparent rate of quinone A (QA) reduction and an apparent obstruction of QB reduction, which were not prevented by excess HCO3?; the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) did not increase chlorophyll fluorescence in salt-grown cells. These results indicate that photosynthesis in Euglena grown under salt stress exhibits: (1) diminution of the HCO3? dependent water-splitting activity of PSII; (2) inhibition of the electron transfer at the quinone pool level; (3) probable increase in thylakoid stacking (as indicated by the effect on the chlorophyll alb ratio); and (4) dissipation of the H+ gradient across the thylakoid membranes (as indicated by the decrease of qN).  相似文献   

17.
We investigated the photosynthetic characteristics of Chorispora bungeana under conditions of drought stress caused by different concentrations of polyethylene glycol-6000 (PEG; 0, 5, 20, and 40%) and various concentrations of exogenous glycine (0, 5, 10, and 20 mM) with 20% PEG. We showed that moderate and severe drought stress of PEG reduced the chlorophyll (Chl) content (both Chl a and b), maximal quantum yield of PSII photochemistry (Fv/Fm), actual photochemical efficiency of PSII in light (YII), and quantum yield of regulated energy dissipation (YNPQ), while Chl a/b and quantum yield of nonregulated energy dissipation (YNO) increased. The low and moderate drought stress increased Mg2+ and Fe3+ contents, while a decrease in Mg2+ and Fe3+ was found under severe drought stress. Compared to sole PEG stress, the addition of exogenous 10 mM glycine increased Chl, Mg2+ and Fe3+ contents, Fv/Fm, YII, and YNPQ, and reduced YNO. On the contrary, 20 mM glycine showed an opposite effect, except for YNO. Our results proved that Chl contents and fluorescence parameters are reliable indicators for drought tolerance of C. bungeana. We suggest that a proper glycine content can relieve the effect of drought stress on C. bungeana.  相似文献   

18.
Gibberellic acid improves water deficit tolerance in maize plants   总被引:1,自引:0,他引:1  
The combination effects of water stress and gibberellic acid (GA3) on physiological attributes and nutritional status of maize (Zea mays L. cv., DK 647 F1) were studied in a pot experiment. Maize plants were grown in the control (well watered WW) and water stress subjected to treated both water stress and two concentrations of gibberellic acid (GA3 25 mg L−1, 50 mg L−1). WS was imposed by maintaining the moisture level equivalent to 50 % pot capacity whereas the WW pots were maintained at full pot capacity. Water stress reduced the total dry weight, chlorophyll concentration, and leaf relative water content (RWC), but it increased proline accumulation and electrolyte leakage in maize plants and appears to affect shoots more than roots. Both concentrations of GA3 (25 and 50 mg L−1) largely enhanced the above physiological parameters to levels similar to control. WS reduced leaf Ca2+ and K+ concentrations, but exogenous application of GA3 increased those nutrient levels similar or close to control. Exogenous application of GA3 improved the water stress tolerance in maize plants by maintaining membrane permeability, enhancing chlorophyll concentration, leaf relative water content (LRWC) and some macro-nutrient concentrations in leaves.  相似文献   

19.
Transmembrane b-type cytochromes, which are crucially involved in electron transfer chains, bind one or more heme (Fe-protoporphyrin IX) molecules non-covalently. Similarly, chlorophylls are typically also non-covalently bound by several membrane integral polypeptides involved in photosynthesis. While both, chlorophyll and heme, are tetrapyrrole macrocycles, they have different substituents at the tetrapyrrole ring moiety. Furthermore, the central metal ion is Mg2+ in chlorophyll and Fe2+/3+ in heme. As heme and chlorophyll a have similar structures and might both be ligated by two histidine residues of a polypeptide chain, and as the local concentration of chlorophyll a might be up to 100-times higher than the concentration of heme, the question arises, as to how an organism ensures specific binding of heme, but not of chlorophyll, to transmembrane apo-cytochromes involved in photosynthetic electron transfer reactions. As shown here, Fe-protoporphyrin IX derivatives with modified substituents at the tetrapyrrole ring moiety still bind to an apo-cytochrome; however, association appears to be reduced. This indicates that hydrophobic and polar interactions of the ring substituents with the protein moiety stabilize the protein/heme-complex but are not essential per se. However, removal or replacement of the central Fe-ion completely abolishes formation of a holo-protein complex, and thus the central iron ion appears to determine heme binding to apo-cytochrome b6.  相似文献   

20.
We investigated the bioactive potential of fungal endophytes isolated from the roots of Glycine max (L.) Merr. and Cucumis sativus. Initial screening results showed that endophytes, (Chrysosporium pseudomerdarium, Aspergillus fumigates and Paecilomyces sp., Penicillium sp., Phoma glomerata, and Paecilomyces formosus) were promoting the growth attributes (shoot length, chlorophyll contents, and biomass) of mutant and wild-type rice. To know whether, these endophytes were producing bioactive chemical constituents; the endophytes were grown in potato dextrose, czapek broth, and ICI mediums that resulted in varying mycelia biomass. The advance chromatographic analysis of endophytic fungal culture filtrate showed gibberellins (GA) production namely GA1 (0.05–10.55 ngml?1), GA3 (0.48–9.0 ngml?1), GA4 (0.2–8.0 ngml?1), GA7 (1.4–6.5 ngml?1), and GA9 (0.03–1.05 ngml?1) while among endophytes, P. glomerata and P. formosus were highly potent in GAs production. Additionally, the endophyte's culture also contained indole-3-acetic acid (0.23–71.51 µgml?1). Furthermore, oxalic (0.009–0.3 mgl?1), quinic (0.019–0.22 mgl?1), malic (1.94–17.2 mgl?1), and citric (0.012–0.95 mgl?1) acids were also present in the endophytic cultures. The biochemical potential of endophytes greatly varied depending on nutrient source and pH, however, czapek broth rich in carbon revealed higher potential for bioactive chemical constituent's production. In conclusion, the current findings suggest that endophyte can play a vital role in essential crop plant growth by synthesizing a wide array of bioactive metabolites. Furthermore, an increased production of chemical constituents can be achieved by changing the in vitro growth conditions of endophytes  相似文献   

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