碳酸氢钾对大豆幼苗光合作用的影响

研究喷洒碳酸氢钾(KHCO3)对大豆幼苗叶片光合作用影响的结果表明,喷施KHCO3的大豆幼苗光合速率和核酮糖.1,5二磷酸羧化/氧化酶(Rubisco)羧化活性提高,加氧酶活性下降,PSI、PSII和光合电子传递速率均提高,光合色素含量也增加.     

锶对油菜幼苗叶片光合作用的影响

锶对植物光合作用影响尚未见系统研究报道。通过叶绿素荧光诱导动力学和光合气体交换参数详细研究了不同浓度的锶(1、5、10和20 mmol·L^–1SrCl₂)对油菜(Brassica napus)叶片光合作用的影响。荧光诱导动力学分析结果表明, 光系统II(PSII)的潜在活性(F_v/F_o)、实际光化学效率(Y(II))、表观光合电子传递速率(ETR)和光化学淬灭(qP)在低浓度(1和5 mmol·L^–1)锶处理时显著上升, 在高浓度(10和20 mmol·L^–1)锶处理时显著下降; 初始荧光强度(F_o)和非光化学淬灭(NPQ)在低浓度锶处理时变化不明显, 但在高浓度下显著上升。光合气体交换参数分析结果表明, 叶片的净光合速率(P_n)、蒸腾速率(T_r)在低浓度锶处理时显著上升, 而在高浓度锶处理时显著下降; 气孔导度(G_s)随锶处理浓度的增加一直呈显著下降趋势; 胞间CO₂浓度(C_i)在低浓度锶处理时轻微下降, 高浓度锶处理时显著增加。此外, 叶绿素含量在低浓度锶处理时显著增加, 在高浓度处理时则显著下降。这些结果均表明, 低浓度锶处理可以改善油菜叶片的光合功能, 增加叶片光合效率; 而高浓度锶则会妨碍叶片光合功能, 导致光合效率显著下降。     

低浓度NaHSO3处理对温室黄瓜光合作用的影响

为探讨低浓度亚硫酸盐对于黄瓜光合作用的影响及其机制,在温室栽培条件下,以黄瓜品种Deltastar 为试材,采用低浓度的NaHSO3溶液喷施处理不同生育期的黄瓜叶片.结果表明:低浓度NaHSO3可以提高温室黄瓜叶片的光合速率.温室黄瓜NaHSO3处理的适宜浓度为2.0 mmol/L左右,在黄瓜苗期和开花结瓜期喷施低浓度NaHSO3溶液均可提高黄瓜叶片的光合速率,并能持续作用3 d左右.与对照(喷水)相比,2.0 mmoL/L NaHSO3处理提高黄瓜功能叶片光合速率20%左右,且与已知的促进循环光合磷酸化的辅助因子PMS的作用类似,其增加了ATP的供应,而并非影响叶片叶绿素PSⅡ的光化学效率.文章还对设施内光照不足情况下NaHSO3的应用进行了讨论.     

汞胁迫对白骨壤(Avicennia marina)幼苗生理生态的影响

为了解红树植物的重金属抗性机制,对白骨壤(Avicennia marina)幼苗进行不同浓度Hg2+(1、5、10、50、100 mg·L-1)的胁迫实验,测定并分析了Hg2+胁迫对白骨壤幼苗叶片的光合作用和抗氧化酶活性的影响.结果表明:叶片净光合速率随着胁迫时间的延长而降低,高浓度(≥150 mg·L-1)Hg2+胁迫下叶片的净光合速率低于中低浓度胁迫,且高浓度胁迫的叶片净光合速率在48 h后快速下降;叶片净光合速率与胞间二氧化碳浓度呈极显著负相关,叶绿素含量随Hg2+浓度的增加而降低.气孔导度在不同浓度胁迫下反应不同,低浓度Hg2+对白骨壤幼苗光合的影响可能是气孔因素,中高浓度Hg2+对白骨壤幼苗光合作用的抑制主要是非气孔因素.低浓度Hg2+胁迫,白骨壤幼苗叶片SOD、POD活性升高,表现了一定的抗逆性,而高浓度表现为抑制作用,基本在100 mg·L-1 Hg2+胁迫下活性达到最低值.说明Hg2+可以抑制白骨壤叶片的光合活性,高浓度Hg2+胁迫削弱了白骨壤的活性氧清除能力,植物极易受到伤害.     

不同光照强度下三角叶滨藜光合作用对盐激胁迫的响应

以溶液培养的三角叶滨藜植株为材料研究了不同光照条件下其叶片光合作用对盐(NaCl)激胁迫的即刻反应及变化规律.结果表明,三角叶滨藜光合作用对盐激胁迫的响应有8 min左右的滞后期.在光照强度为100umol·m-2·-1和100 mmol·L-1浓度NaCl共同作用下,三角叶滨藜叶片净光合速率略有上升;但随NaCl浓度和光照强度进一步增加,其净光合速率呈下降趋势,且光照越强,盐胁迫导致的净光合速率下降幅度越大.同时,弱光下或强光低浓度NaCl胁迫下,盐激胁迫导致的净光合速率下降主要是气孔限制引起的;而强光下,高浓度的NaCl胁迫导致的净光合速率下降在盐激胁迫处理的前30-40 min主要由气孔限制引起.40 min后则主要由非气孔限制引起.可见,不同光照强度和NaCl浓度胁迫下三角叶滨藜叶片光合作用响应规律不同,引起净光合速率下降机制各异.     

低浓度硫酸甲酯吩嗪（PMS）对叶片光合放氧的促进作用

外加低浓度循环光合磷酸化电子递体硫酸甲酯吩嗪(PMS)对菠菜、大豆、水稻和小麦叶片光合放氧有促进作用,与此同时叶片ATP含量也得到增加。PMS对经8 mmol L~(-1)NH_4Cl处理过的菠菜叶片的光合放氧也有促进,最适促进浓度比未经NH_4Gl处理的叶片高,促进的幅度也大。幼龄叶与成长叶相比,幼龄叶的光合磷酸化活性和P/O比值低于成长叶片,其光合放氧速率受PMS促进的幅度大于成长叶片。因此光合磷酸化也可以成为光合作用的一个重要限制因素。     

光合产物水平与光合机构运转关系的探讨

在作了增加或减少光合产物含量的处理之后测定了菠菜叶片的净光合作用速率及其离体叶绿体的希尔反应、光合磷酸化与碳固定活力和叶片的蔗糖、淀粉含量。 光合产物的短期(6小时)积累对叶片的净光合作用速率和离体叶绿体的 CO_2固定没有明显影响。但是,处理叶片离体叶绿体的光合磷酸化活力往往稍低于对照。光合产物的较长期(3～5天)积累引起叶片净光合作用速率、离休叶绿体的希尔反应、光合磷酸化和碳固定活力的明显下降,而处理叶片的呼吸速率比对照增加二倍多。由遮阴而引起光合产物亏缺后,叶片净光合作用速率和离体叶绿体希尔反应、光合磷酸化活力也下降。在遮阴时将离体叶片的叶柄插在0.1M的蔗糖溶液中,其后来的净光合作用速率比叶柄插在水中的对照提高20％之多。 叶片光合产物含量与净光合作用速率之间的关系,可以用一条钟罩形的曲线来表示。当光合产物含量远低于或高于一个最适值时,光合产物水平与净光合速率之间分别有正相关或负相关;而当光合产物含量处于这个最适值附近的一定范围内时,似乎没有仟么明显的相关。这种曲线可以解释其他作者获得的许多相互矛盾的结果。     

光照下菜豆叶片抗氰呼吸与光合作用关系的分析北大核心CSCD

为了进一步了解光照下植物呼吸作用的内在机理以及呼吸作用和光合作用的关系,该文研究了在光照下菜豆(Phaseolus vulgaris)叶片抗氰呼吸与光合作用的关系。研究发现,将黑暗下生长的菜豆幼苗叶片转到光照下10 h,总呼吸、抗氰呼吸以及抗氰呼吸在总呼吸中的比例均逐步上升;光照也导致了叶片叶绿体光合放氧和CO2固定的出现及其速率的增加,但光合放氧和CO2固定速率的增加均滞后于抗氰呼吸的增加。将黑暗下生长的叶片转到光照下之前用抗氰呼吸的抑制剂水杨基氧肟酸(SHAM)处理叶片,发现用SHAM处理并没有导致叶片在光照下光合放氧和CO2固定速率的明显变化,这也提示了黑暗下生长的叶片转至光照的过程中,抗氰呼吸和光合作用没有产生偶联。进一步研究发现,在黑暗中对叶片施加短时间的光照能够增加抗氰呼吸在总呼吸中的比例,但短时间的光照对叶片光合CO2固定速率没有影响。这些结果表明了光照对抗氰呼吸的诱导可以不依赖于光合作用,光照可能是作为一种直接的信号去诱导抗氰呼吸。     

一氧化氮对杨树耐旱性的影响

探讨了外源NO对水分胁迫下杨树叶片质膜相对透性、叶片光合作用和氧化伤害保护酶的影响.结果表明,NO供体硝普钠(sodiumnitroprusside,SNP)能提高杨树叶片的含水率,在水分胁迫(PEG6000渗透液处理)下,能缓解叶片的水分丢失.NO对杨树叶片光合作用具有双重性,低浓度SNP(200、500μmol·L^-1)能促进叶片的光合,高浓度SNP(1000、2000μmol·L^-1)则明显抑制叶片的光合.较短时间水分处理胁迫(1h))的杨树叶片SOD和POD活性显著高于较长时间(3h)水分胁迫下叶片的酶活性.经SNP处理后,各处理组POD、SOD活性明显上升.同时,随SNP浓度的增加,POD和SOD活性表现出先上升后下降的趋势.外源NO可通过诱导POD和SOD活性的上升,延缓活性氧的积累,从而减轻水分胁迫对杨树的伤害,增强树木的耐旱能力.     

光照下菜豆叶片抗氰呼吸与光合作用关系的分析

为了进一步了解光照下植物呼吸作用的内在机理以及呼吸作用和光合作用的关系, 该文研究了在光照下菜豆(Phaseolus vulgaris)叶片抗氰呼吸与光合作用的关系。研究发现, 将黑暗下生长的菜豆幼苗叶片转到光照下10 h, 总呼吸、抗氰呼吸以及抗氰呼吸在总呼吸中的比例均逐步上升; 光照也导致了叶片叶绿体光合放氧和CO₂固定的出现及其速率的增加, 但光合放氧和CO₂固定速率的增加均滞后于抗氰呼吸的增加。将黑暗下生长的叶片转到光照下之前用抗氰呼吸的抑制剂水杨基氧肟酸(SHAM)处理叶片, 发现用SHAM处理并没有导致叶片在光照下光合放氧和CO₂固定速率的明显变化, 这也提示了黑暗下生长的叶片转至光照的过程中, 抗氰呼吸和光合作用没有产生偶联。进一步研究发现, 在黑暗中对叶片施加短时间的光照能够增加抗氰呼吸在总呼吸中的比例, 但短时间的光照对叶片光合CO₂固定速率没有影响。这些结果表明了光照对抗氰呼吸的诱导可以不依赖于光合作用, 光照可能是作为一种直接的信号去诱导抗氰呼吸。     

Synthesis and hydrolysis of ATP by intact chloroplasts under flash illumination and in darkness

ATP concentrations were measured in isolated intact spinach chloroplasts under various light and dark conditions. The following results were obtained: (1) Even in darkened chloroplasts and in the absence of exogenous substrates, ATP levels in the chloroplast stroma were significant. They decreased on addition of glycerate, phosphoglycerate or dihydroxyacetone phosphate. When dihydroxyacetone phosphate and oxaloacetate were added together, ATP levels increased in darkened chloroplasts owing to substrate level phosphorylation. (2) Under illumination with saturating single turnover flashes, oxygen evolution in the presence of phosphoglycerate, whose reduction requires ATP, was no lower on a unit flash basis at the low flash frequency of 2 Hz than at higher frequencies. Quenching of 9-aminoacridine fluorescence, which indicates the formation of a proton gradient in intact chloroplasts, decreased with decreasing flash frequencies, until there was no significant fluorescence quenching at a flash frequency of about 2 Hz. In contrast to intact chloroplasts, broken chloroplasts did not phosphorylate much ADP at the low flash frequency of 2 Hz. (3) Flashing at extremely low frequencies (0.2 Hz) caused ATP hydrolysis rather than ATP synthesis in intact chloroplasts. At higher flash frequencies, synthesis replaced hydrolysis. Still, even at high frequencies (10 Hz), the first flashes of a series of flashes given after a long dark time always decreased chloroplast ATP levels.From these results, it is concluded that the enzyme, which mediates ATP synthesis in the light, is inactive in darkened intact chloroplasts. Its light activation can be separated from the formation of the high energy condition, which results in ATP synthesis. After its activation, the enzyme catalyzes a reversible reaction.     

Synthesis and hydrolysis of ATP by intact chloroplasts under flash illumination and in darkness.

ATP concentrations were measured in isolated intact spinach chloroplasts under various light and dark conditions. The following results were obtained: (1) Even in darkened chloroplasts and in the absence of exogenous substrates, ATP levels in the chloroplast stroma were significant. They decreased on addition of glycerate, phosphoglycerate or dihydroxyacetone phosphate. When dihydroxyacetone phosphate and oxaloacetate were added together, ATP levels increased in darkened chloroplasts owing to substrate level phosphorylation. (2) Under illumination with saturating single turnover flashes, oxygen evolution in the presence of phosphoglycerate, whose reduction requires ATP, was no lower on a unit flash basis at the low flash frequency of 2 Hz than at higher frequencies. Quenching of 9-aminoacridine fluorescence, which indicates the formation of a proton gradient in intact chloroplasts, decreased with decreasing flash frequencies, until there was no significant fluorescence quenching at a flash frequency of about 2 Hz. In contrast to intact chloroplasts, broken chloroplasts did not phosphorylate much ADP at the low flash frequency of 2 Hz. (3) Flashing at extremely low frequencies (0.2 Hz) caused ATP hydrolysis rather than ATP synthesis in intact chloroplasts. At higher flash frequencies, synthesis replaced hydrolysis. Still, even at high frequencies (10 Hz), the first flashes of a series of flashes given after a long dark time always decreased chloroplast ATP levels. From these results, it is concluded that the enzyme, which mediates ATP synthesis in the light, is inactive in darkened intact chloroplasts. Its light activation can be separated from the formation of the high energy condition, which results in ATP synthesis. After its activation, the enzyme catalyzes a reversible reaction.     

Role of the gamma subunit of chloroplast coupling factor 1 in the light-dependent activation of photophosphorylation and ATPase activity by dithiothreitol

In leaves and intact chloroplasts, oxidation and reduction have been shown previously to regulate the ATPase activity of thylakoids. Illumination of spinach chloroplast thylakoids in the presence of dithiothreitol, which activates the ability of thylakoids to catalyze sustained ATP hydrolysis in the dark, causes increased incorporation of N-ethylmaleimide into the gamma subunit of coupling factor 1 (CF1). A disulfide bond in the gamma subunit is reduced during activation. The residues involved in this disulfide bond are the same as those in the disulfide linkage reduced during dithiothreitol activation of soluble CF1. The disulfide and dithiol forms of the gamma subunit may be separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. N-Ethylmaleimide is preferentially incorporated in the dark into the reduced form of the gamma subunit of CF1 in thylakoids previously exposed to dithiothreitol. Only a subpopulation of the CF1 in thylakoids is susceptible to dithiothreitol reduction and subsequent reaction with N-ethylmaleimide in the dark. Alkylation of the thiol groups exposed by reduction of the disulfide bond protects ATPase activity from inhibition by oxidants. At a given value of the transmembrane pH differential, photophosphorylation rates in dithiothreitol-activated thylakoids can be as much as seven to eight times those of nonactivated controls. N-Ethylmaleimide treatment of activated thylakoids in the dark prevents the loss of the stimulation of ATP synthesis on storage of the thylakoids. Photophosphorylation by intact chloroplasts lysed in assay mixtures is also activated in comparison to that by washed thylakoids. At a low ADP concentration, the rate of photophosphorylation approaches saturation as delta pH increases. These results suggest that the gamma subunit of CF1 plays an important role in regulation of ATP synthesis and hydrolysis.     

Studies on photophosphorylation utilizing methylene diphosphonate analogs of ADP and ATP.

Spinach chloroplasts were able to photophosphorylate the ADP analog alpha,beta-methylene adenosine 5'-diphosphate (AOPCP). Phosphorylation of AOPCP was catalyzed by chloroplasts that were washed or dialyzed to remove free endogenous nucleotides. In the presence of glucose, hexokinase, AOPCP and 32Pi, the 32P label was incorporated into alpha,beta-methylene adenosine 5'-triphosphate (AOPCPOP). In contrast to photophosphorylation of AOPCP, the ATP analog AOPCPOP was a poor substrate for the ATP-Pi exchange reaction and its hydrolysis was neither stimulated by light and dithiothreitol nor inhibited by Dio-9. Photophosphorylation of AOPCP was inhibited by the alpha,beta- and beta,gamma-substituted methylene analogs of ATP, while phosphorylation of ADP was unaffected by them. The ATP-Pi exchange was also unaffected by both ATP analogs, while the weak AOPCPOP-Pi exchange was inhibited by the beta,gamma-methylene analog of ATP. Direct interaction of methylene analogs with the chloroplast coupling factor ATPase was indicated by the enzymatic hydrolysis of AOPCPOP on polyacrylamide gels.     

Decay of membrane potential under phosphorylating conditions in chloroplasts with in vivo activated ATPase

(1) The relation between the membrane potential and phosphorylation was studied in chloroplasts rapidly prepared from illuminated spinach leaves (light chloroplasts) and from dark-adapted leaves (dark chloroplasts). Light chloroplasts had a higher ATP hydrolysis activity than dark chloroplasts. (2) In the presence of ADP or ATP, a rapidly decaying phase of the field-indicating 518 nm absorbance change with a half-time of 15 ms became apparent in addition to the slow phase with a half-time of more than 300 ms in either type of chloroplast. Under these conditions, light chloroplasts showed a larger rapid phase than dark chloroplasts. (3) The rapid phase was suppressed by dicyclohexylcarbodiimide and was assumed to reflect the dissipation of membrane potential due to proton movements inside the CF₁-CF₀ ATP synthetase. (4) A model for the proton movement in ATP synthetase is proposed.     

Studies on the relation between the fast phase of millisecond delayed light emission and the proton released from oxidation of water in spinach chloroplast

The relation between the fast phase of ms-DLE (delayed light emission measured with a phosphoroscope) and the proton released from water oxidation in spinach chloroplasts was studied in several aspects. When photophosphorylation was allowed to be coupled to the Hill reaction the intensity of the fast phase of ms-DLE of chloroplast was lowered more at 1 °C than at 25 °C, and the photophosphorylation rate within 40 ms of flashing light was higher at 1 °C than at 25 °C. Adding the subunit of ATP synthase to the chloroplast preparation to block the leakage of protons through ATP synthase, the intensity of the fast phase of ms-DLE was enhanced, to a larger extent at 1 °C than at 25°C. When the ms-DLE was measured under isotonic conditions, the intensity of fast phase of ms-DLE enhanced by proton released from oxidation of water was more pronounced. The above results support the suggestion that under lower temperature and isotonic conditions, the proton released from water oxidation was liable to be localized and could enhance the intensity of the fast phase of ms-DLE more effectively.     

Thiol modulation of the chloroplast ATP synthase is dependent on the energization of thylakoid membranes

Thiol modulation of the chloroplast ATP synthase γ subunit has been recognized as an important regulatory system for the activation of ATP hydrolysis activity, although the physiological significance of this regulation system remains poorly characterized. Since the membrane potential required by this enzyme to initiate ATP synthesis for the reduced enzyme is lower than that needed for the oxidized form, reduction of this enzyme was interpreted as effective regulation for efficient photophosphorylation. However, no concrete evidence has been obtained to date relating to the timing and mode of chloroplast ATP synthase reduction and oxidation in green plants. In this study, thorough analysis of the redox state of regulatory cysteines of the chloroplast ATP synthase γ subunit in intact chloroplasts and leaves shows that thiol modulation of this enzyme is pivotal in prohibiting futile ATP hydrolysis activity in the dark. However, the physiological importance of efficient ATP synthesis driven by the reduced enzyme in the light could not be demonstrated. In addition, we investigated the significance of the electrochemical proton gradient in reducing the γ subunit by the reduced form of thioredoxin in chloroplasts, providing strong insights into the molecular mechanisms underlying the formation and reduction of the disulfide bond on the γ subunit in vivo.     

The involvement of stromal ATP in maintaining the pH gradient across the chloroplast envelope in the light

The possible involvement of ATP in maintaining the pH gradient across the chloroplast envelope membrane was investigated by simultaneously measuring the stromal ATP concentration and the pH of the stroma and intrathylakoid spaces in intact isolated chloroplasts. Addition of exogenous ATP in the dark increased stromal pH by 0.3–0.4 pH units and increased the pH gradient across the thylakoid membrane by a similar amount. In the dark, dihydroxyacetone phosphate plus oxaloacetate increased stromal ATP to levels equal to those obtained in illuminated chloroplasts, but stromal pH was only increased by 0.1–0.3 pH units compared to an increase of 0.8–1.0 units in the light. The energy-transfer inhibitor, phlorizin, decreased stromal ATP in illuminated chloroplasts almost to dark levels, but did not decrease stromal pH. Inorganic pyrophosphate and an analog of ATP were used to exchange endogenous adenine nucleotides out of chloroplasts, and this also decreased the stromal ATP to dark levels without decreasing stromal pH in the light. Addition of 15–20 μM 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU) reduced both the stromal pH and ATP content of illuminated chloroplasts to dark levels but lower concentrations of DCMU preferentially decreased stromal pH. It is concluded that the pH gradient across the chloroplast envelope is unlikely to be maintained by an electrogenic proton pump driven by ATP hydrolysis. Photosynthetic electron transport is required to maintain the pH gradients across both the chloroplast thylakoid and chloroplast envelope membranes.     

Studies on photophosphorylation II. Uncoupling of chloroplasts by anions at low temperatures and at acidic pH values

Photophosphorylation of spinach chloroplasts was uncoupled bypreincubation at 0°C in the presence of a neutral salt atpH 6.0 to 6.5 ("cold-anion uncoupling"). Preincubation at 20°Ccaused some depression in both photophosphorylation and theHill reaction, but the efficiency of photophosphorylation wasnot depressed much. Low pH values accelerated uncoupling. Theeffectiveness of anions tested as sodium salts in inducing uncouplingwas of the order: SCN->>NO₃^–>Cl^–>SO₄^2–There was little difference in effectiveness among monovalentcations; LiCl, NaCl, KCl, RbCl and CsCl. 10^–4M ATP orADP largely protected chloroplasts from cold-anion uncoupling.Addition of EDTA-extract or dicyclohexylcarbodiimide to uncoupledchloroplasts partially restored photophosphorylation. Theseobservations suggest that inactivation of chloroplast ATPaseis one cause of cold-anion uncoupling. At low light intensities, the time lag and the depression ofthe efficiency of photophosphorylation were more pronouncedin cold-anion uncoupled chloroplasts than in the control chloroplasts. (Received February 15, 1972; )