Influence of high light and UV-B radiation on photosynthesis and D1 turnover in atrazine-tolerant and -sensitive cultivars of Brassica napus

An atrazine-tolerant mutant and an atrazine-sensitive cultivar of Brassica napus L. were grown under visible radiation (400 mumol m-2 s-1, photosynthetically active radiation, PAR) and then subjected to treatment conditions. These included short-term high PAR (1600 mumol m-2 s-1) which was given for 4 h either alone or in combination with an enhanced level of UV-BBE radiation (4.6 kJ m-2 h-1 biologically effective UV-B, 280-320 nm). Recovery from the radiation treatment was studied for 4 h under the light conditions for growth. Since it is known that the atrazine-tolerant mutant is susceptible to photoinhibition, one of the aims of the present study was to determine the effects of a supplemental, enhanced level of UV-B radiation with regard to the mutant. The results indicate an additive effect of UV-B radiation on Fv/Fm, photochemical yield and photosynthetic oxygen evolution during both exposure and recovery, and also a higher susceptibility of the mutant to photoinhibitory PAR conditions alone and in combination with UV-B, which may have implications in a changing environment. Both cultivars also showed a higher D1 turnover during the radiation stress than during recovery, as shown by immunoblotting and 35S-methionine incorporation measurements.     

Site-specific mutations localized in the D-E loop of the D1 protein of photosystem II affect phototolerance in Synechocystis sp. PCC 6803 containing psbAII gene

Photosynthetic characteristics along with phototolerance and photoinhibition of photosystem II (PS II) were monitored in Synechocystis sp. PCC 6803 wild type (KC) and its psbAII mutants viz., I6 (N322I, I326F, and F328S), G6 (N267Y), and H7 (Y254C and I314V) that have up to three point mutations, localized in the D-E loop of the D1 polypeptide of PSII reaction centre. These strains exhibited entirely different growth trends upon shifting from 30 micormol m(-2)s(-1) to high irradiance (500 micromol m(-2)s(-1) , 30 degrees C). The I6 and H7 cells grew well, whereas KC and G6 cells showed inability for cell multiplication. The photosynthetic efficiency demonstrated about 50% loss in chlorophyll fluorescence of variable yield (Fv/Fm) within 20-30 min in all mutants, whereas the wild type (KC) cells could reach the same level of loss in 2 hr. I6 and H7 cells showed continuous cell growth and maintenance under long-term exposure of high light compared to G6 mutant and wild type cells. The wild type cells showed slow decrease in their photochemical activity and Fv/Fm values, compared to mutant cells. The recovery seemed to be almost identical, and also stimulated by growth light, inspite of differential photoinhibitory behaviours. Darkness and translational inhibitor lincomycin both were found to be unassociated with the restoration of photoinhibited process of PS II.     

Photoinhibition of Photosynthesis Without Net Loss of D1 Protein in Wheat Leaves Under Field Conditions

To determine whether the net loss of D1 protein is the main cause of photoinhibition of photosynthesis in wheat leaves under field conditions in the absence of any environmental stress other than strong sunlight, the D1 protein content, photosynthetic evolution of oxygen and chlorophyll a fluorescence parameters were measured in field grown wheat leaves. After exposure to midday strong light for about 3 h, apparent photosynthetic quantum efficiency (Φ), Fv/Fm and Fo in wheat leaves declined, and these parameters recovered almost completely 1 h after transfer to the weak light of 30~40 ttmol photons · m-2 · s-1. No evident change in the D1 protein content was observed in the leaves after exposure to midday strong light for 3 h. After 3 hours exposure to strong light, the slow-relaxed fluorescence quenching in the leaves treated with streptomycin (SM) increased much more than that in the control leaves, but there was no effect SM on the recovery of Fv/Fm and F0; dithiothretol (DTT) treatment enhanced photoinhibition of photosynthesis and reduced the D1 protein content in the leaves after exposure to midday strong light. These results indicated that under field conditions with no environmental stress other than strong sunlight, photoinhibition of photosynthesis in wheat leaves was not due to the net loss of D1 protein, and it could be attributed mainly by the increased nonradiative energy dissipation.     

转C4光合酶基因水稻的CO2交换和荧光特性

用转PEPC、PPDK、NADP-ME、PEPC+PPDK酶基因水稻(Oryza sativa L.)及原种为材料 ,研究了光合作用对光照、温度、CO2的响应和光抑制条件下的叶绿素荧光特性,结果如下: 1.转C4光合酶基因水稻的饱和光合速率比原种高,其中转PEPC、PEPC+PPDK双基因水稻的光饱和点比原种高200 μmol*m-2*s-1,饱和光合速率比原种分别高51.6%和 58.5%;转PEPC基因水稻的羧化效率比原种高49.3%,CO2补偿点降低26.2%;在高温(35 ℃)下,转PEPC基因水稻的光合速率比原种高17.5%.2.经光抑制处理8 d后,转PEPC、PEPC +PPDK酶基因水稻的PSⅡ光化学效率(Fv/Fm)和光化学猝灭(qP)下降20%- 30%,非光化学猝灭(qN)增加了约30%;但原种的Fv/Fm和qP下降了5 0%多,qN变化不明显,表明转C4光合基因水稻耐光抑制能力增强.这些结果为用生物技术提高水稻光合效率研究提供了新的依据和途径.     

In vivo quality control of photosystem II in cyanobacteria Synechocystis sp. PCC 6803: D1 protein degradation and repair under the influence of light, heat and darkness

The cells of Synechocystis sp. PCC 6803 were subjected under photoinhibitory irradiation (600 micromolm(-2)s(-1)) at various temperatures (20-40 degrees C) to study in vivo quality control of photosystem II (PSII). The protease biogenesis and its consequences on photosynthetic efficiency (chlorophyll fluorescence ratio Fv/Fm) of the PSII, D1 degradation and repair were monitored during illumination and darkness. The loss in Fv/Fm value and degradation of D1 protein occurred not only under high light exposure, but also continued when the cells were subjected under dark restoration process after high light exposure. No loss in Fv/Fm value or D1 degradation occurred during recovery under growth/low light (30 micromol m(-2) s(-1)). Further, it helped the resynthesis of new D1 protein, essential to sustain quality control of PSII. In vivo triggering of D1 protein required high light exposure to switch-on the protease biosynthesis to maintain protease pool which induced temperature-dependent enzymatic proteolysis of photodamaged D1 protein during photoinhition and dark incubation. Our findings suggested the involvement and overexpression of a membrane-bound FtsH protease during high light exposure which caused degradation of D1 protein, strictly regulated by high temperature (30-40 degrees C). However, lower temperature (20 degrees C) prevented further loss of photoinhibited PSII efficiency in vivo and also retarded temperature-dependent proteolytic process of D1 degradation.     

干旱胁迫和CO2浓度升高条件下白羊草的光合特征

采用盆栽控制试验,研究了黄土丘陵区乡土种白羊草在不同水分水平(80%FC和40%FC)和CO₂浓度(375和750 μmol·m^-2·s^-1) 处理下的光合生理变化特征.结果表明： 干旱胁迫使白羊草的最大净光合速率(P_nmax)、表观量子效率(AQE)、气孔导度(g_s)、蒸腾速率(T_r)、最大光化学效率(F_v/F_m)、潜在光化学效率(F_v/F_o)和光合色素含量降低,丙二醛(MDA)和脯氨酸(Pro)含量升高.水分充足条件下,与正常大气CO₂浓度相比,大气CO₂浓度倍增下白羊草的P_{n max}、MDA和Pro含量无显著差异.干旱胁迫下,CO₂浓度升高提高了白羊草的最大荧光(F_m)、F_v/F_m、F_v/F_o、叶绿素含量和AQE, P_nmax比正常CO₂浓度下高23.3%,差异达到显著水平,而MDA和Pro含量均显著降低.CO₂浓度升高对干旱胁迫引起的白羊草光合能力下降有一定的补偿作用,减轻了干旱胁迫对白羊草的伤害.     

苋菜的光合特性

宽菜Amaranthus cruentus cv.生长在调控的温室条件。在光强0至800μmol.m~(-2)S~(-1),光合速率(PN,μmol.CO_2m~(-2)、s~(-1))随光强(PFD,μmol、m~(-2)、s~(-1))增高而增大,其关系为PN=56.82 PFD×10~(-3)—2.13。光补偿点为60μmol.m~(-2)、s~(-1)。叶片在1400 μmol.m~(-2)、s~(-1)达到光合光饱和点。在叶温35℃,叶片/空气水蒸汽压陡度20 m Pa、Pa~(-1)和外界CO_2浓度340μ1、1~(-1),光饱和光合速率为51.63±4.90μ mol.CO_2、m~(-2)、S~(-1)。在光强0至600μmol.m~(-2)、s~(-1),气孔传道率随光强增高而增大。光强高于600μmol.m~(-2)、s~(-1),气孔传道率变化较小。细胞间CO_2浓度为120μ1.1~(-1)由于细胞间CO_2浓度在光合速率——CO_2关系曲线的转折点,可能表明光合作用不受气孔限制。结果表明,苋菜适于高光强环境生长,在干旱条件下具有高的光合速率。     

Post-illumination-related loss of photochemical efficiency of Photosystem II and degradation of the D1 protein are temperature-dependent

Photosystem II (PSII) photochemical efficiency (chlorophyll fluorescence ratio Fv/Fm) was recorded in vivo in Synechocystis 6803 during high light illumination and during a subsequent shift of the cells to darkness. A continuing decrease in the Fv/Fm ratio was observed even after the cells were transferred to darkness, provided the temperature was high enough. The decrease in the PSII efficiency after the shifting of the cells to darkness correlated directly with the loss of the D1 protein under different temperatures, suggesting that temperature-dependent proteolysis of the D1 protein in darkness induces the loss of PSII photochemical efficiency under these conditions. Furthermore, the amount of FtsH protease was found to increase during the high light treatment. This observation suggests that the synthesis of the FtsH protein is a light-regulated process and that this protease most probably has a key role in an efficient degradation of the D1 protein even under post-illuminative conditions, provided the temperature is high enough to prevent the initial reversible steps of photoinhibition.     

Blue light and phytochrome-mediated stomatal opening in the npq1 and phot1 phot2 mutants of Arabidopsis

Recent studies have shown that blue light-specific stomatal opening is reversed by green light and that far-red light can be used to probe phytochrome-dependent stomatal movements. Here, blue-green reversibility and far-red light were used to probe the stomatal responses of the npq1 mutant and the phot1 phot2 double mutant of Arabidopsis. In plants grown at 50 micromol m-2 s-1, red light (photosynthetic)-mediated opening in isolated stomata from wild type (WT) and both mutants saturated at 100 micromol m-2 s-1. Higher fluence rates caused stomatal closing, most likely due to photo-inhibition. Blue light-specific opening, probed by adding blue light (10 micromol m-2 s-1) to a 100 micromol m-2 s-1 red background, was found in WT, but not in npq1 or phot1 phot2 double mutant stomata. Under 50 micromol m-2 s-1 red light, 10 micromol m-2 s-1 blue light opened stomata in both WT and npq1 mutant stomata but not in the phot1 phot2 double mutant. In npq1, blue light-stimulated opening was reversed by far-red but not green light, indicating that npq1 has a phytochrome-mediated response and lacks a blue light-specific response. Stomata of the phot1 phot2 double mutant opened in response to 20 to 50 micromol m-2 s-1 blue light. This opening was green light reversible and far-red light insensitive, indicating that stomata of the phot1 phot2 double mutant have a detectable blue light-specific response.     

两种匍灯藓属植物夏季和冬季光合特性的比较研究

分别对生长于冬季和夏季的五倍子蚜虫冬寄主藓类植物湿地匍灯藓(Plagiomnium acutum(Lindb.)T.Kop.)和侧枝葡灯藓(Plagiomnium maximoviczii(Lindb.)T.Kop.)的净光合速率及其与光照、温度的关系进了比较研究.结果表明,2种藓类的最大光合能力在夏季分别为125.67和94.63μmolCO2     

Light availability influences the ratio of two forms of D1 in cyanobacterial thylakoids

The psbA multigene family in Synechococcus sp. strain PCC 7942 encodes two forms of the D1 protein; Form I, the product of psbAI, differs from Form II, the product of psbAII and psbAIII, at 25 of 360 amino acid positions. D1 is essential for photosynthesis as a protein component of the photosystem II reaction center. Antisera were raised against purified hybrid proteins encoded by psbAI-lacZ and psbAIII-lacZ translational gene fusions that contain the unique amino termini of Form I and Form II, respectively. Form specificity of each antiserum was verified by Western analysis using thylakoid membranes from mutant strains containing only Form I or Form II. Western analysis of thylakoid membranes from wild-type cells cultured at different light intensities detected both forms of D1 in the membrane and showed changes in the ratio of the two forms. The D1 composition of the membrane matched predicted ratios of the forms based on differential gene expression: psbAI is expressed highest at low light, and both psbAII and psbAIII are expressed highest at high light. Along a gradient of light intensity from 5 microE. m-2.s-1 to 482 microE.m-2.s-1, the relative amount of Form I in thylakoid membranes decreased 58%, while the relative amount of Form II increased 60%. Maximum detection of Form I coupled with minimum detection of Form II in membranes from cells harvested at light intensities below 390 microE.m-2.s-1 suggests a central role for Form I in photosystem II. Increased incorporation of Form II into the thylakoid membrane occurred at light intensities reported by others to be photoinhibitory, suggesting that Form II serves a role in adaptation to high light.     

广西八角莲与八角莲光响应特性的比较研究

为了解濒危植物广西八角莲对环境光强的适应性,该研究以广西八角莲同属渐危种八角莲为对照,采用Li-6400便携式光合测定系统对两种植物的光合光响应特性进行了比较研究,进而探讨广西八角莲的濒危机制。结果表明:广西八角莲与的八角莲的光饱和点分别为440和530μmol·m~(-2)·s~(-1),光补偿点为13.25和13.10μmol·m~(-2)·s~(-1),最大净光合速率为3.62和6.81μmol·m~(-2)·s~(-1),表观量子效率为0.065和0.042μmol·μmol~(-1),两种八角莲均具阴生草本植物的光合特性,但其光补偿点与饱和点均高于一般阴生草本,10%~30%阴蔽度的林下生境有利于两种八角莲的生长;两种植物相比较,广西八角莲的光合能力较弱,光饱和点较低,但其弱光下的量子效率较高。大部分光强下,八角莲的净光合速率、气孔导度和蒸腾速率均高于广西八角莲,但广西八角莲的瞬时水分利用效率却高于八角莲,表明广西八角莲的光合策略比较保守,以较低的光合积累为代价来维持较高的水分利用效率,以保持体内水分平衡。     

Effects of Strong Light and Active Oxygen on Photosynthesis in Soybean

With the use of chlorophyll fluorescence technique, it was found that the net photosynthetic oxygen evolution rate decreased after strong light (2 000 μmol· m-2·2-1 ) treatment for two hours in soybean ( Glycine max L. ) leaves. The chlorophyll fluorescence parameters, Fm/Fo, Fv/Fm, ФPSII, qp and qN decreased along with the increase of light intensity. In strong light, exogenous active oxygen H202、·OH and 'O2 were harmful to soybean leaves. The destruction of 'O2 and·OH to leaves was most evident, as was shown that Fv/Fm and PS H decreased significantly. The antioxidants DABCO, mannitol, ascorbate and histidine protected the leaves, but weakly, from strong light. In darkness, the SOD inhibitor sodium diethyldithiocar- bamate (DDC) had no significant effect on Fm/Fo and Fv/Fm, but NAN,, the ascorbate peroxidase (APX)inhibitor, significantly decreased Fm/Fo, Fv/Fm and ФPS II. In strong light, however, beth DDC and NaN3 reduced the above-mentioned fluorescence parameters, but NaN3 was more effective than DDC. The results suggested that photoinhibition did take place in soybean leaves under strong light, and it was related to active oxygen in vivo.     

不同光照强度和温度对金钗石斛生长的影响

为了系统地研究不同光照强度下温度对金钗石斛(Dendrobium nobile)生长的影响,在金钗石斛分蘖期,于80μmol·m-2·s-1、160μmol·m-2·s-1、320μmol·m-2·s-1、640μmol·m-2·s-1的不同光强下,各设置5个温度(15℃、20℃、25℃、30℃、35℃)梯度对石斛进行处理。结果表明：石斛的生长与代谢随温度由低到高,表现出弱—强—弱的变化规律;80μmol·m-2·S-1光强下,石斛生长以25～30℃较为适宜;160μmol·m-2·s-1光强下则以20～25℃为适宜温度范围;320μmol·m-2·s-1与640μmol·m-2·s-1的中、强光照下,25℃处理石斛的生长优势尤为明显;不同光强下,石斛鲜重的增长大多以25℃处理更快,繁殖力则以20℃与25℃处理较高,各光强下的MDA含量随温度升高而先降后升,且均以25℃最低;可溶性蛋白质、可溶性总糖及叶绿素含量则表现出随温度由低到高而先增后减的趋势,其含量最高点均出现在25℃左右;净光合速率和叶绿素含量随光强和温度的变化趋势基本一致;各种光强下的暗呼吸速率均随温度升高而增大。因此,在不同的光照条件下,石斛生长的适宜温度均在25℃左右。光温处理引起石斛生理生化过程明显的相应变化表现出：高温和弱光照条件有利于石斛的株高增长,但不利于产量和质量提高;石斛的生长与MDA含量呈显著负相关(r80＝-0.9082、r160＝-0.9816、r320＝-0.8075、r640＝-0.8586),与可溶性糖含量呈一定正相关(r80＝0.7673、r160＝0.8892、r320＝0.8179、r640＝0.9278),并且石斛的生长与可溶性蛋白质含量、叶绿素含量、光合速率之间的变化趋势基本一致。     

Photosynthetic utilization of radiant energy by CAM Dendrobium flowers

14CO2 fixation was observed in orchid Dendrobium flowers; its rate decreased with the flower development. Chlorophyll (Chl) fluorescence in different developmental stages of flowers was compared to other green plant parts (leaf, inflorescence stalk, and fruit capsule). The photochemical efficiency of photosystem 2 (PS2) (Fv/Fm) of a leaf was 14-21 % higher than that of a mature flower perianth (sepal, petal, and labellum) which had a much lower total Chl content and Chl a/b ratio. A higher quantum yield of PS2 (ΦPS2) than in the mature flowers was observed in all green parts. Flower sepals had higher Chl content, Chl a/b ratio, and Fv/Fm values than the petal and labellum. During flower development the Chl content, Chl a/b ratio, Fv/Fm, and qN decreased while ΦPS2 and qP remained constant. An exposure of developing flowers to irradiances above 50 µmol m-2 s-1 resulted in a very drastic drop of ΦPS2 and qP, and a coherent increase of qN as compared to other green plant organs. A low saturation irradiance (PFD of 100 µmol m-2 s-1) and the increase in qN in the flower indicate that irradiation stress may occur since there is no further protection when the flower is exposed to irradiances above 100 µmol m-2 s-1. A low Chl/carotenoid ratio in mature flower perianth as a consequence of Chl content reduction in the course of flower development suggests a relief of irradiation stress via this mean.     

Redox Regulation of Light-Harvesting Complex II and cab mRNA Abundance in Dunaliella salina

We demonstrate that photosynthetic adjustment at the level of the light-harvesting complex associated with photosystem II (LCHII) in Dunaliella salina is a response to changes in the redox state of intersystem electron transport as estimated by photosystem II (PSII) excitation pressure. To elucidate the molecular basis of this phenomenon, LHCII apoprotein accumulation and cab mRNA abundance were examined. Growth regimes that induced low, but equivalent, excitation pressures (either 13[deg]C/20 [mu]mol m-2 s-1 or 30[deg]C/150 ([mu]mol m-2 s-1) resulted in increased LHCII apoprotein and cab mRNA accumulation relative to algal cultures grown under high excitation pressures (either 13[deg]C/150 [mu]mol m-2 s-1 or 30[deg]C/2500 [mu]mol m-2 s-1). Thermodynamic relaxation of high excitation pressures, accomplished by shifting cultures from a 13 to a 30[deg]C growth regime at constant irradiance for 12 h, resulted in a 6- and 8-fold increase in LHCII apoprotein and cab mRNA abundance, respectively. Similarly, photodynamic relaxation of high excitation pressure, accomplished by a shift from a light to a dark growth regime at constant temperature, resulted in a 2.4- to 4-fold increase in LHCII apoprotein and cab mRNA levels, respectively. We conclude that photosynthetic adjustment to temperature mimics adjustment to high irradiance through a common redox sensing/signaling mechanism. Both temperature and light modulate the redox state of the first, stable quinone electron acceptor of PSII, which reflects the redox poise of intersystem electron transport. Changes in redox poise signal the nucleus to regulate cab mRNA abundance, which, in turn, determines the accumulation of light-harvesting apoprotein. This redox mechanism may represent a general acclimation mechanism for photosynthetic adjustment to environmental stimuli.     

不同水分条件下三种附生地衣的光合作用特性

附生地衣是哀牢山湿性常绿阔叶林生态系统中重要的结构性组分。通过对该区域山地森林中3种典型附生地衣平滑牛皮叶 (Sticta nylanderiana)、网肺衣 (Lobaria retigera) 和橄榄斑叶 (Cetrelia olivetorum)在不同水分条件下的光合光响应及荧光参数的测定分析,结果显示,附生地衣光补偿点 (LCP)、光饱和点 (LSP)较高,对强光适应能力较强。在水分胁迫 (含水量5%~10%) 条件下,3种附生地衣的最大净光合速率 (Pmax) 仅为17~50nmol·g-1·s-1。随着含水量的增加,地衣的最大净光合速率 (Pmax) 与暗呼吸速率 (Rday) 逐渐增大,LCP降低,而LSP随之提高,这表明3种附生地衣具备“阳生植物”的某些特性,从而能够在一定程度上适应野外光照较强的灌丛、向阳林冠等生境。地衣叶绿素光反应中心初始荧光参数 (F0) 和最大光化学效率 (Fv/Fm) 随含水量下降而显著降低,暗示其光反应中心对水分有很强的敏感性。水分条件的改善有助于附生地衣的光反应中心进入到较高的生理活性状态。     

不同含水量下尖叶拟船叶藓光合速率对光温的响应及其模型

对不同大气温度、藓体含水量及光照条件下尖叶拟船叶藓光合速率测定研究结果表明,光合速率(Pn)与光照强度(PAR)、大气温度(Ta)及藓体含水量(PWC)之间密切相关,光合速率的光响应曲线为直角双曲线,温度、藓体含水量影响图形的曲度参数,在低含水量、高气温组合和高含水量、低气温组合的藓体高光强下都使光合速率降低．弱光下(PAR<200μmol·s^-1·m^-2),光合速率最大值Pmax出现在PWC：为50％～80％,但随着Ta的升高而增大,当Ta>25℃,Pmax随Ta升高而降低;随着光照强度的增大,Pmax出现的PWC水平随之提高,当PAR<200μmol·s^-1·m^-2时,光合速率最大值Pmax出现在Ta比较高的范围(20～25℃),并随PWC的升高而增大,当PWC>80％时,Pmax随PWC升高而降低;随着光照强度的增大,Pmax出现的Ta水平降低、在230     

Light-activated heterotrophic growth of the cyanobacterium Synechocystis sp. strain PCC 6803: a blue-light-requiring process.

A glucose-tolerant strain of Synechocystis sp. strain 6803 will not grow on glucose under complete darkness unless given a daily pulse of white light, typically 5 min of 40 mumol m-2 s-1 (light-pulsed conditions). The light pulse is insufficient for photoautotrophy, as glucose is required and growth yield is dependent on glucose concentration. Growth rate is independent of fluence, but growth yield is dependent on fluence, saturating at 40 to 75 mumol m-2 s-1. A Synechocystis strain 6803 psbA mutant strain grows under light-pulsed conditions at rates similar to those for the glucose-tolerant strain, indicating that photosystem II is not required for growth. The relative spectral sensitivity of the growth of light-pulsed cultures (growth only in blue light, 400 to 500 nm, maximum at 450 nm) precludes energetic contribution from cyclic electron transport around photosystem I. Pulses of long-wavelength light (i.e., 550 and 650 nm) did not support the growth of Synechocystis strain 6803 and, when supplied before or after a blue-light pulse, did not inhibit blue-light-stimulated growth of Synechocystis strain 6803. We conclude that the required blue-light pulse does not support growth via photosynthetic electron transport but appears instead to function as an environmental signal regulating heterotrophic metabolism, cell division, or other photomorphogenic processes. We have termed the growth of Synechocystis strain 6803 pulsed with light and kept otherwise in complete darkness light-activated heterotrophic growth. This observation of a blue-light requirement for the growth of Synechocystis strain 6803 represents a novel blue light effect on the growth of a cyanobacterium.     

热带雨林冠层树种绒毛番龙眼两种发育阶段叶片的光抑制

 通过测定西双版纳热带雨林冠层树种绒毛番龙眼(Pometia tomentosa)完全伸展嫩叶和成熟叶的叶片解剖、生理特征和雨季晴天自然条件下叶绿素a荧光以及午间强光对部分保护酶活性和膜脂过氧化作用的影响,探讨了两种不同发育阶段叶片光合作用的光抑制与强光和温度的关系。结果表明：绒毛番龙眼全展嫩叶和成熟叶表现出明显的解剖和生理特征差异。与全展嫩叶相比,成熟叶的叶片较厚、叶绿素含量高、气孔导度大、羧化效率高、最大净光合速率和光饱和点高,而气孔密度和保卫细胞长度没有显著差别。在雨季晴天自然条件下,午间最高光强可达2 200 μmol·m-2·s-1以上,最高叶温比气温高7～8 ℃,而成熟叶片的最高温度比全展嫩叶高1.5～2 ℃。上午随光强的增大,两种叶片的非光化学猝灭系数（NPQ）增大,PSⅡ原初光化学效率(Fv/Fm)、实际光化学效率［(Fm′_Fs)/Fm′］逐渐减小,在15∶30左右达最小。下午随着光强的减弱,Fv/Fm逐渐恢复,在傍晚基本恢复到清晨值。初始荧光(F0)在一天中变化很小。这表明绒毛番龙眼叶片光抑制是非辐射能量耗散增加引起的保护光合机构免受光破坏的保护性反应,而非光破坏。全展嫩叶比成熟叶有较低的光化学效率和非辐射耗散能力,对强光和高温处理的敏感性也较强,但在自然条件下一天中的光抑制程度与成熟叶没有显著差别。田间午间强光导致两种叶片的保护酶活性(超氧化物歧化酶,SOD;抗坏血酸过氧化物酶,APX)升高,而H2O2含量变化较小。其中,全展嫩叶的保护酶活性高,丙二醛(MDA)含量低。这表明自然条件下,与成熟叶相比,绒毛番龙眼全展嫩叶通过较低的光能利用效率、较低的叶温和高的保护酶活性减轻了强光高温的光抑制程度。