光胁迫对沙冬青叶绿素荧光特征和光呼吸的影响

使用LI-6400测定乌兰布和沙漠东北缘的沙冬青在不同光合有效辐射下的叶绿素荧光特征和光呼吸变化,进而研究其光破坏防御特征的变化。结果表明,PSⅡ最大光化学量子产量(Fv/Fm)可作为衡量沙冬青光胁迫程度大小指标,有效光化学量子产量(Fv′/Fm′)、总光合速率(Pt)、非光化学猝灭(qN)、光呼吸速率(Rp)和Rp/Pt等指标的光进程曲线临界点值和临界点光强度与Fv/Fm的关系都具有明显的规律性。随着Fv/Fm降低,光胁迫程度增加,导致沙冬青光胁迫的最小光合有效辐射降低。可见,沙冬青光破坏防御的一种策略是在胁迫程度较小时通过提高热耗散和光呼吸相对比值(Rp/Pt)来消耗过剩能量,而在胁迫程度较大时可通过增加抑制热耗散和光呼吸的光合有效辐射实现对过剩光能的消耗。     

Diurnal variations in gas exchange,chlorophyll fluorescence quenching and light allocation in soybean leaves: The cause for midday depression in CO2 assimilation

Gas exchange and chlorophyll fluorescence quenching analysis were carried out to investigate the diurnal variations in photosynthesis and light allocation in leaves of soybean. Leaf net CO₂ assimilation rate showed a bimodal diurnal pattern and midday depression of CO₂ assimilation was observed at 13:00 h. Depression in CO₂ assimilation at midday was mostly attributed to non-stomatal limitation since the reduction in net CO₂ assimilation rate was not followed by significant reductions in stomatal conductance and intracellular CO₂ concentration. Midday depression in CO₂ assimilation was found to be associated with reversible inactivation of photosystem II reaction centers and increases of antenna heat dissipation and photorespiration in response to the high light intensity. It is likely that PS II down-regulation, heat dissipation and photorespiration co-operated together to prevent the chloroplast from photodamage.     

Changes in carotenoids and ABA content in Citrus leaves in response to girdling

The effect of girdling on abscisic acid, carotenoids content, xanthophylls cycle and non-photoquemical quenching was studied in leaves from different shoot types of containerized two-year-old ‘Loretina’ mandarin during spring flush period. Girdling increased abscisic acid in young leaves and decreased it in mature leaves. These changes were accompanied by a significant increase in leaf carotenoids, carotenoids:chlorophylls ratio, xanthophylls and xanthophylls cycle pool size and its de-epoxidation state in vegetative and multiflowered young leafy shoots. However, changes in de-epoxidation state did not correlate with the energy-dependent non-photochemical quenching. The role of carotenoids and abscisic acid as photoprotecting agents during the oxidative stress caused by girdling is discussed. In conclusion, this study provides evidence linking carotenoids-based photoprotecting mechanisms in the response to the stress induced by girdling in Citrus trees.     

Deg2蛋白酶在拟南芥光损伤D1降解及光保护中的作用

己有研究表明叶绿体内有200种蛋白酶,然而,多数蛋白酶的作用机制尚不清楚,尤其哪些蛋白酶参与了D1蛋白周转。其中Deg2蛋白酶体外实验证明,其参与了光损伤D1蛋白的的初步剪切。为了进一步研究Deg2蛋白酶在植物体内的作用机制,我们筛选了拟南芥De醇蛋白酶功能缺陷型突变体。在120μmol·m-2：·S^-1光照生长条件下,出萨突变体与野生型的生长曲线基本一致;在进一步的高光胁迫（1800μmol·m-2·S^-1）处理及相同的光胁迫处理条件下,无论林可霉素存在与否,突变体PSⅡ的最大光化学效率（Fv／Fm）都和野生型没有区别;利用蛋白免疫印迹实验同样证明了光损伤D1蛋白的降解速度在cfe霞突变体和野生型之间也没有明显区别。我们认为Deg2蛋白酶在光抑制情况下对于光损伤D1蛋白的降解以及PsⅡ的修复不是必需的。     

植物叶黄素循环及其光保护作用的研究进展

当植物吸收过量光能时会产生光抑制,引起光合器官的破坏,甚至导致植物死亡。叶黄素循环是植物应对过量光能时主要的光保护机制,可以有效清除并阻止有害副产物三线态的叶绿素分子和单线态氧的积累。因此,植物叶黄素循环相关机理的研究具有重要的理论和实际意义。综述了植物叶黄素循环的组成、关键酶的功能与调节及其在光保护中的作用。     

Protective effect of sodium selenite on human keratinocytes from ultraviolet-B irradiation

AIM: To investigate the protective effect of sodium selenite (Na₂SeO₃) on human keratinocytes under ultraviolet-B (UVB) irradiation. METHODS: The cultured HaCaT cells were divided into 4 groups: (1) normal control group; (2) Na₂SeO₃ group: pretreated with Na₂SeO₃ at doses of 10 nmol/L, 50 nmol/L, 100 nmol/L, 200 nmol/L and 1 μmol/L for 24 h; (3) UVB group: irradiated with UVB at doses of 300, 600 and 900 J/m² ; (4) Na₂SeO₃+UVB group: after pretreated with Na₂SeO₃ for 24 h, irradiated with UVB at doses of 300, 600 and 900 J/m² . The cell proliferation was detected by MTT assay. The apoptotic rates of HaCaT cells treated with UVB at dose of 300 J/m² were assessed by flow cytometry. RESULTS: Compared with normal control group, the cell proliferation activity in UVB group decreased significantly (P<0.05). The cell activity was inversely correlated with the irradiation intensity. No significant difference of the cell activity between Na₂SeO₃ group and normal control group was observed. The cell proliferation in Na₂SeO₃+UVB group was higher than that in UVB group significantly (P<0.05). Na₂SeO₃ at concentration of 100 nmol/L showed the strongest activity to promote cell proliferation. After 300 J/m² UVB irradiation, the apoptotic rate in Na₂SeO₃+UVB group decreased significantly (P<0.05) compared with UVB group. The inhibitory effect of Na₂SeO₃ at concentration of 100 nmol/L on apoptosis was the strongest.CONCLUSION: The damage of human keratinocytes by UVB irradiation is in a dose-dependent manner. The photoprotection performance of Na₂SeO₃ reduces the damage of human keratinocytes induced by UVB irradiation.     

强光胁迫下银杏叶片的光抑制及其防御机制

为探讨强光对银杏叶片光合特性的影响 ,对银杏叶片进行强光 (12 0 0 μmolphotons·m- 2 s- 1 )胁迫 5h ,通过分析叶绿素a荧光参数和叶黄素循环组分研究了强光胁迫下银杏叶片的光抑制以及相关的光破坏防御机制。强光胁迫过程中 ,银杏叶片的PSⅡ最大光化学效率 (Fv Fm)明显下降 ,胁迫结束时 ,Fv Fm 接近 0 3。而初始荧光(Fo)则在整个胁迫过程中呈上升趋势。PSⅡ实际光化学效率 (ФPSⅡ)和表观光合电子传递速率 (ETR)均大幅度下降 ,而非光化学猝灭 (NPQ)和天线热耗散 (HDR)明显上升 ,叶黄素循环关键组分玉米黄质 (Z)的相对含量则随着强光处理时间的延长而增加 ,由处理前的 3%上升到胁迫结束时的 6 6 %。结果表明 ,强光胁迫过程中 ,银杏叶片发生了严重的光抑制 ,依赖于叶黄素循环的非光化学猝灭和天线热耗散起到了有效耗散过剩光能的作用 ,但是PSⅡ反应中心可逆失活是银杏叶片Fv Fm 下降的主要原因。     

Comparison of Susceptibility to Photoinhibition and Energy Partitioning of Absorbed Light in Photosystem II in Flag Leaves of Two Rice (Oryza sativa L.) Cultivars that Differ in Their Responses to Nitrogen-Deficiency

Abstract

Abstract: The energy partitioning in photosystem II (PSII) and the susceptibility to photoinhibition in PSII were investigated in flag leaves of two rice cultivars, Shirobeniya (a traditionaljaponica) and Akenohoshi (an improved japonica-indica intermediate) grown under standard-nitrogen (N) (SN) and low-N (LN) conditions. N-deficiency resulted in significant decreases in total dry weight, net photosynthetic rate (P_n), the energy flux via carboxylation (J_c), and content of ribulose-1,5-bisphosphate carboxylase /oxygenase (Rubisco) in flag leaves in the two cultivars, and these parameters of Shirobeniya were lower than those in Akenohoshi under the LN condition. In the two cultivars, the energy flux via alternative electron flow was significantly increased by N-deficiency, which was accompanied by enhanced activity of superoxide dismutase (SOD). Although under the LN condition no cultivar differences were found in J_a and SOD, ascorbate peroxidase activity in Shirobeniya was lower than that in Akenohoshi. N-deficiency resulted in more significant increases in the susceptibility to photoinhibition (the degree of decrease in maximum quantum yield of PSII), hydrogen peroxide (H₂O₂) content and malondialdehyde content after exposure to high irradiance in Shirobeniya than those in Akenohoshi. These results indicated that the increased susceptibility to photoinhibition in the LN plants of Shirobeniya was mainly due to oxidative damages to chloroplasts, resulting from lower carboxylation and H₂O₂-scavenging capacities. Therefore, both carboxylation and H₂O₂-scavenging capacities could be important factors in determining the cultivar difference in the productivity of rice under LN conditions.     

番茄叶黄素合成突变与光能分配和抗氧化酶活性的关系

以叶黄素（Lutein）缺失的番茄突变体（Xa）为材料,研究其光合和叶绿素荧光特性、吸收光能分配、细胞器水平抗氧化酶活性及抗氧化物质含量。结果表明：Xa突变体的非光化学猝灭系数（qN）、叶片吸收光能分配依赖于△pH和叶黄素的非结构性热耗散（J_NPQ）显著低于其野生型Ailsa Craig,但净光合速率（Pn）、羧化效率（CE）、光化学猝灭系数（qP）与Ailsa Craig相似。此外,Xa突变体叶片细胞器水平的抗氧化酶活性和抗氧化物质含量大多数显著高于Ailsa Craig。这些结果表明,叶黄素缺失体主要通过降低光能吸收和提高抗氧化能力来避免过剩光能导致光氧化胁迫的产生。     

小麦不同品种叶片对光氧化胁迫响应的比较研究

利用叶片浸水或甲基紫精(MV)处理造成光氧化条件,研究了小麦品种(系)鲁原102(LY102)和54368对光氧化的抗性.发现在浸水处理诱导的光氧化条件下,小麦品种LY102叶片叶绿素含量和可溶性蛋白质含量的降幅大于54368.光系统II最大光化学效率(Fv/Fm),光系统II电子传递效率(ΦPSⅡ)和非光化学猝灭值(NPQ),超氧化物歧化酶(SOD)和抗坏血