Chen Li-Song, Qi Yi-Ping, Liu Xing-Hui
College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
Ann Bot. 2005 Jul;96(1):35-41. doi: 10.1093/aob/mci145. Epub 2005 Apr 13.
Under high photon flux, excitation energy may be in excess in aluminum (Al)-treated leaves, which use a smaller fraction of the absorbed light in electron transport due to decreased CO2 assimilation compared with normal leaves. The objectives of this study were to test the hypothesis that the antioxidant systems are up-regulated in Al-treated citrus leaves and correlate with protection from photoxidative damage, and to test whether xanthophyll cycle-dependent thermal energy dissipation is involved in dissipating excess excitation energy. *
'Cleopatra' tangerine seedlings were fertilized and irrigated daily for 8 weeks with quarter-strength Hoagland's nutrient solution containing Al at a concentration of 0 or 2 mM from Al2(SO4)3.18H2O. Thereafter, leaf absorptance, chlorophyll (Chl) fluorescence, Al, pigments, antioxidant enzymes and metabolites were measured on fully expanded leaves. *
Compared with control leaves, energy was in excess in Al-treated leaves, which had smaller thermal energy dissipation, indicated by non-photochemical quenching (NPQ). In contrast, conversion of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z) at midday increased in both treatments, but especially in Al-treated leaves, although A + Z accounted for less 40 % of the total xanthophyll cycle pool in them. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase (CAT), and concentrations of ascorbate (AsA), dehydroascorbate (DASA), reduced glutathione (GSH) and oxidized glutathione (GSSG) were higher in Al-treated than in control leaves. *
These results corroborate the hypothesis that, compared with control leaves, antioxidant systems are up-regulated in Al-treated citrus leaves and protect from photoxidative damage, whereas thermal energy dissipation was decreased. Thus, antioxidant systems are more important than thermal energy dissipation in dissipating excess excitation energy in Al-treated citrus leaves.
在高光量子通量下，铝（Al）处理的叶片中激发能可能过剩，与正常叶片相比，由于二氧化碳同化作用降低，其在电子传递中利用的吸收光比例较小。本研究的目的是检验以下假设：Al处理的柑橘叶片中抗氧化系统上调并与免受光氧化损伤相关，以及检验叶黄素循环依赖的热能耗散是否参与耗散过剩的激发能。
用含0或2 mM Al（来自Al2(SO4)3·18H2O）的四分之一强度霍格兰营养液，每天对‘埃及艳后’蜜柑幼苗施肥和灌溉8周。此后，在完全展开的叶片上测量叶片吸收率、叶绿素（Chl）荧光、Al、色素、抗氧化酶和代谢物。
与对照叶片相比，Al处理的叶片中能量过剩，通过非光化学猝灭（NPQ）表明其热能耗散较小。相反，两种处理在中午时紫黄质（V）向花药黄质（A）和玉米黄质（Z）的转化均增加，但在Al处理的叶片中尤其明显，尽管其中A + Z占叶黄素循环总库的比例不到40%。Al处理的叶片中超氧化物歧化酶（SOD）、抗坏血酸过氧化物酶（APX）、单脱氢抗坏血酸还原酶（MDAR）、脱氢抗坏血酸还原酶（DHAR）、谷胱甘肽还原酶（GR）和过氧化氢酶（CAT）的活性，以及抗坏血酸（AsA）、脱氢抗坏血酸（DASA）、还原型谷胱甘肽（GSH）和氧化型谷胱甘肽（GSSG）的浓度均高于对照叶片。
这些结果证实了以下假设：与对照叶片相比，Al处理的柑橘叶片中抗氧化系统上调并免受光氧化损伤，而热能耗散降低。因此，在Al处理的柑橘叶片中，抗氧化系统在耗散过剩激发能方面比热能耗散更重要。
