Samson G., Herbert S. K., Fork D. C., Laudenbach D. E.
Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305 (G.S., S.K.H., D.C.F.).
Plant Physiol. 1994 May;105(1):287-294. doi: 10.1104/pp.105.1.287.
The acclimation of the photosynthetic apparatus to growth irradiance in a mutant strain of Synechococcus sp. PCC 7942 lacking detectable iron superoxide dismutase activity was studied. The growth of the mutant was inhibited at concentrations of methyl viologen 4 orders of magnitude smaller than those required to inhibit the growth of the wild-type strain. An increased sensitivity of photosynthetic electron transport near photosystem I (PSI) toward photooxidative stress was also observed in the mutant strain. In the absence of methyl viologen, the mutant exhibited similar growth rates compared with those of the wild type, even at high growth irradiance (350 [mu]E m-2 s-1) where chronic inhibition of photosystem II (PSII) was observed in both strains. Under high growth irradiance, the ratios of PSII to PSI and of [alpha]-phycocyanin to chlorophyll a were less than one-third of the values for the wild type. In both strains, cellular contents of chlorophyll a, [alpha]-phycocyanin, and [beta]-carotene, as well as the length of the phycobilisome rods, declined with increasing growth irradiance. Only the cellular content of the carotenoid zeaxanthin seemed to be independent of growth irradiance. These results suggest an altered acclimation to growth irradiance in the sodB mutant in which the stoichiometry between PSI and PSII is adjusted to compensate for the loss of PSI efficiency occurring under high growth irradiance. Similar shortening of the phycobilisome rods in the sodB mutant and wild-type strain suggest that phycobilisome rod length is regulated independently of photosystem stoichiometry.
研究了缺乏可检测到的铁超氧化物歧化酶活性的聚球藻属蓝细菌PCC 7942突变株中光合装置对生长光照强度的适应性。与抑制野生型菌株生长所需的浓度相比，甲基紫精浓度低4个数量级时，该突变株的生长就受到了抑制。在该突变株中还观察到，光系统I（PSI）附近的光合电子传递对光氧化应激的敏感性增加。在没有甲基紫精的情况下，即使在高生长光照强度（350 μE m-2 s-1）下，该突变株的生长速率与野生型菌株相似，而在这种光照强度下，两种菌株的光系统II（PSII）均受到长期抑制。在高生长光照强度下，PSII与PSI的比值以及α-藻蓝蛋白与叶绿素a的比值不到野生型菌株的三分之一。在两种菌株中，叶绿素a、α-藻蓝蛋白和β-胡萝卜素的细胞含量以及藻胆体棒的长度均随着生长光照强度的增加而下降。只有类胡萝卜素玉米黄质的细胞含量似乎与生长光照强度无关。这些结果表明，sodB突变株对生长光照强度的适应性发生了改变，其中PSI和PSII之间的化学计量比被调整，以补偿在高生长光照强度下发生的PSI效率损失。sodB突变株和野生型菌株中藻胆体棒的类似缩短表明，藻胆体棒的长度是独立于光系统化学计量比进行调节的。
