Leaves of Arabidopsis thaliana plants grown in short days (8 h light) generate more reactive oxygen species in the light than leaves of plants grown in long days (16 h light). The importance of the two PsaE isoforms of photosystem I, PsaE1 and PsaE2, for O2 reduction was studied in plants grown under these different growth regimes. In short day conditions a mutant affected in the amount of PsaE1 (psae1-1) reduced more efficiently O2 than a mutant lacking PsaE2 (psae2-1) as shown by spin trapping EPR spectroscopy on leaves and by following the kinetics of P700+ reduction in isolated photosystem I. In short day conditions higher O2 reduction protected photosystem II against photoinhibition in psae1-1. In contrast in long day conditions the presence of PsaE1 was clearly beneficial for photosynthetic electron transport and for the stability of the photosynthetic apparatus under photoinhibitory conditions. We conclude that the two PsaE isoforms have distinct functions and we propose that O2 reduction at photosystem I is beneficial for the plant under certain environmental conditions.

中文翻译：

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拟南芥中两个PsaE亚型在光系统I的O2还原中的作用。

在短日（8 h光照）下生长的拟南芥植物叶片比在长日（16 h光照）下生长的植物叶片在光照下产生更多的活性氧。在这些不同生长方式下生长的植物中研究了光系统I的两种PsaE亚型PsaE1和PsaE2对于减少O2的重要性。在短日情况下，受影响的PsaE1（psae1-1）量的突变体比缺少PsaE2（psae2-1）的突变体更有效地减少O2，如通过在叶片上的自旋捕集EPR光谱法和遵循分离的P700 +还原动力学所表明的那样光系统I。在短时间内，较高的O2还原量可保护光系统II免受psae1-1中的光抑制作用。相比之下，在漫长的白天条件下，PsaE1的存在明显有利于光合电子传输和光合条件下光合装置的稳定性。我们得出结论，这两个PsaE同工型具有不同的功能，并且我们建议在某些环境条件下，在光系统I处减少O2对植物有益。