Santabarbara Stefano
Centre for Fundamental Research in Photosynthesis, Hendon, 67 The Burroughs, London NW4 4AX, UK.
Arch Biochem Biophys. 2006 Nov 1;455(1):77-88. doi: 10.1016/j.abb.2006.08.017. Epub 2006 Sep 1.
Light-induced pigment oxidation and its relation to excited state quenching in photosystems antennae have been investigated in isolated thylakoids. The results indicate that (i) chlorophyll oxidation takes place in two sequential steps. A slow initial phase is followed by a steep increase in the bleaching rate when more than one quarter of the chromophores are oxidised. (ii) During the initial slow phase, the carotenoid pool is bleached with an apparent rate which is about three times faster than that found for chlorophyll a and more than six times faster than that of chlorophyll b. (iii) Pigment bleaching has been observed both in photosystem I and photosystem II, and it has been possible to estimate a similar carotenoid bleaching rate in the two photosystems. (iv) The protection conferred by singlet state quenchers in the initial slow phase of pigment oxidation is modest. Taking into consideration that both the photosystems are subjected to the oxidative treatment, a somewhat larger protective effect than those estimated for photo-inhibition in thylakoids [S. Santabarbara, F.M. Garlaschi, G. Zucchelli, R.C. Jennings, Biochim. Biophys. Acta 1409 (1999) 165-170] can be computed, although it is less than 50% of the expected level on the basis of the observed reciprocity to the number of incident photons. (v) Pigment oxidation is associated with the loss of membrane ultra-structure, which is interpreted as originating from a decrease in grana stacking. The dynamics of loss of membrane ultra-structure parallel the phases observed for chlorophyll photo-bleaching.
在分离的类囊体中研究了光诱导的色素氧化及其与光合系统天线中激发态猝灭的关系。结果表明：（i）叶绿素氧化分两个连续步骤进行。初始阶段较为缓慢，当超过四分之一的发色团被氧化时，漂白速率急剧增加。（ii）在初始缓慢阶段，类胡萝卜素库被漂白，其表观速率比叶绿素a快约三倍，比叶绿素b快六倍以上。（iii）在光系统I和光系统II中均观察到色素漂白，并且有可能估计两个光系统中类似的类胡萝卜素漂白速率。（iv）单线态猝灭剂在色素氧化初始缓慢阶段提供的保护作用较小。考虑到两个光合系统都受到氧化处理，可以计算出比类囊体中光抑制估计值略大的保护作用[S. Santabarbara, F.M. Garlaschi, G. Zucchelli, R.C. Jennings, Biochim. Biophys. Acta 1409 (1999) 165 - 170]，尽管它不到基于观察到的与入射光子数的倒数关系所预期水平的50%。（v）色素氧化与膜超结构的丧失有关，这被解释为源于基粒堆叠的减少。膜超结构丧失的动力学与叶绿素光漂白观察到的阶段平行。
