Karapetian N V, Bukhov N G
Mol Biol (Mosk). 1979 Jul-Aug;13(4):947-54.
The functional activity of both photosystems of higher plants and their thermoresistance in conditions of dehydratation of chloroplasts or subchloroplast fragments were studied. It is shown that dehydratation of the sample does not change the P700 amount capable to photooxidation. At 20 degrees in the time course of dark reduction of photooxidized P700 P(700+) in films two phases differing in rate were found. The relative contribution of each phase depends on the illumination duration. Since dehydratation blocks electron transfer between photosystems, the double phase dark reduction of P700+ in films reflects the electron flow from various components of potosystem 1 acceptor part. Dehydratation has little effect on properties of photosystem 1 acceptor part, because at low temperature the time courses of P700+ dark reduction in films and chloroplast or subchloroplast suspensions are similar. In contrast with potosystem 1, the functioning of photosystem 2, studied by light induced increase of fluorescence yield of chloroplasts, is blocked abruptly by water removal, but it could be partly restored by rehydratation of dried chloroplasts. The water removal increases the thermostability of both photosystems, however in suspension of the studied samples and also in their films photosystem 1 is more thermostable in comparison with photosystem 2.
研究了高等植物两个光系统的功能活性及其在叶绿体或亚叶绿体片段脱水条件下的耐热性。结果表明，样品脱水不会改变能够进行光氧化的P700的量。在20摄氏度下，在光氧化的P700 P(700+)的暗还原过程中，在薄膜中发现了两个速率不同的阶段。每个阶段的相对贡献取决于光照持续时间。由于脱水会阻断光系统之间的电子传递，薄膜中P700+的双相暗还原反映了来自光系统1受体部分各种组分的电子流。脱水对光系统1受体部分的性质影响很小，因为在低温下，薄膜以及叶绿体或亚叶绿体悬浮液中P700+暗还原的时间进程相似。与光系统1不同，通过叶绿体荧光产量的光诱导增加来研究的光系统2的功能，会因水分去除而突然受阻，但干燥叶绿体的再水化可以使其部分恢复。水分去除增加了两个光系统的热稳定性，然而在所研究样品的悬浮液及其薄膜中，光系统1比光系统2更耐热。
