Kruk Jerzy, Trebst Achim
Department of Plant Physiology and Biochemistry, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
Biochim Biophys Acta. 2008 Feb;1777(2):154-62. doi: 10.1016/j.bbabio.2007.10.008. Epub 2007 Oct 25.
It has been found that in Chlamydomonas reinhardtii cells, under high-light stress, the level of reduced plastoquinone considerably increases while in the presence of pyrazolate, an inhibitor of plastoquinone and tocopherol biosynthesis, the content of reduced plastoquinone quickly decreases, similarly to alpha-tocopherol. In relation to chlorophyll, after 18 h of growth under low light with the inhibitor, the content of alpha-tocopherol was 22.2 mol/1000 mol chlorophyll and that of total plastoquinone (oxidized and reduced) was 19 mol/1000 mol chlorophyll, while after 2 h of high-light stress the corresponding amounts dropped to 6.4 and 6.2 mol/1000 mol chlorophyll for alpha-tocopherol and total plastoquinone, respectively. The degradation of both prenyllipids was partially reversed by diphenylamine, a singlet oxygen scavenger. It was concluded that plastoquinol, as well as alpha-tocopherol is decomposed under high-light stress as a result of a scavenging reaction of singlet oxygen generated in photosystem II. The levels of both alpha-tocopherol and of the reduced plastoquinone are not affected significantly in the absence of the inhibitor due to a high turnover rate of both prenyllipids, i.e., their degradation is compensated by fast biosynthesis. The calculated turnover rates under high-light conditions were twofold higher for total plastoquinone (0.23 nmol/h/ml of cell culture) than for alpha-tocopherol (0.11 nmol/h/ml). We have also found that the level of alpha-tocopherolquinone, an oxidation product of alpha-tocopherol, increases as the alpha-tocopherol is consumed. The same correlation was also observed for gamma-tocopherol and its quinone form. Moreover, in the presence of pyrazolate under low-light growth conditions, the synthesis of plastoquinone-C, a hydroxylated plastoquinone derivative, was stimulated in contrast to plastoquinone, indicating for the first time a functional role for plastoquinone-C. The presented data also suggest that the two plastoquinones may have different biosynthetic pathways in C. reinhardtii.
研究发现，在莱茵衣藻细胞中，高光胁迫下还原型质体醌的水平显著增加，而在存在质体醌和生育酚生物合成抑制剂吡唑酸盐的情况下，还原型质体醌的含量迅速下降，与α-生育酚的情况类似。关于叶绿素，在低光照下添加抑制剂生长18小时后，α-生育酚的含量为22.2 μmol/1000 μmol叶绿素，总质体醌（氧化型和还原型）的含量为19 μmol/1000 μmol叶绿素，而在高光胁迫2小时后，α-生育酚和总质体醌的相应含量分别降至6.4和6.2 μmol/1000 μmol叶绿素。单线态氧清除剂二苯胺部分逆转了这两种异戊二烯脂类的降解。得出的结论是，在高光胁迫下，质体醌醇以及α-生育酚会因光系统II中产生的单线态氧的清除反应而分解。在没有抑制剂的情况下，由于这两种异戊二烯脂类的高周转率，即它们的降解被快速的生物合成所补偿，α-生育酚和还原型质体醌的水平均未受到显著影响。高光条件下计算得出的总质体醌周转率（0.23 nmol/h/ml细胞培养物）比α-生育酚（0.11 nmol/h/ml）高出两倍。我们还发现，随着α-生育酚的消耗，其氧化产物α-生育醌的水平会升高。γ-生育酚及其醌形式也观察到了相同的相关性。此外，在低光照生长条件下存在吡唑酸盐时，与质体醌相反，羟基化质体醌衍生物质体醌-C的合成受到刺激，这首次表明了质体醌-C的功能作用。所呈现的数据还表明，这两种质体醌在莱茵衣藻中可能具有不同的生物合成途径。
