Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas y Universidad de Sevilla, 41092 Seville, Spain.
Plant Physiol. 2012 Sep;160(1):274-88. doi: 10.1104/pp.112.201491. Epub 2012 Jul 24.
Arabidopsis (Arabidopsis thaliana) chloroplasts contain two O-acetyl-serine(thiol)lyase (OASTL) homologs, OAS-B, which is an authentic OASTL, and CS26, which has S-sulfocysteine synthase activity. In contrast with OAS-B, the loss of CS26 function resulted in dramatic phenotypic changes, which were dependent on the light treatment. We have performed a detailed characterization of the photosynthetic and chlorophyll fluorescence parameters in cs26 plants compared with those of wild-type plants under short-day growth conditions (SD) and long-day growth conditions (LD). Under LD, the photosynthetic characterization, which was based on substomatal CO(2) concentrations and CO(2) concentration in the chloroplast curves, revealed significant reductions in most of the photosynthetic parameters for cs26, which were unchanged under SD. These parameters included net CO(2) assimilation rate, mesophyll conductance, and mitochondrial respiration at darkness. The analysis also showed that cs26 under LD required more absorbed quanta per driven electron flux and fixed CO(2). The nonphotochemical quenching values suggested that in cs26 plants, the excess electrons that are not used in photochemical reactions may form reactive oxygen species. A photoinhibitory effect was confirmed by the background fluorescence signal values under LD and SD, which were higher in young leaves compared with mature ones under SD. To hypothesize the role of CS26 in relation to the photosynthetic machinery, we addressed its location inside of the chloroplast. The activity determination and localization analyses that were performed using immunoblotting indicated the presence of an active CS26 enzyme exclusively in the thylakoid lumen. This finding was reinforced by the observation of marked alterations in many lumenal proteins in the cs26 mutant compared with the wild type.
拟南芥（Arabidopsis thaliana）叶绿体含有两个 O-乙酰丝氨酸（硫醇）裂解酶（OASTL）同源物，OAS-B 是一种真正的 OASTL，CS26 具有 S-磺酰半胱氨酸合酶活性。与 OAS-B 不同，CS26 功能丧失导致了明显的表型变化，这种变化依赖于光处理。我们对 cs26 植株与野生型植株在短日照生长条件（SD）和长日照生长条件（LD）下的光合作用和叶绿素荧光参数进行了详细的表征。在 LD 下，基于亚细胞 CO2 浓度和叶绿体 CO2 浓度曲线的光合作用特征表明，cs26 的大多数光合作用参数都显著降低，而在 SD 下则没有变化。这些参数包括净 CO2 同化率、叶肉导度和黑暗下的线粒体呼吸。分析还表明，LD 下的 cs26 需要更多的吸收量子来驱动电子流和固定 CO2。非光化学猝灭值表明，在 cs26 植株中，未用于光化学反应的多余电子可能形成活性氧物质。背景荧光信号值在 LD 和 SD 下证实了光抑制效应，在 SD 下，年轻叶片的信号值高于成熟叶片。为了假设 CS26 在光合作用机制中的作用，我们研究了其在叶绿体内部的位置。使用免疫印迹进行的活性测定和定位分析表明，活性 CS26 酶仅存在于类囊体腔中。这一发现得到了在 cs26 突变体中观察到的许多腔室蛋白明显改变的支持，与野生型相比，这些改变在 cs26 突变体中更为明显。
