Jin EonSeon, Yokthongwattana Kittisak, Polle Juergen E W, Melis Anastasios
Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, California 94720-3102.
Plant Physiol. 2003 May;132(1):352-64. doi: 10.1104/pp.102.019620.
The Dunaliella salina photosynthetic apparatus organization and function was investigated in wild type (WT) and a mutant (zea1) lacking all beta,beta-epoxycarotenoids derived from zeaxanthin (Z). The zea1 mutant lacked antheraxanthin, violaxanthin, and neoxanthin from its thylakoid membranes but constitutively accumulated Z instead. It also lacked the so-called xanthophyll cycle, which, upon irradiance stress, reversibly converts violaxanthin to Z via a de-epoxidation reaction. Despite the pronounced difference observed in the composition of beta,beta-epoxycarotenoids between WT and zea1, no discernible difference could be observed between the two strains in terms of growth, photosynthesis, organization of the photosynthetic apparatus, photo-acclimation, sensitivity to photodamage, or recovery from photo-inhibition. WT and zea1 were probed for the above parameters over a broad range of growth irradiance and upon light shift experiments (low light to high light shift and vice versa). A constitutive accumulation of Z in the zea1 strain did not affect the acclimation of the photosynthetic apparatus to irradiance, as evidenced by indistinguishable irradiance-dependent adjustments in the chlorophyll antenna size and photosystem content of WT and zea1 strain. In addition, a constitutive accumulation of Z in the zea1 strain did not affect rates of photodamage or the recovery of the photosynthetic apparatus from photo-inhibition. However, Z in the WT accumulated in parallel with the accumulation of photodamaged PSII centers in the chloroplast thylakoids and decayed in tandem with a chloroplast recovery from photo-inhibition. These results suggest a role for Z in the protection of photodamaged and disassembled PSII reaction centers, apparently needed while PSII is in the process of degradation and replacement of the D1/32-kD reaction center protein.
对野生型（WT）和一个突变体（zea1）的杜氏盐藻光合机构的组织和功能进行了研究，该突变体缺乏所有源自玉米黄质（Z）的β,β-环氧类胡萝卜素。zea1突变体的类囊体膜中缺乏花药黄质、紫黄质和新黄质，但持续积累Z取而代之。它还缺乏所谓的叶黄素循环，在光照胁迫下，该循环通过脱环氧化反应将紫黄质可逆地转化为Z。尽管在WT和zea1之间观察到β,β-环氧类胡萝卜素组成存在明显差异，但在生长、光合作用、光合机构的组织、光适应、对光损伤的敏感性或从光抑制中恢复方面，这两个菌株之间没有观察到明显差异。在广泛的生长光照强度范围内以及在光转换实验（从低光转换到高光以及反之亦然）中，对WT和zea1的上述参数进行了探测。zea1菌株中Z的持续积累并不影响光合机构对光照强度的适应，WT和zea1菌株叶绿素天线大小和光系统含量中与光照强度相关的调整无法区分就证明了这一点。此外，zea1菌株中Z的持续积累并不影响光损伤速率或光合机构从光抑制中的恢复。然而，WT中的Z与叶绿体类囊体中光损伤的PSII中心的积累平行增加，并随着叶绿体从光抑制中恢复而同步衰减。这些结果表明Z在保护光损伤和解聚的PSII反应中心方面发挥作用，显然在PSII进行D1/32-kD反应中心蛋白降解和替换的过程中是需要的。
