Baroli Irene, Melis Anastasios
Department of Plant Biology, University of California, 411 Koshland Hall, 94720-3102, Berkeley, CA, USA.
Planta. 1996 Apr;198(4):640-646. doi: 10.1007/BF00262653. Epub 2017 Mar 18.
The light-dependent rate of photosystem-II (PSII) damage and repair was measured in photoautotrophic cultures of Dunaliella salina Teod. grown at different irradiances in the range 50-3000 μmol photons · m· s. Rates of cell growth increased in the range of 50-800 μmol photons·m·s, remained constant at a maximum in the range of 800-1,500 μmol photons·m ·s, and declined due to photoinhibition in the range of 1500-3000 μmol photons·m·s. Western blot analyses, upon addition of lincomycin to the cultures, revealed first-order kinetics for the loss of the PSII reaction-center protein (D1) from the 32-kDa position, occurring as a result of photodamage. The rate constant of this 32-kDa protein loss was a linear function of cell growth irradiance. In the presence of lincomycin, loss of the other PSII reaction-center protein (D2) from the 34-kDa position was also observed, occurring with kinetics similar to those of the 32-kDa form of D1. Increasing rates of photodamage as a function of irradiance were accompanied by an increase in the steady-state level of a higher-molecular-weight protein complex (≈ 160-kDa) that cross-reacted with D1 antibodies. The steady-state level of the 160-kDa complex in thylakoids was also a linear function of cell growth irradiance. These observations suggest that photodamage to D1 converts stoichiometric amounts of D1 and D2 (i.e., the D1/D2 heterodimer) into a ≈160-kDa complex. This complex may help to stabilize the reaction-center proteins until degradation and replacement of D1 can occur. The results indicated an intrinsic half-time of about 60 min for the repair of individual PSII units, supporting the idea that degradation of D1 after photodamage is the rate-limiting step in the PSII repair process.
在盐生杜氏藻（Dunaliella salina Teod.）的光合自养培养物中，测定了光系统II（PSII）依赖光的损伤和修复速率。该培养物在50 - 3000 μmol光子·m⁻²·s⁻¹的不同辐照度下生长。细胞生长速率在50 - 800 μmol光子·m⁻²·s⁻¹范围内增加，在800 - 1500 μmol光子·m⁻²·s⁻¹范围内保持最大值不变，而在1500 - 3000 μmol光子·m⁻²·s⁻¹范围内由于光抑制作用而下降。向培养物中添加林可霉素后进行的蛋白质免疫印迹分析表明，PSII反应中心蛋白（D1）从32 kDa位置丢失呈现一级动力学，这是光损伤的结果。这种32 kDa蛋白丢失的速率常数是细胞生长辐照度的线性函数。在林可霉素存在的情况下，还观察到另一种PSII反应中心蛋白（D2）从34 kDa位置丢失，其动力学与32 kDa形式的D1相似。随着辐照度增加，光损伤速率的上升伴随着一种与D1抗体发生交叉反应的高分子量蛋白复合物（≈160 kDa）稳态水平的增加。类囊体中160 kDa复合物的稳态水平也是细胞生长辐照度的线性函数。这些观察结果表明，D1的光损伤将化学计量的D1和D2（即D1 / D2异二聚体）转化为一种≈160 kDa的复合物。这种复合物可能有助于稳定反应中心蛋白，直到D1发生降解和替换。结果表明，单个PSII单位修复的内在半衰期约为60分钟，这支持了光损伤后D1的降解是PSII修复过程中限速步骤的观点。
