Effect of Mn cluster on the formation of superoxide radicals in photoinhibition of photosystem Ⅱ

To further realize the action of superoxide radicals (O₂^{− .}) in photoinhibition of photosystem Ⅱ (PSⅡ), we employed 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap, associated with EPR spectroscopy, to study the effect of illumination time on O₂^{− .} formation during high light photoinhibition in PSⅡ membranes and Mn-depleted PSⅡ membranes. Results indicated that the removal of Mn cluster from PS
membranes has a strong influence on the dynamics of superoxide formation. The relative mechanism was also discussed. These novel findings may further promote the studies of the structure and function of PSⅡ and the mechanism of photoinhibition.     

Relationships between D1 protein, xanthophyll cycle and photodamage-resistant capacity in rice (Orysa sativa L.)

Relationships between D1 protein, xanthophyll cycle and subspecific difference of photodamage-resistant capacity have been studied in O. japonica rice varieties 02428 and 029 (photoinhibition-tolerance) and O. indica rice varieties 3037 and Palghar (photoinhibition-sensitivity) and their reciprocal cross F1 hybrids after photoinhibitory treatment. It was shown that PSⅡ photochemical efficiency (Fv /Fm) decreased, and xanthophyll cycle from violaxanthin (V), via anaxanthin (A), to zeaxanthin (Z) was enhanced and non-photochemical quenching (qN) increased accordingly in SM-pretreated leaves of rice when the synthesis of D1 protein was inhibited, and that there was a decrease in qN and, as a result, more loss of D1 protein and a big decrease in Fv /Fm in DTT-pretreated leaves when xanthophyll cycle was inhibited. O. japonica subspecies had a higher maintaining capacity of D1 protein and a decrease of Fv /Fm in a more narrow range, and exhibited more resistance against photodamage, as compared with O. indica subspecies. The above physiological indexes in reciprocal cross F1 hybrids, though between the values of their parents, were closer to maternal lines than to paternal lines. Experimental results support the concept that the turnover capacity for D1 protein is an important physiological basis of photoinhibition-tolerance, and will provide the physiological basis for selection of the photoinhibition-tolerant parents and develop a new approach to breed hybrids with high photosynthetic efficiency.     

Effect of calcium ions on the secondary structures of photosystemⅡ and its relations with photoinhibition

Calcium ions play an important role in the oxygen_evolving process of photosystem Ⅱ as demonstrated in many experiments. The changes of the secondary structures of PS Ⅱ induced by the depletion of Ca 2+ were reported. The results indicated that the removal of Ca 2+ led to the transition of α helix to turns and sheet structures. While Ca 2+ was re_added to the media, only the structures changed to turns could be recovered. The protein conformational changes of PS Ⅱ during the donor side photoinhibition induced by the depletion of Ca 2+ were also studied. This showed that the protein conformational changes differed between the control and Ca 2+ _depleted samples in a short period of illumination (within 10 min). However, the changes became similar when the illumination time was increased.     

弱光和Tris处理条件下PSⅡ放氧核心复合物的损伤

弱光条件下(120μmol·m-2·s-1)用Tris(0.8mol/L,pH6.5～10.0)处理具有放氧活性的PSⅡ核心复合物,可引起33kD锰稳定蛋白的释放和锰复合物的破坏,并导致核心复合物的结构发生明显的改变.温和电泳、SDS-PAGE和双向电泳分析表明,主要是PSⅡ核心复合物的二聚体和单体减少,并且复合物部分解体;除反应中心D1和D2蛋白外,核心天线CP43和CP7的量也减少,33kD锰稳定蛋白要发生降解.避光时,PSⅡ核心复合物不受影响.     

光周期对葛仙米生长和光合系统活性的影响

通过设置光暗比(L∶D)24h∶0h、12h∶12h和8h∶16h三个光周期处理组,对葛仙米(Nostoc sphaeroides Kutzing)依次开展了三个批次的培养,测定光周期对葛仙米生长和光合活性的影响.结果表明,24h连续光照对葛仙米生长具有显著抑制作用,不适合应用于葛仙米的长期连续批量培养中.3个光周期处理组中,葛仙米叶绿素荧光Fv/Fm在第一个培养批次中降低,但是很快都在第二个和第三个培养批次中得到缓和.葛仙米PS捕光天线色素含量的变化表明,葛仙米能够通过下调该色素的含量来降低较长光照对葛仙米光合系统的光抑制和破坏,从而获得较高的光合作用效率.     

Effect of calcium ions on the secondary structures of photosystem II and its relations with photoinhibition

Calcium ions play an important role in the oxygen-evolving process of photosystem II as demonstrated in many experiments. The changes of the secondary structures of PS II induced by the depletion of Ca²⁺ were reported. The results indicated that the removal of Ca²⁺ led to the transition of ahelix to turns and sheet structures. While Ca²⁺ was re-added to the media, only the structures changed to turns could be recovered. The protein conformational changes of PS II during the donor side photoinhibition induced by the depletion of ca²⁺ were also studied. This showed that the protein conformational changes differed between the control and Ca²⁺-depleted samples in a short period of illumination (within 10 min). However, the changes became similar when the illumination time was increased.