光胁迫下银杏光合作用的光抑制

Photoinhibition of photosynthesis in Ginkgo biloba L. under high light stress

自然条件下晴天银杏叶片光系统Ⅱ光化学效率（ Ｆｖ／ Ｆｍ ）表现明显日变化。上午 Ｆｖ／ Ｆｍ 随光照的增强而降低，至 １４：００ 左右达最低值。其后随着光强的减弱 Ｆｖ／ Ｆｍ 缓慢恢复。一天中叶黄素循环关键组分玉米黄质（ Ｚ）含量与 Ｆｖ／ Ｆｍ 呈负相关。用二硫苏糖醇（ Ｄ Ｔ Ｔ）阻断 Ｚ的形成后，光抑制程度大大加深。结果表明与叶黄素循环有关的非辐射能量耗散的增加是产生光抑制的原因之一。强光处理前饲喂 Ｄ１ 蛋白合成抑制剂林可霉素（ Ｌ Ｍ ）， Ｆｖ／ Ｆｍ 下降幅度增加，而且在暗中与弱光下的恢复出现差异，但强光处理后再引入 Ｌ Ｍ ，则对 Ｆｖ／ Ｆｍ 两种恢复无明显影响。这表明强光可引起银杏叶片 Ｄ１ 蛋白的快速周转而植物体内这种 Ｄ１ 蛋白钝化、复活之间的动态平衡可能是避免强光损伤的保护性反应。自然条件下强光胁迫并不能导致银杏叶片 Ｄ１ 蛋白的净损失。

The significant diurnal variation of photochemical efficiency of PSⅡ (Fv/Fm) was observed in Ginkgo biloba L.leaves on a clear day.In the morning,the Fv/Fm ratio kept on decreasing until it reached its minimum at 14:00,while the reverse change occurred in the later afternoon.Accompanying with the consistent decline of Fv/Fm,the level of zeaxanthin (Z) increased.The reduction of zeaxanthin content and enhancement of photoinhibition of photosynthesis after dithiothreitol (DTT) pretreatment suggestedthat xanthophyll cycle dependent nonradiation energy dissipation was one of the mechanisms of photoinhibition.In the presence of Lincomycin (LM),the Fv/Fm ratio showed a much greater decrease followed by an incomplete dark recovery compared with the control after 2 hours of high light stress.But no marked difference between dark and low light recovery was observed when Lincomycin was exerted after light stress.All these facts supported a conclusion that the reduction in photochemical efficiency of PS Ⅱ was a combination of at least two events:the D1 protein turnover including inactivation and reactivation,which came to a balance under natural conditions and an enhanced xanthophyll cycle dependent nonradiation energy dissipation.