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研究了遮荫棉花 (GossypiumhirsutumL .)突然由遮荫条件暴露在自然强光下时 ,叶绿素荧光发射、叶绿体色素组成、净光合速率 (Pn)等在光照转换当天以及随后的适应过程中 (光照转换后 15d内 )的变化。遮荫棉花突然转到强光下 ,叶片发生了严重的光合作用光抑制 ,叶绿素荧光参数Fv/Fm 和ΦPSⅡ急剧降低 ,且明显低于自然光照下生长的叶片 ,而Fo 值却明显升高。这些参数即使在光照转换的次日清晨也不能完全恢复。Fv/Fm 和Pn 在光照转换以后的 4d内持续降低 ,在第 6天以后开始逐渐升高 ,在 10～ 12d达到稳定值 ,表现出遮荫棉花叶片对光强变化的一定适应性 ,但Fv/Fm 和Pn 均未达到自然光照条件下生长的棉花叶片的相应值。最后的Pn 值较遮荫下叶片增加 6 0 % ,但同自然光照下生长的叶片相比只有后者的 40 %。试验结果还表明 ,光照转换以后叶片内叶黄素循环库逐渐增大 ,在较短的时间内 (3d)即可达到较高的水平。遮荫棉花突然转到自然强光下 ,叶片Fv/Fm 及Pn 的降低与PSⅡ反应中心的破坏有关 ,在对强光的适应过程中依赖叶黄素循环的热耗散等保护机制增强。光保护机制的逐渐完善有助于减轻叶片由遮荫转到强光下遭受的光破坏
The results showed that chlorophyll fluorescence emission, chloroplast pigment composition, net photosynthetic rate (Pn) and the like of Gossypium hirsutum L. exposed to natural light suddenly under shading conditions. During the light adaptation and subsequent adaptation (light conversion After 15d) changes. Shade cotton suddenly turned to bright light, and photosynthetic photosynthesis was depressed in leaves. The chlorophyll fluorescence parameters Fv / Fm and ΦPSⅡ decreased sharply, and were significantly lower than those grown under natural light, but the Fo value was significantly increased. These parameters do not fully recover even in the early morning of the day after the light is switched. Fv / Fm and Pn decreased continuously within 4 days after light conversion, and gradually increased after day 6, reaching stable values from day 10 to day 12, indicating that Fv / Fm and Pn had certain adaptability to light intensity changes. However, Fv / / Fm and Pn did not reach the corresponding values of cotton leaves grown under natural light conditions. The final Pn value increased by 60% compared with shaded leaves, but only 40% of the latter compared with leaves grown under natural light. The test results also showed that after the light conversion, the lutein cycle library in the leaves gradually increased, reaching a higher level in a short period of time (3d). Shade cotton suddenly turned to natural light, and the decrease of Fv / Fm and Pn in leaves was related to the damage of PSⅡ reaction center. The protection mechanism of heat dissipation dependent on xanthophyll cycle in the adaptation process to strong light was enhanced. The gradual improvement of the photoprotection mechanism helps to reduce the light damage suffered by the leaves from shading to intense light