State Key Laboratory of Crop Stress Biology in Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.
Plant Physiol Biochem. 2012 Jun;55:16-22. doi: 10.1016/j.plaphy.2012.03.007. Epub 2012 Mar 23.
Effects of light irradiation on the photosynthetic electron transport chain between P680 and P700 in apple tree leaves was probed with chlorophyll a fluorescence transient and 820 nm transmission measurements during dehydration under different light intensities. The results showed that light accelerated the leaf water-loss rate during dehydration. Leaf dehydration lowered the maximum quantum yield of PSII and the far-red light induced maximal transmission change at 820 nm, but increased the relative variable fluorescence intensity at J-step, especially under increasing irradiation conditions. During leaf dehydration, irradiation lowered the relative variable fluorescence intensity at I-step. At the beginning of leaf dehydration, moderate light accelerated the leaf water-loss rate and then lowered the maximal light-trapping efficiency of P₆₈₀. Upon further dehydration under moderate light or dehydration under high light, light accelerated the water-loss rate and also directly decreased the maximal light-trapping efficiency of P680. The more significant decrease in the exchange capacity of plastoquinones at the Q(B) site was mainly attributed to the faster water-loss rate under moderate light than in the dark. Under high light, irradiation also directly lowered the capacity. The reoxidation of PQH₂ in the dehydrated leaves was enhanced by the light irradiation. The rapidly decreased contents of P700 + plastocyanin were mainly attributed to the faster water-loss rate under light conditions in contrast with that in the dark. The different effects of light irradiations on the photosynthetic electron transport chain might be involved in the acclimation of apple tree leaves to dehydration.
光照对苹果树叶片 P680 和 P700 之间光合电子传递链的影响，通过叶绿素 a 荧光瞬变和 820nm 透射测量在不同光照强度下脱水过程中进行了研究。结果表明，光照会加速叶片在脱水过程中的水分流失率。叶片脱水会降低 PSII 的最大量子产量和远红光诱导的 820nm 最大透射变化，但会增加 J 步的相对可变荧光强度，特别是在光照增强的情况下。在叶片脱水过程中，光照会降低 I 步的相对可变荧光强度。在叶片脱水开始时，适度的光照会加速叶片的水分流失率，然后降低 P₆₈₀ 的最大光捕获效率。在适度光照下或在高光下进一步脱水时，光照会加速水分流失率，并直接降低 P680 的最大光捕获效率。拟醌 Q(B) 位点的电子交换能力下降更为显著，主要是因为适度光照下的水分流失率比黑暗中更快。在高光下，光照也会直接降低其容量。光照射增强了脱水叶片中 PQH₂的再氧化。迅速下降的 P700 + 质体蓝素含量主要归因于光照条件下比黑暗中更快的水分流失率。光照对光合电子传递链的不同影响可能涉及苹果树叶片对脱水的适应。
