PSⅡ膜脂肪酸的脱饱和与黄瓜低温光抑制关系的研究

STUDIES ON RELATIONSHIP BETWEEN FATTY ACIDS DESATURATION OF PS Ⅱ MEMBRANE AND LOW TEMPERATURE PHOTOINHIBITIONOF CUCUMBER

低温适应（１２℃，１２０μｍｏｌ／Ｌ·ｍ－２·ｓ－１ＰＰＦＤ）引起黄瓜子叶ＰＳⅡ膜碎片（ＰＳⅡｍｅｍｂｒａｎｅ，下同）饱和脂肪酸分子百分含量的减少，膜脂不饱和度提高。其中，十六碳脂肪酸的脱饱和较为明显，Ｃ１６３脂肪酸的分子百分含量经低温适应后上升。分段测定类囊体膜的电子传递活力发现，低温适应使电子传递Ｈ２Ｏ→ＭＶ和ＤＰＣ→ＭＶ呈现先降后恢复的趋势，其中ＰＳⅡ的电子传递活力在低温适应７２ｈ内受影响较小；而ＰＳⅠ的活力受到明显抑制。经叶绿素ａ荧光测定也证实，低温适应后ＰＳⅡ的荧光化学效率仍较高，同时，黄瓜子叶对低温光抑制的抗性提高。本文认为，ＰＳⅡ膜碎片中饱和脂肪酸含量的降低有可能提高膜的流动性，从而增强黄瓜幼苗对低温光抑制的抗性。

The percentage of saturated fatty acids from purified photosystem Ⅱmembrane of cucubber(Cucumis Sativa L.)was reduced during cold acclimation(with temperature 12℃,and PPFD 120 μmol.m-2.s-1).Among the various fatty ads from PS Ⅱ membrane, the desaturation of 16C fatty acids was obvious, especially the percentage of C16:3 fatty acid was increased after 24 and 48 hours cold acclimation. Meanwhile,the electron transport activity (H2O→MV and DPC→MV) of thylakoid membrane reduced firstly, then recovered during the cold acclimation course. Activity of PS Ⅱ (H2O→BQ) was little affected, while activity of PS Ⅰ(Asc/DCIP→MV) was inhibited with no recovery within 72 hours cold acclimation.The results of chlorophyll fluorescence also showed that the photo-chemical effciency (Fv/Fm)was not changed during the cold acclimation course, but inhibited greatly only after cooler treatment (with temperature reduced to 6℃ and PPFD as the same).Tests showed that the resistance of cucumber leaves to low temperature photoinhibition increased after cold acclimation.It imlplies that desaturation of fatty acids in PS Ⅱ membrane may maintain membrane fluidity in cold environment, thus increase the resistance of cucumber to low temperature photoinhibition.