低温弱光胁迫下芸豆叶片光抑制与类囊体膜脂构成变化

Changes in photoinhibition and fatty acid composition in the thylakoid membrane of kidney bean leaves under low temperature and weak light stress

以对低温弱光敏感性有差异的两个红芸豆品种为材料,研究了低温弱光胁迫处理及恢复过程中幼苗叶片的叶绿素含量、荧光参数和类囊体膜脂肪酸组成的变化。结果表明:与对照相比,随胁迫时间延长,叶片中Chl a、Chl b和Chl(a+b)含量降低(P<0.05);Fv/Fm、Fv′/Fm′、qP、ΦPSⅡ和ETR下降(P<0.05),Chl a/b和NPQ上升(P<0.05);类囊体膜脂MGDG、DGDG和SQDG中的亚麻酸(C18:3)含量显著降低(P<0.05),棕榈酸(C16:0)含量显著升高(P<0.05),PG中的棕榈酸(C16:0)和反式十六碳-烯酸[C16:1(3t)]含量降低(P<0.05),而亚麻酸(C18:3)和亚油酸(C18:2)含量升高(P<0.05),在叶片抵御低温弱光胁迫过程中维持一定的膜脂不饱和度的重要作用。随胁迫时间延长,类囊体膜总饱和脂肪酸(SFA)含量升高,多不饱和脂肪酸(PUFA)含量以及膜脂不饱和度(U/S)显著降低,恢复期则相反。在胁迫处理和恢复期,“英大红”和“小红芸豆”的U/S变化差异不明显,PUFA含量变化差异显著(P<0.05),且与Fv/Fm的相关性分别达到86.21%和83.92%,表明低温弱光处理及恢复过程中,光抑制后PSⅡ功能的修复与PUFA含量增加存在一定关系。因此,低温弱光胁迫下“英大红”光抑制程度较“小红芸豆”轻,可能是较高含量的PUFA增加了类囊体膜的不饱和度,维持膜的稳定性,减轻了光抑制。

This research investigated the changes in photoinhibition and fatty acid composition in thylakoid membrane under combined stresses of low temperature and weak light in two varieties of kidney bean,‘British big red’and‘Shanxi small red’,which have different sensitivity to low temperature and weak light.The main lipids in the thylakoid membrane are monogalactosyl diglyceride(MGDG),digalactosyl diglyceride(DGDG),phosphatidylcholine,phosphatidylglycerol(PG)and sulphoquinovosyl diglyceride(SQDG).The fatty acid composition of the thylakoid membrane,together with photosynthetic and chlorophyll(Chl)fluorescence parameters were determined during stress and recovery.It was found that with increase in stress duration,the content of Chl a,Chl b and Chl(a+b)decreased while the ratio of Chl a/b increased.Compared to the control,the maximum quantum yield of PSⅡ(Fv/Fm),the efficiency of excitation capture by open PSⅡreaction centers(Fv′/Fm′),the photochemical quenching coefficient(qP)and the actual PSⅡefficiency(ΦPSⅡ)declined,but Chl a/b and the non-photochemical quenching(NPQ)increased.With more prolonged stress duration MGDG,DGDG and SQDG,and thylakoid membrane content of linolenic acid(C18:3)were substantially reduced and the content of palmitic acid(C16:0)was concomitantly increased.These changes with increased stress duration represented an increased content of saturated fatty acids,and a decreased content of unsaturated fatty acids(UFA),polyunsaturated fatty acids(PUFA)and degree of membrane unsaturation in the thylakoid membrane lipids.However,there were also changes in the PG fraction which contributed to maintaining the overall degree of unsaturation in membrane lipids.This pattern was reversed during the recovery period.The correlation coefficients between PUFA and Fv/Fm of‘British big red’and‘Shanxi small red’kidney beans were 0.8621 and 0.8392,respectively.Compared to‘British big red’kidney beans,stress caused more serious photoinhibition in PSⅡof‘Shanxi small red’kidney bean leaves.Therefore,it can be postulated from these results that the reason for the increased the stability of the thylakoid membrane and reduced photoinhibition of PSⅡin‘British big red’kidney beans may be the higher membrane content of UFA,especially PUFA.