桑树叶片光合环式电子流和抗氧化酶活性对干旱的响应

Responses of Cyclic Electron Flow and Antioxidant Enzyme Activities in Leaves of Mulberry to Drought

以生长在由草炭土和蛭石(V(草炭土)∶V(蛭石)=2∶1)均匀混合的培养基质中高50 cm左右的桑树(Morus alba L.)为供试植株,以土壤田间持水量(40±5)%的含水量为干旱处理,以土壤田间持水量(80±5)%的含水量为对照。利用多功能植物效率分析仪和脉冲调制式荧光仪联合的方法测定了不同处理的桑树叶片环式电子流,结合经典方法测定叶片在干旱胁迫下生理指标和净光合速率等指标的变化,分析干旱对桑树叶片净光合速率、光合色素质量分数、丙二醛质量摩尔浓度、相对电导率、保护酶活性、环式电子流的影响。结果表明:干旱处理的桑树叶片净光合速率显著降低,比正常浇水(对照)降低了57.4%;叶片相对电导率、丙二醛质量摩尔浓度,分别增加了56.8%、65.2%。干旱处理的桑树叶片光合色素质量分数降低,其中叶绿素a和b质量分数比对照分别降低了57.4%和53.7%,类胡萝卜素质量分数比对照降低了35.4%。干旱处理的桑树叶片超氧化物歧化酶、过氧化物酶、过氧化氢酶活性显著增强,分别比对照高56.6%、56.0%、49.7%。桑树叶片质子梯度调节蛋白(PGR5)和还原型烟酰胺腺嘌呤二核苷酸磷酸脱氢酶复合物(NDH)复合体介导的两种环式电子流,分别比对照提高了51.1%和23.5%。说明干旱胁迫下的桑树,除了以经典的抗氧化酶活性提高抗旱性之外,光合环式电子流在提高桑树抗旱性、保护光合机构方面也非常重要。

The responses of cyclic electron flow and antioxidant enzyme activities in leaves of mulberry to drought,with soil field water holding capacity of 40%±5% as drought treatment and 80%±5% as control,were investigated using mulberry grown in mixed medium of turfy and vermiculite soil(volume ratio is 1 ∶ 2) as experimental material. The cyclic electron flow was measured by combined technique of multi-function plant efficiency analyzer and pulse modulated fluorometer to compare with physiological parameters and net photosynthetic rate,and the effects of drought on net photosynthetic rate,pigments,malondialdehyde(MDA) content,the relative conductivity,protective enzyme activity and cyclic electron flow under drought were analyzed. The net photosynthetic rate in mulberry leaves treated with drought decreased significantly by57.4% compared to control(CK). The relative conductivity and MDA content in leaves of mulberry increased by 56.8%and 65.2%,respectively. The photosynthetic pigment content was reduced compared to CK,and the contents of chlorophyll a,chlorophyll b,and carotenoids in leaves of mulberry decreased by 57.4%,53.7%,and 35.4%,respectively. Drought enhanced the activities of superoxide dismutase(SOD),peroxidase(POD) and catalase(CAT) in mulberry leaves,which were 56.6%,56.0% and 49.7% higher than those of CK,respectively. At the same time,the two cyclic electron flows around PSI(PGR5-dependent and NDH-dependent cyclic electron flow) were significantly increased by 51.1% and 23.5%,compared to CK,respectively. It is indicated that it is very important to enhance cyclic electron flow in leaves of mulberry to protect photosynthetic apparatus under drought except the classic ways of increasing antioxidant enzyme activities.