核盘菌(Sclerotinia sclerotiorum (Lib.) de Bary)侵染抑制黄瓜光合作用的机理

 以津春四号黄瓜(Cucumis sativus L. ‘Jinchun 4’)为实验材料,通过同时测定黄瓜叶片叶绿素荧光快速诱导动力学曲线和对820 nm光的吸收曲线,以及过氧化氢含量和过氧化氢酶(CAT)活性的变化,研究了核盘菌(Sclerotinia sclerotiorum(Lib.)de Bary)侵染黄瓜叶片后,对光系统Ⅰ(PSⅠ)和光系统Ⅱ(PSⅡ)功能的影响,并分析了核盘菌侵染后,两个光系统之间的相互影响。结果表明,核盘菌侵染叶片后,叶片过氧化氢(H₂O₂)含量升高,膜脂过氧化的程度加剧,叶片放氧能力下降,快速叶绿素荧光诱导动力学曲线发生变化。核盘菌侵染严重伤害了PSⅡ供体侧(放氧复合体)、受体侧以及反应中心的活性,并且降低PSⅠ最大氧化还原能力(△I/Io)。核盘菌侵染黄瓜后,抑制了CAT的活性,导致过量活性氧的积累,直接伤害了光合机构PSⅠ和PSⅡ的功能;对PSⅠ的伤害抑制了PSⅡ电子向PSⅠ的传递,进一步加剧了PSⅡ的伤害程度,导致更多过剩激发能产生,造成恶性循环,这是核盘菌抑制黄瓜光合作用的主要原因。

Inhibition mechanism of photosynthesis in cucumber leaves infected by Sclerotinia sclerotiorum ( Lib. ) de Bary

By simultaneous measurements of chlorophyll fluorescence transient, light absorbance at 820nm, content of hydrogen peroxide (H_2O_2) and the activity of catalase (CAT), the effect of Sclerotinia sclerotiorum infection on photochemistry activities of photosystem I ( PS I ) and photosystem II (PS II ) was investigated, and the interaction between PS I and PS II was analyzed in cucumber leaves. The results indicated that S. sclerotiorum infection increased the content of H_2O_2, enhanced the peroxidation of membrane lipid, suppressed the rate of O_2 evolution and changed the shape of chlorophyll fluorescence transient significantly. The donor (Oxygen evolution complex) and acceptor sides as well as the reaction centers of PS II were damaged severely by the infection of 5. sclerotiorum. The maximal oxidation-reduction activity of PS I ( ΔI/Io) was also declined by the infection. According to the results, the inhibition of CAT activity and the accumulation of H_2O_2 damaged the function of PS I and PS II. The damage of PS I inhibited the electron transporting from PS II to PS I , which accelerated the damage of PS H leading to an increase of excessive excitation energy. This vicious circle was the main reason of inhibition of photosynthesis in cucumber leaves caused by 5. sclerotiorum infection.