ALA处理对遮荫下西瓜幼苗叶绿素荧光参数的影响

Effects of 5-Aminolevulinic Acid (ALA) on Chlorophyll Fluorescence Dynamics of Watermelon Seedlings under Shade Condition

用100mg/L5-氨基乙酰丙酸(5-aminolevulinic acid,ALA)处理遮荫条件下的西瓜幼苗叶片10d后,用PAM-2100型便携式叶绿素荧光仪连续测定其叶绿素荧光特性。结果表明,遮荫显著降低叶片光化学效率,而ALA处理提高弱光下幼苗叶片PSⅡ实际光化学效率(ΦPSⅡ)、表观光合电子传递速率(ETR)、光化学猝灭系数(qP)以及光化学反应能量分配率(Pc)。SOD活性抑制剂二乙基二硫代氨基甲酸钠(DDC)处理降低ΦPSⅡ、ETR、qP和Pc值等荧光参数,而ALA处理可以消除DDC的抑制效应,说明ALA对PSⅡ光化学反应的促进效应与细胞抗氧化酶活性有关。遮荫处理提高叶片初始荧光(Fo),降低PSⅡ最大光化学效率(Fv/Fm),而遮荫下ALA和(或)DDC处理对这些荧光参数变化没有明显效应。据此推测,ALA处理10d时对西瓜叶片PSⅡ本身没有直接影响,它对光化学效率的促进效应可能是通过增强PSⅠ附近SOD等抗氧化酶活性,促进活性氧代谢来实现的。

The influences of the foliar apphcation with 5-aminolevulinic acid （ALA） on dynamics of chlorophyll fluorescence in watermelon （Citndlus lanatus Thunb. Mansfeld） seedlings under shade condition were studied with PAM-2100 Chlorophyll Fluorometer in the work. The results showed that shading significantly depressed chlorophyll fluorescence parameters, whereas ALA improved the actual photochemical efficiency of photosystem Ⅱ （ФPSⅡ）, the electronic transfer rate （ETR）, the photochemical quenching （qP） and the energy distribution in photochemistry （Pc） absorbed by PS Ⅱ reaction center. The treatment with 1% diethyldithiocarbamate （ DDC）, a chelator of Cu^2＋ , which inhibits the activity of Cu-Zn-SOD, decreased all the parameters above, whereas ALA could inverse the inhibition of DDC, suggesting that promotion of ALA on photochemical efficiency of PS Ⅱ might be related with the activities of antioxidant enzymes. The initial fluorescence （Fo） of watermelon leaves was increased by the shade treatment, and companied with a lower level of the maximum photochemical effciency （Fv/Fm）, suggesting that watermelon is a considerably light-loving crop and low light intensity tends to cause hypogenesis of photosynthetic apparatus. But ALA and/or DDC did not show any effect on the fluorescence parameters which suggested the promotion of ALA on photochemical efficiency of PS Ⅱ did not directly relate with the PS Ⅱ reaction centers in watermelon leaves, but related with acceleration of active oxygen metabolism nearby PS I reaction centers by increasing the activities of antioxidant enzymes, such as SOD.