ALA对遮荫条件下西瓜幼苗强光抑制的保护效应

Protection of 5-Aminolevulinic Acid(ALA) on High Light Photoinhibition of Watermelon Grown under Shade Condition

以遮荫生长的盆栽西瓜幼苗为材料,研究了100mg/L5-氨基乙酰丙酸(5-aminolevulinic acid,ALA)处理对暗适应叶片转入强光下叶绿素荧光特性的影响.结果显示,遮荫能显著提高暗适应叶片的Fo,降低Fv/Fm和Fv/Fo;正常光照下生长的植株叶片暗适应后转入1500μmol·m-2·s-1作用光强下5min的ΦPSⅡ、qP和Pc分别为0.176、0.399和0.180,约为600μmol·m-2·s-1作用光强下的62%、72%和64%;而遮荫下生长的幼苗叶片暗适应后转入1500μmol·m-2·s-1作用光强下的ΦPSⅡ、qP和Pc分别为0.089、0.301和0.089,仅为600μmol·m-2·s-1作用光强的40%、66%和40%;遮荫还显著降低西瓜叶片暗适应后转入强光1500μmol·m-2·s-1的PCR和qL,同时提高L(PFD).ALA处理能提高遮荫西瓜幼苗叶片PCR、Pc、qL和Hd等荧光参数,降低Ex、ΦNO和L(PFD);SOD活性抑制剂DDC处理降低PCR、Pc、qL和Hd等荧光参数,而ALA处理可以逆转DDC的抑制效应;ALA处理能提高西瓜幼苗叶片SOD、POD和APX活性.研究发现,遮荫导致西瓜幼苗光抑制程度加重,ALA通过增强PSⅠ附近SOD等抗氧化酶活性,促进水-水循环,增加热耗散,减轻光抑制,提高西瓜幼苗叶片的光化学效率,从而对强光下的光合作用起到保护作用.

In order to demonstrate the protection of 5-aminolevulinic acid （ALA） on photosynthetic photoinhibition of high light,the chlorophyll fluorescence characteristics of watermelon grown under shade condition were analyzed by the leaves that were transferred to 1 500μmol ·m^-2 · s^-1 actinic light intensity. The results indicated that shading significantly increased the initial fluorescence （Fo） of watermelon leaves,and decreased the maximum photochemical efficiency （Fv/Fm） and the potential photochemical efficiency （Fv/ Fo） of PS Ⅱ. The results suggested that watermelon is a considerably light-loving crop. When leaves were transferred to 1 500μmol · m^-2 ·s^-1 for 5 minutes, the actual photochemical efficiency of PS Ⅱ （ФPSⅡ）, photochemical quenching （qP） and the energy distribution in photochemistry （Pc） of leaves of watermelon grown under natural light were 0. 176,0. 399 and 0. 180 respectively,which were 62%,72% and 64% of that when leaves were transferred to 600μmol ·m ^-2 · s^-1. When leaves of watermelon grown under shade condition were transferred to 1 500 μmol · m^-2 · s^-1 for 5 minutes,ФPS Ⅱ ,qP and Pc were 0.089,0. 301 and 0.089 respectively,which were 40%,66% and 40% of that when leaves were transferred to 600μmol·m^-2 · s^- 1. The difference showed that high light photoinhibition was much heavier in the leaves of watermelon grown under shade condition than that under natural light. Moreover, shade decreased leaf photochemical rate （PCR） and photochemical quenching in ＂lake model＂ （qL）, but increased relative limit of photosynthesis （L（PFD）. Nevertheless, ALA treatment increased PCR,Pc, qL and the antenna heat dissipation （Hd）,but decreased the energy dissipation by non-photochemistry in PS Ⅱ reaction center （Ex）,the non-regulated energy dissipation in PSⅡ（ФNO） and L（PFD）. The treatment with 1% diethyldithiocarbamate （DDC）,a chelator of Cu^2＋ ,inhibits the activity of Cu-Zn-SOD, decreased PCR,Pc,qL and Hd,whereas ALA could inverse the inhibition of DDC. The promotion of ALA on photochemical efficiency of PS Ⅱ might be related with the activities of antioxidant enzymes. Measurement of antioxidant enzyme activities approved that ALA treatment increased the activities of superoxide dismutase （SOD）, peroxidase （POD） and ascorbate peroxidase （APX）. The phenomena indicated that the protection of ALA on photosynthetic photoinhibition of high light might be related with acceleration of active oxygen metabolism nearby PSI reaction centers by increasing the activities of antioxidant enzymes,such as SOD.