小麦叶片老化过程中光合功能衰退的可能机制

Studieson Deterioration of Photosynthetic Function and Its Probable Mechanism in Natural Aging of Leaf in Wheat

在小麦旗叶自然老化过程中,叶绿素含量(Chl)和光合速率(Pn)在叶片全展时达最大值,以后至叶片枯黄不断降低;RuBPcase活性于全展后10天达到最大值;PS Ⅰ、PS Ⅱ活性在老化前期(展后20天以前)保持平稳,以后不断下降。RuBPcase活性与PS Ⅰ活性、PSⅡ活性比值也均于全展后10天达最大值,以后呈迅速降低趋势,表明在叶片老化中后期,光合机构的光暗反应出现失衡现象,此外,在旗叶老化期间。O_2^(?)产生速率和H_2O_2含量不断增加,SOD活性和CAT活性呈下降趋势。上述结果说明,叶片老化期间光合机构的“光合同化力形成与碳同化作用失衡”不断加重,诱发了活性氧数量的增加,而同时活性氧的清除能力不断降低,导致了活性氧的累积。这可能是造成光合功能衰退的重要原因之一。杂种小麦较亲本具有较长的功能期,可能与其叶片光合机构“光合同化力形成与碳同化作用失衡”程度较轻及活性氧清除能力较强有关。

During flag leaf growth span of wheat, chlorophyll content (Chl) and photo- synthetic rate (Pn) reached the highest values at leaf full expansion, then decreased gradually. The RuBPcase activity peaked at 10 th day after leaf full expansion. During early aging process (before the 20 th day after leaf full expansion), PS I , PS II activity maintained stable, then de clined. The ratios of RuBPcase activity to PS I , PS II activity also reached the maximum at the 10 th day after leaf full expansion, then decreased sharply. It is suggested that the balance be tween photochemical reactions and photosynthetic dark reactions is broken during the middle-late aging process. O2- producing rate and H2O2 content increased, while SOD activity gradually de clined during leaf aging process. These results indicate that during leaf natural aging process, the imbalance between photochemical reactions and photosynthetic dark reactions gradually increas es, Which may cause an increase in active oxygen production and finally result in the deteriora tion of photosynthetic function. The leaves of hybrid wheat showed much longer function dura tion and higher scavenging capacity for active oxygen.