午间强光胁迫下SOD对大豆叶片光合机构的保护作用

晴天田间大豆叶片Ｐｎ与Ｐｒ均表现出明显的日变化，Ｐｎ日变化曲线里双峰型，中午前后降低。Ｐｒ随日照强度的增加而增加，至上午１１时左右达最大值，然后缓慢下降。普通空气及低氧空气中的ＡＱＹ均在中午前后降低。ＳＯＤ活性也有明显的日变化，最高值出现在下午１６时左右。强光下喷施ＳＯＤ抑制剂ＤＤＴＣ明显降低Ｐｎ及低氧空气中的ＡＱＹ；而在低于叶片光合作用饱和光强下喷施同样浓度ＤＤＴＣ则对Ｐｎ及低氧空气中的ＡＱＹ无明显影响。中午前后ＳＯＤ活性及Ｐｒ的增加对于保护光合机构免受强光的破坏具有重要意义。

The Role of SOD in Protecting the Photosynthetic Apparatus of Soybean Leaves from Midday High Light Stress

The protective effects of SOD in soybean leaves against midday high light stress were studied in Taian,Shandong. Midday depression in net photosynthetic rate (Pn)and apparent quantum yield (AQY) measured both at 21 % O2 and at 2 % O2 was observedin soybean leaves (Fig. 2). The photorespiratory rate (Pr) increased rapidly for a few hours after sunrise, reaching a peak at about 11 A. M. (Fig.1). SOD activity increased during midday (Fig. 3 ), displaying marked diurnal variation. Soybean plants treated with a DDTC (diethyldithiocarbamate) solution and exposed to full sunlight exhibited lower levels of Pn and AQY measured at 2% O2 over the day in comparison with plants untreated with DDTC (Fig. 4). The inhibitory effect of DDTC dwindled when treated plants were exposed to a PFD lower than saturating PFD of leaf photosynthesis (Fig. 5 ). This results indicate that SOD and Pr may play important roles in protecting photosynthetic apparatus from the damaging effects of excessive light energy.