小叶锦鸡儿抗沙埋生长与抗氧化酶及同工酶变化的关系

小叶锦鸡儿(Caraganas tenophylla L.)是广泛应用于流动沙丘治理的优良固沙植物。然而关于其抗沙埋生理机理目前尚不清楚。选择生长在科尔沁沙地的小叶锦儿为试验材料,依据株高对其进行不同程度沙埋(轻度、中度、重度沙埋), 并通过测定沙埋过程中植株高度、不同部位叶片丙二醛(MDA)含量、抗氧化酶活力、抗氧化酶同工酶谱变化, 以揭示其抗沙埋生理适应机理和基因调控机理。结果表明:沙埋6d,植株各部位生长加快,尤其是顶部和基部生长更快。叶片MDA含量降低、整株植物叶片平均过氧化氢酶(CAT)、过氧化物酶(POD)、过氧化物歧化酶(SOD)活力增加,但重度沙埋使抗氧化酶活力下降。沙埋12d,植株各部位生长继续加大, 沙下叶片凋落。与对照相比,沙上叶片MDA含量成倍增加,并与叶片POD、SOD和CAT活力的大幅度提高呈正相关,并与对照差异显著(P < 0.01)。同时,不同厚度沙埋6d,叶片CAT同工酶出现两新带CAT III和CATII;POD同工酶谱带(6条酶带)随沙埋厚度增加,叶片PODII区带加宽、色加深,POD I 和POD III酶带消失。但是,不同厚度沙埋下,沙上和沙下叶片CAT、SOD和POD酶谱带数和活力均相同。这表明在沙埋应激适应反应期(6d),叶片抗氧化酶活力的增强与抗氧化酶基因表达增强和基因启动有关。受到沙埋重力胁迫的成熟叶可能将胁迫信号传递给沙上没有沙埋的叶子及生长点,导致整株叶片产生整体适应性反应,激活抗氧化酶系统,以致加速生长。因此,小叶锦鸡儿萌蘖生物学特性和抗氧化酶对沙埋胁迫快速响应在维护氧自由基代谢平衡和植株快速恢复生长中起重要保护作用。

The relationship between growth of Caraganas stenophylla and the activities and isoforms of protective enzymes under different depths of sand burial

The shrub Caraganas stenophylla is widely distributed and used as a sand binding plant on moving sand dunes in China. The physiological mechanisms involved in C. stenophylla responds to coverage with sand are unknown. Therefore we investigated responses to three levels of sand burial based on plant height: light (1/4 plant height), modest (2/4 plant height), and severe (3/4 plant height) as compared with controls (no sand burial). To understand the physiological and molecular regulatory mechanisms for C. stenophylla in adaption to sand burial, changes in length of different parts of plant stems were observed 3 days (d), 6d, 9d, and 12d after sand burial treatment and contents of malondialdehyde (MDA) and activities of antioxidant enzymes peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) were measured 6d and 12d after treatment. CAT and POD isozymes were also analyzed in leaves 6d after sand burial treatment. Results showed that 6d after sand burial treatment, growth rates of different parts of the stem increased as burial deepened. At the same time, MDA content in the leaves decreased and activities of CAT, POD and SOD in different plant parts increased under light and modest sand burial treatments. Growth rate was higher 12d after treatment than at 6d after treatment but the leaves under sand died. Meanwhile, MDA content and SOD activity were markedly increased by 64% and 121% in leaves above sand under modest and severe sand burial. CAT activity in leaves above sand was also higher under light and modest sand burial. POD activity in the leaves under different depths of sand burial was higher by 308%-104%. SOD activity was higher by 32% and 233% in the leaves with modest and severe sand burial compared with controls. This suggests that the higher growth rate during 7-12d was positively correlated with higher activities in protective enzymes, and increases in antioxidant capacity after sand burial, which might have played an important role in the stem growth and the balance of oxygen free radical metabolism. Analysis of isomers of antioxidant enzymes by native-PAGE and activity staining revealed new isoforms, CAT III and CATII, in the leaves with modest and severe sand burial, and their concentrations were enhanced by sand burial. There are six isoforms of POD; POD II intensity increased with increasing depth of sand burial; a new band, POD IV, was observed while POD I and POD III disappeared. This suggests that during acclimation to sand burial, the activity of protective enzymes is highly related to differential gene expression. Isofo rms of CAT, POD and SOD in the leaves over sand were similar to those under sand 6d after sand burial, which indicates that the signal of sand burial was transduced from leaves under sand to leaves over sand, resulting in the whole plant receiving the signal of sand stress to adapt to sand burial. Therefore, differential gene expression plays an important role in increasing protective enzyme activity to maintain the balance of oxygen free radical metabolism in C. stenophylla.