干旱过程中露花叶片PEPCase酶蛋白量的变化

Change in Protein Mass of PEP Carboxylase in the Leaves of Mesembryanthemum cordifolium under Drought

干旱和盐胁迫使露花叶片中PEPCase活性水平提高数倍。经双相电泳和蛋白免疫印溃(Western immunoblot)发现干旱后露花叶片中PEPCase蛋白量有明显增多。火箭免疫电泳定量分析结果表明,干旱过程中,PEPCase活性水平的提高主要基于其酶蛋白量的增加。干旱引起的这些变化是可逆的,在恢复供水一定时间后可以完全恢复。RubisCO蛋白量在干旱处理的露花叶片中明显减少,恢复供水后又回复到原初水平。PEPCase蛋白量增多,RubisCO蛋白量减少可能是露花叶片CAM途径诱导的生化特征之一。露花叶片中PEPCase活性水平及蛋白量受到叶片发育状况的控制,干旱引起的这两者的变化在中部成熟叶片中最明显,在幼嫩叶片中最小。

The level of PEP-carboxylase activity in the leaves of M. cordifolium, an inducible CAM plant, increased greatly after drought and salt stress (Table 1). Marked increase in PEPcarboxylase protein after drought was shown by two dimensional PAGESDS-PAGE electrophoresis and Western immunoblot (Fig. 1). By using rocket immunoelectrophoresis for quantitative analysis, parallelism in the change of the activity level and protein mass of PEP-carboxylase was observed in the course of drought treatment (Fig. 2, 3), showing that the increase in PEP-carboxylase activity was due to the increase in its protein mass, and not to the modification of preexisting inactive precursor. After rewatering, the levels of PEP-carboxylase activity and protein mass decreased simultaneously, and, two weeks later, both of them decreased to the same levels as those before drought (Fig. 4, 5). Level of RubisCO protein decreased by 30% after 21-day-drought (Fig. 2,3), but showed a tendency to recover after rewatering (Fig. 4, 5). Increase in PEP-carboxylase level and decrease in RubisCO level may be part of the biochemical features of CAM induction by drought in M. cordifolium. In addition, leaf position can influence the distribution of PEP-carboxylase and PubisCO. After drought, the most marked increase in PEP-carboxylase activity and protein mass was observed in middle mature leaves, little change can be seen in the youngest leaf (Fig., 6).