Abstract: A continual drought and waterlogging treatment experiment was conducted to study the variations of chlorophyll, soluble protein, soluble sugar, proline, and MDA contents and antioxidase activities of Scaevola aemula cutting seedlings under different levels of water stress, and to analyze the differences in the response characteristics and related mechanisms. At the early stage of water stress (within 5 days), the injury indices and most of the physiological indices of the cutting seedlings had no significant differences with the control. With the increasing intensity and duration of drought stress, the cutting seedlings
were damaged seriously and finally died. The injury indices, proline content, and SOD, POD, and CAT activities increased sharply, chlorophyll content decreased significantly, and the contents of MDA, soluble protein, and soluble sugar increased after an initial decrease. Under waterlogging stress, the soluble sugar and chlorophyll contents decreased first and increased slightly then, the MDA and soluble protein contents presented a trend of decreasing-increasing-decreasing, the SOD and POD activities decreased somewhat after an initial increase, and the CAT activity and proline content had a persistent increase. Overall, a continual drought and waterlogging stress had serious effects on the morphological and physiological characteristics of S. aemula. The responses of S. aemula cutting seedlings to drought stress were more drastic than to waterlogging stress, and the seedlings were failed to recover their self-adjustment adaptability to the adverse environment under persistent drought stress.

Key words: Wheat genotypes, Aluminum tolerance, Screening parameters, Shoot tolerance parameters, Root tolerance parameters