Studies On Physiological And Biochemical Character Of Tomato Seedling Under Low Temperature

In order to investigate the physiological and biochemical changes of tomato seedling under chill stress, this experiment tested the materials of tomato chill-tolerant cultivars 1386,1481 and chill-sensitive cultivar 010 the activities of POD and SOD, the contents of chlorophyll, MDA, proline, free water and bound water ,the change of ultrastructure under different temperatures of 6 , 10 , 15 and 25 for two weeks or more. The results were shown as follows:The growth of tomato seedling was affected differently under different chill stresses.The degree of chilling effect under 15 stress was the slightest among these three chill stresses, and after a short period of chill stress ,the seedling can continue to grow, and that under 6 stress was the heaviest.The content of chlorophyll in the leaves of tomato gradually decreased under chill stress, the degree of decline was according to the intensity of chill stress, but that of chill- tolerant cultivars relatively decreased less than that of chill-sensitive one. The activities of POD and SOD lessened at the early stage of chill stress, then were induced to increase, and reached the maximum around two weeks later. The speed and the degree of POD activity increase was according to the intensity of chill stress, the POD activity of chill-tolerant cultivars increased more than that of chill-sensitive one.When under chill stress of 10 , the activity of SOD was induced to the maximum, and that of the chill-tolerant cultivars increased more and faster than that of chill-sensitive one. The variations of chlorophyll content and POD activity had significant difference between different cultivars and treatments.The contents of MDA and proline increased greatly and fast with the stress time,whose degree increased with the intensity of chill stress. The proline content of chill-tolerant cultivars increased more and faster than that of chill-sensitive one, which was in opposition to the content of MDA. The content of free water decreased under chill stress, whereas that of bound water increased. The decline degree of free water increased with the intensity of chill stress, so did the increasing degree of the bound water. The content of free water in chill-tolerant cultivars decreased more, and whose bound water content also increased more, these in the chill-sensitive cultivars variated reversely. The variation of MDA content had significant difference between different cultivars and treatments.The structure of chloroplast was partly destroyed under chill stress.The membrane of chloroplast partly disjointed ,and the structure of it arrayed disorderly and twisted, there were numerous and large starch grains, and quite amount of osm iophilic granules in the cell.When under chill stress, the activity of POD and the contents of chlorophyll, MDA, free water and bound water in the leaves of tomato could be taken as good physiological and biochemical index for testing chilling-tolerance in tomato.