Abstract：To investigate the relationships between the tolerance difference to high temperature stress and superoxide dismutases (SODs) in different cultivars of Celosia cristata, ten-leaf stage seedlings of the heat-tolerant cultivar, Century Green and the heat-sensitive cultivar, Century copper were pulsed for 48 h with diethyldithiocarbamate (DDTC) pretreatment（specific inhibitor of SOD） and subjected to high temperature stress under controlled conditions of relative humidity of 75%~90%, 12 h/24 h photoperiod with 1 500 lx and 45 ℃, to research the changes of external morphology and interior physiology. The results showed that SOD activity was remarkably inhibited by 20 mmol/L DDTC pretreatment and the tolerance of Celosia cristata seedling to high temperature stress was obviously decreased, heat-sensitive cultivar was more obviously than that as heat-tolerant cultivar. During the high temperature gradient stress, the band intensity of all SOD isoforms was reduced differentially, in which the band of MnSOD was significant reduction, followed by Cu/ZnSOD， and one new band named as Cu/ZnSOD was appeared at 35 ℃ and 40 ℃ in heat-sensitive cultivar and heat-tolerant cultivar, respectively. When the temperature was 45 ℃, all bands disappeared expect for FeSOD2 , weak FeSOD3 and Cu/ZnSOD1 in heat-tolerant cultivar; while only FeSOD2 band was remained in heat-sensitive cultivar. It was suggested that SOD isoforms of heat-tolerant cultivar had more activity and stability than that of heat-sensitive cultivar. However, the new bands were inhibited by DDTC pretreatment. It is showed that the tolerance to high temperature was highly related to SOD activity and the difference of cultivars to high temperature stress was relative to activity of FeSOD3 and Cu/ZnSOD1.
