Abstract:Two early-bolting cultivars G-B30, G-B31 and late-bolting cultivars G-B4, G-B20 were used to study the dynamic changes of the sugar components, total soluble sugars, starch, soluble protein content and the ratio of carbon and nitrogen to clarify the physiological basis during lettuce bolting at high temperature. The results showed that under higher temperature treatment, apart from G-B20,the content of sucrose, fructose and glucose in 3 kinds of lettuce at bolting critical point were lower than unbolting stage.The content of total soluble sugar in two early-bolting cultivars were the lowest at the bolting critical point, while the content of total soluble sugar in two late-bolting cultivars were lowest at the beginning stage of flower bud differentiation.The content of starch at flower bud differentiation stage reached a maximum, while decreased rapidly during bolting.The content of galactose and soluble protein in early-bolting cultivars were significantly higher than unbolting stage,there was a trend of accumulation,while they were opposite for late-bolting cultivars. At the bolting stage, C/N ratio reached a maximum in two easy bolting species, the ratio continued to rising in two later bolting varieties during high temperature processing.As a summary, soluble protein, galactose content accumulated, soluble sugar, glucose, fructose, sucrose, starch content and C/N declined during bolting. The above finding provides a reference basis for further study on molecular mechanism during lettuce bolting at high temperature.