Effects Of Light And Temperature Stress On The Growth And Development Of Lettuce

Adapted to cool climate, lettuce (Lactuca sativa L.War.angustana Irish.) that grow in Autumn is liable to bring on early bolting because of the high temperature, which affects the form of edible parts. For finding out the guide line of filtrating heat-tolerant variety, this research is to compare the contents of total Chlorophy11 and autioxidant systems in different heat-tolerance lettuce seedlings under high temperature stress, and for investigating the early bolting, this paper is to compare the bolting-tolerance of "Zhongduerhao" under different conditions, along with analysing the impact of bolting seedlings.1. Effects of High Temperature Stress on Chlorophy11 and Autioxidant Systems in Lettuce Seedlings. Effects of two high temperature stress 30℃/25℃(d/n), 35℃/30℃(d/n) on chlorophy11 and autioxidant systems in lettuce seedlings of heat-tolerant "Xiakang40" and heat-sensitive "Zhongdudongqing" were studied. Under high temperature condition, the contents of total chlorophy11 and carotenoid decreased by more than 18 percent as compared with the control, which were hard to recover. With the prolonging time of high temperature stress, MDA content improved fast, showing more significant effects at 35℃/30℃(d/n) in heat-sensitive lettuce seedlings. High temperature stress increased the activities of SOD,CAT and APX . The activities of these enzymes returned to normal after 3 days of recovery under normal conditions. Pro content increased markedly under 30℃/25℃(d/n), at the same time, much less in heat-tolerant "Xiakang40" than in heat-sensitive "Zhongdudongqing".2. The different effects of temperature,length of light,age of seedling and time in Lettuce Seedlings: The cross-over experiment design in lettuce seedling of "Zhongduerhao" contents four factors of two levels: temperature [22℃/18℃(d/n), 35℃/30℃(d/n)],length of light ( 10h/d,15 h/d),age of seedling (30d, 40d),time (5d, 10d) .The aim of this experiment design is to find out the condition under which lettuce is easy to bolt, using DPS to analyse the length of stalk. The effects of four factors are very different, ranging from big to small is length of light > temperature > time>age of seedling. Staying 10days under heat temperature, long light condition, the seedling of 30 days is easier to bolt than other conditions.3. The comparing research between bolting lettuce and unbolting lettuce: Differences between the lettuce seedlings under the condition of common temperature 22℃/18℃(d/n), common light (10h) and the lettuce seedlings under heat temperature 35℃/30℃(d/n), long light (15h) were studied. Under the condition of heat temperature and long light, the lettuce seedlings were easy to bolt, the stalk of which was longer and thinner. Soluble protein content increased fast along with the deeper degree of bolting. POD activity in bolting seedlings was stronger than unbolting ones, and the deeper of bolting degree, the stronger of POD activity. Reducing sugar content increased a little in both bolting and unbolting seedlings. Sucrose and total soluble sugar all decreased, the tending of bolting is obvious.