Carbohydrate metabolism in tomato ( Lycopersicon esculentum Mill.) seedlings and yield and fruit quality as affected by low night temperature and subsequent recovery

In order to clarify carbohydrate content and enzymes activities involved in sugar metabolism in tomato seedling leaves and yield and fruit quality under low night temperature and subsequent recovery, tomatoes ( Lycopersicon esculentum Mill. cv. Liaoyuanduoli) were grown in different climatic controlledenvironment chambers with day/night temperature regimes of 25/15, 25/9 and 25/6°C for 9 days and then were transferred to 25/15°C chamber for 9 days recovery. The results showed that fructose, glucose and sucrose content under low night temperature and starch content at 9°C were higher than that of the control level; only starch content at 6°C decreased and there was no significantly difference in fructose content between 6 and 9°C. Under low night temperature, sucrose phosphate synthase (SPS) activity in tomato leaves significantly increased. NI activity and SS activity decreased after 3 days treatment and soluble acid invertase (SAI) activity increased after 5 days treated. After 9 days recovery, starch content and SAI activity were difficult to return to the level of the control. After fruits were harvested, the marketable yield and single plant yield decreased in the first cluster fruit of the 6°C treated plants. Enhanced SPS activity and sugar accumulation play important roles in tomato leaves under low night temperature stress. Key words: Low night temperature, Lycopersicon esculentum, sucrose metabolism, enzymes related sugar metabolism, yield and quality.