39B-12

J. SHENG JIPING, School of Food Science, China Agricultural University, Beijing, 100094

Changes of Lipoxygenase Activities and the Relationship between Lipoxygenase and ethylene in tomato fruits

SHENG Jiping LUO yunbo SHEN Lin (School of Food Science, China Agricultural University, Beijing 100094, China)

Lipoxygenases comprise of a class of iron-containing enzymes that catalyse the oxygenation of polyunsaturated fatty acids bearing a cis, cis-1.4-pentadiene structure, such as linoleic and linolenic acids. On oxidation they produce fatty acid hydroperoxides and free radical species. Some fractionation studies have indicated that LOXs participate in the formation of ethylene directly or indirectly.

The aim of this study is to achieve a better understanding of the action mode of LOX and the relationship between LOX and ethylene production.

In this study two kinds of tomato fruits which were normal tomato (cv. Lichun) and antisense ACS gene tomato (ethylene deficiency) were used as material. The results showed that LOX activities varied with the ripening stages and the position of the tomato tissue. Pericarp fruit tissue gave the highest LOX activity at every stage of Lichun and also the maximum level at the turning stage. The regression equation between LOX activity (y) and DAA (x) was y=-79.537+720767/x. ACS tomato showed almost a same pattern with Lichun, except the figure was significant lower. The coefficient of LOX activity to fruit development before harvest was r=- 0.9840, the regression equation was y=16.264+8.927/x. LOX and ethylene had a close relationship. One side was that ethylene involved the regulation of LOX activities. 2000ppm ethrel treated LOX extract solution showed no significant increase activity of LOX, but it increased significantly in tissue slices and fruits. Another side was LOX participated indirectly in the ethylene biosynthesis. Several experiments were set to prove the idea. They showed the lipid hydroperoxides which from the polyunsaturated fatty acids catalysed by LOX participated the oxidation of ACC to ethylene. Studies of LOX and the relation between LOX and ethylene can make people know more about the ripening process of fruit and have significance for keeping high quality of fruits.