Ethylene and 1-MCP treatments affect leaf abscission and associated metabolism of Chinese cabbage

Leaf abscission during storage of Chinese cabbage (Brassica rapa, subspecies pekinensis and chinensis) can result in serious losses. To uncover the effects of the plant hormone ethylene on leaf abscission, harvested cabbages were treated with ethylene and its competitive inhibitor, 1-methylcyclopropene (1-MCP), and with 1-MCP followed by ethylene. Ethylene treatment accelerated leaf abscission, altered cell structure of the abscission zones, and increased activity and gene expression of cell wall-degrading enzymes. Expression of genes related to ethylene receptors and signaling pathways including BcERS1, BcERS2, BcETR2, BcCTR1, BcEIL1, BcEIL2, and BcEIL3 were also up-regulated. In 1-MCP-treated samples, leaf breakstrength was higher, and the increase of cell wall-degrading enzyme activity and the expression of enzyme-related genes were reduced. Notably, ethylene sensitivity recovered upon subsequent ethylene treatment following 1-MCP treatment. These results indicated that ethylene may constitute an important factor in leaf abscission of Chinese cabbage.