Effect of ethylene, 1-MCP, ABA and IAA on break strength, cellulase and polygalacturonase activities during cotton leaf abscission

Organ abscission in higher plants has invariably been characterized by higher activities of cell wall hydrolases in the abscission zone of the abscising organ, which facilitates degradation of middle lamella and loosening of cell wall of separation layers. The plant hormone ethylene has been implicated in the induction and progression of the abscission process. In the present study, we have measured activities of cellulase and polygalacturonase (PG) in the abscission zone of cotton (Gossypium hirusutum var RST-39) leaf explants in the presence of ethylene. The effects of abscisic acid (ABA) and indole acetic acid (IAA) were monitored to elucidate the role of other phytohormones in the process of abscission. A several fold increase in cellulase and PG activities and decrease in break strength were observed in the LAZ of ethylene-treated explants. The increase in enzyme activities and decrease in break strength were strongly suppressed in the presence of 1-methylcyclopropene (1-MCP) and IAA. ABA alone was found to stimulate enzyme activities and decrease the break strength though not to the extent of ethylene. 1-MCP pretreatment of ABA and ethylene-treated explants showed significant inhibition in enzyme activities. It is concluded that cotton leaf abscission is ethylene regulated and characterized by increased activities of cellulase and PG in its abscission zone. ABA can induce abscission. However, it appears that ABA induced abscission may be mediated through ethylene.