Ethylene induced cotton leaf abscission is associated with higher expression of cellulase (GhCel1) and increased activities of ethylene biosynthesis enzymes in abscission zone

Ethylene induced cotton (Gossypium hirusutum var RST-39) leaf abscission has been characterized by measuring the activities of ACC synthase (ACS, E.C. 4.4.1.14), ACC oxidase (ACO, E.C. 1.14.17.4) and cellulase (E.C. 3.2.1.4). In addition, a leaf abscission specific cDNA (GhCel1) has been cloned from cotton, which belongs to the α2 subgroup of cellulases that possess a C-terminus carbohydrate-binding domain. Measurement of enzyme activity in the abscission zones of cotton leaf explants exposed to ethylene for 48 h compared to non-treated controls indicated a more than 5-fold increase in the activity of ACS, 1.2-fold increase in the activity of ACO and about 2.7-fold increase in the activity of cellulase in the ethylene treated explants. This increase was accompanied by a substantial decrease in the force required to separate the petiole from the stem (break strength) and an increased accumulation of cellulase transcript in the abscission zone. Treatment of explants with 1-Methylcyclopropene (1-MCP) prior to ethylene resulted in significant inhibition of enzyme activities and transcript accumulation. It is concluded that ethylene response of cotton leaf abscission leads to higher cellulase expression and increased activities of ethylene biosynthesis enzymes in the abscission zone.