The effects of calcium on the expression of genes involved in ethylene biosynthesis and signal perception during tomato flower abscission

Calcium regulation of the genes involved in ethylene biosynthesis and ethylene receptors in flower abscission zones (AZ) of wild-type tomato (Lycopersicon esculentum Mill.) was investigated in this study. Calcium treatment delayed abscission of pedicel explants. However, verapamil (VP, calcium inhibitor) treatments accelerated abscission. Results showed an increase in AZ ethylene production consistent with abscission in both control and treatment explants. Moreover, in the AZ of flower pedicels treated with VP, ethylene production, LeACO1 and LeETR1 expression was elevated, but LeETR4 expression decreased. Calcium treatments delayed the onset and maximum ethylene production, maintained low LeACO1 expression and elevated LeETR2, 3, 4, 5 expressions. Results also found that VP and calcium had little effect on LeACS2 expression. Our hypothesis that calcium is integral in preventing ethylene production at the point when 1-aminocyclopropane-1-carboxylic acid (ACC) is converted to ethylene was supported, but the study also revealed the regulation of expression in the ethylene receptors. The potential roles of LeACO1, LeETR 3, 4, 5 and calcium in AZs during tomato pedicel explants abscission are discussed.