Analysis of Calcium Content, Hormones, and Degrading Enzymes in Tomato Pedicel Explants During Calcium-Inhibited Abscission

This study was designed to analyze the changes of phytohormone concentrations, calcium fraction, and the activities of degrading enzymes during calcium-inhibited and ethyleneglycol-bis-(beta-aminoethyl ether)N, N'-tetraacetic acid (EGTA)induced abscission of tomato pedicel explants. Added calcium caused an increase in the total calcium content within the abscission zone and produced a corresponding reduction (20%) in pedicel explant abscission. As expected, EGTA treatment produced the opposite effect and resulted in a decrease in the total calcium content, while accelerating abscission of pedicel explants. Hormone analysis revealed that indole-3-acetic acid (IAA) concentrations in the abscission zone first decreased and then increased before the occurrence of abscission in all treatments, with the greatest effect produced by addition of EGTA. Similarly, abscisic acid (ABA), and gibberellin (GA(1+3)) concentrations, and ethylene production were elevated in the abscission zone during the first 16 h before abscission when explants imbibed EGTA. With calcium treatment, the concentrations of ABA, ethylene, and GA(1+3) also increased in pedicels throughout the first 16 h following exposure, but the increase was slower and less dramatic than with EGTA. Both cellulase and polygalacturonase were induced in the explants during abscission and the activities were also strengthened by treatment with EGTA. Calcium-treated explants produced lower hydrolysing enzyme activities than controls throughout abscission. Calcium played a role of mediating hormone balance and degrading enzymes activities and affected on abscission.