Calcium effects on mediating polygalacturonan activity by mRNA expression and protein accumulation during tomato pedicel explant abscission

Abstract

Flower abscission is accompanied by a marked increase in polygalacturonase (PG), an enzyme responsible for degradation of the middle lamella, and a subsequent reduction in the abscission zone (AZ) break strength. Calcium (Ca) is reported to bind polygalacturonan to form ‘egg-box’ complexes that effectively inhibit organ abscission. The results obtained from our experiments showed that an 80 mM Ca concentration was most effective in delaying tomato pedicel explants abscission. During abscission, Ca did not suppress increases in endo-PG activity, or change PG mRNA expression and protein accumulation in the abscission zone. In contrast, using ethylene glycol tetraacetic acid (EGTA), verapamil (VP) and trifluoperazine (TFP) treating pedicel explants would accelerate the abscission. Moreover, EGTA, VP and TFP treatments enhanced endo-PG activity and changed PG mRNA expression and protein accumulation timing in the AZ. The results of this study suggest that Ca delays tomato pedicel explants abscission by mediating PG activity at both the transcriptional and translational levels.