Calcium Requirement for Ethylene-Induced Abscission

Ethylene, a gaseous plant hormone, plays an important role in plant organ abscission. Both genetic and biochemical evidence suggest that the response of plants to ethylene is mediated by a specific ethylene receptor. It has been documented that calcium as a second signal is involved in the ethylene-mediated response. However, the mechanism of how calcium (Ca) is associated with ethylene induced abscission on ethylene induced abscission is still unknown. We have investigated calcium concentration, activities of degrading enzymes and PG expressions during ethylene induced abscission of tomato pedicel explants with different calcium treatment. The dates showed that direct application of calcium on explants under ethylene would accelerate abscission. Moreover, cellulase activity, endo-PG activity, and TAPGs mRNA expressions were elevated in explants with calcium treatment. Blocking calcium fluxes with chelators ethylene glycol-bis-(2-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA) or inhibited calmodulin by TFP delayed ethylene induced abscission. Explants incubated in EGTA showed 8% reduction in extractable free calcium of their abscission zone and exhibited a delayed abscission reaction to ethylene. This effect, similar to the ethylene-promoted pathogenesis response and triple response, were found to be calcium dependent. The results indicated that calcium is necessary for the ethylene induced fast abscission.