Role of calcium in ripening and senescence

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Abstract
In view of the possibility that senescence may be a consequence of the deterioration of cell walls and membrane compartments, calcium was studied as a possible agent which might defer senescence. Calcium treatment delayed leaf senescence in corn leaf discs. The effect of calcium on senescencse was additive to the cytokinin deferral of senescence. An increase in hydraulic permeability to [3H] water during senescence was demonstrataed and this increase was deferred by calcium; calcium plus benzyladenine was even more effective. Analysis of inorganic ions in the pericarp of nonripening rin mutant tomajç fruits and isogenic Rutgers revealed higher levels of bound Ca in rin at advanced stages of maturity. In the normal fruits, bound Ca decreased about 3‐fold during maturity. In rin fruits, no change in polygalacturonase (PG) activity was detected, whereas in Rutgers, an increase in PG activity was observed at advanced stages of maturity. Each of the measured changes associated with senescence (pigment changes, protein decrease, hydraulic permeability increase, and an increase in cell wall enzyme activity) was suppressed by calcium, and the interpretation is offered that the effects are a consequence of the calcium function in maintaining cell wall structure and membrane integrity.