CALCIUM-MEDIATED CHANGES IN PEROXIDASE AND O-DIPHENOL OXIDASE ACTIVITIES OF COTTON FIBERS (GOSSYPIUM SPP) AND ITS POSSIBLE RELATIONSHIP TO ABA

This work is an investigation of the influence of ABA and calcium on soluble and wall-bound activities of peroxidase and O-diphenol oxidase of cotton fibres at the stages of primary and secondary wall development, during incubation of intact fibres for 3 h at 28-degrees-C. ABA (10-mu-M) caused marked inhibition of enzyme activities in both the fractions, whereas calcium (1 mM) was promotory. The incorporation of 1 mM EGTA (a calcium chelator) and chlorpromazine (10-mu-g cm-3) (a calmodulin antagonist) resulted in decreased enzyme activities suggesting regulation of enzyme synthesis and/or secretion to the cell wall by calcium-calmodulin. As a general trend, the relative effect of Ca2+ on the activity of peroxidase in the wall was much greater than on the soluble activity, but this was not true of O-diphenol oxidase. It is inferred that ABA inhibits enzymic activities by inhibiting calmodulin synthesis or its mobilization to sites of action.