Carbon and water relations for developing fruits of Opuntia ficus-indica (L.) Miller, including effects of drought and gibberellic acid.

Growth, gas exchange rates, and carbohydrate content were studied for developing fruits of the cultivated cactus Opuntia ficus-indica (L.) Miller, including effects of drought and exogenous gibberellic acid (GA3). Fruit development required 110 d from the time of bud differentiation to ripening at 80 d after anthesis, when the fruit mass averaged 67 g. Stomatal conductance and net CO2 uptake rates for fruits were higher during the night; they were maximal at 7 d before anthesis and decreased as development progressed. Fruits undergoing drought, imposed by detaching terminal stems bearing fruits, were 50% smaller than the control at 80 d after anthesis and did not ripen. Fruits injected with 2 ml of 500 ppm GA3 were 30% smaller than the control at 80 d after anthesis; they contained a large proportion of aborted seeds that produced a weak sink signal for dry mass accumulation. Gas exchange was higher at 21 d after anthesis for fruits treated with GA3. Total soluble sugars represented 40% of the fruit's dry mass until 45 d after anthesis, when the sugar content rapidly increased, reaching 90% at 73 d after anthesis. Such an increase was not observed for fruits treated with GA3, and the sugar content for fruits undergoing drought remained low throughout development. Starch content increased for developing fruits of O. ficus-indica until 14 d after anthesis and, except for the fruits undergoing drought, decreased thereafter. Fruit development for O. ficus-indica is apparently regulated by water availability as well as hormonal signals originating both within and outside the fruit.