Calcium translocation to fleshy fruit: its mechanism and endogenous control

Abstract

The translocation of Ca within the plant and the causes of Ca deficiency in fruit are still a matter of conjecture. The main obstacle for Ca translocation to fruit appears to consist less of deficiencies in the transport channels or the driving forces for Ca transport but rather of the mechanisms that plants have developed for the restriction of Ca transport in order to maintain rapid fruit growth. These seem to be based on a hormonal control, mainly executed by gibberellins (GAs): physiologically active GAs have been shown to inhibit Ca translocation. High levels of GAs during periods of vigorous growth could therefore be responsible for the often-observed decline in the course of Ca uptake during fruit development. Consequently, varying levels of GAs due to environmental factors could be the cause of the observed differences in the Ca content per fruit between different years and different regions. Ca is known to stabilize cell membranes and in this way may prevent physiological disorders attributed to Ca deficiency. As only very limited quantities of Ca can be directly supplied to the fruit, reducing excessive GA levels by various means may be the better way to control such disorders.