Photooxidative Stress Modulation of Endogenous Phytohormone and Antioxidant Accumulations and Fruit Maturity in Date Palm (Phoenix dactylifera L.)

Abstract

A common modern cultivation practice is bagging the fruit bunch if date palm (Phoenix dactylifera L.) which may influence fruit maturity and nutraceutical quality. Exposure of fruits to photooxidative stress induces changes in the endogenous concentrations of plant hormones and other metabolites, which may cause accelerated fruit maturity. This study was conducted to examine the effect of exposure to direct and indirect sunlight on date palm fruit development. The indirect sunlight treatment was simulated by fruit bunch bagging, a common practice in modern date production. The exposure of date palm fruits to direct sunlight-induced photooxidative stress causing an increased concentration of ascorbic acid and decreased content of chlorophyll, anthocyanins, carotenoids, and phenols compared to the fruit bagging treatment. Direct sunlight also reduced the concentration of phytohormones, including indoleacetic acid, gibberellin, and zeatin, but increased abscisic acid accumulation. The directly-exposed fruits reached a partially-mature stage (Rutab) in August, whereas the bagged fruits remained at the immature stage (Khalal). This study is the first to describe the biochemical basis of the observed improvement of date palm fruit development in response to reduced light intensity. Besides, it provides insights into controlling date palm fruit maturity and subsequently prolonging the shelf life dates on the tree; thus, extending the marketing period for the benefit of the farmers.