Shading Inhibits Sugar Accumulation in Leaf and Fruit of Jujube (Ziziphus jujuba Mill.)

Abstract

Jujube is a characteristic light-demanding fruit tree, but fruit quality is frequently degraded because of the weak light in protected cultivation facilities in south China. In this study, a black shade net was used to set three light intensities artificially: no shading (0%, control, NS), moderate shading (45%, MS), and severe shading (76%, SS) to investigate the effect of low light on sugar metabolism of jujube. Compared with NS, chlorophyll and carotenoid contents in shaded leaves were increased, while specific leaf weight was decreased. A decrease in sucrose content, rather than fructose and glucose, was the main factor affecting sugar content in shaded leaves and fruits. Low expression of ZjSS2 and ZjSS3 inhibited sugar synthesis in shaded leaves, thereby reducing sucrose content by 23.7% in SS leaf than that in NS. Compared with NS, sucrose content in SS fruit was decreased by 58.1%, which was mainly caused by the down-regulated expression of ZjSS2 and ZjSPS1. In conclusion, sugar accumulation in leaf and fruit with shading treatment was suppressed, which was associated with differential transcription levels of related metabolic genes. The study provides new insights into sugar metabolism in leaf and fruit of phototropic plants under low light environments, such as jujube.