GA3 Treatment Delays the Deterioration of ‘Shixia’ Longan during the On-Tree Preservation and Room-Temperature Storage and Up-Regulates Antioxidants

Abstract

Gibberellic acids had been proven to improve the fruit quality and storability by delaying deterioration and maintaining the antioxidant system. In this study, the effect of GA3 spraying at different concentrations (10, 20, and 50 mg L−1) on the quality of on-tree preserved ‘Shixia’ longan was examined. Only 50 mg L−1 GA3 significantly delayed the decline of soluble solids (22.0% higher than the control) and resulted in higher total phenolics content (TPC), total flavonoid content (TFC), and phenylalanine ammonia-lyase activity in pulp at the later stages. The widely targeted metabolome analysis showed that the treatment reprogrammed secondary metabolites and up-regulated many tannins, phenolic acids, and lignans during the on-tree preservation. More importantly, the preharvest 50 mg L−1 GA3 spraying (at 85 and 95 days after flowering) led to significantly delayed pericarp browning and aril breakdown, as well as lower pericarp relative conductivity and mass loss at the later stages of room-temperature storage. The treatment also resulted in higher antioxidants in pulp (vitamin C, phenolics, and reduced glutathione) and pericarp (vitamin C, flavonoids, and phenolics). Therefore, preharvest 50 mg L−1 GA3 spraying is an effective method for maintaining the quality and up-regulating antioxidants of longan fruit during both on-tree preservation and room-temperature storage.

Sugar Receding in Aril Benefits the Recalcitrant Seeds of Litchi (Litchi chinensis) and Longan (Dimocarpus longan) to Cope with Dry Spells after Maturation

“…It is a special phenomenon, for it has rarely been found in other horticultural fruits. Although many previous studies have attempted to understand the phenomenon, the underlying mechanism is still debated [8][9][10][11][12]. Here, we showed that the "sugar receding" of lichi and longan fruits could play a role in seed vigor maintenance via sugar supply for the seeds, which could spread the seed germination risk in unpredictable dry weather.…”

“…For such a mission, maintenance of high seed vigor for a long time is a prerequisite, in particular when no photosynthate is assigned after fruit maturation. It has long been found that a phenomenon called "sugar receding" of fruits commonly occurs in litchis and longans after fruit maturation, leading to a dramatic decrease in the aril sugar contents in around a week [8][9][10][11][12]. To date, the mechanism of "sugar receding" of fruits is still unclear.…”

“…Sweetness is an important eating quality for litchi and longan fruits. However, a phenomenon called "sugar receding" of the fruits, known as a significant decline in sweetness or total soluble solids (TSS) content of the arils soon after fruit maturation, has been found to largely reduce the fruit quality [8][9][10][11]. This trait is the main factor shortening the harvest period (about 1 week) and limiting the industry development of the fruits.…”

“…However, the transport back hypothesis controverts to the general photosynthate partition law in plants [16]. So far, the studies on "sugar receding" mainly focused on the changes in sugar components, activities of sugar-metabolism-related enzymes, and their coding genes [8][9][10][11][12]. These studies help us to understand the sugar metabolism in the arils during the "sugar receding", but they cannot explain the reason for or role of the phenomenon.…”

Comprehensive Evaluation of the ‘Shixia’ Longan Quality under Postharvest Ambient Storage: The Volatile Compounds Played a Critical Part

“…Its edible aril accumulates high-leveled nutritive phytochemicals such as polysaccharides, vitamin C (about 0.8 mg g −1 fresh weight), polyphenols (about 0.75 mg g −1 fresh weight), and carbohydrates (about 150 mg g −1 fresh weight), which confers it not only the unique and appealing flavor but also the bioactive effects including antitumor, immunomodulatory and antioxidant capacity [4,5]. Thus, it is widely consumed and gains popularity with the global people [6].…”