Relationship between water loss and water status, osmotic substances, and AQP expression in Ponkan (Citrus reticulata Blanco) fruit during storage
Qiaoli Ma, Xiong Lin, Lingcai Zeng, Wenjia Xie, Yingying Chen, Minxuan Zhan, Feng Li, Jinyin Chen, Qingjiang Wei
Abstract
Water loss is a prevalent physiological disorder observed in postharvest horticultural products. Aquaporins (AQPs) function as channel proteins that facilitate water movement across biological membranes along the water potential gradient. In this investigation, the water loss rate, water content and potential, osmotic substances, including sugars, citric acid, soluble protein, and inorganic mineral elements, and CitAQP expression in the peel and pulp of Ponkan ( Citrus reticulata ) fruit during storage were examined to elucidate the key factors determining postharvest water loss. The results indicated that water loss persistently increased and accelerated at 15–30 d and 90–105 d. Both water content and potential were higher in the pulp than in the peel. The water content increased before 45 d, the water potential of the peel decreased, and the water potential gradient between the peel and pulp increased after 75 d. Osmolytes, such as sucrose and citric acid, were more highly accumulated in pulp and decreased to a minimum at approximately 45 d, whereas glucose, fructose, soluble protein, and inorganic mineral elements accumulated more in the peel. Most of the 30 expressed CitAQPs were up-regulated 2–10 fold in peel and pulp, and were classified into four clusters based on their expression pattern. Among these AQPs , CitTIP2;2/3;1/6;1 in group I and CitPIP1;2 in group Ⅳ were substantially up-regulated 10–242 times in peel, and CitTIP1;3/2;1/2;3/4;1/6;1 , CitSIP1;1 , and CitXIP1;1/1;2 in group Ⅳ were 10 times more up-regulated in pulp, particularly at 105 d. The weight loss rate, water content, and water potential gradient exhibited positive correlations with the CitAQP genes of Clusters III and Ⅳ. These findings suggest that the upregulation of CitAQP genes contributes to the acceleration of water loss in Ponkan fruit during storage. • Water potential gradient between peel and pulp increased resulting in greater water loss after 75 days. • Pulp osmolytes decreased, while peel osmolytes increased. • CitAQPs were predominantly upregulated 2-10-fold, with some genes exhibiting extremely high expression. • CitAQPs in Clusters III and IV upregulated in peel and/or pulp particularly at 105 d, positively correlated with water loss.