International Journal of Horticulture, 2025, Vol.15, No.5, 234-241 http://hortherbpublisher.com/index.php/ijh 234 Research Insight Open Access Physiological Mechanisms of Fruit Ripening in Yellow Pitaya Genetic Regulation of Softening, Sugar Accumulation, and Antioxidant Metabolism Hongpeng Wang 1, Dandan Huang 2 1 Biotechnology Research Center of Zhuji Cuixi Academy of Biotechology, Zhuji, 311800, Zhejiang, China 2 Hainan Institute of Biotechnology, Haikou, 570206, Hainan, China Corresponding author: dandan.huang@hitar.org International Journal of Horticulture, 2025, Vol.15, No.5 doi: 10.5376/ijh.2025.15.0024 Received: 04 Jun., 2025 Accepted: 20 Sep., 2025 Published: 18 Oct., 2025 Copyright © 2025 Wang and Huang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Wang H.P., and Huang D.D., 2025, Physiological mechanisms of fruit ripening in yellow pitaya genetic regulation of softening, sugar accumulation, and antioxidant metabolism, International Journal of Horticulture, 15(5): 234-241 (doi: 10.5376/ijh.2025.15.0024) Abstract Pitaya (Hylocereus spp.) is a climacteric tropical fruit of nutritional and economic importance. Fruit ripening is associated with intricate physiological and biochemical processes, such as softening, the accumulation of sugars, and the control of dynamic antioxidant metabolism. The softening of the fruit is mainly the consequence of cooperative action of cell wall-degrading enzymes with ethylene and other hormonal regulators' control. Sugar content is a major reason that is responsible for Pitaya quality and taste, with metabolic catabolism of glucose, fructose, and sucrose, central sugar metabolizing enzymes playing a pivotal role in the same. In addition, reactive oxygen species (ROS) generation and their processes of scavenging during fruit ripening play roles in modulating antioxidant capacity. Furthermore, the shifting composition of key antioxidant enzymes (i.e., superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)) and non-enzymatic antioxidants such as phenols, flavonoids, and vitamin C also contribute significantly towards providing the storage characteristics to the fruit. In this research, molecular regulation of fruit softening, sugar accumulation, and antioxidant metabolism was examined in Pitaya. It studied the role of ethylene signaling in regulating sugar metabolism, coordination of cell wall breakdown and sugar transport, and antioxidant metabolic regulatory function in fruit ripening. It serves as a theoretical foundation for research on Pitaya ripening physiological mechanism and basis for providing scientific recommendations for increasing cultivation and postharvest management of improved varieties. Keywords Pitaya; Fruit ripening; Softening; Sugar accumulation; Antioxidant metabolism; Gene regulation; Breeding strategies 1 Introduction Pitaya (Hylocereus spp.) is a fruit of high nutritional value and tremendous economic potential. It contains a high content of dietary fiber, vitamins (particularly vitamin C), minerals, and bioactive molecules like betaine and flavonoids with excellent antioxidant properties. Because of its health quality, international market demand for Pitaya consumption has increased (Mou et al., 2022). Economically, its price quotation, flexibility under varied climatic conditions, and low capital investment in planting make it a cash crop of interest. Despite all these merits, there are still issues such as inconsistency in fruit quality and postharvest losses, which show that further study of its maturation processes is necessary (Xie et al., 2021). As Pitaya ripens, the texture is modified, sugar builds up, and the action of antioxidants is dramatically changed. The fruit softens largely because two enzymes break down the cell wall. Two of the major enzymes whose action softens the fruit are polygalacturonidase (PG) and pectin methyl esterase (PME) (Zhang et al., 2021). During the process of fruit ripening, the metabolism of sugar is changed. Levels of glucose, fructose, and sucrose rise. This is controlled by key enzymes like sucrose phosphate synthase (SPS) and convertase (INV). Additionally, antioxidant metabolism also plays a role in fruit quality maintenance. Both enzymatic antioxidants (like APX, CAT, and SOD) and non-enzymatic antioxidants (like vitamin C, flavonoids, and phenols) participate. The antioxidants all play a role together in the process of ripening to reduce oxidative stress (Wei et al., 2019; Xie et al., 2022). This study investigates the physiological and molecular regulatory mechanisms of softening, sugar content accumulation and antioxidant metabolism during Pitaya ripening, and identifies key genes, metabolic pathways and their interactions to provide theoretical guidance and practical recommendations. Studies on its mechanism of
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