Asif Alaiha, Iqbal Shahid, Aucique-Perez Carlos Eduardo, Leaks KeAndree, Balal Rashad M, Mattia Matthew, Chater John M, Alferez Fernando, Shahid Muhammad Adnan
Horticultural Science Department, North Florida Research and Education Center, University of Florida/IFAS, Quincy, FL, 32351, USA.
Department of Horticulture, College of Agriculture, University of Sargodha, Sargodha, 40100, Pakistan.
Plant Physiol Biochem. 2025 Sep 12;229(Pt B):110500. doi: 10.1016/j.plaphy.2025.110500.
Aberrant and sporadic freezing temperatures significantly challenge citrus production, leading to considerable economic losses and threatening long-term food security. In North Florida, freezing temperatures are the primary limiting factor for citrus cultivation, often resulting in severe yield reductions. This study investigates how different durations of cold acclimation (CA) influence the freezing tolerance of Valencia orange (Citrus sinensis) grafted onto two commercial rootstocks, US-942 and C-54. Plants underwent CA for 4, 8, 16, and 32 h (h) before being exposed to freezing stress in a controlled freezing chamber. CA durations of 16 and 32 h markedly enhanced freezing tolerance in both rootstocks, evidenced by reduced visible injury and physiological damage. These improvements correlated with increased activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), along with elevated levels of osmoprotectants such as proline and glycine betaine (GB). Additionally, soluble sugars (glucose, fructose, sucrose, total soluble sugars), starch, and key carbohydrate-metabolizing enzymes were significantly higher in plants acclimated for 16 and 32 h compared to non-acclimated (control) plants and those acclimated for 4 h. These findings suggest that cold acclimation enhances freezing tolerance through strengthening the antioxidant defense system and supporting osmotic and metabolic adaptations. An acclimation period of 16 h was identified as optimal for improving cold hardiness in Valencia orange trees. These results provide a valuable framework for developing effective cold management strategies for commercial applications and may inform breeding programs aimed at creating and enhancing freeze-tolerant citrus varieties. Future research should focus on identifying the molecular regulators that determine the optimal cold acclimation duration in citrus, especially those that improve membrane stability and antioxidant defenses. Furthermore, combining transcriptomic and metabolomic profiling will help reveal key signaling pathways and biomarkers associated with increased freezing tolerance.
异常和偶发的低温对柑橘生产构成了重大挑战，导致了可观的经济损失，并威胁到长期粮食安全。在佛罗里达州北部，低温是柑橘种植的主要限制因素，常常导致产量大幅下降。本研究调查了不同时长的低温驯化（CA）如何影响嫁接到两种商业砧木US-942和C-54上的伏令夏橙（Citrus sinensis）的抗冻性。在可控的冷冻室中对植株施加冷冻胁迫之前，使其分别经历4、8、16和32小时的低温驯化。16小时和32小时的低温驯化显著提高了两种砧木的抗冻性，可见损伤和生理损伤的减轻证明了这一点。这些改善与抗氧化酶活性的增加相关，包括超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）和抗坏血酸过氧化物酶（APX），同时渗透保护剂如脯氨酸和甘氨酸甜菜碱（GB）的水平也有所升高。此外，与未驯化（对照）植株以及驯化4小时的植株相比，经过16小时和32小时低温驯化的植株中的可溶性糖（葡萄糖、果糖、蔗糖、总可溶性糖）、淀粉和关键碳水化合物代谢酶显著更高。这些发现表明，低温驯化通过加强抗氧化防御系统以及支持渗透和代谢适应来提高抗冻性。已确定16小时的驯化期对于提高伏令夏橙树的抗寒性最为适宜。这些结果为制定有效的商业应用冷害管理策略提供了有价值的框架，并可能为旨在培育和改良抗冻柑橘品种的育种计划提供参考。未来的研究应专注于确定决定柑橘最佳低温驯化时长的分子调控因子，尤其是那些能提高膜稳定性和抗氧化防御的因子。此外，结合转录组学和代谢组学分析将有助于揭示与抗冻性增加相关的关键信号通路和生物标志物。
