Influence of drought-priming on the improvement of cold-hardiness in grapefruit (Citrus paradisi) through the enhancement of physiological and biochemical attributes
Shahid Iqbal (shahidiqbal@ufl.edu) * USA
Carlos Eduardo Aucique-Perez (c.auciqueperez@ufl.edu) * USA
Muhammad Adnan Shahid (mshahid@ufl.edu) * USA
Priming is a phenomenon through which plants are initially exposed to one type of stress to prepare them to better handle another. There is a lack of scientific knowledge regarding the effect of drought-priming on the freeze tolerance mechanism in cold-sensitive grapefruit (Citrus paradisi). To investigate whether pre-freezing drought stress can serve as a primer in cold-hardiness, we subjected plants to drought-priming (50%, 75%, and 100% field capacity) and post-priming freezing stress (-6 °C). Drought-priming memory was found to enhance the ability of plants to withstand freezing temperatures by regulating their antioxidant system, osmolyte production, and carbohydrate metabolism. Drought-priming triggered the activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione peroxidase (GPX), and ascorbate peroxidase (APX), in the range of 1.21, 0.11, 0.10, 1.42, 0.41, and 1.16 U mg-1 protein, respectively, to reduce oxidative damage caused by an excessive formation of reactive oxygen species (ROS) like superoxide (O2•-) and hydrogen peroxide (H2O2), with a minimum concentration of 0.10 and 0.44 nmol g-1 protein in primed plants. Drought-priming also accelerated the accumulation of osmolytes, including proline (0.91 mg g-1 FW) and glycine betaine (0.98 mg g-1 FW), and soluble sugars such as glucose (12.58 mg g-1 DW), fructose (6.60 mg g-1 DW), and sucrose (19.85 mg g-1 DW), which help stabilize cellular structures and maintain osmotic balance under stressed conditions. Drought-primed plants also showed modulated carbohydrate metabolism, sugar biosynthesis, and reduced starch reserves. These adaptive changes helped plants better cope with subsequent freezing stress, improving their resilience by sustaining energy production, maintaining cellular integrity, and ensuring metabolic activity. This corresponding response highlights the valuable impact of drought-priming in improving cold-hardiness in young grapefruit plants through a comprehensive physiological and biochemical stress-alleviating mechanism and highlights the practical potential of drought-priming as a cost-effective and non-invasive strategy to improve cold-hardiness in citrus and related species. By integrating drought-priming into management practices, growers can enhance the resilience of young grapefruit plants to freezing conditions, contributing to sustainable citrus production in regions prone to cold stress or unexpected freeze events in winter or late summer.
