Drought-stress memory confers cold hardiness in grapefruit (Citrus paradisi) through modulations in antioxidant system, osmolyte production and carbohydrate metabolism
Shahid Iqbal, Carlos Eduardo Aucique‐Pérez, Sajjad Hussain, Rashad Mukhtar Balal, Guillaume Charrier, Matthew Mattia, John M. Chater, Muhammad Adnan Shahid
Abstract
• Drought-priming improved the freeze tolerance of cold-sensitive grapefruit by strengthening physiological and biochemical responses under subsequent freezing stress conditions. • Drought-priming activated key antioxidant enzymes (SOD, POD, CAT, GPX, and APX), reducing oxidative damage caused by reactive oxygen species (ROS) under freezing stress. • Increased levels of osmolytes (proline, glycine betaine, and soluble sugars) and regulated carbohydrate metabolism supported cellular stability and osmotic balance, enhancing cold resilience. • The drought-stress memory effect in primed plants maintained cellular integrity, energy production, and metabolic activity, improving overall cold hardiness in young grapefruit plants. Priming is a phenomenon in which plants are initially exposed to mild stress to develop resilience to subsequent or severe stress. There is a lack of scientific knowledge regarding the drought-priming (DP) effect on the freeze tolerance mechanism in cold-sensitive grapefruit ( Citrus paradisi ). Therefore, the present study was conducted to gain insight into how plants perform under freezing stress (FS) when given short-term drought stress (DS) as a priming event. This study investigated the potential of DP to enhance freeze tolerance in cold-sensitive grapefruit. The plants were subjected to drought-priming at 50% and 75% field capacity (FC), with control (non-stress- 100% FC) for three weeks before being subjected to freezing stress (-6°C). DP exhibited enhanced freezing tolerance through an improved antioxidant system, osmolyte production, and carbohydrate metabolism. It also triggered the activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione peroxidase (GPX), and ascorbate peroxidase (APX), mitigating oxidative damage caused by reactive oxygen species (ROS). The accumulation of osmolytes, including proline, glycine betaine (GB) and soluble sugars, was also induced, stabilizing cellular structures and maintaining osmotic balance. Additionally, carbohydrate metabolism shifted towards sugar biosynthesis, with reduced starch reserves providing energy for stress adaptation. It is concluded that drought-stress memory as a primer acclimated the plants to freezing stress by alleviating oxidative damage to membranes and maintained high energy production through enhanced antioxidant activities, osmolyte accumulation, and regulating carbohydrate metabolism. This study 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.