Effects of regulated deficit irrigation on antioxidant system and the ascorbate-glutathione cycle in processing...

Water scarcity is a major constraint on agricultural production in arid and semi-arid regions, particularly in Xinjiang, China, where processing tomato is an economically important yet water-sensitive crop. This study evaluated the physiological and biochemical responses of processing tomato (Solanum lycopersicum L. cv. 'Heinz 1015') to regulated deficit irrigation (RDI) and subsequent rewatering under field conditions. Five irrigation regimes were applied, including a conventional irrigation control (CK) and four deficit irrigation treatments (W1-W4). Drought stress significantly increased malondialdehyde (MDA) and H₂O₂ accumulation, indicating enhanced oxidative damage. For example, during the flowering stage, MDA and H₂O₂ contents in the most severe treatment (W4) were 12.46 and 11.98 µmol·g^-1 FW higher than those in the control, respectively. Proline, soluble sugars, and soluble proteins increased markedly, while antioxidant defenses were activated, as reflected by higher POD, CAT, APX, GR, DHAR, and MDHAR activities. SOD activity increased under mild and moderate stress but declined under severe drought. Changes in GSH, GSSG, and the GSH/GSSG ratio further demonstrated active redox regulation. Rewatering alleviated drought-induced physiological disturbances, although recovery depended on stress severity. The mild deficit treatment (W1) exhibited the strongest compensatory response, with most physiological parameters recovering to levels comparable to the control. These findings indicate that mild deficit irrigation can enhance drought adaptation while maintaining physiological stability, providing a promising strategy for water-saving tomato production in arid regions.