Low-light (LL) stress is a major abiotic limiting factor in protected cherry tomato production, adversely affecting vegetative growth, inducing oxidative damage, and disrupting fruit sugar metabolism. To clarify the regulatory role of exogenous abscisic acid (ABA) in mitigating LL stress, we examined the effects of varying ABA concentrations on plant growth, antioxidant capacity, and fruit sugar metabolism in cherry tomatoes under low-light conditions. A two-factor randomized complete block design, with two light regimes—normal light (NL, 100% natural sunlight) and low light (LL, 25% natural sunlight)—and three ABA concentrations (CK: 0 mg·L−1, T1: 10 mg·L−1, T2: 20 mg·L−1). Fruits were sampled at three typical ripening stages (green mature, breaker, and red ripe) to evaluate vegetative and reproductive physiological responses. The results showed that exogenous ABA application effectively suppressed LL-induced excessive stem elongation and alleviated LL-caused reductions in stem diameter and biomass accumulation. ABA treatment significantly increased peroxidase (POD) activity and reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation, thereby relieving LL-triggered oxidative damage. In addition, ABA regulated key sugar-metabolizing enzymes (soluble acid invertase (SAI), sucrose synthase (SS), sucrose phosphate synthase (SPS), and amylase (Amy)) and the transcript levels of related functional genes (HXK1, SPS, SS, AI), thereby mediating stage-dependent fruit sugar metabolism under LL stress. In conclusion, exogenous ABA effectively modulates vegetative growth, antioxidant homeostasis, and stage-specific fruit sugar metabolism, ultimately alleviating low-light stress damage in cherry tomato. Among the tested treatments, 20 mg·L−1 ABA exhibited the most pronounced mitigation effects, which can be recommended as an optimal foliar application concentration for cherry tomato cultivation in low-light protected facilities.
Yang et al. (Sat,) studied this question.