Foliar application of abscisic acid mitigates cadmium stress and increases food safety of cadmium-sensitive lettuce (Lactuca sativa L.) genotype

Cadmium (Cd2+) is among the toxic non-essential heavy metals that adversely affect plants metabolic processes and the safety of produce. However, plant hormones can improve plant's tolerance to various stresses. This study investigated the effect of exogenous abscisic acid (ABA) on the biochemical and physiological processes and food safety of cadmium (Cd2+)-sensitive lettuce genotype (Lusu). Seedlings were subjected to five treatments: [(i) Control (untreated plants), (ii) 100 mu M CdCl2, (iii) 100 mu M CdCl2 +10 mu g L-1 ABA (iv) 10 mu g L-1 ABA, and (v) 0.01 g L-1 ABA-inhibitor (fluridone)] for fourteen days in hydroponic system. The 100 mu M CdCl2 increased the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA), decreased photosynthesis and plant biomass. Moreover, it decreased the contents of essential nutrients (except copper) in the leaves but increased the contents of toxic Cd2+ in the leaves and roots of the plants. Foliar application of fluridone (0.01 g L-1) also caused oxidative stress by increasing the contents of H2O2 and MDA. It also decreased the contents of nutrient elements in the leaves of the plants. However, exogenous ABA (10 mu g L-1) mitigated the Cd2+-induced stress, increased antioxidant enzymes activities, photosynthesis and plant biomass under CdCl2 treatment. Remarkably, exogenous ABA increased the contents of essential nutrient elements but decreased the Cd2+ content in leaves under the CdCl2 treatment. Our results have demonstrated that foliar application of ABA mitigates Cd2+ stress and increases the nutritional quality and food safety of Cd2+-sensitive lettuce genotype under CdCl2 treatment.