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

Abstract

Cadmium (Cd^{2 +}) 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 (Cd^{2 +})-sensitive lettuce genotype (Lüsu). Seedlings were subjected to five treatments: [(i) Control (untreated plants), (ii) 100 µM CdCl₂, (iii) 100 µM CdCl₂+10 µg L^-1 ABA (iv) 10 µg L^-1 ABA, and (v) 0.01 g L^-1 ABA-inhibitor (fluridone)] for fourteen days in hydroponic system. The 100 µM 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 Cd^{2 +} 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 µg L^-1) mitigated the Cd^{2 +}-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 Cd^{2 +} content in leaves under the CdCl₂ treatment. Our results have demonstrated that foliar application of ABA mitigates Cd^{2 +} stress and increases the nutritional quality and food safety of Cd^{2 +}-sensitive lettuce genotype under CdCl₂ treatment.

Keywords: ABA-inhibitor; Antioxidant enzymes; Cadmium stress; Chlorophyll content; Hydrogen peroxide; Lactuca sativa; Malondialdehyde; Nutrient elements.