Abstract
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 (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 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 µg 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.
Highlights
Cadmium (Cd2+) is a non-essential heavy metal, which is highly toxic and adversely affects several plant metabolic processes by causing oxidative stress (Gratão et al, 2015)
The effect of CdCl2 on oxidative stress was determined by measuring the contents of H2O2 and MDA in the root and leaf tissues of the plants
Fluridone treatment decreased the contents of chlorophyll and carotenoids (Fig. 3), inhibited photosynthesis by decreasing PN, Gs and transpiration rate (Tr) (Fig. 4) and decreased the contents of nutrient elements in the leaves of the plants (Table 2). These results demonstrate that abscisic acid (ABA) play a crucial role in mitigating the Cd2+-induced stress and in improving the food safety of the Cd2+-treated lettuce plants by decreasing the content of Cd2+ in the leaves to levels within the acceptable
Summary
Cadmium (Cd2+) is a non-essential heavy metal, which is highly toxic and adversely affects several plant metabolic processes by causing oxidative stress (Gratão et al, 2015). Cd2+ can interfere with numerous biochemical and physiological processes including photosynthesis, respiration, nitrogen and protein metabolism, and nutrient uptake (Clemens, 2006; Sanitàdi Toppi & Gabbrielli, 1999) and these results in the increase production of the reactive oxygen species. Higher Cd2+ concentrations strongly reduces the maximum photochemical efficiency of PSII, impairs net CO2 assimilation rate, decreases nutrient uptake and adversely affects plant growth in lettuce (Dias et al, 2012). Cd2+ treatment was found to have increased lipid peroxidation, decreased photosynthesis, shoot growth as well as the contents of nutrient elements (Fe, Mn, Zn and Cu) in lettuce plants. Lettuce is among the high risk crops with regard to Cd2+ contamination since the plants can accumulate greater amount of Cd2+ without exhibiting marked symptoms of Cd2+ toxicity (Zhang et al, 2013)
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