Abstract
Melatonin (MLT) is a hormonal substance found in many organisms and can improve plant stress resistance. In this study, the japonica rice variety Y32 and indica rice variety NJ6 were cultivated in hydroponics under different concentrations of CdCl2 at the two-leaf stage. The growth, physiological and biochemical responses of the seedlings and the expression of cadmium (Cd)-related genes under exogenous melatonin (MLT) treatment were assessed. The results indicated that Cd stress destroyed the dynamic balance between reactive oxygen species (ROS) production and removal, resulting in ROS accumulation, membrane lipid peroxidation, and impaired growth and development. Following the application of exogenous MLT to rice seedlings, increases in plant biomass including both underground and above-ground areas were observed. MLT also relived the inhibition of superoxide dismutase (SOD) and peroxidase (POD) in a concentration dependent manner in response to Cd stress. Catalase (CAT) activity and malondialdehyde (MDA) expression also decreased following MLT treatment. Amongst the six Cd-related genes assessed, five genes were down-regulated and one was up-regulated in response to MLT treatment. Taken together, these data demonstrate that MLT improves the resilience of rice seedlings at the biochemical, physiological, and molecular levels, and alleviates the damage caused by Cd stress.
Highlights
Cadmium (Cd) is a highly toxic and widely distributed heavy metal
Tab. 2 shows that the fresh weight of rice seedlings changed significantly under Cd stress
Cd stress reduced the biomass accumulation of above-ground and root of rice, and after applying the exogenous MLT, Cd stress in rice was effectively diminished, which proved that MLT is effective in promoting plant growth while harmful in other aspects and is consistent with the previous research
Summary
Cadmium (Cd) is a highly toxic and widely distributed heavy metal. 30,000 tons of Cd per year enter the environment due to human factors of which 82%-94% are discharged into the soil [1]. 1.13 × 106 hm of cultivated land in China is thought to be Cd polluted. Up to 12 million tons of grains are polluted by heavy metals each year, of which 10 million tons of grains are lost, with economic losses of up to 20 billion Yuan RMB [3,4]. Cd in cultivated soil is absorbed by crops, accumulates in the body, and is biomagnified, seriously afflicting crop yields [5]. Strategies to improve Cd-resistance and plant yields under Cd stress conditions are highly sought
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