Exogenous melatonin improved potassium content in Malus under different stress conditions

Abstract Melatonin mediates many physiological processes in plants. We investigated its role in regulating growth, potassium uptake, and root system architecture under three types of stress: salinity or a deficiency of all nutrients in Malus hupehensis Rehd., as well as a K deficiency in Malus rockii Rehd. Each treatment caused a reduction in growth rates and disrupted the absorption of potassium. However, pretreatment with 0.1 μmol/L melatonin significantly alleviated such inhibitions. The addition of melatonin also upregulated genes for antioxidant enzymes involved in the ascorbate–glutathione cycle ( MdcAPX , MdDHAR1 , MdDHAR2 , MdMDHAR , and MdcGR ) and helped decrease the accumulation of H 2 O 2 while improving the expression of K transporters and genes for the CBL 1– CIPK 23 pathway. These results indicated that melatonin can regulate the ROS signal and activate the CBL 1– CIPK 23 pathway to regulate the expression of a potassium channel protein gene, thereby promoting the absorption of potassium ions. Our findings demonstrate that inducing melatonin production is an important mechanism for plant defenses that can serve as a platform for possible applications in agricultural or related fields of research.