Effects of salicylic acid, Epi-brassinolide and calcium on stress alleviation and Cd accumulation in tomato plants

Salicylic acid (SA), Epi-brassinolide (EBL) and calcium (Ca) play crucial roles in plant development and mediate plant response to biotic and abiotic stress. This study was aimed to investigate the possible mediatory role of SA, EBL, Ca or their combination in protecting tomato plants from cadmium (Cd) toxicity. According to the results, Cd stress resulted in a significant reduction of plant dry mass, photosynthetic pigment content as well as photosynthetic rate. Exogenous application of SA decreased the malondialdehyde (MDA) level by 39.27% and increased catalase (CAT) activity by 81.17%. SA and EBL treatment significantly increased chlorophyll a (Chl a), chlorophyll b (Chl b) content, photosynthetic rate (Pn) as well as water use efficiency (WUE). SA + EBL (1:1)/Ca + SA + EBL (1:1:1) treatment obviously alleviated Cd-induced growth inhibition, the dry mass of different tomato organs were significantly increased (p < 0.05). Especially in Ca + SA + EBL treated plants, the dry mass of roots, stems and leaves increased by 141.18%, 128.57% and 118.52%, respectively. Besides, SA + EBL and Ca + SA+ EBL treatments reduced the MDA level, but increased photosynthetic pigment concentration and photosynthetic efficiency. CAT activity was increased by 62.92% in Ca + SA + EBL treated plants, the WUE was increased by 557.76% in SA + EBL pretreated plants. Moreover, exogenous application of SA, SA + EBL and Ca + SA + EBL significantly decreased Cd accumulation in tomato organs (p < 0.05) compared with Cd-stressed plants. Taken together, our results indicated that exogenous application of SA, EBL and Ca individually or in combination could alleviate Cd toxicity in tomato plants, although the extent varies.