Exogenous Melatonin and Catechol Application Modulate Physio-Biochemical Attributes and Early Growth of Fragrant Rice Under Cd Toxicity

Melatonin and catechol regulate plant growth, but their effects on early growth of fragrant rice and related physio-biochemical attributes under Cd stress are rarely studied. A pot experiment was conducted to evaluate the effects of exogenous melatonin, i.e., 0 and 100 μmol L −1 , and catechol, i.e., 0 and 20 μmol L −1 , application regarded as M0, M100, C0, and C20, respectively, on early growth and physio-biochemical attributes of two fragrant rice cultivars, i.e., Yuxiangyouzhan and Xiangyaxiangzhan. Both rice cultivars were grown under two Cd levels, i.e., 0 and 150 μmol L −1 denoted as Cd0 and Cd150, respectively. Melatonin application improved the dry weight of rice seedlings due to modulations in the growth and antioxidant response under Cd-induced toxicity. The superoxide dismutase (SOD) and peroxidase (POD) activities in root were increased, whereas malondialdehyde (MDA) content in root and shoot was decreased with melatonin application. Catechol also regulated the growth and antioxidant response of fragrant rice seedlings under Cd-induced toxicity. The interactive effects of melatonin and catechol, i.e., M100 + C0 treatment resulted in the maximum plant dry weight, whereas the M100 + C0 + Cd150 treatment resulted in the lowest Cd concentration in roots and shoots of Xiangyaxiangzhan as well as in roots of Yuxiangyouzhan. Furthermore, multivariate analysis revealed that the POD activity in root was an important limiting factor for fragrant rice seedlings to mitigate Cd-induced toxicity. Overall, melatonin and catechol could modulate the early growth and antioxidant response of fragrant rice seedlings under Cd-induced toxicity.