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.

褪黑激素和儿茶酚调节植物生长，但很少研究它们在镉胁迫下对香稻早期生长和相关生理生化特性的影响。进行盆栽实验以评价外源性褪黑激素（即0和100 μmol L ^-1）和儿茶酚（即0和20 μmol L ^{-1 ）的作用}，分别被视为M0、M100、C0和C20。两个香稻品种玉香油盏和香芽香盏的早期生长及理化特性研究。两个水稻品种都在两种 Cd 水平下生长，即 0 和 150 μmol L ^-1分别表示为 Cd0 和 Cd150。由于在镉诱导的毒性下生长和抗氧化反应的调节，褪黑激素的应用改善了水稻幼苗的干重。随着褪黑激素的应用，根中超氧化物歧化酶（SOD）和过氧化物酶（POD）活性增加，而根和地上部丙二醛（MDA）含量降低。儿茶酚还调节了镉诱导毒性下香稻幼苗的生长和抗氧化反应。褪黑素和儿茶酚的交互作用，即M100+C0处理导致植物干重最大，而M100+C0+Cd150处理导致香芽香沾根和芽以及鱼香油沾根中Cd浓度最低。此外，多变量分析表明，根中的 POD 活性是香稻幼苗减轻 Cd 诱导毒性的重要限制因素。总体而言，褪黑激素和儿茶酚可以调节镉诱导毒性下香稻幼苗的早期生长和抗氧化反应。