Growth, physiological, and heavy metal accumulation traits at seedling stage under heavy metal stress in castor (<italic>Ricinus communis</italic> L.)

Abstract

<p indent=0mm>Agricultural ecology environment and human health are seriously threated by aggravating agricultural non-point source and heavy metals pollution. It is of great significance to explore the cumulative effect of crops on heavy metal pollution and its physiological mechanism. A castor (<italic>Ricinus communis </italic>L.) variety Zibi 5 was used to study the accumulation effect of heavy metals and associated physiological mechanism under heavy metals treatments (Cu, Zn and Cd at 0, 30, 60, and <sc>120 mg L^-1</sc> concentrations). The results showed that seedling growth, physiological traits and heavy metals accumulation significantly affected by heavy metal treatments. Plant height was increased to the maximum with <sc>60 mg L^-1</sc> and then decreased. However, root length, fresh weight and dry weight were all decreased under heavy metal treatments. In general, SOD activity was decreased at low treatment concentration but increased at high treatment concentration, the highest activity was showed at <sc>120 mg L^-1</sc> under Cu and Zn treatments at 10 DAS (days after sowing), which were 45.5% and 31.8% higher than that under CK, respectively. POD activity was first decreased and then increased on 10 DAS, but significantly increased in both 25 DAS and 45 DAS, as well as prominently increased with prolonged the growth periods. Soluble protein was only significantly increased under <sc>120 mg L^-1</sc> Cu treatment, and increased by 18.8%, 66.7%, and 83.3% at each growth stage, respectively. MDA content was significantly increased with the increase of treatment concentration and significantly decreased with prolonged the growth periods, and MDA content was significant higher under Cd treatment than that under Cu and Zn treatments. The accumulation contents of Cu, Zn, and Cd in castor plant were gradually increased with the increase of treatment concentration, and the maximum accumulation was at <sc>120 mg L^-1</sc> concentration. Among of them, the accumulation of treatment concentration increased, and the maximum accumulation showed at <sc>120 mg L^-1</sc> concentration. Among them, the accumulation of Zn was the highest, followed by Cd. The accumulation content of heavy metals in each organ was shown as root > stem > leaf. This study suggested that castor has a certain tolerance to heavy metals, which was increased the antioxidase activity to alleviate heavy metals stress. The castor has organ specificity in heavy metals accumulation. It is an effective approach to plant castor to repair soil pollution by heavy metals such as Cu, Zn, and Cd.