Copper Toxicity on the Development and Architecture of Rice Root

Three years of pot soil experiments showed that copper (Cu) could be toxic to rice root depending on its concentrations. Root development began to be inhibited at the soil Cu concentration of 100 mg kg^-1. About half of root dry weights lost at the soil Cu concentration of 300 - 500 mg kg^-1. Root growth nearly stopped at the soil Cu concentration of 800 - 1000 mg kg^-1. There were interactions between rice growth stages and soil Cu concentrations on Cu toxicity to rice root. The soil Cu level of 400 mg kg^-1 inhibited total root length per plant and average length of root system significantly (P<0.05), and the inhibiting effects increased with the time of soil Cu stress. However the differences between two rice cultivars (Shanyou 63 and Wuxiangjing 14) were small respecting reducing rates of root length under soil Cu stress. Soil Cu treatment increased cell layers and the thickness of cell wall in epidermis at root bases and root tips. The thickness of epidermis was 75% more at root base, and 27% more at root tip, for soil Cu treatment than for the control Under soil Cu treatment, the cells of cortex were larger and distorted, and the vessels were distorted and lessened, compared to the control.