Zinc Efficiency is Correlated with Root Morphology, Ultrastructure, and Antioxidative Enzymes in Rice

To elucidate physiological mechanisms of zinc (Zn) efficiency in rice (Oryza sativa L.), comparative studies on root morphology, ultrastructure, and oxidative enzyme activities were investigated using Zn-efficient rice genotype ('IR8192') and Zn-inefficient rice genotype ('Erjiufeng'). The results showed that moderate Zn-deficient conditions increased root length, root surface, and root tips in both genotypes, but a greater extent occurred in 'IR8192'. Under moderate Zn deficient conditions, many swollen mitochondria were observed in the root tip cells of 'Erjiufeng', whereas most root cells in 'IR8192' remained intact. Disturbances in the ultrastructure of these organelles were accompanied with elevated oxidative stress in both genotypes and the increases were less in 'IR8192' than in 'Erjiufeng'. This may result from the differences that existed in the activities of antioxidative enzymes between these two genotypes. These results suggest that Zn efficiency in 'IR8192' is closely associated with its high root tolerance to Zn-deficiency by maintaining a relatively higher efficient antioxidative system and intact root tip cell and functions.