Difference in Al sensitivity between seminal and crown roots of rice nursery seedlings

Abstract

The crown roots of rice (Oryza sativa L. cv. Nipponbare) nursery seedlings were more tolerant of Al than the seminal roots, in terms of elongation. Intense hematoxylin staining was observed in the root cap and meristem for the seminal roots, whereas in the meristem for the crown roots, which correspond to the Al concentration in both types of roots. Mottled hematoxylin staining was observed in the basal area, in a region located at approximately 4 mm from the tip of the seminal roots, in contrast to the crown roots, which showed laterally-striped staining. The concentration of callose induced by Al in the seminal roots was comparable to that in the crown roots, regardless of the root growth. Confocal laser scanning microscopy of roots stained with fluorescein diacetate-propidium iodide (FDA-PI) indicated that the plasma membrane of the epidermis of the root tip was damaged even in the absence of Al treatment. Al further impaired the plasma membrane of the root cap cells in the seminal and crown roots to a similar extent. These findings contradicted typical Al-injury phenomenon reported for Al-sensitive and Al-tolerant plants. It is also likely that different metabolic processes operate in the crown and seminal roots. Crown roots can develop Al tolerance either constitutively or inductively by exposure to Al. A comparison of gene expression should lead to the isolation of the genes that confer Al tolerance in higher plants.