Induction of ultrastructural specialization for ureide metabolism in non-nodule soybean tissues cultured in vitro

Abstract

Root nodules of tropical legumes, such as beans and soybeans, produce ureides from nitrogen fixed by bacterial symbionts. Ultrastructural specialization for ureide production, including the appearance of abundant tubular ER and marked enlargement of peroxisomes, is known to occur in uninfected cells in the root nodule. Here we have investigated the capability of non-nodule tissues of soybean to specialize for ureide metabolism. Soybean embryonic axes excised from imbibed seeds were cultured in vitro on media with various nitrogen sources. The axes grew well on media containing urate or allantoin as the sole nitrogen source, but grew poorly on media with asparagine or glutamine as the sole nitrogen source. Root tissue and callus induced from segments of soybean embryonic axes also grew well on media containing urate or allantoin as the major nitrogen source. Numerous peroxisomes were observed in the root tissue and in proliferating callus cells growing on media containing urate as the major nitrogen source, whereas abundant ER was observed in the root tissue and callus cells growing on media containing allantoin. The capacity of non-nodule tissue cells to ultrastructurally differentiate for metabolizing externally supplied urate or allantoin was demonstrated.