Tissue specificity of assimilation and transport of nitrogen in the root ofZea mays L. seedlings. I. Transformations of14C- sucrose and the nitrogen metabolism enzymes in cortex and stele

Abstract

An investigation has been carried out to find out in what compounds carbon is radially transported from stele to the cortex and to study sucrose metabolism in the root. These tissues were fed with14C-sucrose either directly or through the mesocotyle. In the latter case, the bulk of radioactivity, both in the stele and cortex, was concentrated in sucrose rather than in mono saccharides. This corresponds to the radial transport of carbon from stele to cortex predominantly in the form of sucrose. In the case of a direct exposure of stele and cortex,14C-sucrose was utilized for respiration, amino acid biosynthesis, and accumulation of carbon in the form of glucose. The hydrolysis of sucrose to the monosaccharides and subsequent utilization of the latter in respiration was more intensive in the stele. In the cortex, the sucrose carbon was more actively used for amino acid synthesis, owing to a high concentration of nitrate reductase, glutamate dehydrogenase and glutamine synthetase. It was concluded that the cortex is the main issue zone providing nitrogen assimilation in the root.