Studies on the Developmental Physiology of the Lateral Roots in Rice Seminal Roots

Abstract

During the growth of seminal root, the dividing character of root apex is converted into the elongating one and the protein synthetic character into the cell wall synthetic one, when supply of nitrogen and phosphorous from endosperm to seminal root ceases. The changes in the characters of root apex effected the morphogenetic processes of the root, that is, the decrease in number of cortical layers in main root axis due to the fall of the dividing activity in epidermis-cortex initial cells, and the decrease in cell number of central cylinder, especially of phloem elements in the lateral root axis. The lateral roots are divided into the following three types according to size of root diameter and presence of an inner-cortical sclerenchymatous tissue as well as of a central metaxylem vessel. S type (Photo. 3) : Lack of an inner-cortical sclerenchymatous tissue and of a central meta-xylem vessel, degenerative tendency of phloem elements, 50∼60μ in root diameter. L type (Photo. 1) : The same structure and tissue orientation as seminal root fundamentally, 120∼140μ in root diameter. T type (Photo. 2) : The same structure and tissue orientation as L type except lack of an inner cortical sclerenchymatous tissue, 80∼110μ in root diameter. It was observed that laterals of S type were dominantly distribute dover all parts, especially over the parts formed by utilizing nitrogen and phosphorous derived from the cortical disintegration of aged root region, but laterals of L and T type were detectable only in the parts formed by utilization of the same from endosperm. All these laterals were active in the absorption of NH4-nitrogen and phosphorous.