Distribution and Connection of Vascular Bundles in Relation to the Accumulation of Starch Grains in the Potato Tuber

Abstract

By making serial sections, the distribution and connection of vascular bundles in the potato tubers were observed by light microscope. The vascular bundles entered from stolon into the rose end of tuber separate to the external phloem of cortex, to the bundles of vascular bundle ring, and to the internal phloem in perimedulla. Each of the external phloem in cortex and the bundle of vascular bundle ring have the anastomosing network which runs parallel to periderm. The internal phloem in perimedulla contains each of phloems which run to the direction of eye and to the center of tuber, forming three-dimensinal network. The external phloem and the internal phloem of vascular bundle ring have radial connetions respectively to external phloem in cortex and to internal phloem in perimedulla. Perimedulla is separated by the rays into the clusters which homologize to the vascular cylinder of aerial stem, and those clusters separate and join each other at the base of eyes. From observations of the tuber in rapid development, it was suggested that the starch grains density of each tissue is related to the distribution of vascular bundles, the starch grains are more densely accumulated in parenchyma cells around phloem in cortex and perimedulla, than those in the central medulla and the ray containing no vascular bundle. From the observations of the distribution and connection of vascular bundles in tuber, it was assumed how the pathway of assimilate transport exist in tuber at stage of tuber development, and the relation was discussed between the distribution of vascular bundles and accumulation of starch grains in the tissues. © 1993, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.