REGULARITY IN VARIATION OF LEAF COLOR AND NITROGEN DISTRIBUTION IN HALF-LEAF BLADES BY LEAF POSITION ON THE STEMS OF RICE PLANTS .2. UNEVENTRANSLOCATION OF NITROGEN BETWEEN OUTSIDE AND INSIDE HALF-LEAVES

We have reported in a previous paper that the outside half-leaf had a smaller volume and deeper leaf color than the inside half-leaf. The ha lf-leaf color was not dependent only on the difference in leaf volume but also on the ability of nitrogen absorption. The difference in nitr ogen absorption was considered as another factor involved. We, therefo re, measured the volumes of nodal roots on both sides of a half-leaf a nd found that the nodal roots of an outside half-leaf had a larger vol ume and higher ability of absorption. Considering that the difference in translocation and retranslocation of absorbed nitrogen might be inv olved as a third factor, we investigated the difference in the distrib ution of N-15 fed to the roots on fixed tillers. It was found that abs orbed N-15 was translocated only to the side of N-15 feeding tillers, and that each nodal root, being related to specific parts of tillers o nly, played an extremely limited role in distributing nitrogen. We fur ther investigated the translocation of N-15 applied to the surface of an outside or inside half-leaf to find how N-15 was translocated throu gh the midrib to an opposite half-leaf. It was found that N-15 transfe rred to the top and base of a half-leaf and did not transfer across th e midrib. Consequently, it was assumed that an outside half-leaf maint ains its deeper leaf color.