CHANGES IN THE ENDOGENOUS LEVEL OF ZEATIN RIBOSIDE, ABSCISIC-ACID AND INDOLE ACETIC-ACID DURING FORMATION AND THICKENING OF TUBEROUS ROOTS IN SWEET-POTATO

Changes in zeatin riboside (ZR), abscisic acid (ABA) and indole acetic acid (IAA) contents of roots in sweet potato (Ipomoea batatas) during their development were investigated by using two cultivars which differed in the thickening potential of tuberous roots and a related wild species, I. trifida, which formed no tuberous roots. Although ZR contents of fibrous roots did not differ among the materials, it apparently increased at the formation of tuberous roots in the cultivars. In the wild species, ZR content slightly increased later when root diameter exceeded 2mm. ZR contents of tuberous roots was a little higher in one cultivar, which had more tuberous roots but of smaller weight of tuberous roots than the other. ABA contents of fibrous roots did not differ between two cultivars and was smaller in the wild species. ABA contents of tuberous roots in the cultivars increased after the time of increase in ZR contents. In the wild species, it was almost steady. Remarkable difference in ABA contents of tuberous roots was found between two cultivars; it was higher in the cultivar which had higher weight of tuberous roots. Regarding IAA contents of roots, no tendencies were found in the cultivars after fluctuation. From these results with the results of anatomical observations of roots, the differential roles of these plant hormones on the formation and thickening of tuberous roots was suggested.