Spatial and temporal distribution of sucrose synthase in the radish hypocotyl in relation to thickening growth

Sucrose synthase (SuSy) is a key enzyme in the development of storage root of radish. Clarification of its spatial and temporal expression during the thickening growth of radish hypocotyl, which later develops into storage ro ot, was carried out immunologically using fight microscopy, Sequential harv ests at 3, 7, 11 and 13 d after sowing (DAS) were performed on two radish c ultivars having different sink capacity. A very low level of SuSy was obser ved 3 DAS for both cultivars, White Cherrish (WC; strong storage root) show ed the maximum level of SuSy between 7 and II DAS with increased cell devel opment (thickening), while in Kosena (K; low storage root) the level remain ed high after 13 d of growth. A high level of SuSy was found in companion c ells, which was consistent with previous observations, but SuSy was also fo und in the xylem parenchyma and in some cortical cells. The level of SuSy d iffered according to the localization and depended highly on cell developme nt. Both cell division and cell enlargement were stimulated in WC compared with K. The role of SuSy during thickening growth of radish hypocotyl is di scussed in terms of utilizing photosynthates.