DEVELOPMENT-SPECIFIC AND ORGAN-SPECIFIC EXPRESSION OF THE GENES FOR SUCROSE SYNTHASE AND 3 ISOENZYMES OF ACID BETA-FRUCTOFURANOSIDASE IN CARROT

The steady-state levels of transcripts for cell-wall beta-fructofurano sidase (cw beta F), for isoenzymes I and II of soluble acid beta-fruct ofuranosidase (sI, sII), and for sucrose synthase (ss) were determined in the sink and source organs of developing carrot (Daucus carota L.) plants. The expression patterns of the four genes clearly differed. T he expression of the gene for cw beta F was development-specific but n ot organ-specific; high transcript levels were only found in plants wi th primary roots, with about equal amounts in leaf lamina, petioles an d roots. The genes for sI and sII were mainly expressed in roots, sI p redominating in primary roots and sII in developing tap roots. Transcr ipts for ss were found at a low level in all developing plant organs a nd were markedly up-regulated during the development of young leaves a nd during the transition of primary roots to tap roots. Developing tap roots contained only transcripts for sII and for ss. Marked alteratio ns in the expression of these two genes after manipulation of the sour ce/sink balance of these plants indicates their importance in sucrose partitioning. We suggest that ss regulates sucrose utilization in deve loping tap roots, whereas sII located in the vacuole controls sucrose storage and sugar composition.