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-fructofuranosidase (cw beta F), for isoenzymes I and II of soluble acid beta-fructofuranosidase (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. The expression of the gene for cw beta F was development-specific but not organ-specific; high transcript levels were only found in plants with primary roots, with about equal amounts in leaf lamina, petioles and roots. The genes for sI and sII were mainly expressed in roots, sI predominating in primary roots and sII in developing tap roots. Transcripts for ss were found at a low level in all developing plant organs and were markedly up-regulated during the development of young leaves and during the transition of primary roots to tap roots. Developing tap roots contained only transcripts for sII and for ss. Marked alterations in the expression of these two genes after manipulation of the source/sink balance of these plants indicates their importance in sucrose partitioning. We suggest that ss regulates sucrose utilization in developing tap roots, whereas sII located in the vacuole controls sucrose storage and sugar composition.