COMPARISON OF THE CONTENTS OF SUCROSE AND AMINO-ACIDS IN THE LEAVES, PHLOEM SAP AND TAPROOTS OF HIGH AND LOW SUGAR-PRODUCING HYBRIDS OF SUGAR-BEET (BETA-VULGARIS L)

The contents of sucrose and amino acids in the leaves, phloem sap and taproots have been analysed in three experimental hybrids of sugar bee t and compared with earlier analysed leaf and phloem sap contents in s pinach and barley. The three hybrids accumulated sucrose and amino aci ds to various extents in the mature roots as well as in the young tapr oots (9-12 weeks). The differences in the sucrose-to-amino acid ratios in the taproots were reflected in the corresponding ratios in the phl oem sap. The leaf contents of sucrose and amino acids in the three hyb rids were found to be very similar to each other and also to those in spinach and barley. In contrast, the phloem concentration of sucrose ( 1.3 M) was much higher, and that of amino acids much lower than in spi nach and barley. In the taproots, the overall concentration of sucrose was about half that in the phloem sap. From these findings it is conc luded that the decisive factor in the high sucrose accumulation in sug ar beet roots is the very efficient process of phloem loading in the l eaves. The patterns of the amino acids in the phloem sap and in the ta proots resembled those in the leaves, indicating that there is no spec ial transport form for alpha-amino nitrogen from the leaves to the roo ts, but all amino acids which are present in the cytosol are transloca ted.