MOLECULAR DETERMINANTS OF SINK STRENGTH

The manipulation of sink to source relations has been subject to exten sive plant breeding programs aiming to improve harvest index and there by crop yield. The introduction of molecular and biochemical tools has enabled scientists to investigate the underlying principles. This has opened up the fascinating possibility of identifying molecular determ inants of sink strength and to further increase yield on a rational ba sis. In the past, transgenic plants with alterations in the activity o f only one putative molecular determinant have been created and this s trategy has not resulted in substantial and reliable increases in yiel d. Yet, careful molecular and biochemical investigations have provided valuable insight about carbon flux into different metabolic pathways at different stages of sink development and it has become apparent tha t this metabolic channelling needs to be exploited by using stage- and cell-specific promoters in attempts to increase sink strength.