CONTROL OF RIPENING

Ripening of fleshy fruits involves major changes in physiology and bio chemistry that alter their colour, flavour, texture, aroma and nutriti onal value. These changes affect all cell compartments and require the expression of new genes encoding enzymes that catalyse reactions esse ntial for the development of quality attributes. In climacteric fruits , such as tomato, ethylene functions as a hormone to stimulate changes in gene expression required for ripening. Molecular cloning experimen ts have led to the isolation of cDNAs encoding many ripening proteins. This has enabled the identification and manipulation of novel plant g enes encoding enzymes involved in cell wall texture change, carotenoid biosynthesis, ethylene synthesis and the identification of gene contr ol regions involved in fruit-specific, ripening-specific, and ethylene -regulated gene expression. Antisense and partial sense gene technique s have been developed to generate genetically modified plant lines in which specific genes have been permanently inactivated. These fundamen tal studies have led to production and evaluation of genetically modif ied tomato lines with improved colour, texture, storage life, and proc essing characteristics. Zeneca Seeds has established a new business di vision, the aim of which is to utilize these techniques for the develo pment of improved fruit and vegetable varieties. In collaboration with Petoseed, Zeneca Seeds is in the process of transferring the genes le ading to quality improvement of tomatoes to Petoseed's elite tomato ge rmplasm. The primary focus is on the development of improved processin g hybrids. These are being evaluated in collaboration with Hunt Wesson , a large and diversified tomato processing company. It is planned tha t products based on this research will be introduced in the USA in 199 5.