Methods for making such plants, by genetic manipulation of known tomato plants, are fully described in the aforesaid European Patent Application No 271988 and in U.S. application Ser. 119614, the complete disclosures of which applications are incorporated herein by reference. 1 shows the base sequence for polygalacturonase CONA pTOM6. 2 shows the base sequence for pectin methylesterase cDNA clone pPE1. A convenient method of obtaining such plants is to grow the seeds from tomato fruit according to the invention.
Fruit ripening is a complex physiological and biochemical process.
It requires the activation of specific genes which are required to give fruit the desirable characteristics important for human consumption, and for industrial processing for consumption. In biochemical terms these attributes are brought about through the action of enzymes that are responsible for the breakdown of chlorophyll and the synthesis of lycopene .beta.-carotene for colour production, the synthesis of flavour components through lypoxygenase, the synthesis of enzymes involved in the maintenance of water and mineral balance, enzymes controlling vitamin production, and most importantly for the purposes of the present invention, the production of cell wall degrading enzymes leading to fruit softening. Preferred fruit according to our invention show reduced levels of expression of the polygalacturonase or the pectin methylesterase gene, or both. This may result from the presence in the genome of one, or several, antisense constructs to either or both genes. Both pectinesterase and polygalacturonase are involved in the biochemical conversion of pectic cell wall substances during fruit ripening.