Action of the Gene B in Biosynthesis of Carotenes in the Tomato

1. When excised normal red tomato fruits are ripened artificially at temperatures of 31.5⚬ or 32.5⚬ C., lycopene synthesis is inhibited, but β-carotene production appears not to be affected. This has suggested that in the tomato β-carotene is not formed from lycopene by isomerization as has been postulated. However, when strains which produce more than normal quantities of β-carotene, because they possess the gene B, are examined, it is found that a major portion of the β-carotene fraction is also temperature-sensitive. This, together with prior evidence, suggests that in strains carrying B, the action of this gene is to mediate the formation of the beta-ionone ring. 2. The quantitative data obtained from excised fruits were verified with quantitative data from fruits ripened on the vine under conditions of controlled temperature, light, and humidity.