Relationship between Chlorophyll and Carotenoid Biosynthesis in Dirty-Red (Green-Flesh) Mutant in Tomato

Abstract

In a tomato mutant, dirty red, both chlorophylls and carotenoids are present in the ripe fruit resulting in a dirty-red flesh color. Since it had been proposed that the phytol chain of the chlorophyll molecule may be utilized as a precursor for carotenoid during maturation, the dirty-red mutant was studied to determine the effect of chlorophyll retention on carotenoid synthesis. An inheritance study revealed that dirty red is controlled by a single recessive gene and is synonymous or allelic to the green-flesh mutant (gf). Analyses of chlorophylls a and b indicated that the action of the dirty-red gene becomes evident as the ripening process commences. The chlorophyll contents of the parental strains (Rutgers and dirty red) and the F2 red and dirty-red recombinants were almost equal at the immature green stage. Upon ripening, the dirtyred fruits contained some chlorophyll, while none was detected in the normal red fruits. The chlorophyllase activities of the red and dirty-red F2 progenies were determined. At the green stage, both segregates showed almost equal enzyme activities, indicating that, at this early stage, there was no loss or impairment of enzyme activity in the dirty-red plants. At incipient color, the dirty-red segregates showed higher chlorophyllase activity than the red F2 progeny. No enzyme activity was detected in the ripe fruits of red segregates, while the dirty-red recombinants exhibited slight chlorophyllase activity. Tests indicated that chlorophyllase from either normal or dirty-red plants could degrade chlorophyll from either source. These results suggest that impaired degradation by this enzyme is not responsible for the chlorophyll content of the ripe dirty-red fruits. The dirty-red gene also influences carotenoid synthesis and accumulation, and a relationship between the two pigment systems was demonstrated. The p3-carotene, y-carotene, lycopene, phytofluene, and phytoene contents were determined. Where the dirty-red factor was homozygous, chlorophyll was present in the ripe fruits, and the carotenoid content was lower than in normal red sibs. The differences in carotenoid contents between the two types were highly significant in the F2 recombinant classes.