The aurea and yellow-green-2 mutants of tomato are deficient in phytochrome chromophore synthesis.

The phytochrome-deficient aurea mutant of tomato has been widely used for the study of both phytochrome function and the role of other photoreceptors in the control of development in higher plants. To date the exact nature of the aurea mutation has remained unknown, though this information is clearly important for the interpretation of these studies. It has been proposed that aurea and yellow-green-2, another mutant of tomato that has a similar phenotype to aurea, could be deficient in phytochrome chromophore synthesis. We have examined this hypothesis by measuring the activity of the enzymes committed to phytochrome chromophore synthesis in these mutants. The approach takes advantage of a recently developed high pressure liquid chromatography-based assay for the synthesis of the free phytochrome chromophore, phytochromobilin from its immediate precursors biliverdin IXalpha and heme. Isolated etioplasts from aurea and yellow-green-2 seedlings were specifically unable to convert biliverdin IXalpha to 3Z-phytochromobilin and heme to biliverdin IXalpha, respectively. In addition, the level of total noncovalently bound heme in the mutants was the same as in wild type seedlings. Together, these results identify both aurea and yellow-green-2 as mutants that are deficient in phytochrome chromophore synthesis.