Biochemical and ultrastructural analysis of the y10 mutant of maize

Abstract

The y10 mutant of maize has been categorized as a carotenoid mutant due to its pale-yellow endosperm color and the albino seedling that develops following germination of the kernel. Analysis of endosperm and seedling leaf extracts revealed that the carotenoid content of endosperm and seedling leaf is significantly reduced compared to wild-type siblings. However, a block at a specific step in the carotenoid biosynthetic pathway was not detected. When y10y10 seedlings were grown on defined medium containing geraniol or farnesol, which are isoprenoid precursors for both carotenoids and the phytyl chain of chlorophyll, we found a significant increase in the amount of carotenoids in the leaf tissue. These isoprenoid precursors appear to complement the y10 mutation, although not to wild-type sibling levels. Thus the apparent defect in the y10 mutant affects a step in isoprenoid biosynthesis that precedes the synthesis of geranylgeranyl pyrophosphate. Examination of seedling leaves by light and transmission electron microscopy revealed that the drastic reduction in photosynthetic pigments in the y10 mutant has a dramatic effect on the cellular architecture of leaf tissue. In comparison to other albino mutants of maize that have been analyzed at the ultrastructural level, the alterations in plastid architecture of y10 mutants are quite severe.