Leaf sheath cuticular waxes on bloomless and sparse-bloom mutants of Sorghum bicolor

Leaf sheath cuticular waxes on wild-type Sorghum bicolor were approximately 96% free fatty acids, with the C-28 and C-30 acids being 77 and 20% of the se acids, respectively. Twelve mutants with markedly reduced wax load were characterized for chemical composition. In all of the 12 mutants, reduction in the amount of C-28 and C-30 acids accounted for essentially all of the reduction in total wax load relative to wildtype. The bm2 mutation caused a 99% reduction in total waxes. The bm4, bm5, bm6, bm7 and h10 mutations cau sed more than 91% reduction in total waxes, whereas the remaining six mutan ts, bm9, bm11l, h7, h11, h12 and h13, caused between 35 and 78% reduction i n total wax load. Relative to wild-type, bm4 caused a large increase in the absolute amount of C-22, C-24 and C-26 acids, and reduction in the C-28 an d longer acids, suggesting that bm4 may suppress elongation of C-26 acyl-Co A primarily. The h10 mutation increased the absolute amounts of the longest chain length acids, but reduced shorter acids, suggesting that h10 may sup press termination of acyl-CoA elongation. The bm6, bm9, bm11, h7, h11, h12 and h13 mutations increased the relative amounts, but not absolute amounts, of longer chain acids. Based on chemical composition alone, it is still un certain which genes and their products were altered by these mutations. Nev ertheless, these Sorghum cuticular wax mutants should provide a valuable re source for future studies to elucidate gene involvement in the biosynthesis of cuticular waxes, in particular, the very-long-chain fatty acids. (C) 20 00 Published by Elsevier Science Ltd.