CLASSIFICATION AND CHARACTERIZATION OF THE VIVIPAROUS MUTANTS OF MAIZE (ZEA-MAYS L.)

S1 nuclease protection assays were used to examine 26 previously undef ined, carotenoid-containing, viparous mutants of maize. Embryo extract s of 4 of the mutants were completely devoid of Vp1 mRNA, identifying them as class I mutants. The remainder were tentatively classified as class III mutants, 18 of which were further analyzed using HPLC. By co mparing the profile of xanthophylls present in mutant embryos to that in normal embryos from the same ear, it was possible to separate the m utants into groups that appear to share a common metabolic block. Thes e procedures can greatly reduce the time and labor required for alleli sm tests using conventional crossing. Zeaxanthin comprised a higher pr oportion of the xanthophylls extracted from embryos from vp10 and 4 vp 10-like mutants than from non-mutant seeds segregating on the same ear s. Viviparous mutants in this group had relatively lower levels of epo xy-xanthophylls, especially violaxanthin. These mutations thus appear to impair the epoxidation of zeaxanthin. In contrast, zeaxanthin compr ised a smaller proportion of the xanthophylls extracted from embryos o f vp8 and 9 vp8-like mutants than in their normal counterparts. In the se mutants, the relative levels of 9'-cis-neoxanthin and neoxanthin we re increased. These mutations appear to affect an oxidative cleavage s tep late in the ABA biosynthesis pathway. The decrease in zeaxanthin i n these mutants suggests that one of the accumulated compounds may ser ve as a feedback inhibitor for zeaxanthin synthesis. Embryos homozygou s for the vp-92EP8 mutation accumulated violaxanthin, while two mutant s, vp-92GN24 and vp-90GS8 accumulated violaxanthin and neoxanthin. The se results are compatible with a pathway where neoxanthin. Under this model, vp-92EP8 limits the isomerization of violaxanthin to neoxanthin , while vp-92GN24 and vp-90GS8 limit the isomerization of neoxanthin t o 9'-cis-neoxanthin. The xanthophyll composition in embryos homozygous for one mutation was almost identical to that in normal embryos, and in three mutants small decreases in zeaxanthin were offset by an incre ased percentage of 9'-cis-neoxanthin. These mutants may be blocked in ABA synthesis at a point or points beyond xanthoxin.