RAFFINOSE ACCUMULATION IN MAIZE EMBRYOS IN THE ABSENCE OF A FULLY FUNCTIONAL VP1 GENE-PRODUCT

The maize (Zea mays L.) Viviparous-1 (Vp1) gene encodes the cotranscri ptional activator VP1 protein and regulates biosynthesis of anthocyani ns, sensitivity to abscisic acid, repression of alpha-amylase. and oth er factors related to quiescence during embryo maturation. Five mutant vp1 alleles were used to determine if the Vp1 gene regulates raffinos e accumulation and the onset of desiccation tolerance in isolated embr yos. Embryos of wildtype Vp1-R (purple, non-viviparous) kernels acquir ed desiccation tolerance to fast drying in association with a sucrose: raffinose mass ratio of 10:1 or lower. After slow driving, germinabili ty was related to stage of embryo development. Embryos of mutant vp1-R (yellow, viviparous) kernels, in which the Vp1 gene is not expressed, accumulated only trace amounts of raffinose and never acquired desicc ation tolerance. Embryos from kernels (yellow, non-viviparous) carryin g the modified mutant allele vp1-McWhirter (which encodes a VP1 protei n that is truncated at the C-terminal end), the ''Coe'' mutant allele vp1-1695. or the mutant: alleles vp1-A1 or vp1-C821708 all become quie scent. Developing embryos of kernels with the modified mutant alleles vp1-McWhirter and vp1-1695 were desiccation tolerant in association wi th the sucrose:raffinose mass ratio having a value of 20:1 or lower. E mbryos from wild-type kernels segregated on the same ears (Vp1-1695, p urple) also were desiccation tolerant in association with a sucrose:ra ffinose mass ratio of less than 20:1. The acquisition of desiccation t olerance in developing maize embryos may be associated with raffinose accumulation, and raffinose biosynthesis may occur in the absence of a fully functional vp1 gene product.