Raffinose accumulation in maize embryos in the absence of a fully functional Vp1 gene product

Abstract.

The maize (Zea mays L.) Viviparous-1 (Vp1) gene encodes the cotranscriptional activator VP1 protein and regulates biosynthesis of anthocyanins, sensitivity to abscisic acid, repression of α-amylase, and other factors related to quiescence during embryo maturation. Five mutant vp1 alleles were used to determine if the Vp1 gene regulates raffinose accumulation and the onset of desiccation tolerance in isolated embryos. Embryos of wild-type Vp1-R (purple, non-viviparous) kernels acquired desiccation tolerance to fast drying in association with a sucrose:raffinose mass ratio of 10:1 or lower. After slow drying, germinability 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 desiccation tolerance. Embryos from kernels (yellow, non-viviparous) carrying the modified mutant allele vp1-McWhirter (which encodes a VP1 protein 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 quiescent. Developing embryos of kernels with the modified mutant alleles vp1-McWhirter and vp1-1695 were desiccation tolerant in association with the sucrose:raffinose mass ratio having a value of 20:1 or lower. Embryos from wild-type kernels segregated on the same ears (Vp1-1695, purple) also were desiccation tolerant in association with a sucrose:raffinose mass ratio of less than 20:1. The acquisition of desiccation tolerance 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.