Regulation of lipase activity by viviparous-1 and abscisic acid during development of the caryopsis of Zea mays L

Abstract

Ultrastructural comparisons of aleurone tissues from wild type, vp/vp and vp5/vp5 maize kernels were made at 16, 25 and 35 days after pollination (DAP). Wild type and vp5 aleurone cells were similar at 16 and 25 DAP, but obvious changes in spherosome structure had occurred by 35 DAP in vp5 aleurone cells. These spherosomes had a diffused appearance and appeared to be undergoing degradation. Spherosome structural differences in vp aleurone cells were detectable at 16 DAP and obvious at 25 DAP. Spherosome appearance in 25 DAP vp cells was similar to that observed in vp5 at 35 DAP. Spherosomes were largely degraded by 35 DAP in vp aleurone cells. Lipase activity was assayed in aleurone and scutellum tissues. High lipase activity, with and without substrate (trilinolein) was detected at 16 DAP in vp aleurone but not until 25 DAP in vp5 aleurone. Lipase activity in scutellum was detected at 25 and 35 DAP for vp and vp5, respectively. No measurable lipase activity was detected in wild type tissues at any age. Lipase data from 13 to 17 DAP wild type kernels cultured in vitro with fluridone were similar to 16 DAP vp data. Fluridone cultured kernels have almost no abscisic acid (ABA), vp5 is ABA-deficient but ABA levels are higher than in fluridone cultured kernels, and vp is ABA-insensitive. Results from the electron microscopic studies and lipase assays suggest that lipase causes degradation of spherosomes in viviparous tissues. Lipase suppression during normal kernel development appears to be regulated by ABA and the Vp gene product.