Regulation of RNA synthesis in early germination of isolated wheat (Triticum aestivum L) embryo

Abstract

THE change from dormancy to germination of seeds requires water and an appropriate temperature. Wheat embryo germination is characterised by an initial increase in fresh weight, followed by a 5-h lag¹. Although RNA synthesis is one of the earliest biologically measurable activities in wheat embryo germination^2,3, its mode of regulation has not been established. Reports^3–6 have suggested that the rate of synthesis does not change during the first 6 h of germination. But no adjustment was made for the specific activities of ribonucleoside triphosphate, UTP. This would have led to a misinterpretation of incorporation data when there was either a change in the concentration of the nucleotide or a difference in the rate of phosphorylation from nucleoside to nucleotide as germination progressed. To investigate further whether there is a change in the rate of RNA synthesis in the germination phase, we have used recentlydeveloped enzyme assays^7–9 to measure picomole changes in purine pyrimidine ribonucleotide levels. We found a threefold increase in the rate of RNA synthesis of wheat embryos germinated for 40 min–5.5 h. We used the reaction catalysed by uridine 5′-diphosphoglucose pyrophosphorylase to determine the content of UTP. The key step in this analysis is the selective adsorption of the reaction product, UDP-¹⁴C-glucose, on to activated charcoal in the presence of 0.8 M Trizma base⁹.