Polyadenylated RNA metabolism and loss of vigour and viability in germinating wheat embryos

C. A. D. Smith, P., Rusbton and C. M. BraySmith, C. A. D. , Rushton, P. and Bray, C. M. 1986. Polyadenylated RNA metabo-lism and loss of vigour and viability in germinating wheat embryos. - Physiol. Plant.67; 310-314.The quiescent wheat (Triticum aestivum L. cv. Hobbit) embryo contains polyade-nylated RNA species (polyA* RNA, presumptive mRNA species) which are rapidlydegraded upon water imbibition by the embryo even when the embryo has lost viabil-ity. The level of polyA* RNA species in the quiescent embryo does not reflect thevigour or viability rating of the seed lot. Embryos which have lost viability appear tohave lost the capacity for de novo transcription of polyA* RNA species during thehours following water imbibition by the embryo. Embryos from seed lots of differingvigour ratings can be distinguished by their very different patterns of polyA* RNAmetabolism during gennination at a sub-optimal temperature. In embryos of reducedvigour there is a delayed onset of degradation of polyA* RNA species during germi-nation at 10°C and a reduced rate of polyA* RNA synthesis through the first 6 h ofgermination compared with these processes in high vigour embryos. However, at la-ter gennination stages embryos of reduced vigour synthesise polyA* RNA species atrates similar to those found in high vigour embryos yet newly synthesised polyA'RNA species accumulate in embryos of reduced vigour only to a level which is 50%of that found in high vigour embryos of comparable viability. Results suggest that ad-ditional lesiotis affecting the stability and/or turnover of the messenger ribonucleo-protein complex containing polyA* RNA are present in embryos of reduced vigour atlater stages of gennination at a sub-optimal temperature.Additional key word - Protein biosynthesis.C. A. D. Smith (present address), Dept of Health cE Human Services, National Inst. ofHealth, National Cancer Inst. , Bethesda, MD 20205, U.S.A. ; P. Rushton and C. M.Bray (reprint requests), Dept of Biochemistry, Univ. of Manchester, Oxford Road,Manchester Ml3 9PT, V.K. This paper is part of the contribution to the workshop on Control Processes in Seeds,held in Wageningen, The Netherlands, 18-24 August, 1985.IntroductionA viable, non-dormant seed will be expected to germi-nate when given optimal germination conditions such asthose supplied in the standard germination test. How-ever, within a cultivar, seed lots which exhibit a highpercentage germination under the optimal conditions ofthe statidard germination test may vary with respect totheir rate of germination and seedling establishment inthe field according to their vigour (Stormonth 1978). Such variations in vigour are rarely seen when growthconditions are optimal but become apparent upon ger-mination under conditions in which a stress is put uponthe seed. Under stress germination conditions, such as asub-optimal germination temperature, seeds low in vig-our fail to germinate or germinate more slowly thanseeds of high vigour. Winter wheat varieties which aresown in the autumn and harvested the following sum-mer often have to germinate and establish under sub-optimal conditions and field trials have shown that seedvigour is a significant factor affecting seedling estab-lishment, growth and yield in cereals (Stormonth andDoling 1979, Hampton 1981). Investigations into the molecular events occurring inReceived 10 September, 1985; revised 23 January, 1986310