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

The quiescent wheat ( Triticum aestivum L. cv. Hobbit) embryo contains polyadenylated RNA species (polyA + RNA, presumptive mRNA species) which are rapidly degraded upon water imbibition by the embryo even when the embryo has lost viability. The level of polyA + RNA species in the quiescent embryo does not reflect the vigour or viability rating of the seed lot. Embryos which have lost viability appear to have lost the capacity for de novo transcription of polyA + RNA species during the hours following water imbibition by the embryo. Embryos from seed lots of differing vigour ratings can be distinguished by their very different patterns of polyA + RNA metabolism during germination at a sub‐optimal temperature. In embryos of reduced vigour there is a delayed onset of degradation of polyA + RNA species during germination at 10°C and a reduced rate of polyA + RNA synthesis through the first 6 h of germination compared with these processes in high vigour embryos. However, at later germination stages embryos of reduced vigour synthesise polyA + RNA species at rates 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 additional lesions affecting the stability and/or turnover of the messenger ribonucleo‐protein complex containing polyA + RNA are present in embryos of reduced vigour at later stages of germination at a sub optimal temperature.