Annals of Botany

Shocking treatment goes against the grain

All our students know that GA induces a-amylase synthesis in the aleurone layer of germinating cereal grains and that α-amylase is one of a suite of enzymes that mobilize the nutrient reserves of the endosperm. However, it is much less well known that α-amylase may be produced prematurely in grain development. Sometimes this is associated with precocious germination of the grain while still on the parent plant but often it happens without any other visible sign of germination. There are obvious implications for the quality of the grain at harvest and thus Farrell and Kettlewell at Harper Adams University College, Shropshire, UK (pp. 287–293) have conducted a systematic investigation of possible factors that may cause pre-maturity a-amylase (PMA) activity. Winter wheat genotypes that differed in their susceptibility to PMA were grown in the glasshouse; at anthesis they were transferred to ‘high’ (30/15 °C) or ‘mid’ (20/10 or 22/22) temperature regimes. At 25–30 d after anthesis (depending on the pre-treatment), plants were exposed for 8 d to a temperature shock (mid-to-low, 22/22 → 12/12 8C; mid-to-high, 20/10 → 30/20; high-to-mid, 30/15 → 18/12). Other plants were partially de-grained in order to increase grain size in the remaining grains; some of these were also subjected to a midto-low (25/15 → 13/11) temperature shock. Amylase was assayed both by enzyme activity and by ELISA determination of protein levels. Analysis of results by ANOVA showed very clearly that the key factors in the occurrence of PMA were environment and genotype. Both high and low temperature heat-shock treatments (but especially low temperature) induced PMA in susceptible varieties but hardly at all in resistant varieties. Cold-shock treatment also led to the formation of larger grains, giving a correlation between grain size and PMA. Grain size itself was not a determinant of PMA, as indicated by the data obtained with the larger grains of partially de-grained plants.