Mechanisms leading to excess alpha-amylase activity in wheat (Triticum aestivum, L) grain in the UK

The frequency and mechanisms of four modes of alpha-amylase enzyme accumula tion in U.K. wheat, retained pericarp alpha-amylase activity (RPAA), pre-ma turity alpha-amylase activity (PMAA), prematurity sprouting (PrMS) and post -maturity-sprouting (PoMS), were investigated in field and laboratory exper iments. Of 56 cultivar site year combinations four model cultivars grown at up to Four sites From 1994-1997, enzyme activity was detected in 32 cases, in 23 cases sufficient to reduce Hagberg falling number (the usual industr y measure of alpha-amylase) below the commercial criterion (250 s). The fre quency of occurrence of different modes of enzyme accumulation was in the o rder PoMS > PMAA > PrMS > RPAA. Both PMAA and PrMS were more common than ex pected and the most usual pattern was for alpha-amylase to accumulate by se veral modes. Although green grains are rejected as impurities, study of gra in colour in relation to pericarp alpha-amylase activity showed that the en zyme could persist in non-green grains in levels sufficient to affect the H agberg value. Two Factors thought to promote PMAA. grain drying rate and tr ansient changes in temperature in early development, were studied in the fi eld and controlled environment cabinets. No significant difference uas foun d in grain drying rare between samples where PMAA was or was not identified . However, out of 19 transfers from a cool (16/10 degreesC) to a warm (26/2 0 degreesC) temperature regime, six led to significant increases in PMAA. N o transfers after 45% grain moisture increased PMAA. PrMS occurred as early as 67% grain moisture and susceptibility usually increased with stage of d evelopment being greatest in the grain dough stage. PrMS susceptibility var ied with cultivar (in the same order as PoMS sensitivity) and M as affected by environmental factors. (C) 2001 Academic Press.