Effect of high temperature during grain filling on starch synthesis in the developing barley grain

Abstract

Plants of malting barley variety Schooner were exposed to 5 days of high temperatures (up to 35°C) during mid grain filling under controlled environment conditions. Grains from heat treated plants accumulated c. 30% less starch than grains from control plants (21/16°C; 14 h day). Reduced starch deposition was not limited by assimilate levels in heat treated grains, but high temperature reduced the conversion of sucrose to starch. The reduction in starch synthesis appeared to result from the effects of diminished catalytic activity of a number of enzymes in the committed pathway of starch synthesis, and/or delayed recovery of enzyme activity in the cooler recovery conditions. Reductions of 11–75% in the activity of the enzymes under investigation followed high temperature exposure. In addition, ADPglucose pyrophosphorylase, branching enzyme and granule bound starch synthase showed increased activity during exposure to moderate temperatures (28–32°C), but reduced activity at high temperatures, while soluble starch synthase showed an immediate loss of activity, even at moderate temperatures. Sucrose synthase and UDPglucose pyrophosphorylase showed the greatest reduction in catalytic activity after plants were returned to cooler conditions. Individual enzymes showed variation in the level of recovery under the cooler temperature conditions which followed the heating period.

The Variation of β-amylase Activity and Protein Fractions in Barley Grains as Affected by Genotypes and Post-anthesis Temperatures

“…MacLeod and Duffus 17 reported that the supply of sucrose for starch synthesis may be increased under elevated temperatures in barley, the contradiction between sink and source may inhibit conversion of sucrose to starch, which may be associated with reduced activity of one or several starch synthesis enzymes 31 . Those changes might directly influence A-and B-granule formation.…”

“…On the other hand, high temperatures during grain filling have been reported to severely affect starch and protein accumulation in grains 31 . Starch accounts for approximately 70% of grain weight, and mature endosperms of barley grains generally consist of two distinct starch granules, large, lenticular A-granules and small, spherical Bgranules.…”

Molecular basis of barley quality

“…The reduction in starch content can be attributed to the reduced enzymic activity associated with the synthesis of amylose and amylopectin. Wallwork et al (1998b) reported that high temperatures (>35°C) resulted in a reduced activity of the granule-bound starch synthase that is responsible for the synthesis of amylose and causes an immediate loss of activity for soluble starch synthase, which is involved in the synthesis of amylopectin. Izydorczyk et al (2001) showed that growing environment had a significant (P ≤ 0.05) effect on amylopectin and amylose content and subsequent biochemical changes during germination.…”

In vivo studies on artificial induction of thermotolerance to detached panicles of wheat (Triticum aestivum L) cultivars under heat stress

“…Supply of assimilates is never the limiting factor rather its utilization within the grain is the controlling factor of sink activity (Cheikh and Jones 1995;Wallwork et al 1998). Sucrose upon entering into the grain is metabolized by invertases, sucrose synthases and sucrosephosphate synthase (Ho 1988;Yang et al 2004).…”