Starch Accumulation and Related Enzyme Activities in Superior and Inferior Grains of Large Spike Wheat

Abstract

Starch, the major component of grain, consists of amylose and amylopectin. It is synthesized and accumulated during grain filling in wheat (Triticum aestivum L.), and regulated by many enzymes including sucrose synthase (SS), adenosine diphos- phorate glucose pyrophosphorylase (AGPase), uridine diphosphorate glucose pyrophosphorylase (UGPase), soluble starch syn- thase (SSS), granule-bound starch synthase (GBSS), starch branching enzyme (SBE) and so on. According to recent studies, AG- Pase, starch synthase, and SBE are the key enzymes controlling starch synthesis. Previous researches have revealed that the allo- cation of carbohydrate, grain weight, and the transformation of sucrose to starch were significantly different between superior and inferior grains of wheat. But to date, there are few reports about the differences of starch accumulation and the relationship be- tween starch accumulation and related enzyme activities in superior and inferior grains. Therefore, a field experiment was carried out, and two large-spike type cultivars, SN 12 and PH01-35 were used to investigate the mechanism of starch accumulation and the relationship with related enzyme activities in superior and inferior grains. Forty spikes was sampled at 7, 14, 21, 28, and 35 d after anthesis, and partitioned into two groups, superior grain (the 1st and 2nd grains from the basal part of a spikelet) and inferior grain (the 3rd and 4th grains from the basal part of a spikelet). Half grains of each group were used to determine the enzyme ac- tivities, and the other half for starch content measurement. The result showed that the accumulation of amylose and amylopectin in superior grain were significantly higher than those in inferior grain. The simulation with Logistic equation showed that the accu- mulation rate and initial potential were higher, the accumulation duration was longer, so the starch final amount was higher in superior grain. The activities of SS, AGPase, UGPase, SSS, and GBSS changed in the pattern of a single-peak curve during grain filling. The related enzyme activities in superior grain, which had higher starch accumulation, were higher than those in inferior grain. The sucrose content in inferior grain was much higher than that in superior grain at 7–14 d after anthesis, indicating that the substrate of starch synthesis should not be the limiting factor for starch accumulation in inferior grain, which related to starch synthesis efficiency, also the number of endosperm cells at early grain filling stage.