Abstract
ABSTRACTAllelic variation at the Wx locus plays a vital role in regulating apparent amylose content (AAC) as well as other important starch properties in rice grain. However, the extent of Wx allelic variation affecting amylopectin fine structure and enzymatic hydrolysis properties of rice starch remains unknown. In this paper, a series of rice single-segment substitution lines with five different Wx alleles (wx, Wxt, Wxg1, Wxg2 and Wxg3) were used for comparative studies. The results showed that the five Wx alleles exhibited a wide variation in amylopectin molecular structure, hydrolysis and in vitro digestion properties of rice starch. Amylopectin chain length distribution as evaluated by fluorophore-assisted capillary electrophoresis was significantly different for the five Wx alleles, which might result in different functional properties. The hydrolysis degree of the five Wx genotype starches by α-amylase or amyloglucocidase was in the order wx > Wxt > Wxg1 > Wxg3 > Wxg2. The rapidly digestible starch (RDS) content of the tested rice starches followed the order wx = Wxg3 > Wxt = Wxg1 > Wxg2. The extent decrease of slowly digestible starch (SDS) content was wx = Wxt > Wxg1 > Wxg2 > Wxg3, while the trend in resistant starch (RS) content was Wxg2 > Wxg3 > Wxg1 > Wxt > wx. Correlation analysis indicated that AAC was significantly positively correlated with RS but significantly negatively correlated with SDS and hydrolysis. The RDS showed a significant positive correlation with amylopectin short chains (DP 6–12) but no significant correlations with other structural properties. The present results could provide important information for the application of rice starches with different Wx genotypes.
Highlights
Rice (Oryza sativa L.) is a major and staple cereal crop in the world
Using single-segment substitution lines (SSSLs) harboring five different Wx alleles as materials, effects of the five different Wx alleles on crystalline structure and some functional properties of starch, including gel consistency, alkali spreading value, pasting viscosity traits, thermal and swelling properties, have been successfully obtained against a same rice genetic background of the recipient HJX74.[6,7] we postulated that amylopectin molecular structure, apart from amylose content, plays a significant role in determining the diversities in rice starch properties that result from the Wx allelic variation.[6,7]
Among the tested rice starches, the glutinous and Wxg3 genotype starches displayed obviously higher proportions of short A chains (DP 6–12) than those of other Wx genotypes, and the lowest amount of short A chains was found in the Wxg2 genotype starch
Summary
Rice (Oryza sativa L.) is a major and staple cereal crop in the world. Rice starch is the primary food source for the humans, but has been widely utilized in various industrial applications.[1]. A few previous studies have reported that higher amylose content is associated with reduced susceptibility to enzymatic hydrolysis of rice starch.[3,4,5,18,19] to what extent the five Wx alleles (or their AAC phenotypes) affect hydrolysis and in vitro digestion properties of rice starch remains unclear, which restricts the utilization of different. This research continues the studies of Teng et al.[6,7] to discover the genetic effects of different Wx alleles on amylopectin fine structure and enzymatic hydrolysis properties of rice starch in a common rice genome background. The results can be used to understand the structural mechanisms of how the Wx allelic variation affects starch functional properties
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