Analysis of grain phenotype, filling characteristics, and starch synthase activity in Chenopodium quinoa with different grain sizes

Abstract

[Objective] Grain size significantly influences the yield, marketability, and processing characteristics of quinoa (Chenopodium quinoa). Understanding the grain phenotypes, filling characteristics, and starch synthase activity of large- and small-grained quinoa during the filling period can provide guidance for the selection and breeding of large grain quinoa varieties. [Methods] Two quinoa samples, one with a thousand grain weight exceeding 5.0 g and the other is below 3.0 g, were selected for a field experiment at the Innovative Experimental Base of Germplasm Resources of Qinghai Academy of Agricultural and Forestry Sciences. The study compared the difference of grain phenotypes, filling characteristics, and starch synthase activity between large- and small-grained quinoa at 7, 14, 21, and 28 days of the filling stage. [Results] (1) The phenotypic traits of large- and small-grained quinoa, including grain area, circumference, diameter, kernel length, and kernel width, were significantly increased during reproductive period. There were significant differences between grain types, where the largest differences were in grain area and circumference, with the large-grained quinoa was significantly higher than small-grained quinoa by 9.12% to 11.54% and 21.49 to 23.92%, respectively. (2) Throughout the filling period, the dry mass of 100 grains of large-grained quinoa exceeded that of small-grained quinoa, with an average increase of 21.23% to 31.04%; the filling rate of large and small-grained quinoa rose first and declined subsequently during the reproductive period, which was in the pattern of “slow-fast-slow”. However, the time to reach the peak and the peak height were different, with large-grained quinoa was early and high, while small-grained quinoa was low and late. (3) The starch branching enzyme (SBE), sucrose synthase (SS), soluble starch synthase (SSS), and ADPG pyrophosphorylase (AGP) varied for both grain sizes, with SBE and SS activities being stronger in small-grained quinoa than in large-grained quinoa, while SSS and AGP activities were stronger in large-grained quinoa than in small-grained quinoa. [Conclusion] Variations in the activities of four starch synthases during grain filling contribute to differences in starch accumulation and peak filling rate, which in turn leads to differences in grain phenotypic traits, whereas SSS and AGPase are the key enzymes affecting quinoa grain size.

Keywords

• quinoa
• grain size
• grain phenotype
• filling characteristics
• starch synthase activity