Genotypic differences in sucrose metabolism with cotton bolls in relation to lint percentage

Abstract

Lint percentage is an important cotton (Gossipium hirsutum L.) lint yield character which may have a close association with photoassimilates partitioning between fibers and seeds. A three-year field experiment was conducted with an aim to determine whether or not the formation of lint percentage is associated with sucrose metabolism in both of fibers and seeds, and potential contributors to the performance of lint percentage. Two upland cotton (Gossypium hirsutum L.) lines A705 and A201 differing in lint percentage and seed size were employed to examine genotypic difference in within-boll yield components, nonstructural carbohydrate components (hexose, sucrose and starch) and key sucrose metabolism enzymes across 2015–2017. A705 had greater lint mass per boll, lint index, and higher lint percentage and cellulose content in fibers, but smaller boll weight, seed mass per boll, seed index and lower oil content in embryos compared to A201. The result indicated that the fiber sink strength was greater in A705 than in A201, but the reverse was true of the seed sink strength. A705 exhibited consistently higher sucrose concentration and sucrose synthase (Sus) activity in fibers during fiber development relative to A201, while the latter recorded consistently higher sucrose concentration and Sus activity in younger ovules during 5–17 days post anthesis (DPA) and in older embryos and seed coats during 24 DPA to 45 DPA. Higher starch concentration and sucrose phosphate synthase (SPS) activity with seed coats were detected in A705 than in A201, implying sucrose synthesized by SPS in A705 at sink storage stage is preferentially partitioned to starch biosynthesis in seed coats. It is concluded that a higher lint percentage in A705 than in A201 is attributable to a combination of greater fiber sink strength and smaller seed sink strength available in the former relative to the latter. Sucrose and Sus may function as key biomarkers for assessing fiber and ovule sink strengths.