Sweet versus grain sorghum: Differential sugar transport and accumulation are linked with vascular bundle architecture

Abstract

Sorghum (Sorghum bicolor L. Moench) is globally produced as a source of food, fiber, feed, and fuel. Sweet and grain sorghums differ in a number of important traits, including biomass production, stem sugar and juice accumulation. In this study, a sweet (KIT1) and a grain (Razinieh) genotype of sorghum were used to investigate major differences between sweet and grain sorghum in terms of stem-sugar accumulation. Differences in stem component traits such as internodes, stem anatomy, but also transcripts of key sucrose transporter genes and their response to salt stress were compared. While internodal traits were similar, differences on anatomical level were observed in internodes. Sugar accumulation was highest in the central internodes in both genotypes. However, phloem to xylem cross areas in internodes was correlated with the amount of sugar stored in stem. Sugar accumulation increased significantly under salinity in both genotypes. The expression of sugar-transporter genes SbSUT1, SbSUT2, and SbSUT6 was higher in the leaves of KIT1 under normal conditions, but significantly increased in the stem of KIT1 under salinity stress. Nevertheless, transcriptional levels of SbSUT genes could not account for the big difference of sugar accumulation in stems between both genotypes. Thus, in addition to anatomical differences, additional (molecular) factors might regulate sugar accumulation in the stem.