Abstract
Main conclusion
A greater rate of phloem unloading and storage in the stem, not a higher rate of sugar production by photosynthesis or sugar export from leaves, is the main factor that results in sugar accumulation in sweet dwarf sorghum compared to grain sorghum.
Abstract
At maturity, the stem internodes of sweet sorghum varieties accumulate high concentrations of fermentable sugars and represent an efficient feedstock for bioethanol production. Although stem sugar accumulation is a heritable trait, additional factors that drive sugar accumulation in sorghum have not been identified. To identify the constraints on stem sugar accumulation in sweet sorghum, we used a combination of carbon-11 (11C) radiotracer, physiological and biochemical approaches, and compared a grain sorghum and sweet dwarf sorghum line that have similar growth characteristics including height. Photosynthesis did not increase during development or differ between the sorghum lines. During the developmental transition to the reproductive stage, export of 11C from leaves approximately doubled in both sorghum lines, but 11C export in the sweet dwarf line did not exceed that of the grain sorghum. Defoliation to manipulate relative sink demand did not result in increased photosynthetic rates, indicating that the combined accumulation of C by all sink tissues was limited by the maximum photosynthetic capacity of source leaves. Nearly 3/4 of the 11C exported from leaves was transported to the lower stem in sweet sorghum within 2 h, whereas in grain sorghum nearly 3/4 of the 11C was in the panicle. Accordingly, the transcripts of several sucrose transporter (SUT) genes were more abundant in the stem internodes of the sweet dwarf line compared to the grain sorghum. Overall, these results indicate that sugar accumulation in sweet sorghum stems is influenced by the interplay of different sink tissues for the same sugars, but is likely driven by elevated sugar phloem unloading and uptake capacity in mature stem internodes.
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All data generated or analyzed during this study are included in this published article and its supplemental information files.
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Acknowledgements
This work was supported in part by MO094 (a Plant Feedstock Genomics for Bioenergy grant) by the United States Department of Energy, Office of Biological and Environmental Research (under contract DE-AC02-98CH10886 and grant no. DE-SC0006810), a Goldhaber Distinguished Fellowship to BAB, the United States Department of Agriculture, National Institute of Food and Agriculture, McEntire-Stennis project number 1009319 (BAB), and the US National Science Foundation Plant Genome Research Program grant (IOS-1025976) to DMB.
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Babst, B.A., Karve, A., Sementilli, A. et al. Physiology and whole-plant carbon partitioning during stem sugar accumulation in sweet dwarf sorghum. Planta 254, 80 (2021). https://doi.org/10.1007/s00425-021-03718-w
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DOI: https://doi.org/10.1007/s00425-021-03718-w