Sucrose accumulation in sweet sorghum stem internodes in relation to growth

Abstract

J, 1996, Sucrose accumulaeion in sweet sorghum stem internodes in relation tO ' growth, Sweet sorghum (Sorghum bicoior L, Moench) stems of different cultivars (NK 405, Keller and Tracy) reveal a different pattem of sucrose accumn]ation with respect to intemodal sugar content and distribution. The onset of sucrose storage is not necessarily associated with the reproductive stage of the plant, as was hitherto assumed, but obviously occurs after cessation of internodal elongation as was postulated for the sugarcane stem. For at least two of the three cultivars, ripening is an internode to internode process beginning at the lowermost culm parts. Intensive growth of the intemodes, combined with a high hexose content in stem parenchyma, shows a strong positive correlation (r > 0,94') to the activity of sucrose synthase (SaSy; EC 2,4,13), but not !0 invertase (EC 3,2,1,26) which is not present as soluble (neutral .and acid) or cell wallbound, salt-extractable enzyme in the three cultivars investigated. Sucrose synthase measured in sucrose cleavage and synthesis direction reveals divergent activity rates and sensitivity towards exogenously applied Mg"* ions and pH, SuSy activity' is connected to the increase of internodal sucrose content in so far as (I) its decline is a prerequisite for the onset of sucrose accumulation and (2) it remains at a constant low level during sucrose storage. Sucrose phosphate synthase (SPS; EC 2,4,1.14) activity in the sorghum stem is low compared to SuSy and uniformly distributed over all internodes. Only source leaves of sorghum show a considerable SPS activity, but neither stem nor leaf SPS reveal a positive correlation to the increase of internodal sucrose content. Sucrose phosphate phosphatase (SPP; EC 3.1.3,24) amounts to only 24-30% of the respective SPS activity bul follows the same distribution pattern. None of the enzymes under study proves to be responsible for the extent of sucrose storage in the stem, so other phenomena such as transport processes within the stem tissue require further investigation.

Screen of Genes Linked to High-Sugar Content in Stems by Comparative Genomics

“…In general, the Brix degree was lower in the mature and immature internodes of the stem, in contrast to maturing internodes. These findings are in agreement with previous studies [16,25]. Consistent with the inability of grain sorghum to accumulate significant levels of sugars in the stem, the Brix degree in BTx623 was low and remained fairly constant for all the internodes along the stem.…”

“…Sugar accumulation in the stem of grain and sweet sorghum cultivars Previous reports have indicated that in sorghum stems, sugars start to accumulate at flowering stage [16,25]. We compared the accumulation of sugars in the stem between six sweet sorghum lines (Dale, Della, M81-E, Rio, Top76-6, and Simon) and one line from grain sorghum (BTx623).…”

“…Interestingly, there is extensive natural intra-species variation for sugar content in sorghum with cultivars that do not accumulate sugars (referred to as grain sorghums) in contrast to those that accumulate large amounts of sugars in their stems [16]. Such intra-species variation can serve as a platform to identify genes linked to increased sugar content and reduced lignocellulose [4].…”

A Sugar-Inducible Protein Kinase, VvSK1, Regulates Hexose Transport and Sugar Accumulation in Grapevine Cells

“…Plant growth and plant productivity are not limited by photosynthesis per se but rather by the ability of the plant to export and to partition its assimilates in a proper way. Increased crop yields are paralleled by a better partitioning of assimilates between the harvestable part of the plant and the rest of the plant (Gifford and Evans, 1981;Gifford et al, 1984;Hoffmann-Thoma et al, 1996). Long-distance and intercellular transport of sugars is mediated by protoncoupled Suc transporters (belonging to the disaccharide transporter family) and hexose and polyol transporters (belonging to the monosaccharide transporter family).…”

Tonoplast Sugar Transporters (SbTSTs) putatively control sucrose accumulation in sweet sorghum stems

“…Previous research found that sucrose accumulation within sweet sorghum stems was not correlated with the activities of enzymes involved in sucrose metabolism, invoking sucrose transport proteins as potentially controlling sucrose content. 19 Transport experiments using asymmetrically radiolabeled sucrose determined that sucrose movement into stems likely included an apoplasmic transport step. 20 Subsequent dye transport studies suggested the phloem tissues within sorghum stems are symplasmically isolated from surrounding tissues, supporting that sucrose phloem unloading occurs apoplasmically, and thus requires sucrose transport proteins.…”