Fructan Metabolism in Stems of Wheat During Grain Development.

We are interested in how carbohydrate storage and subsequent utilization is controlled in plants. We have chosen the wheat stem during the grain filling process as a system to discover this control largely because the wheat stem at first is a storage sink, then a source providing carbohydrate to the plant.  In this study we describe the system, including water soluble carbohydrate content, related gene transcription and enzyme activities in three stem internodes of grain filling field wheat (Triticum aestivum L. cv Patterson).
     Glucose content was high two weeks before anthesis and decreased after anthesis to the same level as fructose and sucrose. Fructans started to accumulate after anthesis and began to be degraded two weeks after anthesis at which time the fructose content in stems and grain weight increased. Fructan content in the peduncle internode was lower than those in the penultimate and the lower internode. The types of fructans accumulating in stems of wheat were graminans (the branched fructans) and phleins (b-(2, 6)-fructo-oligomers) with the highest degree of polymerization around ten. Fructan metabolizing enzyme gene expression studied by Quantitative Real-time PCR showed that genes encoding fructan biosynthetic enzymes (fructosyltransferases) were up-regulated after anthesis and then down-regulated two weeks post anthesis. Transcripts of the gene encoding 1-fructan exohydrolase which hydrolyzes b-(2, 1)-fructan were high during the fructan degradation period, while the gene encoding 6-fructan exohydrolase which hydrolyzed b-(2,6)-fructan had the same expression pattern as fructosyltransferases suggesting this enzyme has a trimming role during fructan  synthesis. There is a correlation between fructan gene expression and fructan structure and content. The correlation between fructan gene expression and enzyme activity will also be presented.