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Title: Comparison of Post-Germination Mobilization of Cell Wall Polysaccharides and Non-Cell Wall Carbohydrates in Soybean (Glycine max L.) Cotyledons

Author
item Gronwald, John
item Jung, Hans Joachim
item LITTERER, LYNN - UNIVERSITY OF MINNESOTA
item SOMERS, DAVID - UNIVERSITY OF MINNESOTA

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2009
Publication Date: 8/30/2009
Citation: Gronwald, J.W., Jung, H.G., Litterer, L.A., Somers, D.A. 2009. Comparison of Post-Germination Mobilization of Cell Wall Polysaccharides and Non-Cell Wall Carbohydrates in Soybean (Glycine max L.) Cotyledons. Journal of the Science of Food and Agriculture. 89(11):1981-1986.

Interpretive Summary: There is a need to increase the production of biofuels to reduce dependence on foreign oil supplies. Biodiesel made from soybeans (soydiesel) holds promise as an alternative fuel. However, to increase the potential of soydiesel as a biofuel the amount of oil in soybean seeds needs to be increased. Our previous research showed that soybean seeds that have low cell wall sugars have high oil. These results suggested that carbon (energy) produced in developing soybean seeds is being divided between making cell wall sugars and oil. One possible approach to increase seed oil content involves redirecting carbon to make more oil and less cell wall sugar. However, in some legume seeds, the sugars stored in cell walls are needed for seedling growth. We examined whether this is the case for soybean by measuring cell wall sugars in germinating seeds. We found that cell wall sugars are not an important source of carbon for germinating soybean seeds. The results suggest that redirecting carbon from making cell walls sugars to making more oil will not reduce seed germination. Reducing cell wall sugars in soybean seed remains a promising strategy to increase seed oil content. The new knowledge gained in this research will be used by plant breeders and molecular biologists to develop high-oil soybean varieties that are needed to increase soydiesel production.

Technical Abstract: Cell wall polysaccharides (CWP) and non-cell wall carbohydrates (NCWC) (sucrose, raffinose, stachyose, starch) were measured in cotyledons of germinating soybean [Glycine max (L.) Merr. cv. Lambert] seedlings grown for 14 d in darkness or under a 16-h photoperiod. Ungerminated seeds contained equivalent amounts [approximately 20 mg (cotyledon pair-1)] of NCWC and CWP. Measured 14 d after planting (DAP), NCWC and CWP levels were reduced 98% and 34%, respectively, in cotyledons of seedlings grown under the 16-h photoperiod. In cotyledons of dark-grown seedlings, NCWC and CWP were reduced by 78% and 53%, respectively, after 14 d. Galactose and arabinose accounted for 47% of total CWP in cotyledons of ungerminated seeds. Measured 14 DAP, greater than 80% of cell wall galactose and arabinose was mobilized in cotyledons of seedlings grown either in darkness or a 16-h photoperiod. For seedlings grown under the 16-h photoperiod, the transformation of the cotyledon to a photosynthetic organ was associated with increases in cell wall uronic acids, xylose, and glucose. Although cell wall galactose and arabinose are mobilized during germination, the amount of carbon mobilized makes only a small contribution to total cotyledon reserves.