Galactinol synthase (UDP-galactose:inositol galactosyltransferase) is the first unique enzyme in the biosynthetic pathway of raffinose saccharides. Its role as a regulator of carbon partitioning between sucrose and raffinose saccharides in developing soybean (Glycine max L. Merrill) seeds was examined. Galactinol synthase activity and concentrations of sucrose, stachyose, and raffinose were compared during seed development between two genotypes that were high and two genotypes that were low in mature seed raffinose saccharide concentration. In all genotypes, sucrose concentration increased as seed development progressed, but in both low raffinose saccharide genotypes, greater increases in sucrose concentration were observed late in seed development. Sucrose to stachyose ratios in mature seeds were 2.3-fold greater in low raffinose saccharide genotypes than in the high raffinose saccharide genotypes. During seed development, higher levels of galactinol synthase activity were observed in the high raffinose saccharide genotypes than in the low raffinose saccharide genotypes. A common linear relationship for all four soybean genotypes was shown to exist between galactinol formed estimated from galactinol synthase activity data and the concentration of galactose present in raffinose saccharides. Results of this study implied that galactinol synthase is an important regulator of carbon partitioning between sucrose and raffinose saccharides in developing soybean seeds.Soluble sugars account for approximately 10% (w/w) of dry weight in mature soybean seeds (8). Sucrose, stachyose, and raffinose constitute greater than 99% (w/w) of the soluble sugars present (9) and occur in a ratio of approximately 8:4:1 (w/w/w), respectively (8). Early in seed development, concentrations of glucose and fructose are high but decline with maturity of the seed (10, 23). In contrast, stachyose and raffinose are absent from the seed until about the midpoint of seed development at which time they begin to accumulate (1, 10, 23). In some species, stachyose is synthesized in the leaves and translocated in the phloem (21, 23). In soybean leaves, no raffinose saccharides are present and only minimal activity ofGS3 (UDP-galactose:inositol

Two soybean [Glycine max (1.) Merr.] lipoxygenase cDNA clones were isolated that represent lipoxygenase genes (designated L0X7 and LOX8) that display increased expression in leaves following wounding. LOX7 and LOX8 were found to be differentially expressed in soybean leaves after wounding. lncreased transcript levels of both genes were detected in wounded leaves within 8 h after wounding, but only the expression of LOX7 displayed a systemic wound response. Additionally, the elevated expression of LOX7in wounded leaves was transient. Twenty-four hours postwounding, LOX7 transcripts were no longer detectable in leaves. In contrast, LOX8 transcript levels were elevated in wounded leaves from 8 to 72 h after wounding. In addition, treatment of soybean plants with methyl jasmonate resulted in higher levels of both LOX7and LOX8 transcripts in leaves. High levels of expression of both genes were also detected in young leaves, flowers, and immature seed pods, and increases in LOX7 and LOX8 transcripts were observed in leaves following the removal of reproductive sink tissues. The expression of LOX7 and LOX8 in unwounded soybean tissues and increased expression following wounding suggest that the lipoxygenases encoded by these genes may participate in general physiological processes that are enhanced following physical damage.

The levels of individual lipoxygenase isozymes in soybean [Clycine max (1.) Merr.] leaves were assessed during leaf development, after mechanical wounding, and i n response to reproductive sink removal. Native isoelectric focusing followed by immunoblotting was employed to examine individual lipoxygenase isozymes. In leaves of all ages, two distinct classes of lipoxygenase isozymes were detected. One class of lipoxygenase isozymes had nearly neutral isoelectric points (pls) ranging from pH 6.8 to 7.2. The other class of lipoxygenase isozymes had acidic pls ranging from pH 4.7 to 5.6. During leaf development, all of the neutral lipoxygenase isozymes and most of the acidic isozymes were present in greatest abundance in the youngest leaves examined and declined in amount as leaf age increased. However, four acidic lipoxygenase isozymes (pl = 4.70, 4.80, 4.90, 4.95) were more abundant in intermediateage leaves than in either the youngest or oldest leaves examined.Following mechanical wounding of leaves, these same four acidic isozymes also increased i n abundance both locally and systemically in leaves from wounded plants. Unlike the specific effects of wounding on the lipoxygenase isozymes in leaves, reproductive sink removal stimulated a general increase in most of the acidic lipoxygenase isozymes in leaves.

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