Fagopyritol accumulation and germination of buckwheat seeds matured at 15, 22, and 30°C

Common buckwheat (Fagopyrum esculentum Moench; Polygonaceae) embryos accumulate six fagopyritols in two unique series: fagopyritol A1, fagopyritol A2, fagopyritol A3, fagopyritol B1, fagopyritol B2, and fagopyritol B3. Fagopyritol A1 is isosteric to a putative insulin mediator believed to be deficient in subjects with noninsulin dependent diabetes mellitus (NIDDM) and polycystic ovary syndrome (PCOS). Fagopyritols accumulate during seed development, and accumulation is enhanced in response to cooler temperatures. The objective was to test the hypothesis that seed maturation at cooler temperature enhances fagopyritol accumulation, improves seed quality, and increases yield of desirable fagopyritols for dietary treatment of NIDDM and PCOS. Seeds from buckwheat plants grown at 15, 22, or 30 degrees C were harvested at 8, 12, 16, 20, and 28 d after pollination (DAP) and analyzed for soluble carbohydrates in the embryos. Remaining seeds were dried and tested for germination and seedling growth. Embryo dry weight increased rapidly between 8 and 12 DAP at 30 degrees C, 12 and 16 DAP at 22 degrees C, and 16 and 20 DAP at 15 degrees C. Seed dry weight declined (-0.86 mg per 1 degrees C) when maturation temperature increased. Total soluble carbohydrates remained constant across seed maturation temperatures, but the composition of carbohydrates changed in response to different maturation temperatures. Fagopyritol A1 and fagopyritol B1 were highest in seeds matured at 15 degrees C, whereas fagopyritol A2, fagopyritol B2, fagopyritol A3, raffinose, and stachyose were higher in seeds matured at 30 degrees C. At harvest, seeds matured at 30 degrees C had highest germination. Cool temperatures during buckwheat seed maturation can result in increased seed size and yield of fagopyritol A1 and fagopyritol B1 in embryos for nutritional and medicinal applications.