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Histochemical Studies in Weed Seed Dormancy

Seeds of Pennsylvania smartweed (Polygonum pennsylvanicum L.), quackgrass (Agropyron repens L. Beauv.), yellow foxtail (Setaria lutescens L. Beauv.), and wild mustard (Brassica kaber (DC) L. C. Wheeler) were studied to determine if histochemical differences existed in seeds of dormant and non-dormant weed species. The hulls (seedcoat) of yellow foxtail and seedcoats of wild mustard and quackgrass had distinct inhibitory effects on germination. Endosperm tissue in wild mustard and Pennsylvania smartweed also inhibited embryo growth in these species. Results obtained from specific staining techniques on seed sections 10μ thick for identification and determination of distribution of proteins, lipids, carbohydrates, and lignin in dormant and germinating seeds suggested that possible mechanisms of seed dormancy are: (a) lower protein content in seed tissues of wild mustard; (b) higher lignification in hull of foxtail and endosperm of Pennsylvania smartweed; (c) lower sterol content in embryo of wild mustard and Pennsylvania smartweed; (d) high cellulose content in hull of foxtail and endosperm of Pennsylvania smartweed. Excised embryos from dormant seeds of Pennsylvania smartweed showed a measurable amount of growth in White's standard agarnutrient. Germinating embryos of wild mustard and quackgrass were larger than those in dormant seeds; therefore, immaturity of embryos might contribute to dormancy in these species.