| Abstract: | The effect of N supply on soybean (Glycine max L. Merrill) seedgrowth was investigated using an in vitro liquid culture system.Sucrose was maintained at 200 mM and N was supplied by asparagineand methion-ine in a 6.25:1 molar ratio. Media N concentrationsfrom zero to 270 mM had little effect on cultured cotyledondry matter accumulation rate for 7 or 14 d, but rates approachedzero after 21 d when there was no N in the media. Only 17 mMN was required for maximum cotyledon growth rate up to 21 d.Cotyledon N accumulation and concentration increased in directproportion to the N concentration in the media. The N concentrationin cotyledons from a high protein genotype was higher than anormal genotype at all media N levels (0–270 mM). Solublesugar and oil concentrations in the cotyledons were highestat zero media N and decreased as media N increased. These datasuggest that the concept of seed N demand, which is thoughtto cause senescence in soybean, is incorrect. Soybean seedscan accumulate dry matter without accumulating N and apparentlyneed only minimal supplies of N (17 mM) to maintain the metabolicenzymes necessary to sustain dry matter accumulation. Geneticdifferences in seed protein concentration seem to be regulatedby the cotyledons not the supply of N. Key words: Seed N demand, seed dry matter accumulation, in vitro culture |
