Nitrogen Metabolism ofLemnaminor.I.Growth, Nitrogen Sources andAminoAcidInhibition'

Lemnaminorgrowninsterile culture ona minerals-sucrose mediumcanutilize asnitrogen source, inorder ofincreasing growth rate:ammonia, nitrate, a mixture ofglutamic andaspartic acids plusarginine, ora balanced mixture ofaminoacids(hydrolyzed oasein). Maximumgrowthisfoundwithnitrate plushydrolyzed casein. Manysynthetic mixtures ofaminoacids areunable tosupport growth. Manysingle amino acids areinhibitory, andwhenadded(at2mM orless) tocultures, growing inthepresence of nitrate, causeadecrease ingrowth rateorevendeath oftheplants (e.g. withalanine, valine, methionine orleucine). Someoftheseinhibitory effects arealsofoundwhentheaminoacid isaddedtocultures growing onammoniaorhydrolyzed casein. Arginine wastheonlyamino acidofthose tested whichgavea markedstimulation ofgrowth whenaddedtocultures growing withinorganic nitrogen. Therapid rateofgrowth, sterile nature oftissue, decreased biological variation ofsamples containing manyplants andability toutilize different culture mediamakethisanattractive organism forstudies onhigher plant metabolism.