Morphogenesis in the Mycelium: Control of Lateral Hypha Frequency in Mucor hiemalis by Amino-Acids

A method is described for the perfusion of growing mycelialmargins with solutions and for the measurement of their effectupon the frequency of lateral hypha production. Perfusion with water induces in Mucor hiemalis Wehm. a highlateral branch frequency which is only moderately diminishedif a minerals+ thiamin+ glucose solution is used. Additionsof various materials to this basal solution may promote or stronglydepress lateral branching. Internode lengthening agents areenzymic digest of casein, or its acid hydrolysate or dialysate,at pH 50. About half the activity of casein hydrolysate is foundwith favourable mixtures of amino-acids, and with arginine orlysine. Some degree of activity is also found with six otheramino-acids alone, Ca(NO₂)₂, uracil plus adenine, and otheras yet unidentified materials. Internode shortening effects are demonstrated for five amino-acidsand asparagine. Evidence is given of interactions between acids. Growth of the fungus for 14 hours removes the internode lengtheningquality from dilute malt-extract medium, and during the sametime its amino nitrogen is markedly reduced. Various inactive materials are mentioned and possible mechanismsof activity are discussed.