Morphological observations on growth and differentiation of Physarum polycephalum grown in pure culture☆

摘要

ThemorphologicalfeaturesofthevegetativeandsporulativestagesinthelifecycleofthemyxomycetePhysarumpolycephalumunderconditionsofcontrolledculturearedescribed.Thevegetativestageischaracterizedbyalargemultinucleateplasmodiumwhichbehaveslikeasinglecell.Whengrownonasurfaceunderoptimalconditions,theplasmodiumisaflat,compact,yellow,disk-shapedmeshworkoftightlyinterwovenstrands.Thenucleiofsuchaplasmodiumundergosynchronousmitosesevenwhentheorganismis5cmindiameter.Inagitatedsubmersedculture,theplasmodiumisfragmentedintomicroplasmodia,whichinturnwillcoalescewhenplacedinintimatecontactwithoneanotheronasurface.Althoughthemicroplasmodiaarenotinmitoticphasewithoneanother,completemitoticsynchronyoccursintheplasmodiaobtainedfollowingtheircoalescence.Microplasmodiainoldsubmersedculturesformmono-andmultinucleatespheruleswhichprobablyareidenticalwiththesubunitsofasclerotium.Whilethewell-nourishedorganismremainssedentary,astarvedplasmodiummigratesrapidlyoverthesurface.Duringprolongedstarvationmanynucleidegenerate,buttheremainingonescontinuetoundergomitosesalthoughatlongerintervals.Sporulationisinducedbyexposingapartiallystarvedplasmodiumtolight.Duringthisprocessarearrangementofprotoplasmoccursintheabsenceofgrowth.