Autoradiographic studies of the synthesis of nuclear DNA in various tissues during leaf development of Xanthium pennsylvanicum☆

[摘要] ThesynthesisofnuclearDNAandtheincorporationofH3-thymidineintoleafnucleiofvarioustissueshasbeenstudiedduringtheentirecourseofleafdevelopmentofXanthiumpennsylvanicum.Leafplastochronindex(L.P.I.)developedbyEricksonandMichelini(1957)wasusedfordesignationofdevelopmentalstages.Theautoradiographicslidesyieldeddataonthepercentageoflabelednucleiandtheaveragenumberofgrainspernucleusintheupperandlowerepidermisandpalisadelayerandinthemesophyllcells.ThepercentageoflabelednucleiindicatedarelativenumberofcellsengagedinDNAsynthesisoftheabovetissues,whereastheaveragenumberofgrainspernucleuswasindicativeoftheamountoftheradioisotopicprecursorincorporatedintonuclearDNAofasinglecell.TheamountofDNAsynthesisdecreasedsignificantlywiththeageoftheleafinthecourseofdevelopment.AtL.P.I.1.72,fewercellswereengagedinDNAsynthesisandalsoasmalleramountoftheradioactiveprecursorwasincorporatedinasinglenucleusthanatL.P.I.−0.56.AfterL.P.I.1.72,theamountofsynthesisdecreasedrapidly.However,theamountofincorporationoftheradioisotopeonasinglecelllevelincreasedsharplystartingwithL.P.I.1.72.InleavesolderthanL.P.I.2.78,fewcellswereengagedinDNAsynthesis,buttheyincorporatedmoreoftheH3-thymidinepernucleusthanatanyyoungerplastochronicage.TheamountofDNAsynthesisinepidermalandmesophylllayersdecreasedsignificantlybetweenL.P.I.'s−0.56and1.72anddroppedveryrapidlythereafter.Inthepalisadelayer,however,DNAsynthesisfollowedadifferentpattern.BetweenL.P.I.'s−0.56and0.94,itwasconstant,butsmallerthanintheothertissues.AttheplastochronicrangeofL.P.I.0.94and2.2,analmostlinearincreasewasnoticeable.DuringthisperiodofdevelopmentahighlysignificantdifferenceintheamountofDNAsynthesiswasdemonstratedbetweenthepalisadecellsandcellsofanyothertissue.Thenucleicacidsynthesisinthepalisadelayercontinuedlongerandatasignificantlyhigherratethanintheepidermalandmesophyllcellsofthelaminaforatleastoneplastochron.

[学科分类] 生物科学（综合）