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Lot.Mag.Tokyo90:129—1411977AnatomicalStudyontheShootApexofOsmundajaponicaThunb.关于紫萁枝条尖的解剖研究RYOKOJMAIcHI*Depart,eentofBiology,FacultyofScience,OckanomizuUniversity,Oktsuka,Bunkyo-ku,Tokyo112TheontogeneticandseasonalvariationsintheorganizationoftheshootapicalmeristemofOsmundajaponicaThunb.wereinvestigated.Themeristemiscomposedofanapicalsegmentationzone(SZ),amothercellzoneofthestele(MS)andaperipheralzone(PZ).Asingleapicalcellismostlydiscernibleinallseasonsthrooghoutthewholeprocessofontogenyobservedinthepresentstudy.Theapicalcellisusuallyfour-sided,nearlytriangular,witharegularsegmentationpatternintransverseview.However,itissometimesaccuratelythree-sidedwithahighlyregularsegmentationpatternintheactiveseason,whileitisoftenfour-sided,nearlytrapezoidorfive-orsix-sided,withalessregularsegmentationpatternintheinactiveseason.Thesizeoftheapicalcellrepresentedbyitsfreesurfaceareaincreaseswiththeincreaseinsizeoftheplantbodyintheyoungplants.However,intheadoltplants,thesizeoftheapicalcellissmallerintheactiveseasonandlargerinthedormantseason.Theorganizationpatternoftheshootapicalmeristemof0.joponicadoesnotshowanintermediatetypebetweentheeusporangiateandtheleptosporangiateferns,buttheleptosporangiateferntype.对于紫萁枝条顶端分生组织的介体娄生和季节变异的机体形成过程我们已有所了解。其分生组织包括顶端分节区域（SZ），中柱的母细胞区域（MS）和外周区域（PZ）。在目前的研究中指出单个顶端细胞在个体发生整个过程的各个时期大部分可被识别。在横向视野中顶端细胞通常是接近三角形的四边形，具有一个规律性的分节模式。然而，有时候它会是具有高度规律分节模式的标准三边形在生长活跃期，在生长不活跃的时期它又经常是四边形，接近梯形或五边六边形，并罕有规律分节模式。在幼年植物中，顶端细胞的大小是由它的自由表面积随着植物体大小的增长而增长来表现的。然而，在成年植物中，顶端细胞的大小在生长活跃期会变小，在休眠期会变大。紫萁的枝条顶端分生组织的构成模式不能说明它是存在于厚囊蕨类和薄囊蕨类之间的中间130R.IraArdHr型，而是属于薄囊蕨类植物。Shootapicalpatternsinpteridophyteshavearousedarenewedinterestinrecentyearsinregardtothezonationandtissuedifferentiationwithintheapicalmeristem(McAlpinandWhite,1974;Hébant-Mauri,1975)andtotheactivityoftheapicalcell(IJ’Amato,1975).WithregardtotheshootapicesoftheFilicales,itisgenerallyacceptedthatintheleptosporangiatefernsthereisclearlyasingleapicalcell,usuallywiththeshapeofatetrahedron,whileintheeusporangiatefernsasexemplifiedbytheMarattiaceaeafewinitialcellsarerecognizedinsteadofanapicalcell(Bower,1889;Wardlaw,1945;Gnttenberg,1966).蕨类植物的茎端模式中关于顶端分生组织内部的成带现象和组织分化(McAlpinandWhite,1974;Hébant-Mauri,1975)以及顶端细胞的活性(IJ’Amato,1975).在近年来引起了更新的关注。还有关于真蕨目的枝条根尖，普遍公认的是在薄囊蕨类植物中是一个明显的，形状为四面体的顶端细胞，而在厚囊蕨类中是由Marattiaceae证明的公认的由少数原始细胞代替顶端细胞。WithrespecttoshootapicalpatternsandotheradditionalcharactersBower(1889)regardedtheOsmundaceaewiththeirregularshootapicalmeristemasoccupyinganintermediatephylogeneticstatusbetweentheleptosporangiateandtheensporangiateferns.Later,Cross(1931)reachedthesameconclusionshowingthattheshootapexofOsmundacinnamomeagrewbymeansofanapicalcellinthesporelingstage.thepatterngenerallyseenintheleptosporangiateferns,andthatastheplantreachedmaturitytheidentityoftheoriginalapicalcellbecameobscureandgrowthtookplace*bytheactivityoftwoormoreinitialsasobservedintheeusporangiateferns.Ontheotherhand,Steeves(1963)reportedontheadultplantof0.cinnamomeathatthesegmentationpatterninthesuperficiallayeroftheshootapex,andconsequentlythedistinctnessoftheapicalcell,werephenomenawhichexhibitedseasonalvariations.在枝条顶端模式和另外的特征方面Bower(1889)认为带有不规则变化的枝条顶端分生组织的蕨类是类似于植物系统发生过程中位于薄囊和厚囊蕨类之间的中间情形。后来，Cross(1931)得出了相同的结论说明Osmundacinnamomea的枝条尖的生长是依靠孢子期的顶端细胞。这种模式在薄囊蕨类中能普遍看到，在厚囊蕨类中可以观察到，当植物体到达成熟期的时候，原始顶端细胞的特性会变得模糊不清，会因为两个或更多的原始细胞的活性使其生长发生变化。在另一方面，Steeves(1963)提出在0.cinnamomea的成熟植株上，分节模式位于枝条尖的表皮层，结果导致顶端细胞的显著差异，这是带有季节性变化的现象。ThepresentstudyhasbeendonetoclarifytheorganizationoftheshootapicalmeristemofOsmunclajaponicaThunb.inregardtothevariationsduringgrowthfromthejuveniletotheadultstagesaswellasduringseasonsoftheyear.先前的研究已经让我们清楚地了解到紫萁枝条顶端分生组织的机体形成。关于从幼年期到成年期的生长的变化也就是在不同季节中的变化。MaterialsandMethods材料和方法Morethanthreehundredrhizomes,youngandaged,ofOsmundajaponicawereusedasmaterials.TheywerecollectedneartheFudagoStationofTokyoUniversityForestinChibaataboutthebeginningofeverymonthfromSeptember,1974untilDecember,1975.有超过三百株的根状茎，年幼和年老的紫萁作为原料。它们是在FudagoStationofTokyoUniversityForestinChiba，大约从1974年的9月到1975年的12月收集的。Beforeexcisingtherhizometipforfixation,numerousyoungleavesandleafprimordiawereremoved,fromthelowestupwards,andtheapicaldomeprovidedwithafewyoungleafprimordiawasexposedunderthebinoculardissectingmicroscope.Then,alongitudinalhand-cutpieceoftherhizometipabout2mminthicknessandabout5mmindepthincludingtheapicaldomeandthesmallestleafprimordiumwasexcised.Theaimofmakingthispiecepriortofixationwastogetsectionsinapreciseorientation,themicrotomeknifebeingsetalwaysparalleltothesidesofthispiece.Fortransversesections,therhizomewascutatafewmillimetersbelowthetopthroughaplaneperpendiculartotheaxisoftheapicaldome,andsectioningwasalwaysmadeparalleltothisplane.ThematerialsthusobtainedwerekilledandfixedinCrafHI(Sass,1958)for24hr.在剪下根茎尖端固定之前，要从最底部往上剪去许多幼叶和叶原基，顶端圆顶只有带有少数叶原基的情况下才能在双筒解剖显微镜下裸露。接着，切取厚度为2毫米的根茎尖纵向徒手切片和顶端圆顶以及最小的叶原基深切大约5毫米。固定之前做这些片子的目的是得到精确的截面，显微镜用薄片切片机的刀片要与这个片子平行。对于横截面，从根茎顶部下方通过与顶端圆顶轴线的垂直平面切取几毫米，这个截面通常是平行于这个平面的。以这种方式获得的材料在CrafHI(Sass,1958)中杀死和固定24小时。ThesporelingswerecollectedbothinthefieldatFudagoandfromculturedproth