Apical Cell Segmentation and Its Relationship to the Peristome-Forming Layers in the Funariaceae Author(s): Owen M. Schwartz Source: International Journal of Plant Sciences, Vol. 158, No. 3 (May, 1997), pp. 236-248 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/2475273 Accessed: 17/11/2010 10:28 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=ucpress. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences. http://www.jstor.org Int. J. Plant Sci. 158(3):236-248. 1997. ? 1997 by The Universityof Chicago. All rightsreserved. 1058-5893/97/5803-0002$03.00 APICALCELL SEGMENTATION ANDITS RELATIONSHIP TOTHE PERISTOME-FORMINGLAYERS IN THEFUNARIACEAE OWEN M. SCHWARTZ' Departmentof Botany,Duke University,Durham, North Carolina 27706 Six taxa in the Funariaceae were examined to compare developmentand cell division patternsin moss capsules with and withoutperistome teeth. The peristomedifferentiates from a series of apical cell segmentsthat are foundto develop by a similar patternof cell divisions. The youngestapical cell segmentsdo not complete the entiredevelopmental sequence observed in the more proximalsegments. Few differencesin developmentwere foundamong the taxa, other than in the timingof transversecell divisions. Segmentsin the gymnostomoustaxa (Ephemerum,Aphanorrhegma) do not complete the entire sequence of divisions, with only three amphitheciallayers present in the mature capsule. Spiralingof the peristometeeth of Funaria is suggestedto be the resultof differentialcell expansionduring the course of developmentof the distal apical cell segments,although oblique division of the apical cell mightalso be responsible for the spiralingof the cell files. Moss sporophytesare bilaterallysymmetrical in theirdevelopment although forming a radially symmetricalcapsule. Because peristometeeth differentiate from several differentlevels in several different segments,cell position as well as cell lineage obviously is responsiblefor guidingdifferentiation. Introduction these apical cell derivativeshave been describedmany times,although not withrespect to peristometooth for- Although aspects of peristomedevelopment in the mation (De Bary 1884; Kienitz-Gerloff1878; Sachs Funariales have been studied for more than a century 1887; Goebel 1905; Evans and Hooker 1913). Some (Sachs 1887; Goebel 1905; Campbell 1913; Smith differencesin the orientationof early divisions in the 1955; Proskauer1958; Shaw et al. 1987, 1989), apical segmentsof Funaria and Ephemerumwere described segmentationand its relationshipto peristomedevel- but were not traced to the final morphologyof the opment have not been well documented.Aside from capsule. studies on embryology,nearly all published illustra- The sequence of cell divisions withina given seg- tions are of cross sections of sporophytes,probably ment of certainother taxa has been described as ex- because the importantsystematic characters associated tremelyregular. In the shoot apices of liverworts,a with the peristomeare usually seen in this plane of precise series of cell divisions within each segment section. In particular,development as viewed in three gives rise to leaves and lateral branches in specific dimensions has never been fully explored. A three- positions (Schuster 1966). Precise patternsof cell di- dimensionalview of developmentreveals the relation- vision withinsegments in the roots of heterosporous ship between cell lineages, segments sensu Gifford ferns,e.g., Azolla, also show thatcell position within (1983), Gunning(1978), and Schuster(1966), and dif- a segmentguided differentiation(Chiang 1970; Gun- ferentiation. ning et al. 1978). In contrast,initiation of leaf primor- A single meristematicinitial is presentat the apex dia in fern apices depends only on position on the of the Funaria sporophyte(Hofmeister 1862). Deriv- apex, withno regardto segmentboundaries (Bierhorst atives of the apical cell, oftenreferred to as segments, 1977). Are segmentboundaries and cell positionwith- are formedby inclinedtransverse divisions on two cut- in a given segmentimportant in guidingdifferentiation two vertical tingfaces, and derivativesare arrangedin of peristometeeth? Regular patternsof cell division files on opposite sides of the sporophyteaxis. Early in and leaf initiationwithin segmentsof moss gameto- the cell divides sporophytegrowth, apical frequently phyteshave been reported(Merl 1917; Berthier1971- (Hebant 1973), cuttingoff 10-14 segments.From two 72), but segmentationin moss sporophyteshas not of the earliestapical cell segments,an intercalarymer- been completelyinvestigated. The lack of information istem differentiates(Roth 1969; French and Paolillo led Proskauer(1958) to point out thatthe relationship 1975, 1976). Elongation of the intercalarymeristem of the peristomiallayers to apical cell segmentation derivativesis responsiblefor the increase in lengthof had never been properlydescribed. the seta portionof the sporophyte.Segments formed I initiatedthis investigationto resolve differingde- afterthose differentiatinginto the intercalarymeristem in the literatureand to relate apical cell seg- remain,with few internaldivisions, until much laterin scriptions development. mentationto peristometooth differentiation. Although of was re- The firstthree or fourplanes of cell division within the developmentof the peristome Funaria cently reinvestigated(Shaw et al. 1989), apical cell segmentationwas not considered. Patternsof cell di- 'Address for correspondence and reprints:Plant Cell Biology Group,Research School of Biological Sciences, GPO Box 475, Aus- vision and apical cell segmentationin cleistocarpous tralianNational University,Canberra, ACT 2601 Australia;E-mail: taxa are even less well understood,with only a very [email protected]. limited number of taxa examined (Hofmeister1862; Manuscript received July 1996; revised manuscript received Muller 1868; Kienitz-Gerloff1878; Sachs 1887; Goe- December 1996. bel 1905; Snider 1975; Rushing and Snider 1980). 236 SCHWARTZ-FUNARIA APICAL SEGMENTATION 237 None of these studies described segmentationduring the later stages of development. 3 The following questions will be addressed: Do all A apical cell derivativesfollow the same patternof de- velopment?Do taxa with peristomesfollow the same patternof developmentas cleistocarpous taxa? How ' , 1 ~~~~~~~7b are the positionsof the peristometeeth related to seg- 7a ~ 7b mentboundaries? Materialand methods Moss sporophytesand attachedgametophytes were fixed in FAA (formalin-aceticacid-ethanol 1: 1:18). Afterfixa- 14~~~~~~~~1 tionwas complete,sporophytes and embryoswere dissected fromthe archegonia. Plants were cleared in a diluteClorox solution,dehydrated through a gradedethanol series, and stainedin fastgreen FCE Whole embryosand sporophyte 1 4~~~~ 11 1W 8 apices weremounted in gumdammar or cedaroil and pho- tographedon a LeitzOrtholux microscope. For complete de- Fig. 1 Schematic diagram of cell divisions withina single seg- tailsof themethods used, see Schwartz(1994). ment of Funaria. The outer surfaceof the sporophyteis to the left In orderto followthe cell divisionpattern within a single on each segment.The rightside of each segmentforms the central segment,it is essentialto comparethe development of sev- axis of the sporophyte.The numbersadjacent to each segmentare erallayers of cells.Therefore, cleared sporophyte apices and cell division planes which formthe common developmentalpattern embryoswere used ratherthan longitudinal sections. This followed by all segments.The apparentgaps in the numberingsys- tem are anticlinal divisions which cannot be seen in longitudinal permittedoptical sectioning of thesporophytes and compar- section.A, An undividedsegment. The firstdivision of the segment ison of surfacewith median views within the same sample. cannot be seen in longitudinalsection because it is parallel to the Furthermore,segment boundary walls are muchmore dis- plane of section, as are all anticlinal/radialdivisions. 2 = the first tinctin clearedsporophytes than in longitudinalsections. If periclinaldivision; 3 = the firsttransverse division; 5 = formation longitudinalsections were used, segmentboundary infor- of the second amphitheciallayer; 7a = transversedivisions of the mationwould be lost. lower half of the segment; 7b = transversedivisions of the upper half of the segment;8 = formationof the thirdamphithecial layer; Definitions