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Persea Americana, Mesocarp Cell Structure, Light and Electron Microscope Study Author(S): Flora Murray Scott, Barbara G

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Persea Americana, Mesocarp Cell Structure, Light and Electron Microscope Study Author(S): Flora Murray Scott, Barbara G Persea americana, Mesocarp Cell Structure, Light and Electron Microscope Study Author(s): Flora Murray Scott, Barbara G. Bystrom and E. Bowler Reviewed work(s): Source: Botanical Gazette, Vol. 124, No. 6 (Dec., 1963), pp. 423-428 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/2473211 . Accessed: 09/02/2013 21:55 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . 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 Botanical Gazette. http://www.jstor.org This content downloaded on Sat, 9 Feb 2013 21:55:02 PM All use subject to JSTOR Terms and Conditions 1963] HAIGH & GUARD-ROOT-TIP MITOSES 423 the rest of the quiescentarea, as delineatedby the boundaries of the quiescent zone on the side away CLOWES, only one division has been observed, from the root cap cannot be definedwith precision. whereasin the epidermalportion, a much smaller In the remainder of the apex behind this region, area, seven distinctdivisions are recorded.While there appears to be a fairlyuniform distribution of approximately1800 divisionshave been plotted,it divisions, with perhaps a rather higher density of would be desirableto studymany more sections in orderto clearlydefine the status of the epidermal division in the central, or "columella" area, than in region. the cortical and epidermal regions. In thearea immediatelysurrounding the quiescent DEPARTMENT OF BIOLOGICAL SCIENCES centerthere is a gradualshading off of quiescence, PURDUE UNIVERSITY divisionsbecoming gradually more frequent, so that LAFAYETTE, INDIANA LITERATURE CITED 1. CLOWES, F. A. The cytogenerativecentre in roots with 3. ---. Nucleic acid in root apical meristemsof Zea. New broad columellas.New Phytol. 52:48-57. 1953. Phytol. 55:29-35. 1956. 2. --. The promeristemand the minimalconstructional 4. JENSEN, W. A., and KAVALJIAN, L. G. An analysis of cell centrein grass root apices. New Phytol. 53:108-116. 1954. morphologyand periodicityof divisionin the root tips of Allium cepa. Amer. Jour.Bot. 45:365-372. 1958. PERSEA AMERICANA, MESOCARP CELL STRUCTURE, LIGHT AND ELECTRON MICROSCOPE STUDY' FLORA MURRAY SCOTT, BARBARA G. BYSTROM, AND E. BOWLER Introduction Ergasticsubstances, in particularoil and starch,were The mesocarpof the avocado fruitconsists pri- tested by stainingwith Sudan III, Sudan black, marilyof parenchymawith abundant oil and a net- osmicacid, and I2KI. Aqueousstains including neu- workof vascular strands(1, 19). The oil occursas tral red,Janus green, anilin blue, and thioninwere dropletsin the cytoplasmof unspecializedcells and usefulin stainingdifferentially but not definitively in oil sacs in scatteredidioblasts (3, 4). theoils in parenchymatouscells and oil-sac idioblasts. The structureof the oil-sac idioblasthas been For electronmicroscope study of cell walls,young describedin detail in the leaf of avocado, but the and maturetissues were cleared of the abundantoil interconnectionof idioblastswith surroundingcells and proteinaceousmaterials. Existing techniques is not indicatedin the originaldiagrams (4). The weremodified as required.The mostsuccessful meth- presentpaper deals with cell-wallstructure, inter- ods involvedthe use of acid maceration:1:1 10% cellularconnections, and theprotoplasts in thetissue chromicand 10% nitricacids; or acetylization:1:4 of the mesocarpof the fruitof Persea americana, glacial and concentratedsulfuric acids. These treat- var. Haas, as seen underlight and electronmicro- mentswere followed, when necessary, by removalof scopes. fattycomponents and by washingin 50% alcohol Material and methods followedby distilledwater. For cell-wallstudy cleared materialin distilled Fresh materialof youngand mature2fruits was waterwas fragmentedultrasonically for 25 secondsor sectionedand examinedunder the lightmicroscope, less in ultrasoniccell fragmentizerSF-50 (McKenna beforeand afterstaining with aqueous stains,also Laboratories,Santa Monica, California)and there- during and after treatmentwith standardmicro- aftermounted on Formvar-coatedgrids and shad- chemical reagents. owed withpalladium. Uncleared material was simi- The distributionof cellulose,pectic substances, larlyprocessed for comparison. lignin,and suberinwas determinedby I2KI-H2SO4, substancesin situ, ultrathin rutheniumred, phloroglucinol-HCl, and Sudan III. For thestudy of fatty sectioningwas effective.Segments of fruit were fixed 1 The authors thank the National Science Foundation in bufferedOS04 (7) or in KMnO4 (5) and wereim- for of this work. (NSF G23387) support bedded in Epon 812. Material was sectionedat 2 The term "mature" is used of fruitsat the "harvesting and 1000 on a Porter-Blummicro- ripe" stage, full grown and firmin texture.Softening of the between600 A A fruitoccurs after picking. tome. All sections were stained with Protargol. This content downloaded on Sat, 9 Feb 2013 21:55:02 PM All use subject to JSTOR Terms and Conditions 424 BOTANICAL GAZETTE Observations were made on an RCA-EMU-2 micro- The polyhedralidioblasts in the same fruitsare scope. distinguishedfrom the parenchymaby largersize Observations and thickerwalls and by the presenceof oil sacs. Traces of ligninoccasionally occur in the cell wall. LIGHT MICROSCOPE.-In the youngestmesocarp examinedthe parenchymatouscells are polyhedral The patternof pittingon all cell facesis evidentin and approximatelyequal in size. The futureidio- youngerfruits before the wall is too heavilysuber- in blastsare alreadymarked by therefringence of their ized. In oldersuberized walls pittingis observed protoplast contents.Small air-filledintercellular spaces are ultrasonicallyshattered fragments. The defined ubiquitous.Mitosis occurs during the growthof the is vacuolated,and thestalked oil sac is clearly of growth.The sac membrane fruit,and recentcell divisionis indicatedby varia- duringvarious stages but are impregnated tionin cell outline,diameter, and alignment,and by and stalk consistof cellulose fromthe earlieststages with a certainamount of thepresence of new thin cell walls between daughter The membraneap- nuclei.Idioblasts grow more rapidly than unspecial- lipid-a suberin-likematerial. ized parenchymaand are distinguishedby their pearsvery finely punctate or ultraporous.From the sheaththat surroundsthe sac, cytoplasmicstrands radiatebetween vacuoles toward the peripheral cyto- plasm, as in developingcystoliths and calcium oxalateidioblasts (9, 10). In thefull-grown idioblast, theoil sac fillsalmost the entire cell cavity and masks the nucleusand otherorganelles. In the tissuesof youngerfruits the cell walls and theprotoplasts of the idioblast react immediately by changein colorto standardmicrochemical reagents and to aqueousstains. In maturefruits the idioblasts generallyremain impervious indefinitely to the same reagentsand stains.It is not knownat what stage of developmentthis impermeabilitybecomes effec- tive. p 0 Pd OS ELECTRON MICROSCOPE.-The cellulose micro- FIG. 1. Diagramof avocado mesocarp cells showing pitted fibrillarpattern of the youngest cell walls examined cell wall and oil drops in protoplastsof parenchymacells and is a reticulum with pores and groups of pores that thickenedcell wall and oil sacs of idioblasts. In latter note mark the beginningof pits (15). Differentiationand and older oil at groupedpits, younger sacs, plasmodesmata wall thickeningof unspecialized parenchymatousand base, and radiatingprotoplasmic strands. P. pits; 0, oil; OSO oil sac; Pd, plasmodesmata.Actual diameterof idioblasts is idioblast cells is evident at an early stage of growth. 25 ,u. In the interparenchymatouscell faces, as already noted, the ubiquitous pits are large, elliptical or cir- thickerwalls and the presenceof youngstalked oil cular in outline, and become delimited by a macro- sacs. reticulum of microfibrils(fig. 2). In maturing cells, In maturefruits the distribution of thepolyhedral while deposition of microfibrilsthickens the wall as parenchymacells and the scatteredidioblasts is a whole, the pit membrane also thickens (fig. 3). clearlyseen. The cell faces of the parenchyma appear Near the rimof a cell face, some smallerpits, possibly netlike because of the very numerous pits (fig. 1). adjacent to an intercellular space, and others in The pits are elliptical,oval, or occasionally circular; random locations, are partially or completely oc- the major axis or diameteris from3 to 5 s0,except on cluded by microfibrils.Conspicuous pits remain un- cell faces contiguous with the idioblasts. On the obstructedand functional,however. latter,the pits, smaller, circular in outline,and more On cell faces contiguousto idioblasts,the pit numerous,match those of the idioblast wall. All pattern is similarto that of the idioblast. The meshes intercellularspaces throughoutthe tissue,including of the macroreticulum surround numerous small thosearound the idioblasts,are linedwith a suberin circularpits (fig.4). film. The protoplastof unspecializedparenchymatous The vacuolesof mature l parenchyma cells are filled cells includesnucleus and cytoplasm,chloroplasts, withconspicuous oil dropsof varying size in addition
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