Author Institution: Department of Botany and Plant Pathology, The Ohio State University, Columbus 1

Henry, Robert D.

Popham, Richard A.

The Ohio Journal of Science

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MULTICELLULAR ROOT HAIRS ON ADVENTITIOUSROOTS OF KALANCHOE FEDTSCHENKOI1RICHARD A. POPHAM AND ROBERT D. HENRYDepartment of Botany and Plant Pathology, The Ohio State University, Columbus 10In the course of examining root tips of various greenhouse plants, freehandsections were made of the stiff, pink-colored aerial adventitious roots of Kalanchoefedtschenkoi. Upon examining sections of these roots, structures resemblingmulticellular root hairs were observed. Since we were unable to discover anaccount of multicellular root hairs in recent botanical literature or a textbookof botany, we decided to look into the matter further.Dittmer (1949) states that he has never seen a septate root hair although heexamined "many millions of root hairs on hundreds of plants". He does mentionthat some of the earlier workers reported septate root hairs but that the structuresdescribed were judged by "many workers since" to be fungal hyphae. A ratherthorough survey of the literature failed to yield the name of a single specific plantfor which multicellular root hairs are claimed.We at first speculated that the structures which superfically looked verymuch like aerial adventitious roots of Kalanchoe might in reality be abnormalleafless branches with trichomes. However, if they turned out to be adventitiousroots we surmised that they might possibly have arisen exogenously as do theadventitious roots of Radicula aquatica, in which case the hairs might also beout-growths of cells of the epidermis of the stem. In water cress, epidermalcells of the stem in the vicinity of the exogenous root primordium become meriste-matic and form a continuous layer of epidermis over the entire root primordium.Both of these possibilities were investigated even though we found no epidermalhairs of any kind on the smooth stems of Kalanchoe fedtschenkoi.MATERIAL AND METHODSAdventitious root primordia and many sizes of adventitious roots includingbranched roots seven or more inches long were studied. Fresh freehand sectionsas well as microtomed transverse and longitudinal sections were prepared. Piecesof aerial adventitious roots preserved in FPA (5 ml. formalin, 5 ml. propionicacid, 90 ml. 50 percent ethyl alcohol) were dehydrated in an ethyl alcohol seriesand embedded in a special paraffin embedding mass (Popham, 1947) using tolueneas the vehicle for infiltration. Microtomed sections were cut at 10 M and werestained with safranin and anilin blue according to a procedure described by Pophamet al. (1948).ROOT APEX ZONATIONAn examination of transverse sections of the aerial adventitious roots revealeda rather large pith, xylem (usually 10 to 15 areas) and phloem in radial polyarcharrangement, a pericycle of 1 to 3 cell layers, a uniseriate endodermis, 3 to 5layers of cortical parenchyma, a uniseriate hypodermis which is poorly differ-entiated from cells of the cortical parenchyma, and a uniseriate epidermis. Neitherstelar cambium nor cambium initials were observed. Anthocyanin was clearlyvisible in cells of the cortex of fresh, freehand transverse sections.1 Papers from the Department of Botany and Plant Pathology, No. 581. Supported inpart from funds allocated by the University Advisory Committee on Research Grants.THE OHIO JOURNAL OF SCIENCE 55(5): 301, September, 1955.302 RICHARD A. POPHAM AND ROBERT D. HENRY Vol. LVf.FIGURE 1. Longitudinal section of stem and aerial adventitious root illustrating the en-dogenous origin of the latter. X120.FIGURE 2. Median longitudinal section of aerial adventitious root tip illustrating Janczewski'stype III, Convolvulus sub-type, of zonal organization in the promeristem. Theplerome lies just above the top indicator marker, the several-layered periblemlies between the two markers, and the dermato-calyptrogen lies just below thelower marker. X330.No. 5 MULTICELLULAR ROOT HAIRS 303In median longidutinal sections of the apex we found an unmistakable rootapex organization (fig. 2). Three histogens2 were observed: (1) a plerome, (2)a periblem, and (3) a dermato-calyptrogen. This zonal pattern is, in general,the same as that frequently designated as the common dicotyledenous type,Janczewski's (1874) type III. However, the cortex of Kalanchoe fedtschenkoioriginates from two or more (usually more) layers of cells (periblem) lying betweenthe plerome and the dermato-calyptrogen (fig. 2). The hypodermis does notoriginate from a separate histogen.I 1 jflprr -FIGURE 3. Longitudinal section of aerial adventitious root tip with multicellular root hairswithin 380 /* of the tip cell of the root. Notice that a root hair in an early stageof formation is farther from the tip than those composed of many cells. X130.In describing his type III zonation of roots, Janczewski states that the cortexof Helianthus and Fagopyrum originates from one or more cells disposed in asingle layer (periblem). He regarded the root promeristems of Linum usitatissimumas representing a sub-type of this general zonal organization. In Linum thecortex originates from two layers of cells, the outer of which gives rise to thehypodermis exclusively. Although the general zonal pattern is the same forKalanchoe as for Helianthus and Linum, the multi-layered condition of the periblem2Some_ anatomists seem to feel that the use of Hanstein's histogen terminology andJanczewski's typology imply a constancy of root apex zonation for the individual plant and/orthe species. Be this as it may, we have used their terms solely as a convenient means of de-scribing what we observed.304 RICHARD A. POPHAM AND ROBERT D. HENRY Vol. LVplaces the root of Kalanchoe in a separate and second sub-category of Janczewski'stype III.Just such a sub-category was described by Eriksson (1878) and was namedthe Convolvulus sub-type. Janczewski's type III and his Linum sub-type wererecognized by Eriksson (1878) although he referred to them as type I and theLinum sub-type. The Convolvulus sub-type, which Eriksson discovered, is char-acterized by a periblem consisting of three to several superposed layers of cells.The cells of the outer layer are described as dividing anticlinally and onlyoccasionally periclinally. Root apices of the following plants were found by himto exhibit this Convolvulus sub-type of zonal organization: Hoja carnosa(Asclepiadeae); Abutilon molle, Pavonia weldini, P. spinifex {Malvaceae); Villarsianymphaeoides (Menyantheae); Convolvulus cneorum (Convolvulaceae); Begonianelumbifolia, B. ricinifolia, B. glacialis (Begoniaceae).Neither Janczewski (1874) nor Eriksson (1878) recorded observations on aspecies belonging to the Crassulaceae. Adventitious root primordia of Sedumsieboldtii and Bryophyllium calycinum as well as lateral root primordia of Sedumacre and 5. maximowiczii were studied by Van Tieghem and Douliot (1888).They described them as having the common dicotyledenous type of root zonationwith a periblem composed of a single cell or a single layer of cells. The sametype of organization was seen by Koch (1874-77) in root apices of Sedum spuriumand S. album. In the root apex of another plant (Umbilicus horizontalis) be-longing to the Crassulaceae, Flahault (1878) observed and described a zonalorganization like Janczewski's type III. The periblem in the promeristem ofUmbilicus is a single layer of cells.We were unable to discover a description in the literature which claimedEriksson's (1878) Convolvulus type of zonal organization for the root apex of anyspecies belonging to the family Crassulaceae.ORIGIN AND GROWTH OF THE MULTICELLULAR ROOT HAIRSAfter thus completely satisfying ourselves that the structures observed onKalanchoe aerial stems were roots, we turned our attention to the problem ofascertaining whether the root hairs arose from a bonafide root epidermis or whetherthey arose from cells of stem epidermis overlying the root apex proper.Serial transverse and longitudinal sections were made of portions of stemson the surface of which slight protuberances were observed. After sectioningmany such stem pieces, we were able to assemble an intergrading series of longi-tudinal sections of adventitious root primordia and adventitious roots whoseapices had grown several millimeters beyond the epidermis of the stem. All ofthese sections showed evidence of an endogenous root origin (fig. 1). The ad-ventitious roots probably arise in phloem parenchyma although this point was notsurely confirmed. In any event, the origin is internal to the cortex since thelayers of cortex are compressed and subsequently punctured as the root primordiumenlarges and elongates. In every case where the root apex was found protrudingbeyond the epidermis of the stem, the epidermis was clearly broken and showedno evidence of continuity with that of the root.One of the facts that had originally made us doubtful as to whether we wereobserving bonafide root hairs was their occurrence at levels extremely close tothe root tip, even on roots several centimeters long. Many were found as closeas 380 fi back of the tip ce.ll of the root cap (fig. 3); some were seen closer to theroot tip. Many persisted as long as the epidermis remained firmly attached tothe root but hairs composed of living cells were usually found less than 1 cm.from the root tip.The first sign of root hair formation was the radial elongation of one of thetypically radially elongated cells of the epidermis. Accompanying the radialelongation of the trichoblast was an expansion of the outer end of the cell andNo. 5 MULTICELLULAR ROOT HAIRS 3054ft «iFIGURE 4-9. Cross sections of aerial adventitious roots illustrating stages in the formationof uniseriate and biseriate multicellular hairs. X650.306 RICHARD A. POPHAM AND ROBERT D. HENRY Vol. LVthe contraction of the end of the cell adjacent to the hypodermis (fig. 4). Duringthese early phases of root hair formation the nucleus retains an approximatelycentral location in the cell (fig. 4, 7). In contrast to typical root hair formationduring stages of which a portion of the free wall bulges, the entire free wall ofthe multicellular root hair initial was forced out into a dome. Concomitantlythe nucleus moved outward toward the bowed surface of the cell. After becomingconspicuously more radially elongated and vacuolated than neighboring epidermalcells, the trichoblast divided either transversally (fig. 5) or longitudinally (fig. 7).In either event enlargement of the two cells formed was followed by one or severalsuccessive transverse divisions in the one (fig. 6) or the two (fig. 8 ,9) tiers ofcells. Transverse wall formation in adjacent cells nearly always occurred at thesame level and simultaneously resulting in two tiers of nearly equal size corres-ponding cells. It was inferred that growth of the hairs was due to divisionsoccurring in the terminal cell of each tier although confirming mitotic figureswere not observed. On older portions of roots, hairs consisting of two tiers ofcells sometimes split throughout one-fourth to three-fourths of their length. Thisappeared to be due to the dissolution of the middle lamellae holding cells of thetwo tiers together although no microchemical tests were conducted to verifythis thesis.Few hairs attain lengths greater than 75 ju. Due to the short maximumlength and due to the fact that the maximum length is rapidly attained, zonescomposed of root hairs of decreasing lengths and ages, such as those often seenat root tips, are not evident in Kalanchoe fedtschenkoi (fig. 3).HAIRS OF AERIAL VS. SUBTERRANEAN ADVENTITIOUS ROOTSIt appears somewhat incongruous that multicellular root hairs have not beenfound to occur on adventitious as well as on primary and lateral roots of plantshaving multicellular stem hairs. Most botanists will probably agree thatanatomical form is controlled by and is the result of the combined influences ofgenes and the environment to which cells are exposed. If we wish to assumethat the gene complements of cells of roots and stems of a plant are identical,differences in stem vs. rpot epidermal hair structure for any particular plant mustbe attributed to differences in the environment to which the cells are exposed.It would seem that occasionally, at least, epidermal cells of roots would be ex-posed to environmental conditions identical, or nearly so, to those of stem epidermalcells. It is therefore interesting that this first documented occurrence of multi-cellular root hairs is reported for aerial adventitious roots whose initiating epidermalcells are exposed to environmental conditions similar to those of stem epidermalcells. Hairs of the aerial roots of Kalanchoe fedtschenkoi, whether original ad-ventitious roots or lateral roots arising from them, are multicellular. It is equallynoteworthy, but not astonishing, that roots of the adventitious root systemgrowing in the soil were found to have unicellular hairs. We did not observemulticellular hairs on any subterranean root, although we did not conduct anexhaustive search for them.The adventitious root system of Kalanchoe fedtschenkoi would seem to affordexperimental material for a new avenue of approach to the solution of a funda-mental problem of living organisms, namely, what combination of environmentalfactors is responsible for the initiation of the process of mitosis ?SUMMARYThe zonal organization of the aerial adventitious root apex is describedas conforming to Eriksson's Convolvulus sub-type of Janczewski's commondicotyledonous type III. A plerome, a several-layered periblem, and a dermato-calyptrogen are clearly defined in the root promeristem.No. 5 MULTICELLULAR ROOT HAIRS 307It was found that true multicellular root hairs arise from epidermal cells ofaerial adventitious roots of Kalanchoe fedtschenkoi. The hairs were found to beuniseriate or biseriate. They persist until the epidermis separates from the root,although hairs composed of living cells are usually found only on the tip 1 cm.of the roots.Hairs of adventitious roots growing in the soil are most commonly or alwaysunicellular and look very much the same as hairs of many other roots.It is suggested that the adventitious root system of Kalanchoe fedtschenkoimay provide suitable material for a new approach to investigations aimed atdiscovering the combination of environmental factors responsible for the initia-tion of mitosis.Since completing this paper, we have found multicellular root hairs, similarto those described, on the aerial adventitious roots of Kalanchoe somaliensis, K.daigremontiana, and an unidentified Kalanchoe species.In addition, two papers (Haberlandt, 1915 and Juri§ic, 1934) dealing withglandular hairs ("Drusenhaare") of roots were found. Diagrams accompany theformer but not the latter paper. Descriptions of the hairs indicate that thestructures which these authors saw on adventitious roots of several plants[Bryophyllum pinnatum and B. crenatum (Haberlandt, 1915); Bryophyllum pro-liferum, B. verticillatum, B. daigremontianum, and B. pinnatum (Jurisic, 1934)] arevery similar to those described in this paper. These two papers have apparentlybeen generally overlooked.LITERATURE CITEDDittmer, H. J. 1949. Root hair variations in plant species. Amer. Jour. Bot. 36: 152-155.Eriksson, J. 1878. Ueber das Urmeristem der Dikotylen—Wurzeln. Jahrb. Wiss. Bot. 11:380-436.Flahault, C. 1878. Recherches sur l'accroissement terminal de la racine chez les phanerogames.Ann. Sci. Nat. Bot. VI. 6: 1-168.Haberlandt, G. 1915. Uber Drusenhaare an Wurzeln. Sitzungsber. d. Kgl. Preuss. Akad.d. Wiss., Phys.-Math. Kl. 1: 222-226.Janczewski, E. de. 1874. Recherches sur l'accroissement terminal des racines dans lesPhanerogames. Ann. Sci. Nat. Bot. V. 20: 162-201.Juristic, J. 1934. Zur Kenntnis der Drusenhaare an den Wurzeln von Bryophyllum. Anzeigerder Akademie der Wissenschaften in Wien. 71: 192-195.Koch, L. 1874-77. Untersuchungen uber die Entwicklung der Crassulaceen. Verhandl. desNaturhistorisch—Medicinischen Vereins zu Heidelberg. 1: 421-442.Popham, R. A. 1947. The importance of controlling cooling temperatures during embeddingin paraffin. Science. 106: 475-476., T. J. Johnson, and A. P. Chan. 1948: Safranin and anilin blue with Dela-field's hematoxylin for staining cell walls in shoot apexes. Stain Tech. 23: 185-190.Van Tieghem, P., and H. Douliot. 1888. Recherches comparatives sur l'origine des membresendogenes dans les plantes vasculaires. Ann. Sci. Nat. Bot. VII. 8: 1-660.

Multicellular Root Hairs on Adventitious Roots of Kalanchoe Fedtschenkoi

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Multicellular Root Hairs on Adventitious Roots of Kalanchoe Fedtschenkoi

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