Abbe, Ernst C.

Stein, Otto L.

English

University of Minnesota, Morris (UMM): Digital Well

Journal of the Minnesota Academy of Science Volume 17 Number 1 Article 10 4-1949 Application of Schuepp's Method to Form Analysis of the Shoot Apex in Maize Otto L. Stein University of Minnesota Ernst C. Abbe University of Minnesota Follow this and additional works at: https://digitalcommons.morris.umn.edu/jmas  Part of the Agricultural Science Commons Recommended Citation Stein, O. L., & Abbe, E. C. (1949). Application of Schuepp's Method to Form Analysis of the Shoot Apex in Maize. Journal of the Minnesota Academy of Science, Vol. 17 No.1, 97-103. Retrieved from https://digitalcommons.morris.umn.edu/jmas/vol17/iss1/10 This Article is brought to you for free and open access by the Journals at University of Minnesota Morris Digital Well. It has been accepted for inclusion in Journal of the Minnesota Academy of Science by an authorized editor of University of Minnesota Morris Digital Well. For more information, please contact skulann@morris.umn.edu. PROCEEDINGS, VOLUME SEVENTEEN, 194'9 97 ,Ai,=>PLICATION OF SCHbEPP.'S METHOD TO FORM ANALYSIS OF THE SHOOT APEX IN:·MAIZE OTTO L, STEIN AND ERNST C. ABBE U~iversit·y of Minnesota, Minneapolis The purpose of this study is to evaluate periodic form changes in the shoot apex of Zea mays, by describing form in terms of -the angle included within the shoot apex. This is an application of one · of Schiiepp's (1938) techniques as developed by him in a study of Lathyrus odoratus. Schiiepp's results are compared wit?1 those ob-tained here for Zea mays. MATE)UALS AND METHODS A. Schiiepp' s method Schiiepp (1938) r~ports the following procedure in obtaining ma-terials for analysis: buds of Lathyrus odoratus were hand-sectioned with a razor to provide median sections. These sections were "fairly ' thick." After clearing, these sections furnished well-defined and complete outlines' of the apical meristems .. Median sections were· enlarged, 400 diameters and drawn. The resulting drawings were arranged in order according to the configurations of the apical nieri-stem and of the youngest leaves, thus furnishing a succession, of substages through several plastochfons. The shoot apex during each plastochron (Askenasy, 1880) was thus subdivided into nine substages. This permitted riot only the observation of the total· · growth of the apical meristem but also its b.ehavior within any one · plastochron, On this basis Schiiepp (1938, p. 35) was led to observe (as translated),· that "there exists a .continuous progression in the segm!,:!ntation of the outlines and the entire surface. It appears that a shoot apex and a leaf apex, as long as they retain their meriste-. matic character, cannot grow without changing their form con-tinuously and.dividing perpetually." Schiiepp aptly points out that the apical meristem behaves somewhat like a drop on the end of a leaky faucet. It swells steadily in size and periodiqtlly segments off droplets, is reduced to a minimum size and again increases in size until another droplet separates from it. This periodic process is repeated. The analogy to the behavior of the shoot apex is clear. The shoot apex increases gradually in size as does the drop on the end of the faucet; when a maximum size has been reached a seg-ment of the growing material becomes morphologically distinct (as a leaf primordium plus the associated stem unit) leaving a shoot apex of minimum size; the process then repeats itself again, periodi-cally. · Schiiepp (1938) devised a number of quantitative measurements of the form of the shoot apex. Since these deal with various inter-related angles· erected up,ori the apical do.me, they are obvjously 98 THE MINNESOTA AcAD~MY OF ScIENCE function:, of each other. The present' study re~tricts itself to the angle a measui·ed by two straight lines which intersect at the mid-point of the distal portion of the shoot apex. One leg intersects the · axil of the youngest leaf, the other intersects the axil of the next oldest leaf. (The angle a is illustrated 'as applied to Zea mays in Fig. I). The angle a decreases, with some fluctuations, fl'.om 110 · degrees when first measurable during a given plastochron to 60 · degrees at the end of the following plastochi·on in Lathyrus odora-tus. Schiiepp (1938, p. 66) observes that the measurements of these angles merely serve to "strengthen the impression that the change in form of the shoot apex is· a ·continous process during which a defi-nite moment for the i,nitiation of leaf formation could only be desig- . nated arbitrarily." . It is perhaps worth calling attention to the fact that Schiiepp (1938) has not attempted to establish a correlation between two linear dimensions (such as length and width) which would serve to define form changes in ontogeny on the basis of ~bsolute size. He thus avoids the necessity of dealing with regression coefficients or other measures of the inter-relation between· two interdependent variables; instead he utilizes the measurement of a single angle which is a function of these. Because absolute dimensions are not directly concerned with the objectives of the problem, his method is defi-. nitely adv:antageous. B. Methods used in this study Material used for _this study was planted in the summer,· of 1940 as normal sibs of a foi~ back-crossed to a University of Minne-sota •Agricultural Experiment Station inbred. The population was segregating for d1d1. There was no external means of differentiating between D 1D 1 and D 1d1. The plants were grown in the field and harvested at intervals by removing them in their entirety from the soil. They were then taken to the laboratory, fixed in Randolph's· , "Craf," imbedded in paraffin, sectioned sagittally through the shoot apex and stained according to the usual procedures. In classifying the material according to plastochrons. the first primordiuin formed above the coleoptile .was designated as having be.en fornied dur-ing plastochron I. It was promptly recognized upon the examination of the sections_ made according to the procedure outlined above that only in a ·few cases did they represent mathematically precise median sections. It became necessary to take this fact into account, in applying the method of microprojection to the preparation of the outline draw-ings used subsequently in this study. The section which apparently was most nearly median for the shoot. apex proper ,vas first out- . lined along with its associ!).ted leaf primordia. By comparison with this outline, adjacent sections were. checked to permit identifica-. tion of the most median section of· the leaf primordia themselves: ' I , _PJlOCEEDINGS, · V OL.UME SEVENTEEN; 194_9 99 . . In occasionai sections some rateral distortion had been introduced by ·the pressure of the microtom.e'-knife. Correction -was made for . this distortipn although the· m_6st serious ca,'ies were discardea. There was finally thus obfained a compos1te outline for each shoot apex showing maximum sectioned ·area of the shoot apex and its associated leaf primordia. These composite drawings· provided the ba~is for measurement of the angle a (Fig. 1). F(g. ,I Diagram of median section of - shoot apex of Zea mays, with two associated leaf primordia. The angle a describes the form of the shoot apex. Fig. Z Diagram to illustmt~ criteria used for identifying substages A through E in plas~ochrons-7 through 9. _ The proj~ction system was checked for· linear distortion by ·calibration with a stage mici·ometer, and corrected by readjusting the alignment of the prism and microprojector. The drawings were arranged _,vithin each plastochron according .. ,to their respective stages. Schiiepp's (1988) method was used in ,. measuring and graphtng the angles. ' C. Supplementq,ry methods used in this study In, order to. minimize variability due to limited sampling -eac}r ·plastochron was subdivided into five substages (Fig. 2). These sub-stages were established on_the basis of the extent to which the up-·permost leaf primordium had d,eveloped. The data for each su~stage were averaged ·and plotted on graph paper. Th<e maximum and minimum values in each substage are indicated when possible, since · the. sampling was too limited to justify the computation of meas-ures of statistical error. . · . Data· for five substages in Lathyrus odoratus corresponding to those described above wer_e obtained from Schiiepp's graph (1988, p. 5) by averaging the values for Hand C, E and G, D and A; F · " and I, (represented by a, b, d, and e respectively in Fig. 4) - B ' (c in Fig. 4) still representing a single value. . . OBSERVATIONS AND DrscussIONS ,· Fi'gure 8 shows represe~tative shoot apices of Zea mays arranged according to substages within the plastochron, with the younges~ _ shoot· apex, _in plastochron 7, at the bottom. There. occurs· an in-crease'in volume of the apical dome throughout each of these plas- I I' 100 THE MINNESOTA ACADEMY OF SCIENCE . Fla. 3 Camera lucida diagrams of medi~n sections of rep~esentative shoot apices in suc-cessive substages within plastochrons 7 through·9 in Zea mays. PROCEEDINGS, VOLUME, SEVENTEEN, 1949 ,· 101 tochrons. At the transition from one plastochron to·the next there is a drop to a smaller shoo~ apex size. The apical dome assumes larger final qimensions toward the end of each successive plasto-chron. This aspect has been discussed at length by Abbe, Ran-dolph, and Einset (1941). Thus in Zea mays there is an increase in . size of the apical dome during the individual plastochron. A comparison with Schiiepp's diagram (1938, p. 65, Fig. 3a) of Lathyrus odoratus bud sections sh9ws a definite contrast in the development of the shoot apex_in a plant of indefinite growth. Here, throughout the two plastochrons shown, there is a continuous in-crease in the length of the apical dome w'ith very little increase in width. Thus, Schiiepp (1938) states, that there is no clear delimita-tion of successive plastochrons as observable from the general con-.. figurations of the apical meristems. Figure 4 shows graphically data f,or Lathyrus odoratus adapted frorri Schiiepp (1:938) compared with data for Zea mays as obtained / in this study. The ordinate is the magnitude of the angle a,· meas-ured as described above. In Schiiepp's (1938) data there is a steady downward trend of the magnitude of the angle. Thus the angle decreases from llO degrees to 60 degrees in two successive plastochrons. For some un-known rea_son no further measurements were recorded, although other angular measurements had been graphed through at least a third plastochron. In this curve (Fig. 4, continuous line) a marked transition from one plastochron to the next can be observed, al-though Schiiepp does not recognize its existence in his treatment of the material. , . The curve representing the data for Zea mays (Fig. 4, broken line) shows a lesser range in size of the angle a, the maximum and minimum values obtained being 68 degrees and 45.5 degrees re-. spectively. Here too, a ·general downward trend can be observed during each plastochron. The significant difference however is shown by the sharp increase of the .angle between the last stage· of a younger plastochron and the first stage of the next older plasto-chron. SUMMARY A method proposed by Schiiepp (1938) for the description of changes in form in the apical meristem of Lathyrus odoratus was applied to Zea mays. Bud sec_tions were arranged in developmental order within a plastochi-on. 'J'he shape of the shoot apex in median section is described in terms of the magnitude of the included angle. Schiiepp's graphs imply that the shoot apex in Lathyrus odoratus is characterized by continuous growth, changing the form of its apical meristem continuously through the transition from one plas-tochron to the next. This is not supported by the re-analysis of his data as presented in Figure 4. A sharp break appears when the tran-Schuepp's Data abcdeabcae I I Oo,..,. _______ ,_...,..---,,-.....,--,--,---i ~ 100° \ • 90° Lathyrus ! )( ao0 60° 40° A 8 c, D E A 8 C D E A 8 C D E 7 8 8 Plastoch ron No. in Zea mays -Fig.4 Comparison of Schiiepp's data for Lathyrus odoratus (cf. text) with analog-ous observations on Zea mays; ordinate is in degrees subtended by angle a (cf. Fig. 1), lower abscissa represents substages (cf. Fig. 2) of plastochrons 7 through 9 in Zea mays, upper abscissa substages of two plastochrons in Lathyrus odoratus. ',' ,-PROCEEDINGS, VoLUME SEVENTEEN, 1949. ,. " \ 103 sition is m~de. In 'z~a inays the overall change in fqi!m of th~ shoot -·apex as it go~s through a succession· of plast,ochroris was repeated in detail within 'each plastochron. Thus the apical meristem is of small size at the beginning of the plastochron and increases to a maximum at the end of the plastochron. The following plastochron begins at a somewhat larger initial size of the apical meristem and also terminates with a somewhat Iaw;er -maximum~ The periodk form change of the shoot- apex is thus clearly evident. · , For a more ac;curate representation of the actual behavior of the apical .meristem, a _modification of Schtiepp's (1938) method was - used. -As shown in, Figure 4, distinct groupings representing plasto- · chrons Were obtained, each having a similar decrease in magnitude of angle_ a. When applied to Schtiepp's _ (1938) data· on Lathyrus _ . odoratus two similar groupings resulted. A ,definite break between. -plastochrons was observable. Under ,the assumption that the mate-q•ial used by Schtiepp (1938) was genetically' u,:iiform, this break ·111ust be considered biologically significant, and to have been ob-scured from Schiiepp's attention by his_ method of analy!lis. How-ever in contrast to ·the data for Zea mays, a plant of definitive · growth, in Lathy1:us odoratus the following plastochron was initi-ated by_ a~ apical meristem with lesser angular magnitude th:;m that of the last_ s,tage of the-preceding plastochron,_ This apparently · -· is attributable to the indefinite type, cif- growth, characteristic of · Lathyrus odoratus. , In conclusion, then, it is evident from the very limited data at present available that the sequence of form changes in the onto- -geny of the shoot apex follows at least t\yo very different patterns, -a Lathyrus pattern and a Z(3a pattern. I ' -LITERATURE CITED , Abbe, E. C.;Ra~&ilph, L. F., and Einset, J. The Developmental Rel~tionship Between~-Shoot Apex and Growth ·Pattern of Leaf Blade in Diploid Maize. Amer. Joti_r. Bot. 28:778-784. 1941. _ Askenasy, E. Uber eine neue Methode, um die Vertheilimg- der Wachsthurnsintensita_t in wachsenden Theilen zu bestimrnen. Verh. des Naturhistorisch-Medicinischeri . Vereins, Heidelberg. Neue Folge Vol. II. 70-153. 1880. . - - . Schiiepp, Otto. Wachstumsniessungen an Knospen und Vegetations0punkten. Verh. · haturf. Ges. Basel 34:41-68,-1923. · Uber periodische ;Formbildung bei Pflanzen: Biol. Rev. 13:59-_92. 1938, ., ., ., PLANT SUCCESSION ON A SUBALPINE EARTHFLOW IN COLORADO-- JEAN H. LANGENHEIM _ U~ive~sity of Minnesota, Minneapolis ABSTRACT An investigation was made of the physiographic and vegetationa_l . ' '\ - ,, - ' ' .,· ,, . 

Application of Schuepp\u27s Method to Form Analysis of the Shoot Apex in Maize

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Application of Schuepp\u27s Method to Form Analysis of the Shoot Apex in Maize

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