Summary
Cytokinin stimulates caulonemata ofFunaria to undergo an asymmetric division leading to the gametophore. The earliest detectable event is a small protuberance at the distal portion of the cell accompanied by the reorganization of the underlying organelles into a polarized distribution reminiscent of a tip growing cell. Dictyosomes and associated vesicles accumulate in the protuberance directly beneath the plasma membrane with mitochondria subjacent to the vesicular layer. Endoplasmic reticulum lies beneath the mitochondrial zone directly above the large central vacuole, while chloroplasts are outside the bud. As development continues the bud elongates causing the outer cell wall to exfoliate. During the above events the nucleus migrates toward the bud site concomitant with an increase in the number of microtubules between the nucleus and the base of the outgrowth. Nucleoli, extruded from the nucleus during a previous division, persist as diffuse fragments within the protuberance. Upon reaching the bud site, division occurs with the developing phragmoplast being initiated distal to the caulonema tip cell. The former polarized distribution of the cytoplasm is altered as mitochondria, chloroplasts and small vacuoles become evenly dispersed throughout the cytoplasm; dicytosomes and endoplasmic reticulum occupy a cortical position. These events indicate a change from 2-D tip growth to 3-D diffuse growth. To quantify the ultrastructural changes associated with bud formation we performed a morphometric analysis of cells in various stages of budding. The relative volumes of dictyosomes and vesicles adjacent to the bud apex decrease during bud development coincident with an increase in these organelles in lower portions of the cytoplasm. Mitochondria and chloroplasts follow this same pattern although their highest relative volumes initially are 4 μm from the bud apex and outside the bud site, respectively. These data, as well as density profile topographic maps for vesicle fractions, support the contention that cytokinin induces a change in morphological symmetry and polarity in the fine structure ofFunaria.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Bonnett, H. T., Newcomb, E. H., 1966: Coated vesicles and other cytoplasmic components of growing root hairs of radish. Protoplasma62, 59–75.
Bopp, M., 1963: Development of the protonema and bud formation in mosses. J. Linn. Soc. (Bot.)58, 305–309.
—, 1968: Control of differentiation in fern-allies and bryophytes. Ann. Rev. Plant. Physiol.19, 361–380.
—, 1984: The hormonal regulation of protonema development in mosses. II. The first steps of cytokinin action. Z. Pflanzenphysiol.113, 435–444.
Brandes, H., Kende, H., 1968: Studies on cytokinin-controlled bud formation in moss protonemata. Plant Physiol.43, 827–837.
Cresti, M., Pacini, E., Ciampolini, F., Sarfatti, G., 1977: Germination and early tube developmentin vitro ofLycopersicum peruvianum pollen: ultrastructural features. Planta136, 239–247.
Grove, S. N., Bracker, C. E., Morré, D. J., 1970: An ultrastructural basis for hyphal tip growth inPythium ultimum. Amer. J. Bot.57, 245–266.
Hepler, P. K., 1981: The structure of the endoplasmic reticulum revealed by osmium tetroxide-potassium ferricyanide staining. Eur. J. Cell Biol.26, 102–110.
Herth, W., 1978: Ionophore A23187 stops tip growth, but not cytoplasmic streaming in pollen tubes ofLilium longiflorum. Protoplasma96, 275–282.
Jaffe, L. A., Weisenseel, M. H., Jaffe, L. F., 1975: Calcium accumulations within the growing tips of pollen tubes. J. Cell Biol.67, 488–492.
Jensen, L. C. W., Jensen, C. G., 1984: Fine structure of protonemal apical cells of the mossPhyscomitrium turbinatum. Protoplasma122, 1–10.
Kiermayer, O., 1981: Cytoplasmic basis of morphogenesis inMicrasterias. In: Cytomorphogenesis in Plants (Kiermayer, O., ed.). Wien-New York: Springer.
Laetsch, W. M., 1967: Ferns. In: Methods in Developmental Biology (Wilt, F. H., Wessells, N. K., eds.), pp. 319–328. New York: Thomas Y. Crowell Co.
McKerracher, L. J., Heath, I. B., 1985: Microtubules around migrating nuclei in conventionally-fixed and freeze-substituted cells. Protoplasma125, 162–172.
Meindl, U., 1983: Cytoskeletal control of nuclear migration and anchoring in developing cells ofMicrasterias denticulata and the change caused by the anti-microtubular herbicide amiprophosmethyl (APM). Protoplasma118, 75–90.
—,Kiermayer, O., 1981: Biologischer Test zur Bestimmung der Antimikrotubuli-Wirkung verschiedener Stoffe mit Hilfe der GrünalgeMicrasterias denticulata. Mikroskopie38, 325–336.
Oakley, B. R., Morris, N. R., 1980: Nuclear movement is βtubulin-dependent inAspergillus nidulans. Cell19, 255–262.
Reiss, H-D., Herth, W., 1978: Visualization of the Ca2+ gradient in growing pollen tubes ofLilium longiflorum with chlorotetracycline fluorescence. Protoplasma97, 373–377.
—, 1979 a: Calcium gradients in tip growing plant cells visualized by chlorotetracycline fluorescence. Planta146, 615–621.
—, 1979b: Calcium ionophore A23187 affects localized wall secretion in the tip region of pollen tubes ofLilium longiflorum. Planta145, 225–232.
—, 1982: Disoriented growth of pollen tubes ofLilium longiflorum Thunb. induced by prolonged treatment with the calcium-chelating antibiotic, chlorotetracycline. Planta156, 218–225.
— —,Nobiling, R., 1985: Development of membrane- and calcium-gradients during pollen germination ofLilium longiflorum. Planta163, 84–90.
— —,Schnepf, E., Nobiling, R., 1983: The tip-to-base calcium gradient in pollen in tubes ofLilium longiflorum measured by proton-induced X-ray emission (PIXE). Protoplasma115, 153–159.
Reynolds, E. S., 1963: The use of lead citrate at high pH as an electron opaque stain in electron microscopy. J. Cell Biol.17, 208–212.
Rosen, W. G., Gawlik, S. R., Dashek, W. V., Siegesmund, K. A., 1964: Fine structure and cytochemistry ofLilium pollen tubes. Amer. J. Bot.51, 61–71.
Saunders, M. J., Hepler, P. K., 1981: Localization of membrane-associated calcium following cytokinin treatment inFunaria using chlorotetracycline. Planta152, 272–281.
— —, 1982: Calcium ionophore A 23187 stimulates cytokinin-like mitosis inFunaria. Science217, 943–945.
— —, 1983: Calcium antagonists and calmodulin inhibitors block cytokinin-induced bud formation inFunaria. Dev. Biol.99, 41–49.
Schmiedel, G., Schnepf, E., 1979 a: Side branch formation and orientation in the caulonema of the moss,Funaria hygrometrica: normal development and fine structure. Protoplasma100, 367–383.
— —, 1979 b: Side branch formation and orientation in the caulonema of the moss,Funaria hygrometrica: experiments with inhibitors and with centrifugation. Protoplasma101, 47–59.
— —, 1980: Polarity and growth of caulonema tip cells of the mossFunaria hygrometrica. Planta147, 405–413.
Spurr, A. R., 1969: A low-viscosity epoxy resin embedding medium for electron microscopy. J. Ultrastruct. Res.26, 31–43.
Steer, M. W., 1981: Understanding Cell Structure. Cambridge: Cambridge University Press.
Uwate, W. J., Linn, J., 1980: Cytological zonation ofPrunus avium L. pollen tubesin vivo. J. Ultrastruct. Res.71, 173–184.
Vogelmann, T. C., Bassel, A. R., Miller, J. H., 1981: Effects of microtubule-inhibitors on nuclear migration and rhizoid differentiation in germinating fern spores (Onoclea sensibilis). Protoplasma109, 295–316.
Weibel, E. R., 1973: Stereological techniques for electron microscopic morphometry. In: Principles and Techniques of Electron Microscopy: Biological Applications. Vol. 3 (Hayat, M. A., ed.), pp. 237–296. New York: Van Nostrand Rheinhold Co.
Weisenseel, M. H., Jaffe, L. F., 1976: The major growth current through lily pollen tubes enters as K+ and leaves as H+. Planta133, 1–7.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Conrad, P.A., Steucek, G.L. & Hepler, P.K. Bud formation inFunaria: Organelle redistribution following cytokinin treatment. Protoplasma 131, 211–223 (1986). https://doi.org/10.1007/BF01282984
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01282984