The Vacuole

by Chris Trobacher & Alison Sinclair

Department of Molecular & Cellular Biology, College of Biological Sciences,
University of Guelph. ON N1G 2W1 Canada.

Plant vacuoles are bound by a single membrane, the tonoplast, and participate in a wide variety of cellular functions [1]. Several types of vacuoles exist in plants, and any given cell may contain multiple types [2, 3]. These dynamic structures are able to alter their luminal pH, convert to a different vacuolar class, or fuse together to form a large central vacuole [4, 5, 6]. They participate in growth through regulation of turgor, maintain cellular homeostasis, function as storage organelles, sequester toxic materials, may contain anti-fungal enzymes and anti-herbivory compounds, degrade old organelles (autophagy), and participate in programmed cell death via auto-lysis. Vacuoles are classified primarily by their function; however, molecular markers such as Tonoplast Intrinsic Proteins (TIPs) and constituent enzymes such as proteases provide new tools for vacuolar classification.
The Central Vacuole
The central vacuole of many plant cells is perhaps the most conspicuous organelle occupying up to 90% of a cell’s volume [1]. Meristematic cells contain numerous small provacuoles (resembling animal lysosomes) that arise from fusion of trans-golgi-derived vesicles. As a cell differentiates and expands, the pro-vacuoles fuse, forming a large acidic central vacuole. The well recognized role of the central vacuole is to increase cell size via changes in turgor pressure in concert with alteration of cytoskeletal and cell wall architecture [1]. The vacuole generates this turgor pressure by sequestering osmotic agents such as K+ [1, 7]. Vacuoles can sequester a variety of materials that are toxic to plants. Excess metals such as Cd, Zn, and Ni are stored within the central vacuole of various leaf cells including mesophyll, epidermis, and trichomes [8, 9]. The central vacuole of specialized crystal idioblast cells in developing soybean leaves accumulates calcium oxalate crystals as a mechanism to sequester excess calcium from other developing cells [10]. Crystal idioblasts in species such as Pistia and Tragia participate in plant defence. These cells produce needle-like calcium oxalate crystals that are ejected from thin-walled cells upon mechanical contact, piercing the dermis of unsuspecting animals causing irritation, presumably an effective deterrent against herbivory [10]. Other vacuole mediated defences include antimicrobial pathogenesis-related (PR) proteins. Five groups of PR proteins have two forms, the basic form stored in the central vacuole, and the acidic form found in the apoplast [11].
Vacuoles also participate in autophagy, the process by which the cell digests its own organelles. Upon Tobacco Mosaic Virus infection, mesophyll cells produce autophagosomes, double-membrane bound structures derived from the endoplasmic reticulum. The autophagosomes sequester cytoplasm, organelles, and/or pathogens and subsequently fuse with the central vacuole where the contents are degraded by hydrolytic enzymes [12]. A similar process is induced in sucrose-starved Arabidopsis cell cultures, as well as during reserve mobilization in Vigna mungo cotyledons, however, a lytic vacuole is the site of degradation rather than a central vacuole [13, 14]. Leaf vacuolar anthocyanins impart a reddish colour to leaves at discrete developmental stages, eg. leaf senescence in deciduous trees, or in response to stress. The current paradigm suggests that this pigmentation protects the photosynthetic apparatus against both photoinhibition and photooxidation [15]. Pigments also accumulate in the central vacuole of petal epidermal cells [16, 1], likely serving to attract pollinators.
The central vacuole also plays an important role in programmed cell death through a process known as auto-lysis. After autophagic processes have reclaimed much of the cell’s resources, the tonoplast is permeabilized, or ruptures completely, lowering cytosolic pH and releasing hydrolytic enzymes into the cytoplasm. This leads to bulk degradation of the cell corpse and has been observed in differentiating tracheary elements, in dying endosperm and aleurone cells during seedling establishment, and in dying nucellar cells during seed development [17, 18, 19, 20].
Protein Storage Vacuoles
Protein storage vacuoles (PSVs) in mature seeds are filled with storage proteins during seed development and have several characteristic ultrastructural features. These organelles contain a matrix of soluble storage proteins, crystalloid protein deposits, and globoids of phytic acid or oxalate crystals [21, 22]. The PSV tonoplast is typically marked by alpha and delta tonoplast intrinsic proteins (TIPs), and the crystalloid can be immunolabelled with anti-Dark Intrinsic Protein (DIP) antibodies [22]. Some vegetative tissues contain small neutral vacuoles, or vegetative PSVs, in addition to the lytic central vacuole; these compartments are not well-studied to date [23].
Senescence Associated Vacuoles
During leaf senescence, chloroplast-containing cells of Arabidopsis and soybean form small, acidic, 550-700 nm in diameter senescence associated vacuoles (SAVs). These vacuoles have both a lower luminal pH, and different tonoplast markers, than the central vacuole. The SAVs of Arabidopsis label with a senescence-associated cysteine proteinase-GFP fusion (SAG12-GFP), and contain multiple proteases [24].
List of FP probes for the Vacuole
Probes for Vacuoles

References

1.    Taiz, L. 1992. The plant vacuole. The Journal of Experimental Biology. 172(1): 113-122.

2.    Paris, N., Stanley, C.M., Jones, R.L. and Rogers, J.C. 1996. Plant cells contain two functionally distinct vacuolar compartments. Cell. 85(4): 563-572.

3.    Di Sansebastiano, G.-P., Paris, N., Marc-Martin, S. and Neuhais, J-M. 1998. Specific accumulation of GFP in a non-acidic vacuolar compartment via a C-terminal propeptide-mediated sorting pathway. The Plant Journal. 15(4): 449-457.

4.    He, F., Huang, F., Wilson, K.A. and Tan-Wilson, A. 2007. Protein storage vacuole acidification as a control of storage protein mobilization in soybeans. J. Exp. Bot. 58(5): 1059-1070.

5.    Di Sansebastiano, G.-P., Paris, N., Marc-Martin, S. and Neuhaus, J.-M. 2001. Regeneration of a lytic central vacuole and of neutral peripheral vacuoles can be visualized by green fluorescent proteins targeted to either type of vacuoles. Plant Physiology. 126: 78-86.

6.    Bethke, P.C., Lonsdale, J.E., Fath, A. and Jones, R.L. 1999. Hormonally regulated programmed cell death in barley aleurone cells. Plant Cell. 11(6): 1033-1046.

7.    Walker, D.J., Leigh, R.A. and Miller, A.J. 1996. Potassium homeostasis in vacuolate plant cells. Proceedings of the National Academy of Sciences. 93(19): 10510-10514.

8.    Vögeli-Lange, R., and Wagner, G.J. 1990. Subcellular localization of cadmium and cadmium-binding peptides in tobacco leaves : Implication of a transport function for cadmium-binding peptides. Plant Physiology. 92(4): 1086.

9.    Clemens, S., Palmgren, M.G. and Krämer, U. 2002. A long way ahead: Understanding and engineering plant metal accumulation. Trends in Plant Science. 7(7): 309-315.

10.    Franceschi, V.R., and Nakata, P.A. 2005. Calcium oxalate in plants: Formation and function. Annual Review of Plant Biology. 56: 41-71.

11.    Selitrennikoff, C.P. 2001. Antifungal proteins. Applied and Environmental Microbiology. 67(7): 2883-2894.

12.    Liu, Y., Schiff, M., Czymmek, K., Tallóczy, Z., Levine, B. and Dinesh-Kumar, S.P. 2005. Autophagy regulates programmed cell death during the plant innate immune response. Cell. 121(4): 567-577.

13.    Rose, T.L., Bonneau, L., Der, C., Marty-Mazars, D. and Marty, F. 2006. Starvation-induced expression of autophagy-related genes in arabidopsis. Biology of the Cell. 98(1): 53-67.

14.    Toyooka, K., Okamoto, T. and Minamikawa, T. 2001. Cotyledon cells of vigna mungo seedlings use at least two distinct autophagic machineries for degradation of starch granules and cellular components. J. Cell Biol. 154(5): 973-982.

15.    Gould, K.S. 2004. Nature's swiss army knife: The diverse protective roles of anthocyanins in leaves. J Biomed Biotechnol. 2004(5): 314-320.

16.    Chambers, R. 1941. Blue nuclei in tulip petals. American Journal of Botany. 28(6): 445-446.

17.    Fukuda, H., Watanabe, Y., Kuriyama, H., Aoyagi, S., Sugiyama, M., Yamamoto, R., Demura, T. and Minami, A. 1998. Programming of cell death during xylogenesis. Journal of Plant Research. 111(2): 253-256.

18.    Fath, A., Bethke, P., Lonsdale, J., Meza-Romero, R. and Jones, R. 2000. Programmed cell death in cereal aleurone. Plant Molecular Biology. 44(3): 255-266.

19.    Gietl, C., and Schmid, M. 2001. Ricinosomes: An organelle for developmentally regulated programmed cell death in senescing plant tissues. Die Naturwissenschaften. 88(2): 49-58.

20.    Greenwood, J.S., Helm, M. and Gietl, C. 2005. Ricinosomes and endosperm transfer cell structure in programmed cell death of the nucellus during ricinus seed development. Proceedings of the National Academy of Sciences. 102(6): 2238-2243.

21.    Gifford, D.J., Greenwood, J.S. and Bewley, J.D. 1982. Deposition of matrix and crystalloid storage proteins during protein body development in the endosperm of ricinus communis L. cv. hale seeds. Plant Physiol. 69(6): 1471-1478.

22.    Jiang, L., Phillips, T.E., Rogers, S.W. and Rogers, J.C. 2000. Biogenesis of the protein storage vacuole crystalloid. J. Cell Biol. 150(4): 755-770.

23.    Fluckiger, R., DeCaroli, M., Piro, G., Dalessandro, G., Neuhaus, J.-. and Di Sansebastiano, G.-. 2003. Vacuolar system distribution in arabidopsis tissues, visualized using GFP fusion proteins. J. Exp. Bot. 54(387): 1577-1584.

24.    Otegui, M.S., Noh, Y.-., Martinez, D.E., Petroff, M. G. V., Staehlin, L.A. and Amasino, R.M. 2005. Senescence-associated vacuoles with intense proteolytic activity develop in leaves of arabidopsis and soybean. The Plant Journal. 41(6): 831-844.

25.    Yoshimoto, K., Hanaoka, H., Sato, S., Kato, T., Tabata, S., Noda, T. and Ohsumi, Y. 2004. Processing of ATG8s, ubiquitin-like proteins, and their deconjugation by ATG4s are essential for plant autophagy. The Plant Cell. 16: 2967-2983.

26.    Mitsuhashi, N., Shimada, T., Mano, S., Nishimura, M. and Hara-Nishimura, I. 2000. Characterization of organelles in the vacuolar-sorting pathway by visualization with GFP in tobacco BY-2 cells. Plant Cell Physiology. 41(9): 993-1001.

27.    Kim, D.H., Eu, Y.-J., Yoo, C.M., Kim, Y.-W., Pih, K.T., Jin, J.B., Kim, S.J., Stenmark, H. and Hwang, I. 2001. Trafficking of phosphatidylinositol 3-phosphate from the trans-golgi network to the lumen of the central vacuole in plant cells. The Plant Cell. 13(2): 287-301.

28.    Yamaguchi, T., Aharon, G.S., Sottosanto, J.B. and Blumwald, E. 2005. Vacuolar na /H antiporter cation selectivity is regulated by calmodulin from within the vacuole in a Ca2 -and pH-dependent manner. Proceedings of the National Academy of Science. 102(44): 16107-16112.

29.    Marinova, K., Pourcel, L., Weder, B., Schwarz, M., Barron, D., Routaboul, J.-., Debeaujon, I. and Klein, M. 2007. The arabidopsis MATE transporter TT12 acts as a vacuolar Flavonoid/H -antiporter active in proanthocyanidin-accumulating cells of the seed coat. The Plant Cell. 19: 2023-2038.

30.    Czempinski, K., Frachisse, J.-., Maurel, C., Barbier-Brygoo, H. and Mueller-Roeber, B. 2002. Vacuolar membrane localization of the arabidopsis 'two-pore' K+ channel KCO1. The Plant Journal. 29(6): 809-820.

31.    Saito, C., Ueda, T., Abe, H., Wada, Y., Kuroiwa, T., Hisada, A., Furuya, M. and Nakano, A. 2002. A complex and mobile structure forms a distinct subregion within the continuous vacuolar membrane in young cotyledons of arabidopsis. The Plant Journal. 29(3): 245-255.

32.    Reisen, D., Leborgne-Castel, N., Ozalp, C., Chaumont, F. and Marty, F. 2003. Expression of a cauliflower tonoplast aquaporin tagged with GFP in tobacco suspension cells correlates with an increase in cell size. Plant Molecular Biology. 52(2): 387-400.

33.    Endler, A., Meyer, S., Schelbert, S., Schneider, T., Weschke, W., Peters, S.W., Keller, F., Baginsky, S., Martinoia, E. and Schmidt, U.G. 2006. Identification of a vacuolar sucrose transporter in barley and arabidopsis mesophyll cells by a tonoplast proteomic approach. Plant Physiology. 141(1): 196-207.

34.    Kim, S.A., Punshon, T., Lanzirotti, A., Li, L., Alonso, J.M., Ecker, J.R., Kaplan, J. and Guerinot, M. 2006. Localization of iron in arabidopsis seed requires the vacuolar membrane transporter VIT1. Science. 314(5803): 1295-1298.

35.    Loque, D., Ludewig, U., Yuan, L. and von Wiren, N. 2005. Tonoplast intrinsic proteins AtTIP2 1 and AtTIP2 3 facilitate NH3 transport into the vacuole 1. Plant Physiol. 137: 671-680.

36.    Schaaf, G., Honsbein, A., Meda, A.R., Kirchner, S., Wipf, D. and von Wirén, N. 2006. AtIREG2 encodes a tonoplast transport protein involved in iron-dependent nickel detoxification in arabidopsis thaliana roots. The Journal of Biological Chemistry. 281(35): 25532-25540.

37.    Nelson, B.K., Xue, C. and Nebenfuhr, A. 2007. A multicolored set of in vivo organelle markers for co-localization studies in arabidopsis and other plants. The Plant Journal. 51: 1126-1136.

38.    Hicks, G.R., Rojo, E., Hong, S., Carter, D.G. and Raikhel, N.V. 2004. Geminating pollen has tubular vacuoles, displays highly dynamic vacuole biogenesis, and requires VACUOLESS1 for proper function. Plant Physiology. 134: 1227-1239.

39.    Oufattole, M., Park, J.H., Poxleitner, M., Jiang, L. and Rogers, J.C. 2005. Selective membrane protein internalization accompanies movement from the endoplasmic reticulum to the protein storage vacuole pathway in arabidopsis. The Plant Cell. 17(11): 3066-3080.

40.    Miao, Y., Yan, P.K., Kim, H., Hwang, I. and Jiang, L. 2006. Localization of green fluorescent protein fusions with the seven arabidopsis vacuolar sorting receptors to prevacuolar compartments in tobacco BY-2 cells. Plant Physiology. 142(3): 945- 962.

41.    Oufattole, M., Park, J.H., Poxleitner, M., Jiang, L. and Rogers, J.C. 2005. Selective membrane protein internalization accompanies movement from the endoplasmic reticulum to the protein storage vacuole pathway in arabidopsis. The Plant Cell. 17(11): 3066-3080.

42.    Uemura, T., Yoshimura, S., Takeyasu, K. and Sato, M. 2002. Vacuolar membrane dynamics revealed by GFP-AtVam3 fusion protein. Genes to Cells. 7(7): 743-753.

43.    Thomine, S., Lelièvre, F., Debarbieux, E., Schroeder, J.I. and Barbier-Brygoo, H. 2003. AtNRAMP3, a multispecific vacuolar metal transporter involved in plant responses to iron deficiency. The Plant Journal. 34(5): 685-695.

44.    Latz, A., Becker, D., Hekman, M., T., Beyhl, D., Marten, I., Eing, C., Fischer, A., Dunkel, M., Bertl, A., Rapp, U.R. and Hedrich, R. 2007. TPK1, a Ca2+ -regulated Arabidopsis vacuole two-pore K channel is activated by 14-3-3 proteins. The Plant Journal. Online Early article.

45.    Frigerio, L., Foresti, O., Felipe, D.H., Neuhaus, J.-. and Vitale, A. 2001. The C-terminal tetrapeptide of phaseolin is sufficient to target green fluorescent protein to the vacuole. Journal of Plant Physiology. 158: 499-503.

46.    Lee SM, Kim HS, Han HJ, Moon BC, Kim CY, Harper JF, Chung WS. 2007. Identification of a calmodulin-regulated autoinhibited Ca2+-ATPase (ACA11) that is localized to vacuole membranes in Arabidopsis. FEBS Lett. 581(21): 3943-9.

47.    Hunter PR, Craddock CP, Di Benedetto S, Roberts LM, Frigerio L. 2007. Fluorescent Reporter Proteins for the Tonoplast and the Vacuolar Lumen Identify a Single Vacuolar Compartment in Arabidopsis Cells.Plant Physiol. Sep 28; [Epub ahead of print]

External Links: Wikipedia • Osmosis & Turgor