Plant & Cell Physiology and Grapevine Physiology
Area of expertise:
- Membrane transport, aquaporins and ion channels. Plant water relations.
The Big Question:
- What are aquaporins and non-selective channels really doing in plants?
Research goals
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Determine selectivity of key aquaporins and non-selective channels in biotrophic interfaces.
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Determine the function of non-selective cation and anion channels in roots and seeds.
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Understand how the distribution of nutrients in leaves, particularly calcium, is influenced by the distribution of water flow.
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Understand how turgor regulation occurs in plants.
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Determine new efficient ways of measuring plant water status in the field.
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Understand the hydraulic architecture of grapevines.
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Understand the process of water flows into and out of grape berries.
Current Members
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Zhiwei Wang
PhD Student
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Suzanne Pope
PhD Student
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Nasser Abbaspour
PhD Student |
Background
Role of Aquaporins
Terrestrial plants recycle over half of the annual global precipitation. It has been estimated that over 50% of this water will traverse water channels (aquaporins) in root membranes, but there is still some debate about the significance of aquaporins in root water transport (reviewed in Tyerman et al 1999 and Vandeleur et al. 2005). There is also debate about the true function of aquaporins more generally in both plants and animals, and despite the recent award of the Nobel prize to one of the key discoverers of animal aquaporins (Peter Agre), there are many animal aquaporins that have no clear function. Recently Hill et al. (2004) proposed that many aquaporins may function as osmo- or turgor-sensors, and it is possible to re-interpret some of the results from aquaporin gene silencing and over-expression studies in terms of a sensor role rather than as water or gas channels. 
My laboratory and collaborators have obtained evidence that some aquaporins are tightly regulated via the second messenger signals of pH and pCa, and that they are directly sensitive to osmotic potential. In addition we have evidence that shoot-to-root signalling may regulate aquaporin activity in roots. This may be important in coordinating supply by the root with demand by the shoot (Fig 1). There are many important questions leading from these observations about the function of aquaporins in plant water relations. At the cell level we propose functions in osmotic adjustment and anion nutrient transport and calcium distribution (Fig 2), while at a whole plant level, we propose functions in diversion of water flows into different parts of the root system and in balancing root conductance with shoot conductance. Few studies have attempted to link the molecular behaviour of aquaporins to whole plant function.
Non-selective channels in biotrophic interfaces
Another ongoing project investigates two classes of novel channels that co-occur in biotrophic membrane interfaces involved in nitrogen fixation and seed loading in legumes. The broad aim of the project is to discover the roles of these channels in each system, how they are controlled and how they interact to regulate exchange of nutrients, which ultimately impacts on the growth and yield of grain legumes. In nitrogen fixation, the interface consists of the bacteroid membrane and the plant-derived peribacteroid membrane (PBM) situated within the plant cytoplasm of infected cells in legume root nodules (Fig. 3). In seed loading, the interface consists of the plasma membrane of unloading cells in the seed coat (maternal generation) and the epidermal plasma membrane of cotyledons of the embryo (filial generation) (Fig. 4). The interfaces, defined here in a broad context as biotrophic interfaces, have two membranes that separate the protoplasts of the partner organisms. Nutrient exchange involves transport across the two membranes plus a common space, which can be influenced by either partner and is involved in controlling nutrient fluxes to match demand with supply. Our previous research on these interfaces in legumes has revealed some novel channels and the role of the common space between the membranes in controlling nutrient transport via cell signalling pathways. Despite the different physiological contexts of the two interfaces, a suite of novel channels has a common feature of being permeable to several related compounds. Such broad selectivity, referred to as non-selectivity in the literature may indicate their multifunctional roles. Non-selective channels are currently under intense international scrutiny, because they are anticipated to play important physiological roles in supporting rapid nutrient fluxes ( see cover for Plant Physiology, Feb 02).
Grapevine research
Grapevines like many other horticultural plants transpire large quantities of water as a necessary part of gaining carbon dioxide for photosynthesis and fruit production. In warm climates it would not be uncommon for 3 to 4 ML to be transpired per hectare of vineyard over a growing season. More water is applied than is transpired, and although some of this is required for leaching of salts, a variable proportion, depending on irrigation efficiency, is not productively used. Of the water that is transpired by grapevines, probably over 50% will traverse water channels (aquaporins) in root membranes. These water channels represent points of control in the soil-plant-atmosphere continuum, and like stomata they are regulated by the vine in response to environmental and internal conditions. Their activity in roots may have a profound effect on the extraction of water from the soil (Fig 1). Although stomata play the major role in regulating transpiration and will determine the efficiency of water use (carbon gained/water loss), the roots must be able to carry the supply of water to match demand from the shoots. In this respect roots will determine the operating conditions of the shoot in terms of the shoot water potential and xylem solute concentrations. The hydraulic conductance of roots and the responses to soil conditions and shoot conditions, actually determine the operating water use envelope of the plant, that is, the amount of water that can be extracted from the soil over a range of plant water potentials. The root system hydraulic conductance is variable, the cause of the variability depending on the time scale. For longer time scales hydraulic conductance is determined by changes in the size of the root system, patterns of root growth and changes in root anatomy. Within the time scale of a day variability in root hydraulic conductance, as much as 2-10 fold, is mainly due to the activity of aquaporins. Aquaporins, either directly or indirectly respond to time of day (circadian rhythms ), soil water potential, salinity, nutrient status, soil temperature, root metabolic status, and probably shoot water status via hormone signalling. Now that we are beginning to understand the central role of aquaporins in determining root hydraulic conductance, we can consider the possibility of applying treatments of nutrients and timing of water applications to maximise the water use envelope of grapevines and improve water extraction from the soil under different conditions. This would be analogous to finding a treatment like PRD that “tricked” the roots into responding in a particular way that could be used to optimise water use and to improve yield and quality. Unlike PRD we are able to use more than two dimensions (ie time and space) in order to manipulate root hydraulic conductance. The matrix is likely to be time x space x nutrients x canopy leaf area x transpirational demand, resulting in a second generation of a “PRD type” manipulation. The hydraulics of grape berries is also a continuing line of research particularly in relation to Shiraz berry weight loss.
Collaborations
We have close collaborations with international and national colleagues. Recent international collaborators include Professor Wen-Hao Zhang, Professor Mel Tyree and Professor Grant Cramer. We collaborate with Dr Brent Kaiser, Dr Matthew Gilliham, Professor Roger Leigh, Professor Mark Tester, Assoc. Prof. Robert Reid, Dr Carolyn Schultz, Dr Chris Ford, Dr Matthew Hayes, Dr Cameron Grant, Dr Robert Murray and Professor Sally Smith at the University of Adelaide and Professor John Patrick at the University of Newcastle.
Facilities & Techniques
At the Plant Research Centre we are fortunate in having a wide range of sophisticated molecular and electrophysiological tools and equipment for the investigation of water and ion transport processes and proteins. Core techniques include cell and root pressure probes, hydraulic conductance flow meters, ion-selective electrodes, microelectrode ion flux estimation (MIFE), two-electrode voltage clamp, patch clamp, radioactive trace-flux measurement and heterologous expression in yeast and Xenopus oocytes. We also have access to, and use: single-cell sampling (SiCSA)3,4, X-ray microanalysis2, ICP analysis, q-RT-PCR, gene misexpression techniques such as over-expression and RNAi, the use of T-DNA knockout plants and the GAL4-GFP enhancer trap system. We also have access to the world-class imaging facilities through our collaborators at Adelaide Microscopy. We are also the home of the AIB Labs Membrane Transporter Expression Facility (an AIB Labs facility supported by Bio Innovation SA and The ARC)
Positions Available
PhD Scholarships (Currently Available)
Two PhD scholarships are available to investigate the mechanism and physiological significance of cell-specific calcium accumulation within the leaves of higher plants related to the roles of aquaporins. The research will involve a range of single cell-based biochemical and molecular assays, as well as the construction and physiological analysis of specific plant mutants (see background above).
Informal applications from students who wish to study for a PhD in the Plant and Cell Physiology Lab are always welcome. You should have, or expect to obtain a degree with Honours (Second Class Division A and above). There are many sources of funding for both Australian and International students (see http://www.agwine.adelaide.edu.au/prospective/pg/).
Honours projects (Currently Available)
Honours projects are available in 2007/8
If you have your own ideas related to our research please contact us to discuss opportunities.
Internships
Short-term projects are always open to both Australian and International students. Please contact Professor Steve Tyerman to discuss projects and funding opportunities that are currently available.
Recent Papers
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Zhang, W-H., Walker, N.A., Patrick, J.W., Tyerman, S.D. (2004) Pulsed Cl- currents in coat cells of developing bean seeds are stimulated by hyposomotic shock. Journal of Experimental Botany 55: 993-1001.
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Zhang, W-H., Walker, N.A., Patrick, J.W., Tyerman, S.D. (2004) Calcium-dependent K+ permeable current in plasma membranes of dermal cells of developing bean cotyledons. Plant Cell and Environment 27:251-262.
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Zhang, W-H., Ryan, P.R., Tyerman, S.D. (2004) Citrate-permeable channels in the plasma membrane of cluster roots from while lupin. Plant Physiology 136:3771-3783
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DeBolt, S., Hardie, J., Tyerman, S.D. Ford, C.M. (2004) Composition and synthesis of raphide and druse crystals in berries of Vitis vinifera L. cv. Cabernet Sauvignon: the role of ascorbic acid as the biosynthetic precursor of both oxalic and tartaric acids is revealed by specific radio labelling studies. Aust. J. Grape and Wine Research 10: 134-142.
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Tyerman, S.D., Tilbrook, J., Pardo, C., Kotula, L., Sullivan, W., Steudle, E. (2004) Direct measurement of hydraulic properties in developing berries of Vitis vinifera L. cv Shiraz and Chardonnay. Aust. J. Grape and Wine Research 10: 170-181.
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Obermeyer, G., Tyerman, S.D. (2005) NH4+ currents across the peribacteroid membrane of soybean: Macro- and microscopic properties, inhibition by Mg2+, and temperature dependence indicate a subpico-Siemens channel finely regulated by divalent cations. Plant Physiology 139:1015-1029
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Alleva, K., Niemietz, C.M., Sutka, M., Maurel, C., Parisi, M., Tyerman, S.D., Amodeo, G. (2006) Plasma membrane of Beta vulgaris storage root shows high water channel activity regulated by cytoplasmic pH and a dual range of calcium concentrations. J. Exp. Bot. 57: 609-621.
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Gilliham, M., Sullivan, W., Tester, M., Tyerman, S.D. (2006) Simultaneous flux and current measurement from single plant protoplasts reveals a strong link between K+ fluxes and current, but no link between Ca2+ fluxes and current. Plant Journal 46: 134-144.
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Holland K.L., Tyerman S.D., Mensforth L.J., Walker G.R. (2006) Tree water sources over shallow, saline groundwater in the lower River Murray, south-eastern Australia: implications for groundwater recharge mechanisms. Australian Journal of Botany 54: 193-205.
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Vandeleur, R., Niemietz, C.M. Tilbrook, J., and Tyerman, S.D. (2005) Roles of aquaporins in root responses to irrigation. Plant and Soil 274: 141-161.
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Kaiser, B.N., Gridley, K.L., Brady, J.N., Phillips T. and Tyerman S.D. (2005) The role of molybdenum in agricultural plant production. Annals of Botany 96 (5): 745-754.
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Zhang, W-H., Zhou, Y., Dibley K.E., Tyerman, S.D., Furbank, R.T. and Patrick J.W. (2007) Nutrient loading in developing seeds. Functional Plant Biology 34: 314-331.
For information about studying in this field please visit our Student Services page.
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