Photograph by Campus Photographer Herb Weitman

The
Gladys Levis Allen
Laboratory of
Plant Sensory Physiology

For biographical information about Gladys Levis Allen click here

Current Research Themes

Publications

Special Collaborations and Funding

Free microscopy algorithms and interfaces


Research Themes

Four abstracts from representative papers describe the research focus of the lab.

Contemplating the plasmalemmal control center model

Barbara G. Pickard
Protoplasma (1994) 182: 1-9.
An abundant epidermal mechanosensory calcium-selective ion channel appears able not only to detect mechanical stimuli such as those that initiate gravitropism but also to detect thermal, electrical, and various chemical stimuli. Because it responds to multimodal input with a second messenger output, this channel system seems likely to be an integrator that can engage in feedbacks with many other systems of the cell - and feedback is the hallmark of regulation. In general, the mechanical tension required for channel activation is likely transmitted from the relatively rigid cell wall to the plasma membrane system via linkage or adhesion sites that display antigenicities recognized by antibodies to animal B-1 integrin, vitronectin, and fibronectin and which have mechanical connections to the cytoskeleton. Thus, functionally, leverage exerted against any given adhesion site will tend to control channels within a surrounding domain. Reactions initiated by passage of calcium ions through the channels could presumably be more effectively regulated if channels within the domains were somewhat clustered and if appropriate receptors, kinases, porters, pumps, and some key cytoskeletal anchoring sites were in turn clustered about them. Accumulating evidence suggests not only that activity of clusters of channels may contribute to control of cytoskeletal architecture and of regulatory protein function within their domain, but also that both a variety of regulatory proteins and components of the cortical cytoskeleton may contribute to control of channel activity. The emerging capabilities of electronic optical microscopy are well suited for resolving the spatial distributions of many of these cytoskeletal and regulatory molecules in living cells, and for following some of their behaviors as channels are stimulated to open and cytosolic calcium build in their vicinity. Such microscopy, coupled with biochemical and physiological probing, should help to establish the nature of the feedback loops putatively controlled by the linkage sites and their channel domains.

The Endomembrane Sheath: A Key Structure for Understanding the Plant Cell?

Christophe Reuzeau, James G. McNally and Barbara G. Pickard
Protoplasma (1997) 200: 1-9.

Recent evidence suggests that that integrin is abundant in endomembranes of plant cells, and the endomembranes are clad by a sheath of cytoskeleton including F-actin. A role for endomembrane integrin and the endomembrane sheath is proposed: this system might orchestrate metabolic regulation by providing and modulating loci for channeling, and might accelerate channeling as needed by dragging ER and organelles through the cytoplasm. To accomplish this "streaming", F-actin might lever against the rest of the endomembrane sheath and the ER might also lever against adhesion sites (i.e. plasmodesmata and plasmalemmal control centers). As an important agent in the control of cellular activities, according to this model, the endomembrane sheath would play a major part in responses to diverse signals and stresses, and under extreme stress cell survival would depend on the ability of the system to maintain enough integrity to direct critical syntheses and degradations.

The mechanosensory calcium-selective ion channel: key component of a plasmalemmal control centre?

Barbara G. Pickard and Jiu Ping Ding
Australian Journal of Plant Physiology (1993), 20: 439-459.
Mechanosensory calcium-selective ion channels probably serve to detect not only mechanical stress but also electrical, thermal, and diverse chemical stimuli. Because all stimuli result in a common output, most notably a shift in second messenger calcium concentration, the channels are presumed to serve as signal integrators. Further, insofar as second messenger calcium in turn gives rise to mechanical, electrical, and diverse chemical changes, thae channels are postulated to initiate regulatory feedbacks. It is proposed that the channels and the feedback loops play a wide range of roles in regulating normal plant function, as well as in mediating disturbance of normal function by environmental stressors and various pathogens. In developing evidence for the physiological performance of the channel, a model for a cluster of regulatory plasmalemmal proteins and cytoskeletal elements grouped around a set of wall-to-membrane and transmembrane linkers has proved useful. An illustration of how the model might operate is presented. It is founded on the demonstration that several xenobiotics interfere both with normal channel behavior and with gravitropic reception. Accordingly, the first part of the illustration deals with how the channels and the plasmalemmal control system within which they putatively operate might initiate gravitropism. Assuming that gravitropism is an asymmetric expression of growth, the activities of the channels and the plasmalemmal control system are extrapolated to account for regulation of both rate and allometry of cell expansion. Finally, it is discussed how light, hormones, redox agents and herbicides could in principle affect growth via the putative plasmalemmal control cluster or centre.

Arabinogalactan protein and wall associated kinase in a plasmalemmal reticulum with specialized vertices.

J. Scott Gens, Masaaki Fujiki, and Barbara G. Pickard
Protoplasma (2000) 212:115-134.

Arabinogalactan protein (AGP) and wall associated kinase (WAK) are suspected to be regulatory players at the interface between cytoplasm and cell wall. Both WAK(s) and arabinogalactan shown likely to represent AGP(s) have been visualized there with computational optical sectioning microscopy. The arabinogalactan occurs in a polyhedral array at the external face of the cell membrane. WAK, and other proteins as yet unidentified, appear to fasten the membrane to the wall at vertices of the array. Evidence is presented that the array bears an important part of the mechanical stress experienced by the membrane, and it is speculated that the architectural organization of AGP, WAK and other components of the array is critical for coordination of endomembrane activities, growth and differentiation. The array has been named the plasmalemmal reticulum.

Some current research: Patterns of calcium elevation in individual BY2 tobacco cells following activation of mechanosensory calcium channels by physiologically natural signals and by Yariv phenylglucoside

Masaaki Fujiki and Barbara Pickard

Theorectical arguments pushed a search for a force transmitting and focusing structure to enhance the sensitivity of multimodally modulated mechanosensory calcium channels to mechanical and perhaps to other stimuli. A candidate was identified in BY-2 tobacco cells as described in the previous abstract: it is a plasmalemmal reticulum containing arabinogalactan protein, and the vertices contain wall associated kinase and other proteins which link the wall to the plasma membrane. Our current research follows up work of Roy et al. (Plant J. 19:379, 1999) in which the arabinogalactan protein binding agent glucosyl Yariv phenylglycoside was shown to cause calcium buildup in lily pollen cells. Using a special yellow cameleon and dual camera image capture of ratiometric changes in individual cells, we have explored effects of a number of treatments known to inhibit and activate mechanosensory calcium channels. Our primary conclusion is that the plasmalemmal reticulum indeed controls the activity of the mechanosensory calcium channels. Equally importantly, observations about the consequences of this activation have been permitted by the high-resolution technology.

Web page display of data prior to submission to a journal is sometimes considered to constitute prior publication. To avoid this, but to indicate what the technique can accomplish, we show an image stripped of data content which nonetheless illustrates capabilities. It is a movie (raw data) of onion bulb scale epidermis bombarded with a DNA contruct for Fujiki's yellow cameleon with an attached ER retention signal. Ratio data have been eliminated by adding the paired images of primary light emission and of fluorenscence resonance energy transfer.

Click here to view the movie

Publications

1. Gillespie, B., Briggs, W.R. 1961. Mediation of geotropic response by lateral transport of auxin. Plant Physiol. 36: 364-368.

2. Gillespie, B., Thimann, KV. 1961. The lateral transport of indoleacetic acid-Cl4 in geotropism. Experientia 17: 126-129.

3. Gillespie, B., Thimann, KV. 1963. Transport and distribution of auxin during tropistic response. I. The lateral migration of auxin in geotropism. Plant Physiol. 38: 214-225.

4. Pickard, B.G., Thimann, KV. 1964. Transport and distribution of auxin during tropistic response. II. The lateral migration of auxin in phototropism of coleoptiles. Plant Physiol. 39: 342-350.

5. Pickard, B.G., Thimann, KV. 1966. Geotropic response of wheat coleoptiles in absence of amyloplast starch. J. Gen. Physiology 49: 1065-1086.

6. Pickard, B.G. 1966. Preface to The Power pf Movement in Plants by Charles Darwin. Reprint by Da Capo Press, New York.

7. Pickard, B.G., with participation by Dutson, K, Harrison, V., Donegan, E. 1969. Second positive phototropic response patterns of the oat coleoptile. Planta 88:1-33.

8. Pickard, B.G. 1969. Comparison of calcium and lanthanon ions in the Avena coleoptile growth test. Planta 91: 314-320.

9. Pickard, B.G. 1971. Analysis of the significance of geotonic data for theories of georeception. In: Gravitv and the Organism, pp. 89-96, Gordon, S.A., Cohen, M.J., eds. University of Chicago Press, Chicago - London.

10. Pickard, B.G. 1971. Influence of previous temperature on stomatal response to osmotica. Experientia 27: 594-595.

11. Pickard, B.G. 1971. Action potentials resulting from mechanical stimulation of pea epicotyls. Planta 97: 106-115.

12. Pickard, B.G. 1972. Spontaneous electrical activity in Ipomoea, Pisum, and Xanthium. Planta 102: 91-114.

13. Williams, S.E., Pickard, B.G. 1972. Receptor potentials and action potentials in Drosera tentacles. Planta 103: 193-221.

14. Williams, S.E., Pickard, B.G. 1972. Properties of action potentials in Drosera tentacles. Planta 103: 222-240.

15. Fuller, F.B., Pickard, B.G. 1972. Spontaneous electrical activity in Coprinus. Zeitschr. fur Pflanzenphysiol. 67: 291-292.

16. Pickard, B.G. 1973. Geotropic response patterns of the Avena coleoptile. I. Dependence on angle and duration of stimulation. Can. J. Bot. 51: 1003-1021.

17. Pickard, B.G. 1973. Geotropic response patterns of the Avena coleoptile. II. Induction at low temperature. Can. J. Bot. 51:1023-1027.

18. Pickard, B.G. 1973. Action potentials in higher plants. Bot. Rev. 39: 172-201.

19. Pickard, B.G. 1974. Electrical signals in higher plants. Die Naturwissenschaften 62: 60-64.

20. Williams, S.E., Pickard, B.G. 1974. Connections and barriers between cells of Drosera tentacles in relation to their electrophysiology. Planta ll6: 1-16.

21. Newman, I.A., Pickard, B.G. 1975. Passive responses resembling action potentials: a device for the classroom. Bioscience 25: 502-503.

22. Van Sambeek, J.W., Pickard, B.G. 1976. Mediation of rapid electrical, metabolic, transpirational, and photosynthetic changes by factors released from wounds. I. Variation potentials and putative action potentials in intact plants. Can. J. Bot. 54: 2642-2650.

23. Van Sambeek, J.W., Pickard, B.G., with participation by Ulbright, C.E. 1976. Mediation of rapid electrical, metabolic, transpirational, and photosynthetic changes by factors released from wounds. II. Mediation of the variation potential by Ricca's factor. Can. J. Bot. 54: 2651-2661.

24. Van Sambeek, J.W., Pickard, B.G. 1976. Mediation of rapid electrical, metabolic, transpirational, and photosynthetic changes by factors released from wounds. III. Measurements of C02 and H20 flux. Can. J. Bot. 54: 2662-2671.

25. Cheeseman, J.M., Pickard, B.G. 1977. Electrical characteristics of cells from leaves of Lycopersicon. Can. J. Bot. 55: 497-510.

26. Cheeseman, J.M., Pickard, B.G. 1977. Depolarization of cell membranes in leaves of Lycopersicon by extract containing Ricca's factor. Can. J. Bot. 55: 511-519.

27. Johnsson, A, Pickard, B.G. 1979. The threshold stimulus for geotropism. Physiol. Plantarum 45: 315-319.

28. Williams, S.E., Pickard, B.G. 1980. The role of action potentials in the control of capture movements of Drosera and Dionaea. Plant Growth Substances 1979. F. Skoog, Ed. Berlin - Heidelberg - NewYork: Springer.

29. Ulbright, C.E., Pickard, B.G., Varner, J.E. 1982. Effects of short chain fatty acids on radicle emergence and root growth in lettuce. Plant, Cell and Environ. 5: 293-301.

30. Ulbright, C.E., Pickard, B.G., Varner, J.E. 1982. Effects of short chain fatty acids on seedlings. Plant, Cell and Environ. 5: 303-307.

31. Pickard, B.G. 1984. Voltage transients elicited by sudden step-up of auxin. Plant, Cell and Environ. 7: 171-178.

32. Pickard, B.G. 1984. Voltage transients elicited by brief chilling. Plant, Cell and Environ. 7: 679-681.

33. Harrison, M., Pickard, B.G. 1984. Burst of ethylene upon horizontal placement of tomato seedlings. Plant Physiol. 75: 1167-1169.

34. Pickard, B.G. 1985. Roles of hormones, protons and calcium in geotropism. In: Hormonal Regulation of Development III, Role of Environmental Factors, Vol. 11 of Encyclopedia of Plant Physiolgy, New Series. R.P. Pharis and D.M. Reid, Ed. pp. 193-281. Berlin - Heidelberg - NewYork: Springer.

35. Pickard, B.G. 1985. Roles of hormones in phototropism. In: Hormonal Regulation of Development III, Role of Environmental Factors, Vol. 11 of Encyclopedia of Plant Physiolgy, New Series. R.P. Pharis and D.M. Reid, Ed. pp. 365-417. Berlin - Heidelberg - New York: Springer.

36. Pickard, B.G. 1985. Early events in geotropism of seedling shoots. Annu. Rev. Plant Physiol. 36: 55-75.

37. Harrison, M.A., Pickard, B.G. 1986. Evaluation of ethylene as a mediator of gravitropism by tomato hypocotyls. Plant Physiol. 80: 592-595.

38. Edwards, K.L., Pickard, B.G. 1987. Detection and transduction of physical stimuli in plants. In: The Cell Surface and Signal Transduction. E. Wagner, H. Greppin, and B. Millet, Eds. pp. 45-66. Berlin - Heidelberg - New York: Springer.

39. Millet, B., Pickard, B.G. 1988. Early wrong-way response occurs in orthogeotropism of maize roots treated with lithium. Physiol. Plantarum 72: 555-539.

40. Guinel, F.C., Pickard, B.G., Varner, J.E., McCully, M.E. 1987. Root cap net in corn. In: Physiology of Cell Expansion During Plant Growth. D.J. Cosgrove and D.P. Knievel, Eds. American Society of Plant Physiolgists, Rockville, Md pp. 280-283.

41. Falke, L.C., Edwards, KL., Pickard, B.G., and Misler, S. 1988. A Stretch-Activated Anion Channel in Tobacco Protoplasts. FEBS Letters 237:141-144.

42. Caspar, T., Somerville, C., Pickard, B.G. 1989. Vigorous geotropism by a starchless mutant of Arabiodopsis: implications for the starch statolith theory of gravity sensing. Planta 177:185-197.

43. Harrison, M.A., Pickard, B.G. 1989. Auxin asymmetry during "wrong-way" gravitropic curvature of tomato hypocotyls. Plant Physiol. 89: 652-657.

44. Pickard, B.G., Ding, J.P. 1992. Gravity sensing by higher plants. Chapter 5 in: Advances in Comparative and Environmental Physiology, Vol. 10. Comparative Aspects of Mechanoreceptor Systems. F. Ito, Ed. Berlin - Heidelberg: Springer pp. 81-110.

45. Badot, P.-M., Ding, J.P., Pickard, B.G. 1992. Mechanically activated ion channels occur in vacuoles of onion bulb scale parenchyma. Comptes Rendus Acad. Sci. Paris ser. III, 315: 437-443.

46. Ding, J.P., Pickard, B.G. 1993. Mechanosensory calcium-selective cation channels in onion epidermis. Plant Journal 3: 83-110.

47. Pont-Lezica, R.F., McNally, J.G., Pickard, B.G. 1993. Wall-to-membrane linkers in onion epidermis. Plant, Cell & Environ. 16: 111-123.

48. Ding, J.P., Pickard, B.G. 1993. Modulation of mechanosensitive calcium channels by temperature. Plant Journal 3: 713-720.

49A. Pickard, B.G., Ding, J.P. 1993. The mechanosensory calcium-selective ion channel: key component of a plasmalemmal control center? Australian Journal of Plant Physiol. 20: 439-459.

49B. Pickard,B.G., Ding, J.P. 1993. The mechanosensory calcium-selective ion channel: key component of a plasmalemmal control center? In: Chemical Signalling in Plants, B.D. Glenn, ed. CSIRO Australia, pp. 439-459.

50. Ding, J.P., Badot, P.-M., Pickard, B.G. 1993. Aluminum and hydrogen ions inhibit a mechanosensory calcium-selective cation channel. Australian Journal of Plant Physiol. 20: 771-778.

51. Pickard, B.G. 1994. Contemplating the plasmalemmal control center. Protoplasma 182: 1-9.

52. Talbott, L., Pickard, B.G. 1994. Differential changes of size distribution of xyloglucan in the cell walls of gravitropically responding Pisum sativum epicotyls. Plant Physiol. 106:755-761.

53. Gens, J. S., Reuzeau, C., Doolittle, K.W., McNally, J.G., Pickard, B.G. 1996. Covisualization by computational optical sectioning microscopy of an array of integrin and associated proteins at the cell membrane of living onion protoplasts. Protoplasma 194: 215-230.

54. Reuzeau, C., Doolittle, K.W., McNally, J.G., Pickard, B.G. 1997. Covisualization in living onion cells of putative integrin, spectrin, actin, intermediate filaments and other proteins at the cell membrane and in an endomembrane sheath. Protoplasma 199: 173-197.

55. Reuzeau, C., McNally, J.G., Pickard, B.G. 1997. The endomembrane sheath: A key structure for understanding the plant cell? Protoplasma 200:1-9.

56. Heinlein, M., Padgett, H. S., Gens, J. S., Pickard, B. G., Casper, S. J., Epel, B. L., Beachy, R.N. 1998. Changing patterns of localization of the tobacco mosaic virus movement protein and replicase to the endoplasmic reticulum and microtubules during infection. Plant Cell 10: 1107-1120.

57. Hong, B., Ichida, A., Wang, Y., Gens, J.S., Pickard, B.G., Harper, J.F. 1999. Identification of a calmodulin-regulated Ca2+-ATPase in the ER. Plant Physiology 119: 1165-1176.

58. Pickard,B.G., Beachy,R.N. 1999. Intercellular connections are developmentally controlled to help move molecules through the plant. Cell 98: 5-8.

59.Gens, J.S.,Fujiki,M.,Pickard,B.G. 2000. Arabinogalactan protein and wall associated kinase in a plasmalemmal reticulum with specialized vertices. Protoplasma, 212:115-134.

60. Dammann, C., Ichida, A., Hong, B., Romanowsky, S., Hrabak, E.M., Harmon, A.C., Pickard, B.G., Harper, J.F. 2003. Subcellular targeting of nine calcium-dependent protein kinase isoforms from Arabidopsis. Plant Physiology (in press).

61. LaMotte, C.E., Pickard, B.G. Gravitropism of maize roots requires both gravifacilitation and vectorial gravitropic induction. I: Oblique orientation is due to graded orthogravitropism, not to finding a setpoint. Submitted to Functional Plant Biology.

62. LaMotte, C.E., Pickard, B.G. Gravitropism of maize roots requires both gravifacilitation and vectorial gravitropic induction. II: Further development, wide applicability and implications of the dual receptor model. Submitted to Functional Plant Biology.

Funding

NASA/NSF Research Network for Plant Sensory Systems

Gladys Levis Allen, Glenn L. Allen Jr. and Dow Chemical

USDA, Plant Responses to the Environment Program