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B.S. 1965 Hiram College Ohio
Bio 4 Light and Life
Sub-cellular Localization of the Blue Light Photoreceptor, Phototropin 1
Working with Dr. Winslow Briggs, Dr. Tong-Seung Tseng and Dr. David Ehrhardt (all at the Carnegie Department of Biology at Stanford) and using GFP fluorescent labels and confocal microscopy, we have characterized the sub-cellular localization of phototropin 1 (phot1). The blue light photoreceptor resides on the plasma membrane in dark grown Arabidopsis plants (See panel A below). Exposure to blue light results in movement of phot1 into the cytoplasm. It appears that blue light induces membrane vesiculation (See arrows in panels B and C below). The resultant vesicles carry phot1 into the cytoplasm.
If the plants remain in the dark for 1 hour after blue light exposure, phot1 is seen only in the plasma membrane. This observation is compatible with membrane cycling.
Exposing dark grown Arabidopsis plants to red light 2 hours before blue light treatment prevents movement of phot1 from the plasma membrane to the cytoplasm. In panel A below (no red light treatment) phot1 is clearly seen in the cytoplasm of the cells. In panel B (red light treatment) very little phot1 is seen in the cytoplasm. Thus, red light treatment appears to block the membrane vesiculation that moves phot1 to the cytoplasm. Since far-red light treatment blocks the red light effect on phot1 relocalization, the plant photoreceptor phytochrome must be responsible.
Light Regulation of Guard Cell Function
Working with Dr. Lincoln Taiz and Dr.Roberto Bogomolni (UC Santa Cruz) we resolved the UV action spectrum for guard cell function. In addition to the well known peak of activity at about 360 nm (UVA), we discovered a three times greater peak of response at about 280 nm (UVB). In light mixing studies we discovered that green light strongly inhibits blue light-induced stoma opening. Likewise, UV-B-induced opening is also antagonized by green light. To determine whether UV-B is being absorbed by the blue light photoreceptor or by a separate UV-B receptor, the UV-B responses of two different Arabidopsis mutants, npq1 and phot1/phot2, were tested. Both putative blue light-photoreceptor mutants exhibited normal stomatal opening in response to UV-B, consistent with the existence of a separate UV-B photoreceptor. From light mixing experiments we concluded that both phot1 and phot2 are required for the normal green light inhibition of UV-B. A model for a photoreceptor network regulating stomatal is presented in the accompanying diagram. Unlike the situation in guard cells, the UV-B bending response of Arabidopsis hypocotyls during phototropism appears to be mediated by phototropins.
Role of Microtubules in Guard Cell Function
Working with Dr. Winslow Briggs and Dr. David Ehrhardt (both at the Carnegie Department of Biology at Stanford) we are investigating the role of microtubules in guard cell function. In guard cells with open stomata microtubules are numerous, radially arranged, and bundled (See panel A below). When guard cells close their stomata we see fewer microtubules, they are less ordered and are less bundled (B).
Charlotte Lewis (SCU class of 2010) worked as an intern in my lab for the summer of 2010. Together we developed a quantitative method for measuring guard cell microtubule bundling. Charlotte presented our work at the West Coast Biological Sciences Undergraduate Research Conference and the NASA Ames/Santa Clara University Joint Poster Session.
William R. Eisinger, Roberto A. Bogomolni and Lincoln Taiz (2003). Interactions between a blue-green reversible photoreceptor and a separate UV-B receptor in stomatal guard cells. American Journal of Botany 90 (11):1560-1566.
Yinglang Wan, William Eisinger, David Ehrhardt, Frantisek Baluska, Winslow Briggs (2008). The subcellular localization and blue-light-induced movement of phototropin 1-GFP in etiolated seedlings of Arabidopsis thaliana. Molecular Plant 1:103-117
In-Seob Han, Tong-Seung Tseng, William Eisinger, and Winslow R. Briggs (2008). Phytochrome A Regulates the Intracellular Distribution of Phototropin 1?Green Fluorescent Protein in Arabidopsis thaliana. Plant Cell 2008 20: 2835-2847.
William R. Eisinger, David Ehrhardt, and Winslow R. Briggs (2012). Microtublues Are Essential for Guard-Cell Function in Vicia and Arabidopsis. Molecular Plant: 1-10, 3-7-2012
William R. Eisinger, Viktor Kirik, Charlotte Lewis, David W. Ehrhardt, and Winslow R. Briggs (2012). Quantitative Changes in Microtublue Distribution Correlate with Guard Cell Function in Arabidopsis. Molecular Plant:1-10, 4-5-2012