SGER: Sensory Transduction of Blue Light in Corn coleoptiles

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This proposal requests a Small Grant for Exploratory Research to develop preliminary data for a critical test of the hypothesis that carotenoids function as blue light photoreceptors in the phototropic response of corn coleoptiles. Current thinking in the field ascribes the role of blue light photoreceptor to flavins or flavoproteins. Recent work in this laboratory, however, has provided tantalizing evidence for a role of the carotenoid, zeaxanthin in blue light photoreception. The research proposed here addresses the question of whether this molecule serves as the photoreceptor for coleoptile phototropism, a well characterized blue light response. Pilot studies with corn coleoptiles have shown that they operate the xanthophyll cycle and have zeanthin concentrations that track their light environment. Proposed experiments are designed to correlate the extent of the phototropic response with prevailing zeaxanthin concentrations in the coleoptile, and to establish whether coleoptile chloroplasts show a blue light response. Other experiments with corn mutants having an altered pigment composition will seek to correlate changes in phototropic sensitivity with their pigment content. Characterization of the blue light sensing mechanism in the coleoptile system would significantly enhance our understanding of blue light sensory transduction in plants. %%% One of the most fundamental responses of a plant to its environment is that the growing tip of a young plant shoot turns and grows toward light. Blue light is most effective in eliciting this response, but the mechanism by which plant tips sense blue light is not yet understood. As the first step in the response blue light must be absorbed by a specific chemical compound, but the chemical photoreceptor has not yet been identified with certainty. Establishing the nature of the blue light photoreceptor would be an important contribution to understanding of this fundamental plant response. Circumstantial evidence has led most investigators in the field to believe that the photoreceptor is probably a type of organic molecule known as a "flavin". Dr. Zeiger, however, has obtained some results suggesting that a different class of organic molecule, a "carotenoid" may be the real blue light receptor. If a carotenoid is, indeed, the blue light photoreceptor this would be a very important advance, but the evidence at present is too incomplete to justify launching a full scale research program on the subject. This Small Grant for Exploratory Research will permit Dr. Zeiger to develop sufficient preliminary data to determine whether a full scale project should be undertaken to study the function of carotenoids as blue light photoreceptors.