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KINETICS AND LOCATION OF PHOTOTROPISM IN ZEA MAYS L. ROOTS.   C. Wolverton¹, J.L. Mullen², H. Ishikawa¹, M.L. Evans¹. ¹Dept. of Plant Biology, Ohio State University, Columbus, and ²Dept. of Biology, Indiana University, Bloomington.

It is well established that roots of many species are capable of generating differential growth in response to unilateral light treatment. The importance of this root phototropic response has recently been highlighted as it relates to the characterization of the gravitropic sensitivity of Arabidopsis mutants with reduced levels of starch (Plant Physiol 122: 453). The demonstration of interactions between root gravitropism and phototropism raises fundamental questions regarding the nature of root phototropism: Where is light perceived in the root?  Where is the location of differential growth?  What are the kinetics of the response?

To address these questions, we applied image analysis software to the study of phototropism in roots of Zea mays L. cv. "Merit."  Surprisingly, we found that application of unilateral white light results in differential growth primarily in the central elongation zone (CEZ) within the first hour after light application. This contrasts with the localization of differential growth primarily to the distal elongation zone (DEZ) in roots undergoing gravitropism. As a first step toward elucidating the site of photoperception in roots, we removed the root cap and illuminated with unilateral light. This decapping procedure eliminated phototropic curvature under the fluence rate utilized for these experiments.

(Supported by NASA: NGT5-50015, NAG5-6385, NAG2-1190 and by the NASA/NSF Joint Program in Plant Biology, Network for Research on Plant Sensory Systems: IBN9421856.)