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Roots of Nicotiana sylvestris Lack Phototropism

Sasha Y. Lucas and John Z. Kiss
International Journal of Plant Sciences
Vol. 165, No. 4 (July 2004), pp. 565-570
DOI: 10.1086/383333
Stable URL: http://www.jstor.org/stable/10.1086/383333
Page Count: 6
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Roots of Nicotiana sylvestris Lack Phototropism
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Abstract

The interaction between phototropism and gravitropism is important in early plant development, and these two tropisms are important for the continued survival of the plant. Of these tropisms, root phototropism has been largely unstudied for decades but has received increased attention with the availability of molecular tools associated with using Arabidopsis thaliana as a model plant. Roots of A. thaliana seedlings, while exhibiting a strong positive gravitropism, also have a negative phototropism induced by blue light and mediated by the phototropin family of photoreceptors. In addition, A. thaliana roots exhibit a positive phototropism mediated by phytochromes A and B. The major focus of our research was to examine root phototropism in Nicotiana sylvestris, which also has been a model system in studies of physiology and development. Results with orientation and time course experiments with unilateral illumination demonstrate that roots of N. sylvestris seedlings are not phototropic in the presence of white or blue light. While orientation experiments initially indicated a possible red light–induced phototropic curvature in roots, time course studies and experiments with a high‐resolution computer‐based feedback system confirmed that N. sylvestris roots were phototropically insensitive to red light as well. The reasons for the apparent lack of root phototropism in N. sylvestris may be related to recently reported differences in cytoplasmic regulation of phytochrome compared to A. thaliana and also to the spectral qualities of the soil in which N. sylvestris naturally occurs.

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