JXB Advance Access originally published online on November 8, 2004
Journal of Experimental Botany 2005 56(409):191-203; doi:10.1093/jxb/eri019
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RESEARCH PAPER |
Internal axial light conduction in the stems and roots of herbaceous plants
1Photodynamics Research Center, RIKEN (The Institute of Physical and Chemical Research), Sendai 980-0845, Japan
2Faculty of Science and Engineering, Ishinomaki-Senshu University, Ishinomaki 986-8580, Japan
* Present address and to whom correspondence should be sent: Department of Viticulture and Enology, College of Agricultural and Environmental Sciences, University of California, Davis, CA 95616, USA. Fax: +1 530 752 0384. E-mail: qiasun{at}ucdavis.edu
In order to reveal any roles played by stems and roots of herbaceous plants in responding to the surrounding light environment, the optical properties of the stem and root tissues of 18 herbaceous species were investigated. It was found that light was able to penetrate through to the interior of the stem and was then conducted towards the roots. Light conduction was carried out within the internodes and across the nodes of the stem, and then in the roots from the tap root to lateral roots. Light conduction in both the stem and root occurred in the vascular tissue, usually with fibres and vessels serving as the most efficient axial light conductors. The pith and cortex in many cases were also involved in axial light conduction. Investigation of the spectral properties of the conducted light made it clear that only the spectral region between 710 nm and 940 nm (i.e. far-red and near infra-red light) was the most efficiently conducted in both the stem and the root. It was also found that there were light gradients in the axial direction of the stem or root, and the light intensity generally exhibited a linear attenuation in accord with the distance of conduction. These results revealed that tissues of the stem and root are bathed in an internal light environment enriched in far-red light, which may be involved in phytochrome-mediated metabolic activities. Thus, it appears that light signals from above-ground directly contribute to the regulation of the growth and development of underground roots via an internal light-conducting system from the stem to the roots.
Key words: Axial light conduction, far-red light, herbaceous dicotyledons, light gradients, monocotyledons, optical properties of stem and root tissues, photomorphogenesis, phytochromes
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