JXB Advance Access originally published online on January 30, 2004
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Journal of Experimental Botany, Vol. 55, No. 397, pp. 685-693, March 1, 2004
© 2004 Oxford University Press
Regulation of Growth, Development and Whole Organism Physiology |
Developmental anatomy and auxin response of lateral root formation in Ceratopteris richardii
Received 29 July 2003; Accepted 14 November 2003
1 Plant Biology Division, The Samuel Roberts Noble Foundation Inc., 2510 Sam Noble Parkway, Ardmore, OK 73401, USA
2 Department of Biological Sciences, Idaho State University, Pocatello, ID 83209, USA
* To whom correspondence should be addressed. Fax: +1 580 224 6692. E-mail: eblancaflor{at}noble.org
The homosporous fern Ceratopteris richardii exhibits a homorhizic root system where roots originate from the shoot system. These shoot-borne roots form lateral roots (LRs) that arise from the endodermis adjacent to the xylem poles, which is in contrast to flowering plants where LR formation arises from cell division in the pericycle. A detailed study of the fifth shoot-borne root showed that one lateral root mother cell (LRMC) develops in each two out of three successive merophytes. As a result, LRs emerge alternately in two ranks from opposite positions on a parent root. From LRMC initiation to LR emergence, three developmental stages were identified based on anatomical criteria. The addition of auxins (either indole-3-acetic acid or indole-3-butyric acid) to the growth media did not induce additional LR formation, but exogenous applications of both auxins inhibited parent root growth rate. Application of the polar auxin-transport inhibitor N-(1-naphthyl)phthalamic acid (NPA) also inhibited parent root growth without changing the LR initiation pattern. The results suggest that LR formation does not depend on root growth rate per se. The result that exogenous auxins do not promote LR formation in C. richardii is similar to reports for certain species of flowering plants, in which there is an acropetal LR population and the formation of the LRs is insensitive to the application of auxins. It also may indicate that different mechanisms control LR development in non-seed vascular plants compared with angiosperms, taking into consideration the long and independent evolutionary history of the two groups.
Key words: Auxin, Ceratopteris, development, fern, lateral root.
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