HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: ajb.0800083v1 95/11/1337    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Fisher, J. B. PubMed Articles by Fisher, J. B. Agricola Articles by Fisher, J. B.

Anatomy of axis contraction in seedlings from a fire prone habitat¹

Fairchild Tropical Botanic Garden 11935 Old Cutler Road, Coral Gables, Florida 33156 USA

ABSTRACT

The hypocotyls or roots of many seed plants contract during seedling growth. Anatomical evidence is here reported for the first time that G-fibers (gelatinous or tension wood fibers) may cause contraction of roots and hypocotyls in dicotyledonous seedlings long after germination. To document repositioning of seedling buds, selected perennials (20 dicotyledons and one cycad) native to the fire-prone pine rocklands of subtropical South Florida were germinated and measured for 4–5 mo. The height of cotyledonary nodes above the soil decreased because of axis contraction or bending in eight species. Anatomy suggested that two mechanisms operate: (1) previously well-documented collapse of parenchyma cells in two species (Convolvulaceae and Zamiaceae) and (2) newly documented production of G-fibers in six species (all Fabaceae). Contraction or bending of the hypocotyl and/or taproot moved the cotyledonary and later buds of the seedling closer to the soil surface or buried them. Bud repositioning by these mechanisms may protect the lateral buds from injury by fire or other environmental stresses and allow resprouting.

Key Words: contractile root • fire adaptation • gelatinous fiber • hypocotyl • reaction wood • seedling • tension wood

Received for publication 29 February 2008. Accepted for publication 14 August 2008.

FOOTNOTES

¹ Thanks to D. Walters for germinating seeds; J. Geiger for Ipomoea seeds; Jay Horn for advice on imaging; M. Litzinger for help with German translation; Barry Tomlinson, Joyce Maschinski, Cynthia Jones, and two anonymous reviewers for comments on the manuscript; and G. D. Gann, J. R. Snyder and J. O’Brien for sharing their unpublished field observations. Research was supported in part by Florida Department of Agriculture and Consumer Services, Division of Plant Industry contract 012863 to J. Maschinski.

² Author for correspondence (e-mail: jfisher{at}fairchildgarden.org)