Journal Article

Developmental Changes in Peanut Root Structure during Root Growth and Root-structure Modification by Nodulation

Ryosuke Tajima, Jun Abe, O. New Lee, Shigenori Morita and Alexander Lux

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 4, pages 491-499
Published in print March 2008 | ISSN: 0305-7364
Published online February 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm322
Developmental Changes in Peanut Root Structure during Root Growth and Root-structure Modification by Nodulation

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Basic information about the root and root nodule structure of leguminous crop plants is incomplete, with many aspects remaining unresolved. Peanut (Arachis hypogaea) forms root nodules in a unique process. Structures of various peanut root types were studied with emphasis on insufficiently characterized lateral roots, changes in roots during their ontogenesis and root modification by nodule formation.

Methods

Peanut plants were grown in the field, in vermiculite or in filter paper. The taproot, first-order and second-order lateral roots and root nodules were analysed using bright-field and fluorescence microscopy with hand sections and resin sections.

Key Results

Three root categories were recognized. The primary seminal root was thick, exhibiting early and intensive secondary thickening mainly on its base. It was tetrarch and contained broad pith. First-order lateral roots were long and thin, with limited secondary thickening; they contained no pith. Particularly different were second- and higher-order lateral roots, which were anatomically simple and thin, with little or no secondary growth. Unusual wall ingrowths were visible in the cells of the central part of the cortex in the first-order and second-order lateral roots. The nodule body was formed at the junction of the primary and lateral roots by the activity of proliferating cells derived originally from the pericycle.

Conclusions

Two morphologically and anatomically distinct types of lateral roots were recognized: long, first-order lateral roots, forming the skeleton of the root system, and thin and short second- and higher-order lateral roots, with an incomplete second state of endodermal development, which might be classified as peanut ‘feeder roots’. Formation of root nodules at the base of the lateral roots was the result of proliferating cell divisions derived originally from the pericycle.

Keywords: Endodermis; lateral root structure; nodule structure; peanut; Arachis hypogaea; primary root structure

Journal Article.  5702 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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