Developmental changes in peanut root structure during root growth and root-structure modification by nodulation |
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Authors: | Tajima Ryosuke Abe Jun Lee O New Morita Shigenori Lux Alexander |
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Affiliation: | 1Field Production Science Center, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Nishi-tokyo, Tokyo 188-0002, Japan;2AE-Bio, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan;3Department of Plant Physiology, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynská dolina B-2, SK-842 15 Bratislava, Slovak Republic |
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Abstract: | Background and AimsBasic 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.MethodsPeanut 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 ResultsThree 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.ConclusionsTwo 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.Key words: Endodermis, lateral root structure, nodule structure, peanut, Arachis hypogaea, primary root structure |
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