Autoregulation of root nodule formation: Signals of both symbiotic partners studied in a split-root system of Vicia sativa subsp. nigra

• Published in: Molecular plant-microbe interactions Vol. 15; no. 4; pp. 341 - 349
• Main Authors: VAN BRUSSEL, Anton A. N, TAK, Teun, BOOT, Kees J. M, KIJNE, Jan W
• Format: Journal Article
• Language: English
• Published: St Paul, MN APS Press 01.04.2002; The American Phytopathological Society
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Culture Media - pharmacology; Cytokinins - pharmacology; Economic plant physiology; Fabaceae - drug effects; Fabaceae - microbiology; Fabaceae - physiology; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; legume; Lipopolysaccharides - pharmacology; Nod factor; Parasitism and symbiosis; Plant Growth Regulators - pharmacology; Plant physiology and development; Plant Roots - drug effects; Plant Roots - growth & development; Plant Roots - microbiology; Rhizobium leguminosarum; Rhizobium leguminosarum - growth & development; Rhizobium leguminosarum - metabolism; Signal Transduction - physiology; supernodulation; Symbiosis; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Symbiosis - drug effects; Symbiosis - physiology; Time Factors; vetch; Vicia sativa; zeatin; Zeatin - pharmacology; Acidification; Plant nodule; Signal transduction; Regulation(control); Dicotyledones; Angiospermae; Nitrogen fixation; Bacteria; Plant growth substance; Adenine derivatives; Symbiosis; Symbionte; Symbiotic relation; Root; Nodulation; Source sink relationship; Cytokinin; Infection; Nod factor; Leguminosae; Self regulation; Vicia angustifolia; Spermatophyta; Phytohormone; Fodder crop; Rhizobiaceae; Colonization
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/mpmi.2002.15.4.341

Inhibition of root nodule formation on leguminous plants by already induced or existing root nodules is called autoregulation of root nodule formation (AUT). Optimal conditions for AUT were determined using a split-root technique newly developed for Vicia sativa subsp. nigra. Infection of a root A with nodulating Rhizobium leguminosarum bv. viciae bacteria systemically inhibited nodulation of a spatially separated root B inoculated 2 days later with the same bacteria. This treatment gives complete AUT (total absence of nodules on root B). Only partial AUT of root B was obtained by incubation of root A with mitogenic nodulation (Nod) factors or with a noninfective strain producing normal mitogenic Nod factors. Nonmitogenic Nod factors did not evoke AUT. We identified two systemic plant signals induced by Rhizobium bacteria. Signal 1 (at weak buffering) was correlated with sink formation in root A and induced acidification of B-root medium. This signal is induced by treatment of root A with (i) nodulating rhizobia, (ii) mitogenic Nod factors, (iii) nonmitogenic Nod factors, or (iv) the cytokinin zeatin. Signal 2 (at strong buffering) could only be evoked by treatment with nodulating rhizobia or with mitogenic Nod factors. Most probably, this signal represents the specific AUT signal. Induction of complete AUT appears to require actively dividing nodule cells in nodule primordia, nodule meristems, or both of root A.