Inoculation and nitrate alter phytohormone levels in soybean roots: differences between a supernodulating mutant and the wild type

• Published in: Planta 2000-06, Vol.211 (1), p.98-104
• Main Authors: Caba, Juan M., Centeno, M. Luz, Fernández, Belén, Gresshoff, Peter M., Ligero, Francisco
• Format: Article
• Language: English
• Subjects: Abscisic Acid - physiology; Agronomy. Soil science and plant productions; Auxins; Biological and medical sciences; Cytokinins; Cytokinins - physiology; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Genotype; Genotypes; Glycine max - genetics; Glycine max - physiology; Indoleacetic Acids - metabolism; Inoculation; Mutation - genetics; Nitrates - physiology; Nodulation; Nodules; Parasitism and symbiosis; Plant growth regulators; Plant Growth Regulators - physiology; Plant physiology and development; Plant roots; Plant Roots - genetics; Plant Roots - physiology; Plants; Soybeans; Symbiosis; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...)
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s004250000265

The levels of different cytokinins, indole-3-acetic acid (IAA) and abscisic acid (ABA) in roots of Glycine max [L.] Merr. cv. Bragg and its supernodulating mutant nts382 were compared for the first time. Forty-eight hours after inoculation with Bradyrhizobium, quantitative and qualitative differences were found in the root's endogenous hormone status between cultivar Bragg and the mutant nts382. The six quantified cytokinins, ranking similarly in each genotype, were present at higher concentrations (30—196% on average for isopentenyl adenosine and dihydrozeatin riboside, respectively) in mutant roots. By contrast, the ABA content was 2-fold higher in Bragg, while the basal levels of IAA [0.53 μmol (g DW)-1, on average] were similar in both genotypes. In 1 mM $\mathrm{N}{\mathrm{O}}_{3}^{-}$-fed Bragg roots 48 h post-inoculation, IAA, ABA and the cytokinins isopentenyl adenine, and isopentenyl adenosine quantitatively increased with respect to uninoculated controls. However, only the two cytokinins increased in the mutant. High $\mathrm{N}{\mathrm{O}}_{3}^{-}$ (8 mM) markedly reduced root auxin concentration, and neither genotypic differences nor the inoculation-induced increase in auxin concentration in Bragg was observed under these conditions. Cytokinins and ABA, on the other hand, were little affected by 8 mM $\mathrm{N}{\mathrm{O}}_{3}^{-}$. Root IAA/cytokinin and ABA/cytokinin ratios were always higher in Bragg relative to the mutant, and responded to inoculation (mainly in Bragg) and nitrate (both genotypes). The overall results are consistent with the auxin-burst-control hypothesis for the explanation of autoregulation and supernodulation in soybean. However, they are still inconclusive with respect to the inhibitory effect of $\mathrm{N}{\mathrm{O}}_{3}^{-}$.