biologia plantarum

Biologia plantarum 66:228-239, 2022 | DOI: 10.32615/bp.2022.025

Modulation of tomato root architecture and root hair traitsby Pseudomonas brassicacearum and Variovorax paradoxus containing 1-aminocyclopropane-1-carboxylate deaminase

A.A. BELIMOV^{1, *}, P.S. ULIANICH¹, D.S. SYROVA¹, A.I. SHAPOSHNIKOV¹, V.I. SAFRONOVA¹, I.C. DODD²

¹ All-Russia Research Institute for Agricultural Microbiology, Podbelskogo sh. 3, Pushkin, 196608 Saint-Petersburg, Russia

² Lancaster Environmental Centre, University of Lancaster, Lancaster, LA1 4YQ, UK

By decreasing root 1-aminocyclopropane-1-carboxylate (ACC) content and plant ethylene production, the microbial enzyme ACC deaminase is a widespread beneficial trait of plant growth-promoting rhizobacteria (PGPR), ameliorating ethylene-mediated root growth inhibition. However, relatively little is known about whether bacterial ACC deaminase modulates root architecture and root hair traits. Thus the dwarf tomato (Solanum lycopersicum) cultivar Micro-Tom was inoculated in vitro with Pseudomonas brassicacearum Am3, its ACC deaminase deficient mutant T8-1, a known PGPR strain Variovorax paradoxus 5C-2 or chemically treated with agents that promoted or inhibited ethylene production or sensitivity (Ag⁺, Co²⁺, and ACC). ACC treatment reduced both root elongation and the number of lateral roots, while ethylene inhibitors (Ag⁺, Co²⁺) and V. paradoxus 5C-2 promoted primary root elongation, but differentially affected lateral root length and number. Ag⁺ stimulated lateral root development, while Co²⁺ and V. paradoxus 5C-2 did not. Inoculation with P. brassicacearum Am3 and T8-1 inhibited elongation of the primary and lateral roots at a high inoculum concentration (10⁶ cells cm³). All bacterial strains significantly increased the length and number of root hairs, with these effects more pronounced in P. brassicacearum Am3 than in the mutant T8-1. Treatment with Ag⁺ inhibited root hair formation and elongation, while Co²⁺ had the opposite effects. ACC treatment had no effect on root hair elongation but increased root hair density. While root growth inhibition caused by P. brassicacearum Am3 was independent of ACC deaminase, the promotion of root hair elongation and density by this strain was augmented by ACC deaminase activity. Thus ACC deaminase can modulate the morphological impacts of bacteria on root hair response by affecting plant ethylene content.

Keywords: ACC deaminase, cobalt, ethylene, plant growth-promoting rhizobacteria, Pseudomonas brassicacearum, rhizosphere, silver, tomato, Variovorax paradoxus.

Received: November 11, 2021; Revised: April 15, 2022; Accepted: May 24, 2022; Published online: September 17, 2022  Show citation