Changes of enzyme activities related to oxidative stress in rice plants inoculated with random mutants of a Pseudomonas fluorescens strain able to improve plant fitness upon biotic and abiotic conditions

Abstract

The Pseudomonas fluorescens strain used in this work (Aur 6) has demonstrated its ability to improve fitness of different plant species upon biotic and abiotic stress conditions. Random mutants of this strain were constructed with the Tn5 transposon technology, and biological tests to evaluate loss of salt protection were conducted with all the mutants (104 mutants) on rice seedlings. Mutant 33 showed an evident reduction in its ability to protect plants upon salt stress challenge, whereas mutant 19 was more effective than the wild type. Enzymes related with oxidative stress were studied in both mutants and wild type. Enzyme activities were decreased with mutant 33 with regard to wild type, whereas mutant 19 did not produce important changes suggesting involvement of redox balance associated to the observed modifications in these antioxidant enzymes as one of the probable mechanisms used by these strains. Data of malondialdehyde (MDA) were consistent with this fact. Mutants also affected accumulation of proline, the most common osmolyte in plants. A second experiment to evaluate the ability of both mutants and wild type to stimulate growth on tomato plants was conducted, as this feature was previously demonstrated by wild type. Similar results were obtained in growth of both species, suggesting that mutations of both mutants are related with the capacities of the wild type to stimulate growth. To reveal mutated genes, both mutants were mapped. Three mutated genes were found in mutant 33. A gene related with a general secretion pathway protein D, a gene related with a putative two-component system sensor kinase (ColS), and a gene related with flagellar motor switch protein (FliG). In mutant 19, two mutated genes were found. One gene related with heavy metal efflux pump Czca family, and other gene of 16s rRNA.