Microbial Consortium of PGPR, Rhizobia and Arbuscular Mycorrhizal Fungus Makes Pea Mutant SGECdt Comparable with Indian Mustard in Cadmium Tolerance and Accumulation.

Andrey A Belimov,Vladimir A Litvinskiy,Vladimir V Nosikov,Aleksey A Zavalin,Vera I Safronova,Tatiana S Azarova,Natalia M Makarova,Igor A Tikhonovich,Alexander I Shaposhnikov

doi:10.3390/plants9080975

Abstract

Cadmium (Cd) is one of the most widespread and toxic soil pollutants that inhibits plant growth and microbial activity. Polluted soils can be remediated using plants that either accumulate metals (phytoextraction) or convert them to biologically inaccessible forms (phytostabilization). The phytoremediation potential of a symbiotic system comprising the Cd-tolerant pea (Pisum sativum L.) mutant SGECdt and selected Cd-tolerant microorganisms, such as plant growth-promoting rhizobacterium Variovorax paradoxus 5C-2, nodule bacterium Rhizobium leguminosarum bv. viciae RCAM1066, and arbuscular mycorrhizal fungus Glomus sp. 1Fo, was evaluated in comparison with wild-type pea SGE and the Cd-accumulating plant Indian mustard (Brassica juncea L. Czern.) VIR263. Plants were grown in pots in sterilized uncontaminated or Cd-supplemented (15 mg Cd kg−1) soil and inoculated or not with the microbial consortium. Cadmium significantly inhibited growth of uninoculated and particularly inoculated SGE plants, but had no effect on SGECdt and decreased shoot biomass of B. juncea. Inoculation with the microbial consortium more than doubled pea biomass (both genotypes) irrespective of Cd contamination, but had little effect on B. juncea biomass. Cadmium decreased nodule number and acetylene reduction activity of SGE by 5.6 and 10.8 times, whereas this decrease in SGECdt was 2.1 and 2.8 times only, and the frequency of mycorrhizal structures decreased only in SGE roots. Inoculation decreased shoot Cd concentration and increased seed Cd concentration of both pea genotypes, but had little effect on Cd concentration of B. juncea. Inoculation also significantly increased concentration and/or accumulation of nutrients (Ca, Fe, K, Mg, Mn, N, P, S, and Zn) by Cd-treated pea plants, particularly by the SGECdt mutant. Shoot Cd concentration of SGECdt was twice that of SGE, and the inoculated SGECdt had approximately similar Cd accumulation capacity as compared with B. juncea. Thus, plant–microbe systems based on Cd-tolerant micro-symbionts and plant genotypes offer considerable opportunities to increase plant HM tolerance and accumulation.

Highlights

Most of the commonly known plants recommended for phytoremediation of heavy metal (HM)polluted soils belong to the family Brassicaceae, because of their relatively high metal tolerance and Plants 2020, 9, 975; doi:10.3390/plants9080975 www.mdpi.com/journal/plantsPlants 2020, 9, 975 accumulation [1,2,3]
Inoculation with the microbial consortium significantly increased biomass of both pea genotypes, but of the SGECdt mutant grown in Cd-supplemented soil, suggesting establishment of efficient symbiotic interactions under stressful conditions
Comparing that report with the present results indicates that the components of the microbial consortium used here could have the opposite effects on plant Cd accumulation, and most likely that strain Glomus sp. 1Fo affected the decrease in shoot Cd concentration

Summary

Introduction

Most of the commonly known plants recommended for phytoremediation of heavy metal (HM)polluted soils belong to the family Brassicaceae, because of their relatively high metal tolerance and Plants 2020, 9, 975; doi:10.3390/plants9080975 www.mdpi.com/journal/plantsPlants 2020, 9, 975 accumulation [1,2,3]. Coss) have lower HM tolerance than hyperaccumulators but produce more biomass and extract more HMs. HM-hyperaccumulating species (e.g., Thlaspi caerulescens J.Presl & C.Presl) are very HM-tolerant, their low growth rate and biomass limit their utility for phytoremediation of new sites. HM-hyperaccumulating species (e.g., Thlaspi caerulescens J.Presl & C.Presl) are very HM-tolerant, their low growth rate and biomass limit their utility for phytoremediation of new sites This has stimulated the search for suitable plants of other families, including legumes (family Fabaceae), which grow rapidly to produce high biomass but are characterized by relatively low tolerance to HMs [4,5] and translocation of HMs from roots to shoots [6,7]. An advanced symbiotic potential of legumes helps improve soil fertility, biodiversity and activity of soil biota, soil genesis and maintains and restores healthy ecosystems

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