Lotus corniculatus-rhizobia symbiosis under Ni, Co and Cr stress on ultramafic soil

Marzena Sujkowska-Rybkowska,Dorota Kasowska,Tomasz Stępkowski,Krzysztof Gediga,Joanna Banasiewicz

doi:10.1007/s11104-020-04546-9

Marzena Sujkowska-Rybkowska, Dorota Kasowska + Show 3 more

Open Access

https://doi.org/10.1007/s11104-020-04546-9

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Abstract

AimsUltramafic/serpentine soils constitute a stressful environment with many plant growth constrains such as a lack of macronutrients and high levels of potentially toxic metals. We considered the adaptive strategy of Lotus corniculatus L.-rhizobia symbiosis to Ni, Co and Cr stress conditions.MethodsL. corniculatus nodulating rhizobia from ultramafic soil were isolated, identified and tested for nitrogen fixation, metal tolerance and plant growth promoting abilities. The structural and immunocytochemical analyses of root nodules were also performed.ResultsThe isolates effective in nitrogen fixation were identified as Rhizobium and Mesorhizobium tolerant to Ni, Co, and Cr. Some strains directly promoted root growth of L. corniculatus and non-legume Arabidopsis thaliana under metal stress. The metal treated nodules showed structural alternations, i.e. enhanced accumulation of phenols and wall thickening with higher cellulose, hemicellulose, pectins, glycoproteins and callose content.ConclusionsOur results revealed that metal tolerant, growth promoting rhizobacteria inhabiting L. corniculatus root nodules may improve plant growth in the ultramafic environment. Accumulation of phenols and reorganization of nodule apoplast can counteract harmful effects of Ni, Co and Cr on the symbiosis. These findings imply that L. corniculatus-rhizobia symbiosis is an important element of plant adaptation to metal stress occurring on the ultramafic soils.

Highlights

Ultramafic soils originate from weathered ultramafic rocks such as peridotite and/or serpentinite
Our results revealed that metal tolerant, growth promoting rhizobacteria inhabiting L. corniculatus root nodules may improve plant growth in the ultramafic environment
Accumulation of phenols and reorganization of nodule apoplast can counteract harmful effects of Ni, Co and Cr on the symbiosis. These findings imply that L. corniculatus-rhizobia symbiosis is an important element of plant adaptation to metal stress occurring on the ultramafic soils

Summary

Introduction

Ultramafic soils originate from weathered ultramafic rocks such as peridotite and/or serpentinite. Peridotite consists mostly of olivine and pyroxene, whereas serpentinite, formed from peridotite as a result of low-temperature hydratation, is composed mostly of serpentine group minerals (Coleman 1971; Evans et al 2013) This various mineralogy of the parent rocks is responsible for differentiation of certain ultramafic soil features such as their morphology and mobility of some elements (Alexander 2004; Kierczak et al 2016). Chemical properties such as low availability of calcium in relation to magnesium, deficiency of essential macronutrients (N, P and K) and high levels of potentially toxic metals, mostly Ni, Cr and Co, are especially stressful for plants and most markedly affect the serpentine flora (Brady et al 2005; Kazakou et al 2008). Ni is required for urea metabolism (Gerendás et al 1999), but at elevated levels (> 10 mg kg-1) it causes growth inhibition, chlorosis, necrosis and wilting in non-tolerant plants by impairing a large variety of physiological processes or conditions (e.g., photosynthesis, respiration, water relations, chlorophyll and protein content, metal homeostasis as well as activity of H+-ATPase, and nitrate and glutathione reductase) (Ahmad and Ashraf 2011; Yusuf et al 2011; Bhalerao et al 2015)

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