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

Abstract

Aims Ultramafic/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. Methods L. 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. Results The 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. Conclusions 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.

Glycyrrhiza uralensis Nodules: Histological and Ultrastructural Organization and Tubulin Cytoskeleton Dynamics

“…Another interesting feature of G. uralensis nodules is the presence of numerous drop-shaped inclusions in the vacuoles of meristematic and uninfected cells. Similar osmiophilic inclusions have been found in Lotus pedunculatus inoculated with the fast-growing rhizobia strain NZP2037 [64] and in L. corniculatus when exposed to heavy metals (nickel, cobalt, and chromium) [65]. Electron-dense osmiophilic deposits identified as flavolans [64] or phenolic compounds [65] were also present in the vacuoles of the outer cortical and epidermal cells, but not in the infected nodule cells.…”

Microbial Sensing and Removal of Heavy Metals: Bioelectrochemical Detection and Removal of Chromium(VI) and Cadmium(II)

“…is one of the major elements for the maintenance of soil fertility where it has the ability to fix nitrogen in leguminous plants [ 19 , 20 , 21 ]. Symbiotic nitrogen fixation is sensitive to heavy metals in soil [ 22 ]. Rhizobium can be used as an indicator organism to several toxic chemicals, including heavy metals [ 23 ] and for effective, economical and eco-friendly metal bioremediation technologies [ 24 ] whereas Sinorhizobium meliloti has high tolerance ability for various heavy metals [ 25 ].…”

The Fungicide Tetramethylthiuram Disulfide Negatively Affects Plant Cell Walls, Infection Thread Walls, and Symbiosomes in Pea (Pisum sativum L.) Symbiotic Nodules

“…The thickening of cell walls has been described as a response to the action of heavy metals on plants [66][67][68] and on symbiotic nodules in particular [69]. The thickening of the walls can inhibit the penetration of infection threads into nodules and prevent the release of rhizobia from infection threads and droplets [70].…”

“…Elevated contents of phenolic compounds have been reported in several plant species under stress, including wheat under nickel stress [78], corn under aluminum stress [79], faba beans under cadmium stress, and Phyllanthus tenellus under copper stress [78]. In Lotus corniculatus L. growing on ultramafic soils contaminated with nickel, cobalt, and chromium, vacuoles in the nodule endoderm and some cortical and parenchymal cells were filled with dark phenolic substances [69]. Induction of the synthesis of phenolic compounds in nodules of M. sativa plants was observed in the presence of arsenic [80].…”