Bacteria-zinc co-localization implicates enhanced synthesis of cysteine-rich peptides in zinc detoxification when Brassica juncea is inoculated with Rhizobium leguminosarum.
Some plant growth promoting bacteria (PGPB) are enigmatic in enhancing plant growth in the face of increased metal accumulation in plants. Since most PGPB colonize the plant root epidermis, we hypothesized that PGPB confer tolerance to metals through changes in speciation at the root epidermis. We employed a novel combination of fluorophore-based confocal laser scanning microscopic imaging and synchrotron based microscopic X-ray fluorescence mapping with X-ray absorption spectroscopy to characterize bacterial localization, zinc (Zn) distribution and speciation in the roots of Brassica juncea grown in Zn contaminated media (400 mg kg(-1) Zn) with the endophytic Pseudomonas brassicacearum and rhizospheric Rhizobium leguminosarum. PGPB enhanced epidermal Zn sequestration relative to PGBP-free controls while the extent of endophytic accumulation depended on the colonization mode of each PGBP. Increased root accumulation of Zn and increased tolerance to Zn was associated predominantly with R. leguminosarum and was likely due to the coordination of Zn with cysteine-rich peptides in the root endodermis, suggesting enhanced synthesis of phytochelatins or glutathione. Our mechanistic model of enhanced Zn accumulation and detoxification in plants inoculated with R. leguminosarum has particular relevance to PGPB enhanced phytoremediation of soils contaminated through mining and oxidation of sulphur-bearing Zn minerals or engineered nanomaterials such as ZnS.
School of GeoSciences, The University of Edinburgh, Edinburgh, EH9 3JW, UK.
Gbotemi A
GA
Adediran
School of GeoSciences, The University of Edinburgh, Edinburgh, EH9 3JW, UK.
Bryne T
BT
Ngwenya
Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK.
J Frederick W
JF
Mosselmans
School of GeoSciences, The University of Edinburgh, Edinburgh, EH9 3JW, UK.
Kate V
KV
Heal
D001673:Biodegradation, Environmental; D003545:Cysteine / Q000378:metabolism; D009149:Mustard Plant / Q000378:metabolism / Q000382:microbiology*; D010455:Peptides / Q000378:metabolism*; D019441:Plant Epidermis; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D011549:Pseudomonas / Q000502:physiology*; D016961:Rhizobium leguminosarum / Q000502:physiology*; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology; D056928:X-Ray Absorption Spectroscopy; D015032:Zinc / Q000378:metabolism*
D010455:Peptides; D012987:Soil; D015032:Zinc; D003545:Cysteine
Brassica juncea; X-ray absorption spectroscopy; Zn detoxification; Zn speciation; bacterial localization; cysteine; plant growth promoting bacteria; zinc (Zn) accumulation