Efficacy of a Plant-Microbe System: Pisum sativum (L.) Cadmium-Tolerant Mutant and Rhizobium leguminosarum Strains, Expressing Pea Metallothionein Genes PsMT1 and PsMT2, for Cadmium Phytoremediation

Abstract

Two transgenic strains of Rhizobium leguminosarum bv. viciae, 3841-PsMT1 and 3841-PsMT2, were obtained. These strains contain the genetic constructions nifH-PsMT1 and nifH-PsMT2 coding for two pea (Pisum sativum L.) metallothionein genes, PsMT1 and PsMT2, fused with the promoter region of the nifH gene. The ability of both transgenic strains to form nodules on roots of the pea wild-type SGE and the mutant SGECd t , which is characterized by increased tolerance to and accumulation of cadmium (Cd) in plants, was analyzed. Without Cd treatment, the wild type and mutant SGECd t inoculated with R. leguminosarum strains 3841, 3841-PsMT1, or 3841-PsMT2 were similar histologically and in their ultrastructural organization of nodules. Nodules of wild-type SGE inoculated with strain 3841 and exposed to 0.5 μM CdCl 2 were characterized by an enlarged senescence zone. It was in stark contrast to Cd-treated nodules of the mutant SGECd t that maintained their proper organization. Cadmium treatment of either wild-type SGE or mutant SGECd t did not cause significant alterations in histological organization of nodules formed by strains 3841-PsMT1 and 3841-PsMT2. Although some abnormalities were observed at the ultrastructural level, they were less pronounced in the nodules of strain 3841-PsMT1 than in those formed by 3841-PsMT2. Both transgenic strains also differed in their effects on pea plant growth and the Cd and nutrient contents in shoots. In our opinion, combination of Cd-tolerant mutant SGECd t and the strains 3841-PsMT1 or 3841-PsMT2 may be used as an original model for study of Cd tolerance mechanisms in legume-rhizobial symbiosis and possibilities for its application in phytoremediation or phytostabilization technologies.

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

“…In the present study, the fusion of symbiosomes and degeneration of bacteroids within them led to the formation of "ghost" bacteroids in the TMTD-sensitive cultivar 'Finale' (Figure 12A,B). Similarly, symbiosome fusion and the formation of multiple symbiosomes were found to occur in response to copper exposure in M. lupulina nodules [70,90] and cadmium exposure in pea nodules [49,50]. In the present study, we observed the accumulation of PHB in the symbiosomes in bacteroids, bacteroid contraction, an increase in the peribacteroid space, and destruction of symbiosome membranes as a result of lipid peroxidation.…”

“…Polyhydroxybutyrate protects cells from diverse stresses, including heat shock, ultraviolet radiation, oxidizing agents, and osmotic shock [84]. Previously, we observed accumulation of PHB in bacteroids in response to cadmium exposure [49,50].…”

“…A senescence zone formed in the nodules of the TMTD-sensitive genotype ( Figure 6C). Other studies found that the initiation of premature senescence of pea nodules occurred in darkness and after treatment with exogenous nitrates [48] and cadmium [49,50].…”

Molecular Biology in the Improvement of Biological Nitrogen Fixation by Rhizobia and Extending the Scope to Cereals

“…Two recombinant strains of R. leguminosarum bv. Viciae , each expressing a pea metallothionein gene, PsMT1 or PsMT2 , led to normal development of nodules in pea under Cd stress [ 35 ]. Because the heavy metals cause oxidative stress [ 136 ], the other strategies could be based on maintaining the homeostasis of metals through different mechanisms [ 133 ].…”

Symbiotic Regulatory Genes Controlling Nodule Development in Pisum sativum L.

“…The mutant SGECd t is characterized by an increased tolerance to cadmium and elevated cadmium accumulation [ 184 ]. The mutant demonstrates a higher tolerance to cadmium, both in terms of nodulation [ 185 , 186 ] and the functioning of established nodules [ 187 ].…”