Structural and functional study in the rhizosphere of Oryza sativa L. plants growing under biotic and abiotic stress

Abstract

Aims: A structural and functional study has been carried out in the rice production area of the Guadalquivir marshes in southern Spain aiming to increase knowledge of rice rhizosphere structure and function for further application on integrated management practices. Methods and Results: Rhizosphere bacterial structure (analysis of 16S rRNA partial sequences from total soil DNA), metabolic diversity (analysed by Biolog FF for fungal community and GN for microbial community) and a screening for putative plant growth-promoting rhizobacteria (PGPR) to identify potential isolates for development of local biofertilizers, and biodiversity of culturable micro-organisms (analysis of 16S rRNA partial sequences) from four areas differing in salinity and Magnaporthe oryzae incidence in two moments of the crop cycle were studied. Results indicate that the dominant taxon in libraries from the four areas was Proteobacteria. Metabolic diversity was higher in areas affected only by salinity or incidence of Magnaporthe than in the control or area affected by both stresses. It seems that rice plants selected, in their rhizosphere, micro-organisms able to affect plant hormonal balance under all conditions, and this activity relied in different bacterial genera depending on the environmental stress. Conclusions: Bacterial genera for each stress, as well as generalist strains, were found present in all the studied areas. Potential molecular markers and taxonomic markers (Sphingobacteria for salt and Thermococci for Magnaporthe) of the different stress situations have been highlighted, and Class

Effects of cultivation of OsrHSA transgenic rice on functional diversity of microbial communities in the soil rhizosphere

“…Numerous studies have been carried out to investigate the effects of transgenic crops on soil microbial communities [1][2][3]. Most results indicate that transgenic Bt crops have not caused significant effects on soil microbes compared to conventional crops [4][5][6][7][8][9][10].…”

Deciphering the factors associated with the colonization of rice plants by cyanobacteria

“…Most of the earlier studies on defense enzymes have focused on plant‐pathogen interactions , and its role in growth promotion is less investigated . The positive correlation of PAL activity with fresh weight, dry weight, and PPO with fresh weight and ARA in the present study reveals the positive role of colonization on eliciting of defense enzyme activity, even in the absence of pathogen elicitor such as phytopathogenic fungus/bacterium.…”

“…The plant endo β‐1,4‐endoglucanases have been implicated in cell wall degradation, but they can also play a significant role in cellulose biosynthesis, wall loosening during cell elongation, and in the modification of other cell wall polysaccharides. Therefore, they can be detected during normal growth and development, and also in growing roots and shoots, and during leaf abscission and grain germination or under drought stress . The high correlation between CMCase activity and chlorophyll accumulation in roots and shoots, and dry weight/fresh weight illustrates the direct role of this enzyme in promoting the proliferation and colonization of cyanobacteria in the plant tissues.…”

“…One of the predicted routes of bacterial penetration into plant tissues, besides mechanical/physical modes, is the secretion of an extensive repertoire of glycoside hydrolases, lyases, and esterases which can target the numerous linkages, as a means of cell wall degradation, especially in pathogens . Inoculation of plants with microorganisms elicits enhanced response levels of antioxidant machinery, PR proteins or defense enzymes or volatiles , which serve to protect the plant from salinity or pathogens and pests. Mechanical signals and extracellular cell wall degrading enzymes are also being increasingly investigated as elicitors of infection process by non‐pathogenic organisms, especially endophytes .…”

“…Lucas et al . illustrated the significance of chlorophyll as an index of resistance induced in plants, in response to non‐pathogenic or pathogenic attack.…”