by Paolo Di Mascio
Historically, it was thought that plants derived all nitrogen (N) nutrition from the inorganic forms of N, NO3– and NH4+. However, it is now known that the principal form of N entering soils that do not receive inorganic fertilizer is organic N derived from microbial breakdown of organic matter, including amino acids, di and tri-peptides, DNA and proteins. Plants form symbiotic associations with endophytic bacteria within tissues of leaves, stems, and roots. It is unclear whether or how plants obtain nitrogen from these endophytic bacteria. One possible mechanism for N transfer to host is that plants may scavenge organic nitrogen by oxidation and degradation of endophytic bacteria or their proteins using reactive oxygen species to lyse cells and denature proteins. This mechanism has been termed ‘oxidative nitrogen scavenging’.
The experiments reported in this work were done to evaluate whether 15N incorporated into bacterial endophyte biomolecules such as proteins and nucleic acids could be traced into plant molecules and whether the transfer process involves evidence of oxidative degradation of microbes. Agave tequilana and its seed-transmitted endophyte [15N]-labeled bacteria Bacillus tequilensis were employed to elucidate incorporation of organic [15N]-labeled nitrogen to plants. Incorporation of 15N into tryptophan, deoxynucleosides and pheophytin derived from chlorophyll a were traced. Probes for hydrogen peroxide show its presence during degradation of bacteria in plant tissues, supporting involvement of reactive oxygen in the degradation process. Endophytic bacteria potentially transfer more nitrogen to plants and stimulate greater biomass in plants than heat-killed bacteria that do not colonize plants but instead degrade in the soil. Findings presented here support the hypothesis that some plants under nutrient limitation may degrade and obtain nitrogen from endophytic microbes.
M. J. Beltran-Garcia, J. F. White Jr., F. M. Prado, K. R. Prieto, L. F. Yamaguchi, M. S. Torres, M. J. Kato, M. H. G. Medeiros, P. Di Mascio.
Nitrogen acquisition in Agave tequilana from degradation of endophytic bacteria.
Scientific Reports, 4: 6938, 2014. | http://dx.doi.org/10.1038/srep06938
Paolo Di Mascio, PhD.
Professor at Department of Biochemistry,
Institute of Chemistry, University of São Paulo, Brazil