Nitrogen acquisition in Agave tequilana from degradation of endophytic bacteria

Abstract

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. Here we present evidence showing nitrogen flow from endophytic bacteria to plants in a process that appears to involve oxidative degradation of bacteria. In our experiments we employed Agave tequilana and its seed-transmitted endophyte Bacillus tequilensis to elucidate organic nitrogen transfer from 15N-labeled bacteria to plants. Bacillus tequilensis cells grown in a minimal medium with 15NH4Cl as the nitrogen source were watered onto plants growing in sand. We traced incorporation of 15N into tryptophan, deoxynucleosides and pheophytin derived from chlorophyll a. Probes for hydrogen peroxide show its presence during degradation of bacteria in plant tissues, supporting involvement of reactive oxygen in the degradation process. In another experiment to assess nitrogen absorbed as a result of endophytic colonization of plants we demonstrated that 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.

Review: Endophytic microbes and their potential applications in crop management

“…In one experiment it was found that grass plants obtained approximately 30% of nitrogen from rhizophagy . Gene responses of plants infected with endophytes often show that plant antioxidants and nitrate transporters are among genes upregulated in plants . These upregulated genes may be the result of increased oxidative reactions in roots and increased liberation of nitrates resulting from protein degradation.…”

“…Add to this, the general and prevalent assumption that most microbes on plants are pathogenic or have negligible effects has contributed to lack of efforts to understand the roles of endophytes in plant growth promotion and plant health improvement. Over the past few decades the gradual development of a body of research that demonstrated that endophytes are common in plants and positively affect plant development and health represents an important advancement in understanding the importance and functionality of endophytes . Recently, the exploration for useful endophytes and other microbes for agricultural applications has been enhanced by emergence of companies that have as their primary focus development and marketing of plant biostimulants (including endophytes) .…”

“…3,4 Other endophytes may be recruited from the soil but similarly benefit plants. 4 Endophytic microbes are important components of plants, and they function in the following ways: (i) increase nutrients acquired by plants, [5][6][7][8] (ii) defend plants from pathogens and insects, [9][10][11] (iii) increase stress tolerance in plants, 12,13 (iv) modulate plant development, [13][14][15] and (v) suppress weed growth. 16 The particular mechanisms by which endophytic microbes fill the various functions in plants likely differ depending on the microbe and plant.…”

“…[24][25][26] Gene responses of plants infected with endophytes often show that plant antioxidants and nitrate transporters are among genes upregulated in plants. 7,8,13 These upregulated genes may be the result of increased oxidative reactions in roots and increased liberation of nitrates resulting from protein degradation. Another experiment involving tomato seedlings employed elevated carbon dioxide to suppress superoxide formation and extraction of nutrients from microbes; here rhizophagy cycle suppression resulted in reduced absorption into seedlings of potassium, calcium and sulfur (J.…”

Effects of strategic tillage and plant hormone treatments on wheat-associated microbial communities

“…It was recently found that endophytic bacteria can be directly digested by plant cells to be used as a nitrogen (N) source (Beltran- Garcia et al, 2014). Endophytic bacteria can also protect plants from a series of abiotic stresses, such as drought (Rolli et al, 2015;Sheibani-Tezerji et al, 2015), low temperature (Su et al, 2015;Subramanian et al, 2015), and salinity (Ali et al, 2014).…”