Limits...
A proposed mechanism for nitrogen acquisition by grass seedlings through oxidation of symbiotic bacteria.

White JF, Crawford H, Torres MS, Mattera R, Irizarry I, Bergen M - Symbiosis (2012)

Bottom Line: Experiments on this proposed mechanism employ tall fescue (Festuca arundinaceae) seedlings to elucidate features of the oxidative mechanism.We also made surveys of the seedlings of several grass species to assess the distribution of the phenomenon of microbial oxidation in the Poaceae.Hydrogen peroxide secretion from seedling roots and bacterial oxidation was observed in several species in subfamily Pooideae where seeds possessed adherent paleas and lemmas, but was not seen in grasses that lacked this feature or long-cultivated crop species.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ USA.

ABSTRACT
In this paper we propose and provide evidence for a mechanism, oxidative nitrogen scavenging (ONS), whereby seedlings of some grass species may extract nitrogen from symbiotic diazotrophic bacteria through oxidation by plant-secreted reactive oxygen species (ROS). Experiments on this proposed mechanism employ tall fescue (Festuca arundinaceae) seedlings to elucidate features of the oxidative mechanism. We employed 15N(2) gas assimilation experiments to demonstrate nitrogen fixation, direct microscopic visualization of bacteria on seedling surfaces to visualize the bacterial oxidation process, reactive oxygen probes to test for the presence of H(2)O(2) and cultural experiments to assess conditions under which H(2)O(2) is secreted by seedlings. We also made surveys of the seedlings of several grass species to assess the distribution of the phenomenon of microbial oxidation in the Poaceae. Key elements of the proposed mechanism for nitrogen acquisition in seedlings include: 1) diazotrophic bacteria are vectored on or within seeds; 2) at seed germination bacteria colonize seedling roots and shoots; 3) seedling tissues secrete ROS onto bacteria; 4) bacterial cell walls, membranes, nucleic acids, proteins and other biological molecules are oxidized; 5) nitrates and/or smaller fragments of organic nitrogen-containing molecules resulting from oxidation may be absorbed by seedling tissues and larger peptide fragments may be further processed by secreted or cell wall plant proteases until they are small enough for transport into cells. Hydrogen peroxide secretion from seedling roots and bacterial oxidation was observed in several species in subfamily Pooideae where seeds possessed adherent paleas and lemmas, but was not seen in grasses that lacked this feature or long-cultivated crop species.

No MeSH data available.


Related in: MedlinePlus

a–e Tall fescue seedlings stained with DAB. a Fescue seedlings on agarose showing H2O2 secretion (red coloration) from roots; b and c Fescue root hair showing bacterial cells staining brown due to H2O2 concentration (arrows); d Fescue root hair showing bacterial cells losing rod structure and capacity to stain with aniline blue during oxidation (arrows; stained with DAB/peroxidase, then counterstained with 0.1 % aniline blue; e Seedling mesocotyl showing brown areas (arrows) that mark sites of bacterial oxidation
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3473182&req=5

Fig1: a–e Tall fescue seedlings stained with DAB. a Fescue seedlings on agarose showing H2O2 secretion (red coloration) from roots; b and c Fescue root hair showing bacterial cells staining brown due to H2O2 concentration (arrows); d Fescue root hair showing bacterial cells losing rod structure and capacity to stain with aniline blue during oxidation (arrows; stained with DAB/peroxidase, then counterstained with 0.1 % aniline blue; e Seedling mesocotyl showing brown areas (arrows) that mark sites of bacterial oxidation

Mentions: In microscopic examinations of seedlings using DAB/peroxidase we detected areas of high oxidation activity around bacteria. By counterstaining tissues with aniline blue, it was possible to visualize intact bacteria on plant tissues. During oxidation, bacteria lost capacity to stain with aniline blue/lactic acid. Instead, the bacteria swelled and became spherical or amorphous with diffuse walls. Eventually the bacteria vanished on the surface of plant tissues (Fig. 1). Experiments using seeds of tall fescue obtained from commercial sources gave the same results in this study. Through application of the florescent nucleic acid stain SYTO9®, we were able to observe swollen, oxidizing bacteria become amorphous, with nucleic acids dimming and diffusing away from the original site of the oxidized bacteria. We frequently visualized ‘bulls-eye rings’ around degraded bacteria (Fig. 2d). We characterize these rings as being composed of partially degraded fragments of nucleic acids that adhere to plant cell walls. More intense secretion of H2O2 in the vicinity of the bacterial cells may result in the clearing of nucleic acids nearest to the original bacterial sites, thus producing the ‘bulls-eye ring’ effect.Fig. 1


A proposed mechanism for nitrogen acquisition by grass seedlings through oxidation of symbiotic bacteria.

White JF, Crawford H, Torres MS, Mattera R, Irizarry I, Bergen M - Symbiosis (2012)

a–e Tall fescue seedlings stained with DAB. a Fescue seedlings on agarose showing H2O2 secretion (red coloration) from roots; b and c Fescue root hair showing bacterial cells staining brown due to H2O2 concentration (arrows); d Fescue root hair showing bacterial cells losing rod structure and capacity to stain with aniline blue during oxidation (arrows; stained with DAB/peroxidase, then counterstained with 0.1 % aniline blue; e Seedling mesocotyl showing brown areas (arrows) that mark sites of bacterial oxidation
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3473182&req=5

Fig1: a–e Tall fescue seedlings stained with DAB. a Fescue seedlings on agarose showing H2O2 secretion (red coloration) from roots; b and c Fescue root hair showing bacterial cells staining brown due to H2O2 concentration (arrows); d Fescue root hair showing bacterial cells losing rod structure and capacity to stain with aniline blue during oxidation (arrows; stained with DAB/peroxidase, then counterstained with 0.1 % aniline blue; e Seedling mesocotyl showing brown areas (arrows) that mark sites of bacterial oxidation
Mentions: In microscopic examinations of seedlings using DAB/peroxidase we detected areas of high oxidation activity around bacteria. By counterstaining tissues with aniline blue, it was possible to visualize intact bacteria on plant tissues. During oxidation, bacteria lost capacity to stain with aniline blue/lactic acid. Instead, the bacteria swelled and became spherical or amorphous with diffuse walls. Eventually the bacteria vanished on the surface of plant tissues (Fig. 1). Experiments using seeds of tall fescue obtained from commercial sources gave the same results in this study. Through application of the florescent nucleic acid stain SYTO9®, we were able to observe swollen, oxidizing bacteria become amorphous, with nucleic acids dimming and diffusing away from the original site of the oxidized bacteria. We frequently visualized ‘bulls-eye rings’ around degraded bacteria (Fig. 2d). We characterize these rings as being composed of partially degraded fragments of nucleic acids that adhere to plant cell walls. More intense secretion of H2O2 in the vicinity of the bacterial cells may result in the clearing of nucleic acids nearest to the original bacterial sites, thus producing the ‘bulls-eye ring’ effect.Fig. 1

Bottom Line: Experiments on this proposed mechanism employ tall fescue (Festuca arundinaceae) seedlings to elucidate features of the oxidative mechanism.We also made surveys of the seedlings of several grass species to assess the distribution of the phenomenon of microbial oxidation in the Poaceae.Hydrogen peroxide secretion from seedling roots and bacterial oxidation was observed in several species in subfamily Pooideae where seeds possessed adherent paleas and lemmas, but was not seen in grasses that lacked this feature or long-cultivated crop species.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ USA.

ABSTRACT
In this paper we propose and provide evidence for a mechanism, oxidative nitrogen scavenging (ONS), whereby seedlings of some grass species may extract nitrogen from symbiotic diazotrophic bacteria through oxidation by plant-secreted reactive oxygen species (ROS). Experiments on this proposed mechanism employ tall fescue (Festuca arundinaceae) seedlings to elucidate features of the oxidative mechanism. We employed 15N(2) gas assimilation experiments to demonstrate nitrogen fixation, direct microscopic visualization of bacteria on seedling surfaces to visualize the bacterial oxidation process, reactive oxygen probes to test for the presence of H(2)O(2) and cultural experiments to assess conditions under which H(2)O(2) is secreted by seedlings. We also made surveys of the seedlings of several grass species to assess the distribution of the phenomenon of microbial oxidation in the Poaceae. Key elements of the proposed mechanism for nitrogen acquisition in seedlings include: 1) diazotrophic bacteria are vectored on or within seeds; 2) at seed germination bacteria colonize seedling roots and shoots; 3) seedling tissues secrete ROS onto bacteria; 4) bacterial cell walls, membranes, nucleic acids, proteins and other biological molecules are oxidized; 5) nitrates and/or smaller fragments of organic nitrogen-containing molecules resulting from oxidation may be absorbed by seedling tissues and larger peptide fragments may be further processed by secreted or cell wall plant proteases until they are small enough for transport into cells. Hydrogen peroxide secretion from seedling roots and bacterial oxidation was observed in several species in subfamily Pooideae where seeds possessed adherent paleas and lemmas, but was not seen in grasses that lacked this feature or long-cultivated crop species.

No MeSH data available.


Related in: MedlinePlus