Influence of the Neotyphodium--Tall Fescue Symbiosis on Belowground Processes

Much of the work to date on the relationships between cool season grasses and Neotyphodium fungal endophytes has focused on the physiological, biochemical, and genetic ramifications of the host-fungus relationship and the subsequent influence these effects have on ruminant nutrition, plant adaptation to environmental stresses, and aboveground ecological processes. Relatively little attention has been paid to effects on belowground parameters. In this paper, we review the research evaluating the impact of one endophyte-grass association, the Neotyphodium – tall fescue symbiosis, on underground ecological and biogeochemical processes. We also present some preliminary data showing that the quantity and nature of tall fescue root exudates are influenced by the plant cultivar and fungal genotype. This body of work clearly indicates that effects of the Neotyphodium-tall fescue symbiosis extend to belowground processes; however, additional research is needed to understand the mechanisms driving many of the observed root and soil endophyte effects

Fast X-Ray Fluorescence Microtomography of Hydrated Biological Samples

Metals and metalloids play a key role in plant and other biological systems as some of them are essential to living organisms and all can be toxic at high concentrations. It is therefore important to understand how they are accumulated, complexed and transported within plants. In situ imaging of metal distribution at physiological relevant concentrations in highly hydrated biological systems is technically challenging. In the case of roots, this is mainly due to the possibility of artifacts arising during sample preparation such as cross sectioning. Synchrotron x-ray fluorescence microtomography has been used to obtain virtual cross sections of elemental distributions. However, traditionally this technique requires long data acquisition times. This has prohibited its application to highly hydrated biological samples which suffer both radiation damage and dehydration during extended analysis. However, recent advances in fast detectors coupled with powerful data acquisition approaches and suitable sample preparation methods can circumvent this problem. We demonstrate the heightened potential of this technique by imaging the distribution of nickel and zinc in hydrated plant roots. Although 3D tomography was still impeded by radiation damage, we successfully collected 2D tomograms of hydrated plant roots exposed to environmentally relevant metal concentrations for short periods of time. To our knowledge, this is the first published example of the possibilities offered by a new generation of fast fluorescence detectors to investigate metal and metalloid distribution in radiation-sensitive, biological samples

Influence of the Neotyphodium--Tall Fescue Symbiosis on Belowground Processes

Much of the work to date on the relationships between cool season grasses and Neotyphodium fungal endophytes has focused on the physiological, biochemical, and genetic ramifications of the host-fungus relationship and the subsequent influence these effects have on ruminant nutrition, plant adaptation to environmental stresses, and aboveground ecological processes. Relatively little attention has been paid to effects on belowground parameters. In this paper, we review the research evaluating the impact of one endophyte-grass association, the Neotyphodium – tall fescue symbiosis, on underground ecological and biogeochemical processes. We also present some preliminary data showing that the quantity and nature of tall fescue root exudates are influenced by the plant cultivar and fungal genotype. This body of work clearly indicates that effects of the Neotyphodium-tall fescue symbiosis extend to belowground processes; however, additional research is needed to understand the mechanisms driving many of the observed root and soil endophyte effects

Toxicogenomic Responses of the Model Legume <i>Medicago truncatula</i> to Aged Biosolids Containing a Mixture of Nanomaterials (TiO₂, Ag, and ZnO) from a Pilot Wastewater Treatment Plant

Toxicogenomic responses in Medicago truncatula A17 were monitored following exposure to biosolids-amended soils. Treatments included biosolids produced using a pilot wastewater treatment plant with either no metal introduced into the influent (control); bulk/ionic TiO₂, ZnO, and AgNO₃ added to influent (bulk/dissolved treatment); or Ag, ZnO, and TiO₂ engineered nanomaterials added to influent (ENM treatment) and then added to soil, which was aged in the field for 6 months. In our companion study, we found inhibition of nodulation in the ENM but not in the bulk/dissolved treatment. Gene expression profiling revealed highly distinct profiles with more than 10-fold down-regulation in 239 genes in M. truncatula roots from the ENM treatment, while gene expression patterns were similar between bulk/dissolved and control treatments. In response to ENM exposure, many of the identified biological pathways, gene ontologies, and individual genes are associated with nitrogen metabolism, nodulation, metal homeostasis, and stress responses. Expression levels of nine genes were independently confirmed with qRT-PCR. Exposure to ENMs induced unique shifts in expression profiles and biological pathways compared with bulk/dissolved treatment, despite the lack of difference in bioavailable metal fractions, metal oxidation state, and coordination environment between ENM and bulk/dissolved biosolids. As populations of Sinorhizobium meliloti Rm2011 were similar in bulk/dissolved and ENM treatments, our results suggest that inhibition of nodulation in the ENM treatment was primarily due to phytotoxicity, likely caused by enhanced bioavailability of Zn ions