Adenosine Triphosphate response to stress in key estuarine species, Spartina alterniflora

Smooth cord grass (Spartina alterniflora) is a hardy intertidal species of plant that is very tolerant to fluctuating environments and rapid oscillations of inundation. However S. alterniflora and tidal marsh ecosystems are susceptible to multiple abiotic factors including shifts in salinity, tidal rates, and temperature which will all be affected by future climate change. With an increasingly variable climate, it is imperative to anticipate the variety of different ways radical weather events can affect coastal vegetation. The gradually rising sea level will have widespread impacts for the Atlantic Coast and therefore continuous monitoring of local watersheds is paramount in order to establish baseline data for future stress quantification. Within this study it is important to identify a species that can succeed despite a continually changing climate; for this reason S. alterniflora is a perfect model for study. S. alterniflora is a sessile organism that has been shown to function as an indicator species for biological stress and the general health of an estuarine ecosystem. In addition S. alterniflora is capable of withstanding salinity twice as strong as seawater and is able to grow in high temperatures of water ranging up to 35 °C. Long term goals for this research project are to mitigate the effects of climate change on tidal ecosystems, however at present it is important to establish a biomarker for stress in these organisms. Biomarkers are important measures of stress response and enable us to tell if some perturbation has occurred in an organism’s environment. Our research focused on testing whether Adenosine Triphosphate (ATP) functions as a response to stress in S. alterniflora samples. ATP is a biologically ubiquitous molecule that serves as the primary energy source for cellular work. ATP is maintained at high concentrations inside the plant cell, however mastication and stimulation (i.e. stress) of the cell can cause the release of intracellular ATP into the extracellular matrix where it can then bind to plasma membrane localized purinoceptors. Extracellular ATP has a wide variety of functions in animals including muscle contraction, inflammation, neurotransmission, cell growth and death; however the role of extracellular ATP in plants is still largely unknown. Our hypothesis was that in response to stress, intracellular ATP would be released from plant cells and act as an intermediate signal to activate other stress-responsive pathways (i.e. heat-shock protein production). Using a combination of heat and salt stresses, we quantified ATP expression in Spartina alterniflora using a colorimetric assay for intracellular ATP content. We found that individual stressors increased cellular concentration of ATP which is consistent with other ATP displacements quantified in previous studies.