ACUTE NITRATE EXPOSURE CAUSES PROTEOMIC CHANGES CONSISTENT WITH THE REGULATION OF REACTIVE OXYGEN AND NITROGEN SPECIES

Nitrate is the most common ionic form of nitrogen in aquatic ecosystems. Although nitrate is known to affect ecosystems at high levels through eutrophication, hypoxia and loss of biodiversity, it is considered to be physiologically inert to the individual aquatic organism. To test the physiological effects of nitrate on aquatic life, we exposed gill tissue of the Pacific oyster, Crassostrea gigas, to nitrate and characterized changes in protein expression, using a gel-based proteomics approach. Of the 642 protein spots detected, we found that 24 proteins (15 identified) changed expression in response to a 6-hour exposure to nitrate concentrations ranging from 0-73 mg/L, values that characterize highly contaminated surface and ground waters. Proteins changing expression included the oxidative stress proteins thioredoxin and cavortin (a member of the superoxide dismutase family) as well as proteins that are involved in G-protein signaling (Rho-GDI, ADP-ribosylation factor, G-protein ß-subunit), protein homeostasis (heat shock protein 70, prohibitin, calreticulin, and proteasome &#;-type 4 subunit), glycolysis (enolase), transport of hydrophobic molecules (lipocalin) and cytoskeletal arrangements (intermediate filaments and a gelsolin-like adseverin). The most parsimonious explanation for these changes in protein expression assumes that C. gigas reduces nitrate to nitrite and nitric oxide, which reacts with superoxide anions to form the very reactive peroxynitrite. We propose that part of the cellular response to reactive nitrogen species,phagocytic hemocytes inhibit the production of reactive oxygen species, potentially compromising the immune response of oysters to invading pathogens

Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggregating Case Studies

Flare frequency distributions represent a key approach to addressing one of the largest problems in solar and stellar physics: determining the mechanism that counter-intuitively heats coronae to temperatures that are orders of magnitude hotter than the corresponding photospheres. It is widely accepted that the magnetic field is responsible for the heating, but there are two competing mechanisms that could explain it: nanoflares or Alfv\'en waves. To date, neither can be directly observed. Nanoflares are, by definition, extremely small, but their aggregate energy release could represent a substantial heating mechanism, presuming they are sufficiently abundant. One way to test this presumption is via the flare frequency distribution, which describes how often flares of various energies occur. If the slope of the power law fitting the flare frequency distribution is above a critical threshold, $\alpha=2$ as established in prior literature, then there should be a sufficient abundance of nanoflares to explain coronal heating. We performed $>$600 case studies of solar flares, made possible by an unprecedented number of data analysts via three semesters of an undergraduate physics laboratory course. This allowed us to include two crucial, but nontrivial, analysis methods: pre-flare baseline subtraction and computation of the flare energy, which requires determining flare start and stop times. We aggregated the results of these analyses into a statistical study to determine that $\alpha = 1.63 \pm 0.03$. This is below the critical threshold, suggesting that Alfv\'en waves are an important driver of coronal heating.Comment: 1,002 authors, 14 pages, 4 figures, 3 tables, published by The Astrophysical Journal on 2023-05-09, volume 948, page 7