Redox Signaling in Colonial Hydroids: Many Pathways for Peroxide
Date
2005-01Author
Blackstone, Neil W.
Bivins, Matthew J.
Cherry, Kimberly S.
Fletcher, Robert E.
Geddes, Gabrielle
Metadata
Show full item recordAbstract
Studies of mitochondrial redox signaling predict that
the colonial hydroids Eirene viridula and Podocoryna
carnea should respond to manipulations of reactive oxygen
species (ROS). Both species encrust surfaces with feeding
polyps connected by networks of stolons; P. carnea is more
‘sheet-like’ with closely spaced polyps and short stolons,
while E. viridula is more ‘runner-like’ with widely spaced
polyps and long stolons. Treatment with the chemical antioxidant
vitamin C diminishes ROS in mitochondrion-rich
epitheliomuscular cells (EMCs) and produces phenotypic
effects (sheet-like growth) similar to uncouplers of
oxidative phosphorylation. In peripheral stolon tips,
treatment with vitamin C triggers a dramatic increase of
ROS that is followed by tissue death and stolon regression.
The enzymatic anti-oxidant catalase is probably not taken
up by the colony but, rather, converts hydrogen peroxide
in the medium to water and oxygen. Exogenous catalase
does not affect ROS in mitochondrion-rich EMCs, but
does increase the amounts of ROS emitted from
peripheral stolons, resulting in rapid, runner-like growth.
Treatment with exogenous hydrogen peroxide increases
ROS levels in stolon tips and results in somewhat faster
colony growth. Finally, untreated colonies of E. viridula
exhibit higher levels of ROS in stolon tips than untreated
colonies of P. carnea. ROS may participate in a number of
putative signaling pathways: (1) high levels of ROS may
trigger cell and tissue death in peripheral stolon tips; (2)
more moderate levels of ROS in stolon tips may trigger
outward growth, inhibit branching and, possibly, mediate
the redox signaling of mitochondrion-rich EMCs; and (3)
ROS may have an extra-colony function, perhaps in
suppressing the growth of bacteria.