TRACING BIOCHEMICAL PATHWAYS

In a project funded by the National Science Foundation, von Dassow, Latz, and John Frangos in the UCSD Department of Bioengineering are studying how the fluid forces acting on the cell are translated into a biochemical signal that tells the cell to produce light. Von Dassow is conducting tests to determine if shear causes calcium ions from seawater to enter the dinoflagellate cell, triggering bioluminescence. Shear is known to result in calcium entry into mammalian endothelial cells (cells that form the lining of blood vessels). If his hypothesis is correct, it would indicate that shear affects bioluminescent dinoflagellates-which, unlike endothelial cells, are not attached to anything and must move with the fluid-in a similar way. In the future, Latz plans to test whether other biochemical events in the cells are triggered by fluid motion.

The relatively large shear forces that stimulate dinoflagellate bioluminescence are higher than typical levels of oceanic turbulence. But dinoflagellates are also affected by lower levels of fluid motion, such as those present near the surface on a windy day.

 



"Because dinoflagellates swim to surface layers during the day," explains Latz, "they are exposed to stronger levels of turbulence than exist in deeper layers."

Generally, dinoflagellate red tides occur during calm conditions. In contrast, other planktonic algae, such as diatoms, thrive in more turbulent conditions, which stir up nutrients from deeper layers. Juhl, who is just completing his dissertation, has been studying whether the dinoflagellates' preference for calm conditions results from their extraordinary flow sensitivity. It is possible that red tides don't occur during turbulent conditions because the turbulence prevents dinoflagellate populations from growing.

"The idea that flow affects cell physiology is well developed in other fields of biology, but it is a novel idea for oceanography," says Juhl. "Typically people only think of oceanic flow in terms of its ability to move things from here to there, not in terms of what it is actually doing directly to the cell. I'm looking at whether the growth of dinoflagellates is sensitive to oceanic levels of flow."