A Lab Notebook

 
Fv/Fm, S. costatum
I used the Fast Repitition Rate Fluorometer (FRRF or FRR) to determine the health of my S. costatum culture.
Fv/Fm = 0.286
Fm = 567.6
Where Fv is the variable fluorescence and Fm is the maximum fluorescence. The ratio between the variable and maximum fluorescence is an indicator of the health of a photosynthetic organism. The variable fluorescence is the difference between the initial fluorescence (Fo) and the maximum fluorescence (ie. Fv/Fm = [Fm-Fo]/Fm). Fluorescence is the subsequent emission of lower energy light (longer wavelength) following excitation by higher energy light (shorter wavelngth). In the case of the FRRF, the sample of phytoplankton is bombarded by a very rapidly flashing blue light. Concurrently, the sample is surrounded by a detectors which have been set up to measure red light. The computer controllingthe FRRF knows how much blue light was needed to create the fluorescence (red light) observed. The time lag between exposure to the blue light and fluorescence by the phytoplankton is on the order of picoseconds. The FRR allows us to observe the change in fluorescence. A healthy culture of phytoplankton should have an Fv/Fm > .50 (approximately). As one can see, my S. costatum culture is a bit less than ideal. This is likely due to the low concentration of cells in my relatively young culture. As the culture continues to grow, the cel concentration of the culture should rise, thus increasing the fluorescence of the culture (assuming the plankton don't die too soon). The reason a healthy culture should have a high Fv/Fm is due to the photosynthetic ability of the culture. A healthy photosystem (chlorophylls converting light into cellular energy) can absorb a fair bit of light before it becomes saturated and overflows. In this sense, the overflow of light is manifest as fluorescence. More fluorescence = higher Fv = more healthy photosystem. The reason a healthy photosystem can absorb more light than an unhealthy photosystem is because all of its components within the electron transport chain (the fancy name given to the series of components used to transfer light energy into cellular energy such as ATP or NADPH) are well-nourished and in tip-top shape (highly efficient). If any portion of this electron transport chain is deficient (usually due to some sort of stress such as lack of nutrients or high light) the cell will not be able to transport electrons (energy) at a very high rate, thus hitting its overflow level relatively soon resulting in a low range of fluorescence ( a small difference between Fm and Fo => a small Fv => small Fv/Fm).
But, we can expect the S. costatum to be doing slightly better tomorrow. If experience with past cultures is repeated, S. costatum will bloom and senesce very rapidly.

Above are images of increasing magnification of S. coatatum. Recall S. costatum is a diatom, so the cell is encapsulated by a silicious frustule which is the obvious structure in the obove images. The cell has several long processes that allow it to form a chain with other S. costatum cells. Each individual cell is usually in the size range of 5-8um. With chains sometimes several mm long. The above images were obtained from the website of the department of Marine Ecology, Marine Botany at Göteborg University
- posted by alex @ 13:54