PLANT PHYSIOLOGY , Vol 114, Issue 2 615-622, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Physiological and Biochemical Response of the Photosynthetic Apparatus of Two Marine Diatoms to Fe Stress
R. M. L. McKay, R. J. Geider and J. LaRoche
Oceanographic and Atmospheric Sciences Division, Brookhaven National Laboratory, Upton, New York 11973 (R.M.L.M., J.L.R.)
Flavodoxin is a small electron-transfer protein capable of replacing
ferredoxin during periods of Fe deficiency. When evaluating the suitability
of flavodoxin as a diagnostic indicator for Fe limitation of phytoplankton
growth, we examined its expression in two marine diatoms we cultured using
trace-metal-buffered medium. Thalassio-sira weissflogii and Phaeodactylum
tricornutum were cultured in ethylenediaminetetraacetic acid-buffered
Sargasso Sea water containing from 10 to 1000 nM added Fe.
Trace-metal-buffered cultures of each diatom maintained high growth rates
across the entire range of Fe additions. Similarly, declines in
chlorophyll/cell and in the ratio of photosystem II variable-to-maximum
fluorescence were negligible (P. tricornutum) to moderate (T. weissflogii;
54% decline in chlorophyll/cell and 22% decrease in variable-to-maximum
fluorescence). Moreover, only minor variations in photosynthetic parameters
were observed across the range of additions. In contrast, flavodoxin was
expressed to high levels in low-Fe cultures. Despite the inverse
relationship between flavodoxin expression and Fe content of the medium,
its expression was seemingly independent of any of the indicators of cell
physiology that were assayed. It appears that flavodoxin is expressed as an
early-stage response to Fe stress and that its accumulation need not be
intimately connected to limitations imposed by Fe on the growth rate of
these diatoms.
