Rml. Mckay et al., PHYSIOLOGICAL AND BIOCHEMICAL RESPONSE OF THE PHOTOSYNTHETIC APPARATUS OF 2 MARINE DIATOMS TO FE STRESS, Plant physiology, 114(2), 1997, pp. 615-622
Flavodoxin is a small electron-transfer protein capable of replacing f
erredoxin during periods of Fe deficiency. When evaluating the suitabi
lity of flavodoxin as a diagnostic indicator for Fe limitation of phyt
oplankton growth, we examined its expression in two marine diatoms we
cultured using trace-metal-buffered medium. Thalassiosira weissflogii
and Phaeodactylum tricornutum were cultured in ethylenediaminetetraace
tic acid-buffered Sargasso Sea water containing from 10 to 1000 nM add
ed Fe. Trace-metal-buffered cultures of each diatom maintained high gr
owth rates across the entire range of Fe additions. Similarly, decline
s in chlorophyll/cell and in the ratio of photosystem II variable-to-m
aximum fluorescence were negligible (P. tricornutum) to moderate (T. w
eissflogii; 54% decline in chlorophyll/cell and 22% decrease in variab
le-to-maximum fluorescence). Moreover, only minor variations in photos
ynthetic parameters were observed across the range of additions. In co
ntrast, flavodoxin was expressed to high levels in low-Fe cultures. De
spite the inverse relationship between flavodoxin expression and Fe co
ntent of the medium, its expression was seemingly independent of any o
f the indicators of cell physiology that were assayed. It appears that
flavodoxin is expressed as an early-stage response to Fe stress and t
hat its accumulation need not be intimately connected to limitations i
mposed by Fe on the growth rate of these diatoms.