PHYSIOLOGICAL-RESPONSES TO PHOSPHORUS LIMITATION IN BATCH AND STEADY-STATE CULTURES OF DUNALIELLA-TERTIOLECTA (CHLOROPHYTA) - A UNIQUE STRESS PROTEIN AS AN INDICATOR OF PHOSPHATE DEFICIENCY
Lm. Graziano et al., PHYSIOLOGICAL-RESPONSES TO PHOSPHORUS LIMITATION IN BATCH AND STEADY-STATE CULTURES OF DUNALIELLA-TERTIOLECTA (CHLOROPHYTA) - A UNIQUE STRESS PROTEIN AS AN INDICATOR OF PHOSPHATE DEFICIENCY, Journal of phycology, 32(5), 1996, pp. 825-838
A protein unique to phosphorus stress observed in Dunaliella tertiolec
ta Butcher was studied in the context of phosphate-limited cell physio
logy and is a potential diagnostic indicator of phosphate deficiency i
n this alga. Cells were grown over a range of limited, steady-state gr
owth rates and at maximum (replete) and zero (phosphate-starved) growt
h rates. The stress protein, absent in nutrient-replete cells, was pro
duced under all steady-state phosphate-limited conditions and increase
d in abundance with increasing limitation (decreasing growth rate), Ce
llular carbon : phosphorus ratios and the maximum uptake rate of phosp
hate (V-m) increased with increasing limitation, whereas the ratio of
chlorophyll a: carbon decreased. Alkaline phosphatase activity did not
respond to limitation but was measurable in starved, stationary-phase
cells. F-v/F-m, a measure of photochemical efficiency, was a nonlinea
r, saturating function of mu, as commonly observed under N limitation.
The maximum F-v/F-m of 0.64 was measured in nutrient-replete cells gr
owing at mu(max), and a value of zero was measured in stationary-phase
starved cells. When physiological parameters were compared, the P-str
ess protein abundance and F-v/F-m were the most sensitive indicators o
f the level of deficiency. The stress protein was not produced under N
- or Fe-limited conditions. It is of high molecular weight (>200) and
is associated with internal cell membranes. The stress protein has sev
eral characteristics that make it a potential diagnostic indicator: it
is 1) unique to phosphorus limitation (i.e. absent under all other co
ndititions), 2) present under limiting as well as starved conditions,
3) sensitive to the level of limitation, and 4) observable without tim
e-course incubation of live samples.