120
(Samuelsson and Oquist, 1977; Bates and Platt, 1984). Analogous field experiments have met
with varied success (Cullen and Renger, 1979; Bates and Platt, 1985; Keller, 1987; Heath,
1988). In general, good correlations were found when samples were restricted to well defined
algal populations; correlations determined in different populations showed larger variability.
Even in the best correlations, broad confidence limits on regression data provide for largely
qualitative rate predictions, especially in low biomass samples.
There are several factors that suggest caution in correlating fluorescence parameters and
photosynthetic capacity. Of principal importance is the fact that the variable fluorescence rise
is proportional only to the PS II pool size; estimation of the maximum capacity for electron
transport through PS II requires knowledge of the maximal photochemical turnover rate of
PS II. PS II turnover rate has been shown to vary between species and with growth conditions
(Falkowski et al., 1981; Boardman, 1977). There is also an implicit assumption that PS II
electron transport capacity limits the rate of photosynthesis at light saturation. Recent data
from higher plants contradicts this assumption. Stitt (1986) has demonstrated a 50-100%
excess of electron transport capacity at light saturation and assigned the rate limiting step to
the dark reactions: translocation of inorganic phosphate from the cytoplasm to the chloroplast
(Sharkey et al., 1986). The limitation of photosynthesis by inorganic phosphate translocation
was also concluded by Sivak and Walker (1986). In a green alga, Sukenik et al .. (1987)
showed that light saturated rates correlated with the amount of ribulose biphosphate
carboxylase, the primary CO2 fixing enzyme of the dark reactions. These results suggest that
the mechanistic basis for expecting a relationship between photosynthetic capacity and
variable fluorescence should be reinvestigated in the algae.
Experimentally, samples are routinely dark adapted for some length of time prior to
measurement of variable fluorescence (Bates, 1985). This dark adaptation period is required
so that all non-photochemical fluorescence quenching processes are completely relaxed ('IN
= 0) and that ~ is completely oxidized (qp = 1) and permits the accurate measurement of
both Fo and Fmax. In practice, the time required for complete relaxation of all components of
oxidized after dark adaptation is known to be incorrect in some algal classes (Owens, 1986;
(Samuelsson and Oquist, 1977; Bates and Platt, 1984). Analogous field experiments have met
with varied success (Cullen and Renger, 1979; Bates and Platt, 1985; Keller, 1987; Heath,
1988). In general, good correlations were found when samples were restricted to well defined
algal populations; correlations determined in different populations showed larger variability.
Even in the best correlations, broad confidence limits on regression data provide for largely
qualitative rate predictions, especially in low biomass samples.
There are several factors that suggest caution in correlating fluorescence parameters and
photosynthetic capacity. Of principal importance is the fact that the variable fluorescence rise
is proportional only to the PS II pool size; estimation of the maximum capacity for electron
transport through PS II requires knowledge of the maximal photochemical turnover rate of
PS II. PS II turnover rate has been shown to vary between species and with growth conditions
(Falkowski et al., 1981; Boardman, 1977). There is also an implicit assumption that PS II
electron transport capacity limits the rate of photosynthesis at light saturation. Recent data
from higher plants contradicts this assumption. Stitt (1986) has demonstrated a 50-100%
excess of electron transport capacity at light saturation and assigned the rate limiting step to
the dark reactions: translocation of inorganic phosphate from the cytoplasm to the chloroplast
(Sharkey et al., 1986). The limitation of photosynthesis by inorganic phosphate translocation
was also concluded by Sivak and Walker (1986). In a green alga, Sukenik et al .. (1987)
showed that light saturated rates correlated with the amount of ribulose biphosphate
carboxylase, the primary CO2 fixing enzyme of the dark reactions. These results suggest that
the mechanistic basis for expecting a relationship between photosynthetic capacity and
variable fluorescence should be reinvestigated in the algae.
Experimentally, samples are routinely dark adapted for some length of time prior to
measurement of variable fluorescence (Bates, 1985). This dark adaptation period is required
so that all non-photochemical fluorescence quenching processes are completely relaxed ('IN
= 0) and that ~ is completely oxidized (qp = 1) and permits the accurate measurement of
both Fo and Fmax. In practice, the time required for complete relaxation of all components of
oxidized after dark adaptation is known to be incorrect in some algal classes (Owens, 1986;