121
Bennoun, 1982). A dark reaction known as "chlororespiration" has been shown to maintain
~ and the plastoquinone pool in a semi-reduced state even after long dark adaptation periods
(Bennoun, 1982). However, brief illumination of the sample with low intensity, far red (700710 nm) light just prior to the onset of actinic illumination may oxidize ~ by forcing
turnover of PS I alone (Owens, 1986). The incomplete relaxation of em and partial reduction
of ~ following dark adaptation will lead to an underestimation of fluorescence parameters
associated with the variable fluorescence rise and are likely to increase the error in the
correlation between regression of fluorescence and photosynthetic capacity.
One potentially promising technique for predicting rates of photosynthesis from measurements
of ' 11' and em has been introduced by Weis and Berry (1987). This technique assumes that (1' 11' ) is a good estimate of the fraction of open PS II reaction centers and that em correlates with
the yield of photochemistry in open PS II traps. The technique is calibrated by measuring '11',
to several studies in higher plants and at least one algal system (Holmes et ai., 1989). The
universal applicability of this technique relies on a constant relationship between em and the
yield of photochemistry in open PS II traps under all conditions. That is, will the relationship
between
light history? This important question remains to be answered.
Fluorescence as an indicator of algal biomass. The quantum yield of fluorescence is defined
as the number of fluorescence photons emitted by a sample divided by the number of photons
absorbed. This suggests that in dilute algal suspensions, the in vivo fluorescence emission
intensity is proportional to the number of photons absorbed by the sample, the proportionality
constant being the fluorescence quantum yield. Since absorption (in dilute samples) is largely
determined by the amount of pigment present, in vivo fluorescence should be an indicator of
algal biomass. This relationship probably represents the most highly utilized aspect of chI
fluorescence (Lorenzen, 1966). However, the influence of environmental conditions on
fluorescence quenching processes would suggest that natural variability in the fluorescence
quantum yield would negate, or at least limit, the ability of fluorescence to predict biomass.
Bennoun, 1982). A dark reaction known as "chlororespiration" has been shown to maintain
~ and the plastoquinone pool in a semi-reduced state even after long dark adaptation periods
(Bennoun, 1982). However, brief illumination of the sample with low intensity, far red (700710 nm) light just prior to the onset of actinic illumination may oxidize ~ by forcing
turnover of PS I alone (Owens, 1986). The incomplete relaxation of em and partial reduction
of ~ following dark adaptation will lead to an underestimation of fluorescence parameters
associated with the variable fluorescence rise and are likely to increase the error in the
correlation between regression of fluorescence and photosynthetic capacity.
One potentially promising technique for predicting rates of photosynthesis from measurements
of ' 11' and em has been introduced by Weis and Berry (1987). This technique assumes that (1' 11' ) is a good estimate of the fraction of open PS II reaction centers and that em correlates with
the yield of photochemistry in open PS II traps. The technique is calibrated by measuring '11',
to several studies in higher plants and at least one algal system (Holmes et ai., 1989). The
universal applicability of this technique relies on a constant relationship between em and the
yield of photochemistry in open PS II traps under all conditions. That is, will the relationship
between
light history? This important question remains to be answered.
Fluorescence as an indicator of algal biomass. The quantum yield of fluorescence is defined
as the number of fluorescence photons emitted by a sample divided by the number of photons
absorbed. This suggests that in dilute algal suspensions, the in vivo fluorescence emission
intensity is proportional to the number of photons absorbed by the sample, the proportionality
constant being the fluorescence quantum yield. Since absorption (in dilute samples) is largely
determined by the amount of pigment present, in vivo fluorescence should be an indicator of
algal biomass. This relationship probably represents the most highly utilized aspect of chI
fluorescence (Lorenzen, 1966). However, the influence of environmental conditions on
fluorescence quenching processes would suggest that natural variability in the fluorescence
quantum yield would negate, or at least limit, the ability of fluorescence to predict biomass.