Mireille Consalvey PhD Thesis - University of St Andrews

Chap-wil I
-(_, I C 1)(2 F: l, 1,111 tl-(-) Iý! 'ý I
increases in light energy. A decrease in this parameter can also be indicative of
stress (Underwood and Kromkamp 1999 and references therein).
Light utilisation Fa'
Efficiency Fn
Gentyfactor
Equation 1.5
Using the light utilisation efficiency parameter the electron transport rate (ETR)
can be calculated (Equation 1.6 after Sakshaug et al. 1997).
ETR = E. ' x PPFD x a*
F' 2
ETR is the electron transport rate
PPFD qtMol M-2 s-1) is the photosynthetically available photon
divided by 2 assuming photons divide equally between PSI and PSIl
a* is co-efficient of light absorption
a* is not alw - ays measurable, if this terin is removed from the equation
Relative ETR (rel ETR) is calculated
1.3.3.1. Measuring fluorescence
Equation 1.6
flux density-
To measure fluorescence, a system sensitive enough to detect
fluorescence wavelengths but able to discriminate the light that drives
photochemistry (actinic) is required. Some continuous excitation fluorometers
exist but can only detect a fluorescence signal in the dark, therefore their use is
limited. Pulse amplitude modulated (PAM) fluorometers can be used under many
light regimes, exposing the samples to short (ýtsecond) pulses of
light (the
modulated measuring beam) with a relatively long lag between pulses. This
induces fluorescence but not a photochemical reaction (Schreiber et al. 1986).
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