CHAPTER 12 MEASUREMENTS WITH THE MINI-PAM
which are stored in MEMORY (see 6) or transferred to a PC for
further processing. Light Curves are displayed under WinControl
(see separate manual).
Additional information on the dark-recovery of YIELD-lowering
during actinic illumination can be obtained by the function
L-CURVE+REC. This function can be started either via SET in
menu position 18 or by ON+∨. It can be terminated by the same
commands. The actual illumination program with L - CURVE + REC
is identical to that of a LIGHT CURVE. In addition, after termination
of the last illumination period, in the absence of actinic light the
recovery of YIELD in the dark is assessed by 6 consecutive
saturation pulses applied at 10 s, 30 s, 60 s, 2 min, 5 min, 10 min
after light-off. In this way, different types of non-photochemical
quenching can be distinguished which contribute to the lowering of
the PS II quantum yield. It is generally assumed that the rapid
recovery within the first 30-60 s reflects the disappearance of energy
dependent nonphotochemical quenching, in parallel with the
relaxation of the transthylakoidal ∆pH. The slower recovery within
the first 10-30 min is considered to reflect a change of energy
distribution in favor of PS II (so-called State Shift). The apparently
irreversible YIELD-lowering (with respect to the original dark state)
is expression of "photoinhibition".
LIGHT CURVES as measured with the MINI-PAM contain
somewhat different information than the conventional light response
curves. Correct measurement of the latter requires the attainment of
steady state at each PAR-value, which takes at least 10 min. LIGHT
CURVES recorded with short illumination times (down to 5 s;
so-called Rapid Light Curves, RLC) allow insight into the
physiological flexibility with which a plant sample can adapt its
photosynthetic apparatus to rapid changes of light intensity. Hence,
RLC contain information on induction as well as saturation
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