1 ms (a.u.) (F o) 660 550 1,125 1,025 Rate Salubrinal in vivo constant light excitation (k L) 1.4 1.4 2.3 2.3 Rate constant qPE-release

(k qbf) 9.10−2 1.10−1 9.10−2 9.10−2 Rate constant QA − oxidation (k AB) 1.9 2.2 0.8 1.6 Rate constant QA 2− oxidation (k 2AB) 5.10−2 5.10−2 7.5.10−2 8.10−2 Rate constant conductance leakage (k Hthyl) 1.5.10−2 1.2.10−1 3.10−2 9.10−1 Fraction QB-nonreducing RCs (β) 0.13 0.13 0.27 0.35 Efficiency e-trapping donor side (Ø) 0.3 0.3 0.3 0.3 Normalized variable fluorescence (nF v) 2.3 1.8 2.2 1.5 Amplitude IP rise (F CET) (IP) 0.8 1.2 1.1 0.5 Rate constant IP rise (k IP) 1.10−1 1.1.10−1 1.4.10−1 8.10−2 Steepness IP rise (N IP) 8 5 8 3 Fig. 5 Same as Fig. 4 for low (LL) and high light (HL) pre-conditioned R-type Canola leaf The data collected in Table 1 and Figs. 4 and 5 show clear effects of high light treatment on Canola leaves. Using FIA, these effects can be quantified in terms of changes in:

(i) 9–16% decrease in F o (ii), 22–32% decrease in the normalized variable fluorescence (nF v) associated with full reduction of the primary quinone GPCR & G Protein inhibitor electron acceptor QA and equivalent with a decrease in PSII primary photochemical efficiency (from Øpp [=nF v/(nF v + 1)] ~0.7 towards ~0.6), (iii) a substantial increase in basal proton conductance of the thylakoid membrane (k Hthyl), notably 8- and 30-fold in S- and R-type leaves, respectively, and associated with 65 and 100% suppression, Enzalutamide respectively, of the release of photo-electrochemical quenching q PE(t), and (iv) a decrease in the steepness of the potential-driven stimulation of variable fluorescence (F CET(t)), quantified by N IP (last row in Table 1). The variable fluorescence curves of the respective S- and R-type Canola leaves at the end of a 4 (6) day period with 2 (3) subsequent LL- and HL treatments were found to be qualitatively similar to those at the start of the period (data not shown). This indicates a reasonable

and reversible stability of the system during and after the alternating light protocol that was followed. A comparison of the FIA-parameters Progesterone shows a small attenuation effect in parallel with the duration of the period (data not shown). This effect is most pronounced for the decrease in the magnitude of the variable fluorescence FPE associated with the release of photo-electrochemical quenching as reflected by the increase in the thylakoid proton conductance (k Hthyl). Discussion Carr and Björk (2007) acclimated thalli of Ulva fasciata for a long time to a low light intensity (80 μmol photons m−2s−1) and then exposed them to prolonged high irradiance (1,500 μmol photons m−2s−1) followed by recovery at the low irradiance.