Both reached a low steady state level after about 100 min and recovered fast after thalli were transferred to the low irradiance of 80 μmol photons

m−2s−1: to about 60% of the original values after 200 min at 80 μmol photons m−2s−1. Our experiments aimed at a different goal. We exposed plants during a full day at a high light intensity and then transferred them to very low intensity, again for a full day; and repeated this cycle several times. We measured fast fluorescence induction changes in an adapted steady state situation. Many earlier studies (reviewed by Tyystjärvi (2008) and Takahashi and Badger (2011)) were aimed at different effects of photoinhibition: on its mechanism, on the structure of PSII, damage and repair of PSII, and mechanisms of dissipation of excess light energy. This article deals see more with adaptation of plants to high and low light conditions. The fast fluorescence induction curves were measured up to 2 s, and the transients were analyzed by a fluorescence induction algorithm. In Fig. 1

the OJIP fluorescence transients are presented for Canola leaves under different conditions. The full bold curve Selleck Trichostatin A represents the variable fluorescence for a wild-type (S) leaf Ku-0059436 nmr pre-conditioned at low light (LL, 8 μmol photons m−2s−1). It shows the usual transients O, J, I, and P, as reported earlier for intact leaves under comparable conditions (Strasser et al. 1995; van Rensen and Vredenberg Phospholipase D1 2009). The dashed bold curve is measured after pre-conditioning at high light (HL, between 1,100 and 1,200 μmol photons m−2s−1). While the curves were measured for the same leaf, the J, I, and P transients after pre-conditioning at HL were all lower than after pre-conditioning at LL. The thin lines represent the comparable curves for a triazine-resistant (R) leaf. In Fig. 2, the bold lines show the measurements for an R leaf, pre-conditioned at LL (full line) or at HL (dashed line) and the thin curves are the measurements for the S leaf. As was found in the S leaf, in the R leaf the J, I and P transients after pre-conditioning after HL were also lower than after pre-conditioning at

LL. As can be observed in Figs 1 and 2, F o for the R leaf was substantially higher than for the S leaf; the J-level was comparatively more and the I-transient was less pronounced in the low light-adapted R leaf. This has been observed earlier by Kohno et al. (2000) and van Rensen and Vredenberg (2009). The higher F o in the R leaf is ascribed to a larger fraction of dark-reduced QB-nonreducing reaction centers; the higher J-level in R can be explained by the lower rate of electron flow between QA and QB (Jansen and Pfister 1990). In Fig. 3 the results are presented of a simulation of the curves of LL pre-conditioned S and R leaves using the algorithm as described in Eqs. 1–3. The diamonds of the calculations fit the dashed lines of the measurements very well.