Fig. 2.

UV-B induces the capacity for qE. The qE component of NPQ was determined by chlorophyll fluorescence measurements in the presence (red circles) or absence (black squares) of 10 µM nigericin. Dark-adapted cells (black bar at top) were exposed to strong light for 300 s (750 µmol⋅m⁻²⋅s⁻¹; white bar) and then returned to the dark (dark bar). Fluorescence (relative units; r.u.) was monitored continuously (open symbols) and during saturating flashes (2,500 µmol⋅m⁻²⋅s⁻¹ at 60-s intervals; filled symbols). (A and B) WT (WT 137C) (A) and npq4 (B) after exposure for 6 h to UV-B. (C and D) WT (C) and npq4 (D) after exposure for 6 h to high light (HL). (E and F) qE values after 2, 4 or 6 h of exposure to UV-B (+UV-B) or without exposure (−UV-B) and after 6 h of exposure to high light (HL). Means ± SD are shown (n = 3) for qE calculated at the end of the actinic light treatment. (G) qE values after 6-h exposure of the WT and in mutants npq4, lhcsr1 and npq4 lhcsr1 to UV-B or to high light (HL). Means ± SD are shown (n = 4 for HL; n = 6 for UV samples).