Figure 5. Photosynthetic pigment composition and photoprotection in Col-0, Ws-4 and Ler-0 accessions.

(A) Leaves from plants grown on soil at an irradiance of 120 µmol photons m⁻² s⁻¹ were detached at the end of the dark period, and the pigment composition was determined by HPLC. Amounts of main pigments are expressed relative to Chl a. Neo, neoxanthin; Viola, violaxanthin; Lut, lutein; Chl b, chlorophyll b; ß-car, ß-carotene. The insert presents the total Chl/total Carotenoid ratio. (B) Plot of de-epoxidation ratio (DR) versus irradiance. For determination of xanthophyll cycle activity, leaves were illuminated for 20 min at defined PAR intensity (for 10 min at PAR>1000 µmol photons m⁻² s⁻¹), then the pigments were extracted and quantified. De-epoxidation ratio was calculated as (antheraxanthin+zeaxanthin)/(antheraxanthin+zeaxanthin+violaxanthin) and expressed in %. The data plotted in A and B are means ± SD (n = 3–5). The significant differences are indicated by asterisk (Student's t-test, P<0.05). (C) Plot of NPQ versus irradiance. Chlorophyll fluorescence was measured in leaves illuminated for 20 min at various PAR intensities. NPQ was calculated as (F _m −F _m ′)/F _m ′ and plotted as means ±SD (n = 5–7). SD bars are shown when larger than the symbols.