Fig. 5: Contribution of PGR5 to photoprotection in Scots pine and Norway spruce during the critical spring months.

a, b Abundance of PGR5, PGRL1, and FLVB. Protein levels were examined by immunoblot analyses with specific antibodies against PGR5, PGRL1, and FLVB. Both reduced (red) and oxidized (ox) forms of PGRL1 protein, were detected in Scots pine, were collected from February to June 2017. Twenty-five μg of total protein was loaded per lane, and a representative band from the stained gel is shown as a loading control. Protein levels in Scots pine (black) and Norway spruce (gray) were quantified from three independent experiments using the program ImageJ. Significant differences were indicated with different letters above the bars (one-way ANOVA, P < 0.05). c PSI redox status comparison between spring and summer. The same protocol applied in Fig. 4 was used for samples of Scots pine (dark blue and light blue) and Norway spruce (red and yellow) collected from the field in April (Spring) and in June (Summer). d Effect of antimycin A (AA) treatment upon light fluctuations in a controlled recovery experiment. Scots pine and Norway spruce samples collected from the field in April. After the initial measurements, samples were allowed to recover at room temperature for 24 h, and measured again. Needles were treated with water (orange and yellow circles) or 200 μmol AA (blue and gray circles). The same protocol applied in Fig. 4 was used for the measurements. The parameter Y(I), operating efficiency of PSI is shown. Each data point represents the mean of four biological replicates (mean ± SE, n = 4). e Scots pine samples collected from the field in April and recovered at room temperature for 1 (R-1D), 4 (R-4D), and 6 days (R-6D) were used for determining abundance of PGR5. Representative bands from the ponceau-S stained membranes are shown as loading controls.