Phenolic compounds and carotenoids during acclimation of spring barley and its mutant Chlorina f2 from high to low irradiance

We examined the dynamics of phenolic compounds (PheCs) and carotenoids (Cars) in the leaves of wild type (WT) spring barley (Hordeum vulgare L.) and its mutant lacking chlorophyll b Chlorina f2 (Clo f2) grown from seeds at high irradiance (8 d at 1 000 mu mol m(-2) s(-1); HI) during 9 d of acclimation to low irradiance (50 mu mol m(-2) s(-1); LI). Our results show that a leaf epidermal flavonoid UV-shielding index remained rather constant after transfer of plants from HIto LIconditions and that it was significantly lower in Clo f2 compared to WTplants. This suggests that HIpretreated plants can be well protected against excessive UVfor at least 9 d, as supported also by the constant absorbance of leaf PheCs extracts in the UV-A region (at 335 nm). In contrast, absorbance in the UV-B region (at 270 nm) was reduced, particularly during the initial days of LItreatment, indicating specific changes in PheC profile. High-performance liquid chromatography of soluble PheCs revealed stable content of the major PheC saponarin during LIacclimation, whereas luteolin and feruloylquinic acid content decreased, particularly in WTplants. We also observed a pronounced decrease in Car relative content, particularly a reduction in the xanthophyll cycle pigments (violaxanthin, antheraxanthin, and zeaxanthin, VAZ) pool and diminution of their de-epoxidation state (DEPS) in dark-adapted leaves. As both VAZ and DEPS were higher in HI-acclimated Clo f2 plants than they were in WTplants, the presence of a significant VAZ pool within the lipid phase of thylakoid membrane is indicated. That can contribute to antioxidant capacity particularly in Clo f2 plants. We can therefore conclude that there is a tendency to retain the PheCs responsible for UVshielding during LIacclimation. Meanwhile, the accumulation of both PheCs and zeaxanthin serving as effective antioxidants is considerably downregulated within 9 d.