Characterization of acclimation of Hordeum vulgare to high irradiation based on different responses of photosynthetic activity and pigment composition.

The ability of spring barley (Hordeum vulgare cv. Akcent) to adjust the composition and function of the photosynthetic apparatus to growth irradiances of 25-1200 mumol m(-2) s(-1) was studied by gas exchange and chlorophyll a fluorescence measurements and high-performance liquid chromatography. The increased growth irradiance stimulated light- and CO(2)-saturated rates of CO(2) assimilation expressed on a leaf area basis up to 730 mumol m(-2) s(-1) (HL730), whereas at an irradiance of 1200 mumol m(-2) s(-1) (EHL1200) both rates decreased significantly. Further, the acclimation to EHL1200 was associated with an extremely high chlorophyll a/b ratio (3.97), a more than doubled xanthophyll cycle pool (VAZ) and a six-fold higher de-epoxidation state of the xanthophyll cycle pigments as compared to barley grown under 25 mumol m(-2) s(-1) (LL25). EHL1200 plants also exhibited a long-term inhibition of Photosystem II (PS II) photochemical efficiency (F (v)/F (m)). Photosynthetic capacity, chlorophyll a/b and VAZ revealed a linear trend of dependence on PS II excitation pressure in a certain range of growth irradiances (100-730 mumol m(-2) s(-1)). The deviation from linearity of these relationships for EHL1200 barley is discussed. In addition, the role of increased VAZ and/or accumulation of zeaxanthin and antheraxanthin in acclimation of barley to high irradiance is studied with respect to regulation of non-radiative dissipation and/or photochemical efficiency within PS II.