Evergreen fir Abies mariesii growing at the tree line (near 2 500 m altitude) on Mt. Norikura (36°61'N, 137°33'E, 3 026 m altitude) in Central Japan is exposed to harsh winter stresses. To protect against these stresses, the deep-oxidation state of the xanthophyll cycle pigments increased, because the needles contained large amounts of zeaxanthin, which resulted in an increase of non-radiative thermal dissipation from the antenna system. Not only the antenna system but also the inactivated photosystem (PS) 2 reaction centre (RC) might contribute to the heat dissipation of absorbed excess photon energy. In addition, a decrease in the PS2 activity during winter was derived from the degradation of the PS2 RCs. Thus the needles acclimated to the strong sunlight during the harsh winter. Under such conditions, only the abaxial side of A. mariesii needles occasionally changed colour from green to reddish-brown in early spring. Since this needle damage was only observed in shoots that protruded from the snow surface, this phenomenon might be caused by the interaction between the strong sunlight reflected from the snow surface and the long period of sub-zero temperatures. We also examined how the photoprotective functions of A. mariesii growing at the tree line of a temperate zone mitigate the interactive stresses of high photon flux density and sub-zero temperature in harsh winter. and J.-Y. Yamazaki ... [et al.].
Water deficit is an important exogenous factor that enhances the influx of sucrose into sugarcane (Saccharum spp.) stem internodes during ripening, when photosynthetic ability in supplying sinks is essential. The aim of this study was to test the hypothesis that drought tolerance in sugarcane is associated with an effective antioxidant protection during the ripening phase that might maintain a favorable redox balance in chloroplasts and protect photosynthesis under drought conditions. Two commercial sugarcane varieties, IACSP94-2094 (tolerant) and IACSP96-2042 (sensitive), with contrasting behavior under water deficit, were subjected to water withholding during the ripening stage. Our results revealed that the tolerant variety was less affected by water deficit, maintaining photosynthesis for a longer period and showing a faster recovery after rehydration as compared to the sensitive one. As consequence, the tolerant variety faced lesser excess of light energy at PSII. The maintenance of photosynthesis under water deficit and its fast recovery after rehydration resulted in the lower leaf H2O2 concentration and favorable redox status in the drought-tolerant genotype, which was associated with stimulation of superoxide dismutase during ripening. Our results also revealed that ferric superoxide dismutase isoforms were strongly enhanced under drought conditions, playing an important role in chloroplast redox homeostasis., C. R. G. Sales, P. E. R. Marchiori, R. S. Machado, A. V. Fontenele, E. C. Machado, J. A. G. Silveira, R. V. Ribeiro., and Obsahuje seznam literatury