Effects of UVR on the photochemical efficiency and photosynthetic pigment content of different blade parts in Porphyra yezoensis

In this study,the amount of damage to Porphyra yezoensis by ultraviolet radiation(UVR)was assessed by analyzing the photochemical efficiency and pigment concentration between different blade parts under laboratory conditions.All parts of the blade were exposed to either PAB(PAR+ UV-A+UV-B)(280-700 nm)a full spectrum or partial PAR(395-700 nm)spectrum using cut-off glass filters.It was observed that PAB caused a more significant decrease in the optimal photochemical efficiency than PAR in all blade parts,followed by a lower recovery toward the initial values.Marked differences of the optimal photochemical efficiency between all parts of blade under UV exposure were observed.Apical parts were more resistant but had quicker recovery,basal parts were more sensitive to PAB and had slower recovery.After different radiation treatment,phycoerythrin(PE)and phycocyanin(PC)are more sensitive to PAB treatment and increased significantly in all parts of blade.The PE and PC contents of apical parts had extreme increase,while no remarkable differences of Chlorophyll a and carotenoid were observed.Determination of mycosporine-like amino acids(MAAs)before and during exposure to solar simulated irradiation showed no remarkable differences.The MAAs contents increased from basal to apical parts.Above all,the different parts of Porphyra yezoensis displayed bigger dissimilarity in the photosynthetic physiology characteristics.We presumed that the strategies to cope with UV radiation may including sheltering effect,accumulateing UV absorbing substance and dynamic photoinhibition.