Effects of Mg2+on spectral characteristics and photosynthetic functions of spinach photosystem II

In the present paper we report the results obtained with the photosystem II (PSII) isolated from spinach treated by MgCl2, and studied the effect of Mg2+ on spectral characteristics and photosynthetic functions of PSII. The results showed that Mg2+ treatment at a suitable concentration could significantly increase the absorption intensity of PSII and the intensity ratio of Soret band to Q band of chlorophyll-a. The treatment also elevated the excited peak intensity at 230, 278 and 343 nm, and the emitted peak intensity at 304 and 682 nm, and the ratio of F278/F230, respectively. The results implied that Mg2+ increased absorbance for visible light, improving energy transfer among amino acids within PSII protein complex and accelerating energy transport from tyrosine residue to chlorophyll-a. The photochemical activity and oxygen evolving rate of PSII were also enhanced by Mg2+. This is viewed as evidence that Mg2+ can promote energy transfer and oxygen evolution in PSII of spinach.