Simultaneous Analysis of Photosystem Responses of Microcystis aeruginoga

Chromium (Cr) caused widespread environmental problem since its compounds are widely used in various industrial processes such as leather tanning and textile. Cr occurs mainly as trivalent Cr(III) and hexavalent Cr(VI) species, and the toxicity of Cr depends on its species.

Microalgae and cyanobacteria, as important primary producers in water bodies, are frequently used in environmental risk assessment due to their sensitivity to contaminants. Because Cr is a major pollutant in water bodies, phytoplankton species such as cyanobacteria are frequently exposed to Cr. Physiological responses of microalgae and cyanobacteria to Cr stress have been investigated extensively. Photosynthetic apparatus is one of the sensitive target sites to Cr toxicity. However, to date effects of Cr(VI) on photosystem II (PSII) and photosystem I (PSI) in cyanobacteria and responses of photosynthetic activities such as electron transport in PSII andPSI to Cr(VI) and increasing illumination are unclear.

Microcystis aeruginosa has often been used as a model microbial species for examining effects of contaminants on photosynthesis. Therefore, WANG Shuzhi et al. used M. aeruginosa to detect the effects of Cr(VI) on PSII and PSI activities with the aid of a Dual-PAM-100system. The aim of this study was to detect responses of complementary quantum yields of energy conversion in PSI and PSII and cyclic electron flow (CEF) of PSI at various concentrations of Cr(VI) and increasing illumination.

The result showed that, at 5mgL^-1 Cr(VI), quantum yield and electron transport rate of PSII decreased significantly, and light-induced non-photochemical fluorescence quenching lost. Cr(VI) also inhibited efficiency of PSII to use energy under high light more than of PSI. PSII showed lower maximal electron transport rate and light adaptability than PSI. Electron transport rate of PSI was higher and decreased less than that of PSII, implying less sensitivity of PSI to high light and Cr(VI). Energy dissipation through non-light-induced non-photochemical fluorescence quenching increased with increasing Cr(VI) concentration. CEF was stimulated under Cr(VI) treatment and made a significant contribution to quantum yield and electron transport of PSI, which was essential for protection of PSI from stresses of Cr (VI) and high light.

The result was published in Ecotoxicology and Environmental Safety on February 2013, 88: 163-168.

Contact:

Prof. PAN Xiangliang

Email: panxl@ms.xjb.ac.cn