HEAVY METAL‐INDUCED INHIBITION OF PHOTOSYNTHESIS: TARGETS OF IN VIVO HEAVY METAL CHLOROPHYLL FORMATION¹

Abstract

The targets of heavy metal (here Cu2+ and Zn2+) attack on the photosynthetic apparatus of algae belonging to different phyla were investigated. Experiments with the green alga Scenedesmus quadricauda confirmed previous findings that according to the irradiance level two different phenomena occur, which were further characterized by specific changes in several photosynthetic parameters. The reaction occurring under low irradiance (shade reaction) is characterized by heavy metal substitution of Mg2+ in chl molecules bound predominantly in the light harvesting complex II of Chlorophyta (LHC II). Under high irradiance (sun reaction) the LHC II chls are inaccessible to substitution and the damage occurs in the PSII reaction center instead. Algae with antenna proteins other than the LHC II did not show the two types of heavy metal attack at different irradiances. In red algae (Antithamnion plumula), low Cu2+ concentrations induced the sun reaction even at very low irradiance. In brown algae (Ectocarpus siliculosus) the shade reaction occurred even in saturating irradiance. These results also indicate that despite some similarity in their features, the primary step of the sun reaction and photoinhibition is different.

Induction of expression of a 14-3-3 gene in response to copper exposure in the marine alga, Fucus vesiculosus

“…There is increasing evidence to support the involvement of 14-3-3's in phosphorylation cascades involved in the response to reactive oxygen species (ROS) (Huber 2007). This may provide a connection between ROS generation resulting from copper inhibition of PSII and 14-3-3 induction (Kupper et al 2002;. Additional evidence from mammalian systems has linked various binding partners involved in apoptosis with 14-3-3 and comparative proteomic analysis has suggested that the partners and roles of 14-3-3's have been highly conserved among kingdoms (Paul et al 2009).…”

“…Such chelation has been regarded as important for heavy metal resistance (see Kupper et al 2002). However, the synthesis of phlorotannins (brown algal polyphenolics) has been reported to be unaffected by copper exposure (Toth and Pavia 2000) so that alternate chelators may also be needed.…”

“…Of these proteins the cell surface transporter CPOT1 (CTR family), transcription factors and the P-type copper ATPases (HMA family) contain phosphorylation sites (Heredia et al 2001;Voskoboinik et al 2003), but a link to transduction pathways has yet to be established. In algae, as in plants, a major effect of copper toxicity is photoinhibition primarily through impacts within photosystem II leading to localised reactive oxygen species generation and chloroplast dysfunction (Kupper et al 2002).…”

“…Cairrao et al 2007;Giusti 2001; Barreiro et al 2002) and in in vitro toxicity tests . Copper may target various metabolic processes (Kupper et al 2002) but its inhibition of photosynthesis has attracted the most attention (see e.g. Fernandes and Henriques 1991).…”

Effects of Superparamagnetic Iron Oxide Nanoparticles on Photosynthesis and Growth of the Aquatic Plant Lemna gibba

“…It was reported earlier that metals such as cadmium, copper, and chromium ions directly inhibit PSII electron transport at the water-splitting system of the RC (Küpper et al 2002;Popovic et al 2003;Dewez et al 2005;Ait Ali et al 2006). …”