Copper-induced inhibition of photosynthesis: limiting steps of in vivo copper chlorophyll formation in Scenedesmus quadricauda

Abstract

The in vivo substitution of Mg2+ in chlorophyll by heavy metals is an important damage mechanism in heavy metal-stressed plants that leads to an inhibition of photosynthesis. In photosynthetic organisms with LHC II antennae, the in vivo substitution of Mg2+ by Cu2+ occurs particularly readily under low irradiance with a dark phase — a phenomenon referred to as 'shade reaction'. In the present study the limiting steps of the shade reaction were investigated with synchronised cultures of the chlorococcal green alga Scenedesmus quadricauda (Turp.) Bréb. The rate of copper chlorophyll formation during shade reaction was shown to be controlled by several factors; firstly, in some phases of the cell cycle, especially at the end of the light period, Mg2+ in chlorophyll was not accessible to substitution. This pattern is likely to be caused by cell cycle-dependent changes in photosynthesis and thylakoid ultrastructure, which were published earlier and are reconsidered in the discussion of the present work. Secondly, prolonged culture in a medium containing 3 μM Cu2+ reversibly increased the resistance of the strain to Cu2+. Culturing without added Cu2+ lowered the threshold concentrations of various deleterious effects more than 10-fold within 8 months of de-adaptation. Adaptation to high Cu2+ levels is discussed in the context of studies of the regulation of metal transporter proteins. In addition, it was also observed that toxic Cu2+ levels impaired photosynthesis sooner than cell division.

The effects of copper on the photosynthetic response of Phaeocystis cordata

“…ions, followed by photosynthesis and respiration. In contrast, Miao et al (2005) using batch cultures and environmentally relevant Cu levels (pCu 13 to pCu 5.6) suggested that phytoplankton growth rates were as sensitive as F v /F m (equivalent to U M ) for the detection of Cu toxicity, whereas Kupper et al (2003) observed that toxic Cu levels impaired photosynthesis faster than cell division in Scenedesmus quadricauda cultures. We believe that some of the literature controversial effects of high Cu in U M might be because of whether batch versus semi-continuous cultures were used, as well as the time of sampling.…”

Differential effects of copper and cadmium exposure on toxicity endpoints and gene expression in Chlamydomonas reinhardtii

“…29,2010with increasing concentration over the range of 20 to 80 nM of Cu. Copper has been shown to inhibit photosynthesis through substitution for Mg 2þ in chlorophyll [30], but Cd may act differently to inhibit photosynthesis, such as by binding to a Ca site in Photosystem II [17].…”

Response at Genetic, Metabolic, and Physiological Levels of Maize (Zea mays) Exposed to a Cu(OH)2 Nanopesticide

“…The reduction of chlorophyll content induced by excess copper in chloroplasts has been observed in a variety of species such as Ceratophyllum demersum L., 23 Empetrum nigrum, 24 Brassica pekinensis Rupr, 25 and Triticum aestivum L. 26 It has been proposed that Cu at high concentrations affects plants via two main mechanisms: interference with enzymes associated with chlorophyll biosynthesis and the changes in protein composition of photosynthetic membranes. 27,28 In addition, Cu-induced Fe deficiency 29 and the displacement by Cu of the Mg required for chlorophyll biosynthesis 30 have been proposed as possible additional damage mechanisms.…”