Photosynthetic efficiency was measured as described byAffenzeller et al

Photosynthetic efficiency was measured as described byAffenzeller et al. an unicellular green alga of the family Desmidiaceae is a well-studied cell biological model organism. Cr III and VI had inhibiting effects on its cell development, while cell division rates were only impaired by Cr VI. Transmission electron microscopy (TEM) revealed ultrastructural changes such as increased vacuolization, condensed cytoplasm and dark precipitations in the cell wall after 3 weeks of Cr VI treatment. Electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) were applied to measure intracellular chromium distribution. Chromium was only detected after 3 weeks of 10 M Cr VI treatment in electron dense precipitations found in bag-like structures along the inner side of the cell walls together with iron and elevated levels of oxygen, pointing toward an accumulation respectively extrusion of chromium in form of an ironoxygen compound. Atomic emission spectroscopy (EMS) revealed thatMicrasteriascells are able to accumulate considerable amounts of chromium and iron. During chromium treatment the Cr:Fe ratio shifted in favor of chromium, which implied that chromium may be taken up instead of iron. Significant and rapid increase of ROS production within the MGC18216 first 5 min of treatment confirms an active Cr VI uptake. SOD and CAT activity after Cr VI treatment did not show a response, while the glutathione pool determined by immuno-TEM decreased significantly in chromium treated cells, showing that glutathione is playing a major role in intracellular ROS and chromium detoxification. == 1. Introduction == Chromium is the SEL120-34A HCl seventh most abundant metal in the earth’s crust (Panda and SEL120-34A HCl Choudhury, 2005) and is naturally occurring in soil, but can be found in all phases of the environment. In fresh water concentrations range from 0.1 to 117 g l1, while concentrations in serpentine soils can reach up to 125 g kg1(Shanker et al., 2005). Chromium has a wide industrial use and is released into the environment by processes such as electroplating, tanning, polishing, painting, pigment manufacture and wood preservation (Peralta-Videa et al., 2009). These anthropogenic activities have led to a widespread contamination of the environment. Chromium is not an essential element for plant nutrition, but may nevertheless be taken up by plants (Liu et al., 2008). Only two oxidative forms Cr III and Cr VI are stable enough to occur naturally, but they are drastically different in charge, physiochemical properties as well as chemical and biochemical reactivity (Kotas and Stasicka, 2000). Overall, Cr VI is considered to be the more toxic than Cr III. As an anion it is negatively charged and highly soluble in water and thus has a better bioavailability and is more mobile than the cationic form Cr III. Like other heavy metals chromium is phytotoxic and can result in growth inhibition, degrade photosynthetic pigments, lead to nutrient and water imbalance and induce oxidative stress (Panda and Choudhury, 2005). Terrestrial plants take up essential and nonessential elements from the soil, while aquatic plants take up ions from all their surroundings. There are many studies of the effects of chromium on higher plants (Liu and Kottke, 2003; Rai and Mehrotra, 2008; Upadhyay and Panda, 2010), but in respect to algae most research focuses on biosorption abilities of certain species for phytoremidiation to remove chromium from contaminated water (Sheng et al., 2004; Rai et al., 2005; Gupta and Rastogi, 2008,). Only few studies investigate the effects of chromium on physiological processes in the algal cells (e.g.Hrcsik et al., 2007; Vignati et al., 2010) and none seem to determine where chromium is located intracellular. Nevertheless it is SEL120-34A HCl of relevance to study not only how much metal can be accumulated, but also to understand how the contaminant is entering a plant cell, what effects it causes on cell physiology, as well as development, whether it is compartmentalized and which detoxification mechanisms exist. This is particularly important since plants are an essential source of food to animals and humans and they are also used as resource.