How Plants Cope with Cadmium: Staking All on Metabolism and Gene Expression

Abstract

Environmental pollution is one of the major problems for human health. Toxic heavy metals are normally present as soil constituents or can also be spread out in the environment by human activity and agricultural techniques. Soil contamination by heavy metals as cadmium, highlights two main aspects: on one side they interfere with the life cycle of plants and therefore reduce crop yields, and on the other hand, once adsorbed and accumulated into the plant tissues, they enter the food chain poisoning animals and humans. Considering this point of view, understanding the mechanism by which plants handle heavy metal exposure, in particular cadmium stress, is a primary goal of plant-biotechnology research or plant breeders whose aim is to create plants that are able to recover high amounts of heavy metals, which can be used for phytoremediation, or identify crop varieties that do not accumulate toxic metal in grains or fruits. In this review we focus on the main symptoms of cadmium toxicity both on root apparatus and shoots. We elucidate the mechanisms that plants activate to prevent absorption or to detoxify toxic metal ions, such as synthesis of phytochelatins, metallothioneins and enzymes involved in stress response. Finally we consider new plant-biotechnology applications that can be applied for phytoremediation.Key words: cadmium; heavy metals; metallothioneins; phytochelatins; phytoremediation; transporters. Available online at www.jipb.net As sessile organisms plants have restricted mechanisms for stress avoidance and are subjected to environmental stresses that change growth conditions and alter (or sometimes disrupt) their metabolic homeostasis. Worldwide, these stresses are the most limiting factors for crop productivity: a large proportion of annual yield is lost due to pathogen attack and to unfavorable abiotic conditions such as drought, salinity and extreme temperatures. The average and record yields of many crops were compared in a classical study (Boyer 1982) and it was found that crop plants were reaching only 20% of their genetic yield potential. Diseases, insects and weeds contributed only in part, with the major yield reduction resulting from abiotic stresses. Therefore, understanding how plants cope with stresses and

Expression of stress-related genes in tomato plants exposed to arsenic and chromium in nutrient solution

“…The well-characterized cysteine-rich polypeptides, MTs, can bind to heavy metals in the cytoplasm and sequester them into the vacuoles or out of the cells. Most heavy metals induce the synthesis of MTs, preventing the disruption of homeostasis due to environmental stress (DalCorso , 2008 et al ). This detoxification mechanism is particularly efficient in metallophyte plant tolerant varieties with high transcription rate of MTs (Hall, 2002).…”

Metal uptake, oxidative metabolism, and mycorrhization in pigeonpeaand pea under arsenic and cadmium stress

“…Exposure to Cd drives oxidative injuries, such as lipid peroxidation, which leads to alteration in the membrane functionality and protein carbonylation (Schützendübel et al, 2001;Romero-Puertas et al, 2002;DalCorso et al, 2008DalCorso et al, , 2010Garg and Aggarwal, 2012). A possible constitutive mechanism of detoxification in plants is upregulation of antioxidants such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), peroxidase (POX), and catalase (CAT) (Meharg, 2005;Gomes et al, 2012;Dave et al, 2013;Sobrino-Plata et al, 2014).…”

“…Arsenic (As) and cadmium (Cd) pose serious environmental threats due to their significant toxicities (DalCorso et al, 2008;Bhattacharya et al, 2012) and their contamination in soils can be due to natural (disintegration of rocks and minerals and lixiviation) (Baker et al, 1990) and/or anthropogenic sources (Sun et al, 2008(Sun et al, , 2009Peralta-Videa et al, 2009;Jia et al, 2012;wall and membrane permeability by binding to nucleophilic groups (Ramos et al, 2002;Verbruggen et al, 2009). Thus, plant P/As and P/Cd molar ratios can be a good index for their relative abundance and their important roles in the plant growth.…”

Expression of SOD gene and evaluating its role in stress tolerance in NaCl and PEG stressed Lycopersicum esculentum

“…Nonenzymatic antioxidants include glutathione (GSH), proline, carotenoids, tocopherol, etc. The enzymatic antioxidants are monodehydroascorbate reductase (MDHAR), dehydro ascorbate reductase (DHAR), glutathione reductase (GR), ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD) Verma and Dubey, 2003;Halliwell, 2006;DalCorso et al, 2008).…”