It is recognised that high environmental concentration of metals are a factor of stress for plants. Metal stress occurs with other abiotic stresses, usually as secondary or tertiary stress. Metal stress is associated with oxidative stress (Clemens 2006) and water stress (Fusco et al. 2005). Protein denaturation is also a common feature for several abiotic stresses including metal excess (Suzuki et al. 2001). A recent review by Maksymiec (2007) lists a series of proteins which are induced by metals and by other environmental stresses: the list includes heat shock proteins, pathogen responsive proteins, and drought responsive proteins. Interaction at cellular level between different stress factors is mediated by signalling pathways, involving common molecules such as ethylene, jasmonic acid and abscisic acid. Nitric oxide is one of these mediators, even though the results relating to its role are still preliminary (Xiong et al. 2010). The possibility of interaction among metal-induced stress and other abiotic and biotic stresses is also becoming relevant also due the global climate change, which will lead to an increase of many stresses: temperature increase, floods and air pollution will exacerbate their effects when there is metal excess in the environment. Crop plants seem to be particularly exposed (Hashiguchi et al. 2010).
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