Primary Targets of Heavy Metal Toxicity

Many of the toxic responses induced by heavy metals that have been identified to date have to be classified as being general stress responses, rather than ones that are specific to heavy metals. The question then arises as to whether a specific metal ion actually induces a sensing mechanism in the plant cells for the presence of the toxin at all, or whether it just the damage caused by a heavy metal that induces a signal. According to Clemens (2006), the data that are available to answer this question are "rudimentary at best". To give an example, proline accumulates under Cd2+ stress. However, the accumulation does not occur directly in response to the presence of Cd2+ but because of the disturbance to the water balance caused by the excess of Cd2+. One way to investigate the specificity of the stress caused by an excess of a heavy metal ion is to apply the microarray strategy to mRNA-related cDNAs in order to compare the effects of different heavy metals with those of other stress signals, e.g. water deficiency stress. Some data are already available, but we are at a very early stage in this type of research (Clemens 2006; Zimmermann et al. 2004). There is one exception: metal-induced synthesis of phytochelatins (cf. Clemens 2006). In a posttranslational process, the activity of phytochelatin synthase is upregulated by the heavy metal or a metal-glutathione complex. This response does not need much of a signal transduction chain.

Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

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