Sugarcane A Phytoremediator

Sugarcane (Saccharum spp.) has the potential to be a phytoremediator species due to its outstanding biomass production, but its metal accumulation and tolerance have not been fully characterized. Sugarcane plantlets are able to tolerate up to 100 |M of copper in nutrient solution for 33 days with no significant reduction in fresh weight while accumulating 45 mg Cu kg-1 shoot dry weight. Higher levels of copper in solution (250 and 500 |M) are lethal. Sugarcane exhibits tolerance to 500 |M Cd without exhibiting any symptoms of toxicity; it accumulates 451 mg Cd kg-1 shoot dry weight after 33 days, indicating its potential as a Cd phytoremediator. DNA gel blot analyses yield eight fragments using a metallothionein (MT) Type I probe, ten for the MT Type II, and eight for MT Type III. The number of genes for each type of MT in sugarcane may be similar to those identified in rice, considering the interspecific origin of sugarcane cultivars. The MT Type I gene appears to present the highest level of constitutive expression, mainly in roots, followed by MT Type II, thus corroborating the expression pattern described following large-scale expressed sequence tag sequencing. The MT Type II and III genes are more strongly expressed in shoots, where MT I is also strongly expressed. Increasing the Cu concentration has little or no effect on MT gene expression, while minor modulations of the expressions of some of the MT genes can be detected in Cd treatments. However, the level of response is too small to explain the tolerance and/or accumulation of Cd in sugarcane tissues. Thus, the tolerance and accumulation of cadmium in sugarcane may be derived from other mechanisms, although MT may be involved in oxidative responses to high levels of Cd. As a result, sugarcane should be tested as a potential candidate for Cd phytoremediation (Sereno et al. 2007).

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