Unraveling the crucial role of the ascorbate-glutathione cycle in the resilience of Cistus monspeliensis L. to withstand high As concentrations.

Cistus monspeliensis L. is a species that grows spontaneously in contaminated mining areas of the Iberian Pyrite Belt. This species can accumulate high concentrations of As in the shoots without visible signs of phytotoxicity. In order to understand the physiological mechanisms underlying this tolerance, C. monspeliensis was grown in an Arenosol irrigated with aqueous nutrient solutions containing increasing concentrations of As (0, 1500, 5000, 10000, 15000 µM) and the effects of this metalloid on plant development and on the defence mechanisms against oxidative stress were monitored. Independently of the treatment, As was mainly retained in the roots. The plants with the highest concentrations of As in the shoots (> 5000 µM) showed toxicity symptoms such as chlorosis, low leaf size and decrease in biomass production and also nutritional deficiencies. Most of the studied physiological parameters (pigments, glutathione, ascorbate and antioxidative enzymes) showed significant correlation with As concentration in roots and shoots. Pigments, especially anthocyanins, were negatively affected even in the treatments with the lowest As concentrations. Glutathione increased significantly in roots at low As levels while in shoots this increase occurred in all As treatments. Ascorbate decreased in both tissues with As addition. The highest concentrations of As in shoots of C. monspeliensis triggered defence mechanisms against oxidative stress, namely by inducing the expression of genes coding antioxidative enzymes.

The physiological mechanisms underlying the ability of Cistus monspeliensis L. from São Domingos mine to withstand high Zn concentrations in soils.

Cistus monspeliensis L. is a species that grows spontaneously in contaminated mining areas from the Iberian Pyrite Belt. This species can have high concentrations of Zn in the shoots without visible signs of phytotoxicity. In order to understand the physiological mechanisms underlying this tolerance, C. monspeliensis was grown at several concentrations of Zn(2+) (0, 500, 1000, 1500, 2000µM) and the effects of this metal on plant development and on the defence mechanisms against oxidative stress were evaluated. Independently of the treatment, Zn was mainly retained in the roots. The plants with the highest concentrations of Zn showed toxicity symptoms such as chlorosis, low leaf size and decrease in biomass production. At 2000µM of Zn, the dry biomass of the shoots decreased significantly. High concentrations of Zn in shoots did not induce deficiencies of other nutrients, except Cu. Plants with high concentrations of Zn had low amounts of chlorophyll, anthocyanins and glutathione and high contents of H2O2. The highest concentrations of Zn in shoots of C. monspeliensis triggered defence mechanisms against oxidative stress, namely by triggering antioxidative enzyme activity and by direct reactive oxygen species (ROS) scavenging through carotenoids, that are unaffected by stress due to stabilisation by ascorbic acid.