Phytoremediation potential of moso bamboo (Phyllostachys pubescens) for zinc and ultrastructure changes under zinc toxicity
This study has investigated toxicity of Zn and phytoremediation ability in shoot of moso bamboo. In hydroponic experiment the plants showed high Zn torelence up to application of 400 µM, while there was a general trend of decline in the roots and shoot biomass. Maximum concentration of 1594 mg kg–1 was observed in shoot after treating with 100 µM Zn. The shoot/root ratio reached the level of 0.27 under 10 µM zinc stress. Transmission electron microscopy revealed that electron-dense granules in vacuoles and structure of leaf cells were significantly effected by 200 µM of Zn. However, mitochondria and thylakoid membrane arrangement did not alter. Using scanning electron microscopy, Zn-related changes in the structure of the stoma were uncovered and crystal particles probably of Zinc were observed in stem.
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.
Variations of sulphur dioxide at the cloud top of Venus’s dynamic atmosphere
A pulse of sulphur dioxide in Venus’s upper atmosphere was observed by the Pioneer Venus spacecraft in the 1970s and 1980s and attributed to volcanism. Recent sulphur dioxide measurements from Venus Express indicate decadal-scale fluctuations in sulphur dioxide above Venus’s cloud tops in an atmosphere that is more dynamic than expected. Sulphur dioxide is a million times more abundant in the atmosphere of Venus than that of Earth, possibly as a result of volcanism on Venus within the past billion years1,2. A tenfold decrease in sulphur dioxide column density above Venus’s clouds measured by the Pioneer Venus spacecraft during the 1970s and 1980s has been interpreted as decline following an episode of volcanogenic upwelling from the lower atmosphere3,4. Here we report that the sulphur dioxide column density above Venus’s clouds decreased by an order of magnitude between 2007 and 2012 using ultraviolet spectrometer data from the SPICAV instrument onboard the Venus Express spacecraft. This decline is similar to observations during the 1980s. We also report strong latitudinal and temporal variability in sulphur dioxide column density that is consistent with supply fluctuations from the lower atmosphere. We suggest that episodic sulphur dioxide injections to the cloud tops may be caused either by periods of increased buoyancy of volcanic plumes, or, in the absence of active volcanism, by long-period oscillations of the general atmospheric circulation. The 30-year observational record from Pioneer Venus and Venus Express confirms that episodic injections of sulphur dioxide above the clouds recur on decadal timescales, suggesting a more variable atmosphere than expected.