Response of antioxidant enzymes in Nicotiana tabacum clones during phytoextraction of heavy metals.

Tobacco, Nicotiana tabacum, is a widely used model plant for growth on heavy-metal-contaminated sites. Its high biomass and deep rooting system make it interesting for phytoextraction. In the present study, we investigated the antioxidative activities and glutathione-dependent enzymes of different tobacco clones optimized for better Cd and Zn accumulation in order to characterize their performance in the field. The improved heavy metal resistance also makes the investigated tobacco clones interesting for understanding the plant defense enzyme system in general. Freshly harvested plant material (N. tabacum leaves) was used to investigate the antioxidative cascade in plants grown on heavy metal contaminated sites with and without amendments of different ammonium nitrate and ammonium sulfate fertilizers. Plants were grown on heavily polluted soils in north-east Switzerland. Leaves were harvested at the field site and directly deep frozen in liquid N-2. Studies were concentrated on the antioxidative enzymes of the Halliwell-Asada cycle, and spectrophotometric measurements of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), superoxide dismutase (SOD, EC 1.15.1.1), glutathione peroxidase (GPX, EC 1.11.1.9), glutathione reductase (GR, EC 1.6.4.2), glutathione S-transferase (GST, EC 2.5.1.18) were performed. We tried to explain the relationship between fertilizer amendments and the activity of the enzymatic defense systems. When tobacco (N. tabacum) plants originating from different mutants were grown under field conditions with varying fertilizer application, the uptake of cadmium and zinc from soil increased with increasing biomass. Depending on Cd and Zn uptake, several antioxidant enzymes showed significantly different activities. Whereas SOD and CAT were usually elevated, several other enzymes, and isoforms of GST were strongly inhibited. Heavy metal uptake represents severe stress to plants, and specific antioxidative enzymes are induced at the cost of more general reactions of the Halliwell-Asada cycle. In well-supplied plants, the glutathione level remains more or less unchanged. The lack of certain glutathione S-transferases upon exposure to heavy metals might be problematic in cases when organic pollutants coincide with heavy metal pollution. When planning phytoremediation of sites, mixed pollution scenarios have to be foreseen and plants should be selected according to both, their stress resistance and hyperaccumulative capacity

Copper phytoextraction in tandem with oilseed production using commercial cultivars and mutant lines of sunflower

Use of sunflower (Helianthus annuus L.) for Cu phytoextraction and oilseed production on Cu-contaminated topsoils was investigated in a field trial at a former wood preservation site. Six commercial cultivars and two mutant lines were cultivated in plots with and without the addition of compost (5% w/w) and dolomitic limestone (0.2% w/w). Total soil Cu ranged from 163 to 1170 mg kg−1. In soil solutions, Cu concentration varied between 0.16– 0.93 mg L−1. The amendment increased soil pH, reduced Cu exposure and promoted sunflower growth. Stem length, shoot and capitulum biomasses, seed yield, and shoot and leaf Cu concentrations were measured. At low total soil Cu, shoot Cu mineralomass was higher in commercial cultivars, i.e., Salut, Energic, and Countri, whereas competition and shading affected morphological traits of mutants. Based on shoot yield (7 Mg DW ha−1) and Cu concentration, the highest removal was 59 g Cu ha−1. At high total soil Cu, shoot Cu mineralomass peaked for mutants (e.g., 52 g Cu ha−1 for Mutant 1 line) and cultivars Energic and Countri. Energic seed yield (3.9 Mg air-DW ha−1) would be sufficient to produce oil. Phenotype traits and shoot Cu removal depended on sunflower types and Cu exposure

Increased tolerance of sunflower mutant seedlings to Cd and Zn in hydroponic culture

Cadmium and zinc show similarities in their chemistry, geochemistry and environmental properties. Whereas Cd is a phytotoxic non-essential element, Zn is an essential trace element for plant growth and development. Zinc plays a fundamental role in several key cellular functions, such as protein metabolism, gene expression, chromatin structure, photosynthetic carbon metabolism and indole acetic acid metabolism (Vallee and Falchuk, 1993; Marschner, 1995; Bonnet et al., 2000; Cakmak and Braun, 2001). Zinc is also an important component of many enzymes and proteins (Broadley et al., 2007). Cadmium can readily inhibit most of the Zn-dependent processes by binding to the membrane and to enzyme active sites, thus inactivating their functions (Aravind and Prasad, 2005). However, increasing Zn concentrations can replace such wrongly bound Cd (Van Assche and Clijsters, 1990; Shaw et al., 2004). Cadmium has been shown to cause many morphological, physiological, biochemical and structural changes in plants, such as growth inhibition, reduction in photosynthesis, transpiration or water imbalance (Sanità di Toppi and Gabbrielli, 1999; Schützendübel et al., 2001; Benavides et al., 2005; Mishra et al., 2006). Cadmium and high zinc concentration affect plant growth and metabolism, but the intensity of their toxic effects depends on plant species and the way and duration of metal exposure. Plants called hyperaccumulators are able to tolerate and accumulate extraordinary levels of trace elements in their above-ground tissue without developing any toxicity symptoms (Baker and Brooks, 1989; Reeves and Baker, 2000). Their high metal accumulation capability makes them interesting for the decontamination technique called phytoextraction, which uses plants for environmental clean-up (Salt et al., 1998). However, their low biomass production strongly limits the real application of this soil decontamination strategy. The ideal plant for phytoextraction should provide both a high biomass and a high tolerance and metal accumulation (Schwitzguébel et al., 2002). High biomass producing plants with improved tolerance to trace elements and with an enhanced metal accumulation capacity should be good candidates for metal removal from contaminated area. Previous studies have shown enhanced tolerance and metal accumulation properties in transgenic tobacco plants (Pomponi et al., 2006; Gorinova et al., 2007; Wojas et al., 2008). However, the main disadvantage of genetic engineering is still public acceptance and free-land application. In vitro breeding techniques have also been successfully used to obtain tobacco lines with a considerably enhanced Cd, Zn and Cu tolerance and metal accumulation (Herzig et al., 1997; Guadagnini et al., 1999; Herzig et al., 2003). In addition, the chemical mutagen ethyl methane sulphonate has been used to develop new sunflower lines with a significantly enhanced biomass and metal uptake on a metal contaminated field (Nehnevajova et al., 2007, 2009). Although these field experiments have revealed the potential of sunflower mutants for metal phytoextraction, their tolerance to trace elements and the effect of Cd and Zn on growth and photosynthetic pigments were not studied within previous free-land experimentation. The aim of the present work was thus to assess the tolerance to Cd and excess Zn of selected sunflower mutant lines with improved biomass and metal uptake capacity, by measuring different physiological parameters. For such a purpose, sunflower seedlings of eight selected mutant lines were cultivated under hydroponic conditions in the presence and in the absence of Cd and Zn to study the effect of these trace elements on (1) growth parameters, such as root elongation, root and shoot dry mass; (2) chlorophyll content; (3) carotenoid content; (4) Cd and Zn accumulation capacity of sunflower mutants; and (5) a possible correlation between Cd and Zn accumulation in sunflower shoots and roots

Copper phytoextraction in tandem with oilseed production using commercial cultivars and mutant lines of sunflower

Use of sunflower (Helianthus annuus L.) for Cu phytoextraction and oilseed production on Cu-contaminated topsoils was investigated in a field trial at a former wood preservation site. Six commercial cultivars and two mutant lines were cultivated in plots with and without the addition of compost (5% w/w) and dolomitic limestone (0.2% w/w). Total soil Cu ranged from 163 to 1170 mg kg−1. In soil solutions, Cu concentration varied between 0.16– 0.93 mg L−1. The amendment increased soil pH, reduced Cu exposure and promoted sunflower growth. Stem length, shoot and capitulum biomasses, seed yield, and shoot and leaf Cu concentrations were measured. At low total soil Cu, shoot Cu mineralomass was higher in commercial cultivars, i.e., Salut, Energic, and Countri, whereas competition and shading affected morphological traits of mutants. Based on shoot yield (7 Mg DW ha−1) and Cu concentration, the highest removal was 59 g Cu ha−1. At high total soil Cu, shoot Cu mineralomass peaked for mutants (e.g., 52 g Cu ha−1 for Mutant 1 line) and cultivars Energic and Countri. Energic seed yield (3.9 Mg air-DW ha−1) would be sufficient to produce oil. Phenotype traits and shoot Cu removal depended on sunflower types and Cu exposure

Metal accumulation and response of antioxidant enzymes in seedlings and adult sunflower mutants with improved metal removal traits on a metal-contaminated soil.

Sunflower mutant lines with an enhanced tolerance and metal accumulation capacity obtained by mutation breeding have been proposed for Zn, Cd and Cu removal from metal-contaminated soils in previous studies. However, soils contaminated with trace elements induce various biochemical alterations in plants leading to oxidative stress. There is a lack of knowledge concerning the metal accumulation and antioxidant responses during the growth and development of sunflowers. This study, therefore, aimed to characterise metal accumulation and possible metal detoxification mechanisms in young seedlings and adult sunflowers. Beside the inbred line, two mutant lines with an improved growth and enhanced metal uptake capacity on a metal contaminated soil were investigated in more detail. Sunflowers cultivated on a metal-contaminated soil in the greenhouse showed a decrease in shoot biomass and chlorophyll concentration in two different developmental stages. Adult sunflowers showed a lower sensitivity to metal toxicity than young seedlings, whereas mutant lines were more tolerant to metal stress than the control. Mutant lines also produced a higher amount of carotenoids on a metal contaminated soil than on the control soil, indicating a possible protective mechanism of sunflower mutants against oxidative stress caused by Cd and excess Zn. Heavy metals primarily increased the activity of antioxidant enzymes involved in the ascorbate–glutathione cycle in sunflower leaves. Activity of dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) was strongly increased in young seedlings exposed to heavy metals. The enzyme activities were even more pronounced in mutant lines. A significantly increased ascorbate peroxidase (APOX) activity in adult sunflowers exposed to heavy metals indicated an elevated use of ascorbate after a longer exposure to metal stress. An increased antioxidant level corresponded to a high Cd and Zn accumulation in young and adult sunflowers.Metal distribution, zinc translocation in particular, from the root into the shoot tissue obviously increased during sunflower growth and ripening. Altogether, these results suggest that sunflower plants, primarily the mutant lines, possess an efficient defence mechanism against oxidative stress caused by metal toxicity. A good tolerance of sunflowers toward heavy metals coupled with an increased metal accumulation capacity might contribute to an efficient removal of heavy metals from a polluted area

Bioenergy to save the world. Producing novel energy plants for growth on abandoned land.

Following to the 2006 climate summit, the European Union formally set the goal of limiting global warming to 2 degrees Celsius. But even today, climate change is already affecting people and ecosystems. Examples are melting glaciers and polar ice, reports about thawing permafrost areas, dying coral reefs, rising sea levels, changing ecosystems and fatal heat periods. Within the last 150 years, CO2 levels rose from 280 ppm to currently over 400 ppm. If we continue on our present course, CO2 equivalent levels could approach 600 ppm by 2035. However, if CO2 levels are not stabilized at the 450-550 ppm level, the consequences could be quite severe. Hence, if we do not act now, the opportunity to stabilise at even 550 ppm is likely to slip away. Long-term stabilisation will require that CO2 emissions ultimately be reduced to more than 80% below current levels. This will require major changes in how we operate. RESULTS: Reducing greenhouse gases from burning fossil fuels seems to be the most promising approach to counterbalance the dramatic climate changes we would face in the near future. It is clear since the Kyoto protocol that the availability of fossil carbon resources will not match our future requirements. Furthermore, the distribution of fossil carbon sources around the globe makes them an even less reliable source in the future. We propose to screen crop and non-crop species for high biomass production and good survival on marginal soils as well as to produce mutants from the same species by chemical mutagenesis or related methods. These plants, when grown in adequate crop rotation, will provide local farming communities with biomass for the fermentation in decentralized biogas reactors, and the resulting nitrogen rich manure can be distributed on the fields to improve the soil. DISCUSSION: Such an approach will open new economic perspectives to small farmers, and provide a clever way to self sufficient and sustainable rural development. Together with the present economic reality, where energy and raw material prices have drastically increased over the last decade, they necessitate the development and the establishment of alternative concepts. CONCLUSIONS: Biotechnology is available to apply fast breeding to promising energy plant species. It is important that our valuable arable land is preserved for agriculture. The opportunity to switch from low-income agriculture to biogas production may convince small farmers to adhere to their business and by that preserve the identity of rural communities. PERSPECTIVES: Overall, biogas is a promising alternative for the future, because its resource base is widely available, and single farms or small local cooperatives might start biogas plant operation