Combined endophytic inoculants enhance nickel phytoextraction from serpentine soil in the hyperaccumulator Noccaea caerulescens

This study assesses the effects of specific bacterial endophytes on the phytoextraction capacity of the Ni-hyperaccumulator Noccaea caerulescens, spontaneously growing in a serpentine soil environment. Five metal-tolerant endophytes had already been selected for their high Ni tolerance (6 mM) and plant growth promoting ability. Here we demonstrate that individual bacterial inoculation is ineffective in enhancing Ni translocation and growth of N. caerulescens in serpentine soil, except for specific strains Ncr-1 and Ncr-8, belonging to the Arthrobacter and Microbacterium genera, which showed the highest indole acetic acid production and 1-aminocyclopropane-1-carboxylic acid-deaminase activity. Ncr-1 and Ncr-8 co-inoculation was even more efficient in promoting plant growth, soil Ni removal, and translocation of Ni, together with that of Fe, Co, and Cu. Bacteria of both strains densely colonized the root surfaces and intercellular spaces of leaf epidermal tissue. These two bacterial strains also turned out to stimulate root length, shoot biomass, and Ni uptake in Arabidopsis thaliana grown in MS agar medium supplemented with Ni. It is concluded that adaptation of N. caerulescens in highly Ni-contaminated serpentine soil can be enhanced by an integrated community of bacterial endophytes rather than by single strains; of the former, Arthrobacter and Microbacterium may be useful candidates for future phytoremediation trials in multiple metal-contaminated sites, with possible extension to non-hyperaccumulator plants

Studies on plants that hyperaccumulate copper, cobalt and nickel : their potential for use in phytomining and phytoremediation : a thesis presented in partial fulfillment of the requirements for the degree of Masterate of Science in Soil Science at Massey University

This thesis reviews three lines of research on hyperaccumulators to examine their potential for phytoremediation and phytomining. The first line of research was to test the affect of nutrient addition on biomass and nickel uptake by two nickel hyperaccumulators, Alyssum bertotonii and Streptanthus polygaloides. Addition of fertiliser increased the biomass although the maximum amount added was found to be suboptimal. Nutrient addition did not affect the rate of nickel uptake. Larger plants contained a more dilute nickel content but still had an overall larger amount than smaller plants. The second line of research was to test the affect of chelates on metal uptake by copper and cobalt flora of the Democratic Republic of Congo (formally Zaïre) and a copper tolerant plant from Spain, Erica andevalensis. EDTA and Citric Acid increased uptake of copper in these plants but had no effect on the uptake of cobalt and nickel. EDTA increased the uptake of lead by Alyssum bertotonii but did not affect the uptake of zinc and cadmium. The third line of research was to examine the reality of hyperaccumulators of copper and cobalt. Copper and cobalt hyperaccumulation does in fact exist but not to the extent reported previously. There is a good possibility that the previously reported values for copper and cobalt hyperaccumulation are in some cases erroneous due to high iron levels indicating contamination of plant samples by soil

Heavy metal accumulation in Artemisia and foliaceous lichen species from the Azerbaijan flora

Artemisia plants and foliaceous lichens are known to be capable of accumulating heavy metals (HM) from soil and air. These plant species are widespread on polluted sites of Azerbaijan. However, so far their capacity to accumulate HM in their shoots and roots has not been tested. Three Artemisia and two lichen species were collected from different contaminated sites of Azerbaijan. Plant and surface soil samples were measured for Cd, Cu, Pb, Ni and Zn concentrations by ICP-AES.The results indicated that among the Artemisia species A. scoparia showed the best HM accumulation properties. Lichen species were also distinguished by very high amounts of HM in their biomass, while in surrounding soil samples HM concentrations had higher contents than the soils occupied only with Artemisia species.The results indicate that on contaminated sites Artemisia and lichens accumulated metals in their biomass without toxicity symptoms. Taking large biomass and high adaptation ability into account, A. scoparia represents a good tool for a phytoremediation approach on polluted soils

Effect of arsenic-phosphorus interaction on arsenic-induced oxidative stress in chickpea plants

Arsenic-induced oxidative stress in chickpea was investigated under glasshouse conditions in response to application of arsenic and phosphorus. Three levels of arsenic (0, 30 and 60 mg kg−1) and four levels of P (50, 100, 200, and 400 mg kg−1) were applied to soil-grown plants. Increasing levels of both arsenic and P significantly increased arsenic concentrations in the plants. Shoot growth was reduced with increased arsenic supply regardless of applied P levels. Applied arsenic induced oxidative stress in the plants, and the concentrations of H2O2 and lipid peroxidation were increased. Activity of superoxide dismutase (SOD) and concentrations of non-enzymatic antioxidants decreased in these plants, but activities of catalase (CAT) and ascorbate peroxidase (APX) were significantly increased under arsenic phytotoxicity. Increased supply of P decreased activities of CAT and APX, and decreased concentrations of non-enzymatic antioxidants, but the high-P plants had lowered lipid peroxidation. It can be concluded that P increased uptake of arsenic from the soil, probably by making it more available, but although plant growth was inhibited by arsenic the P may have partially protected the membranes from arsenic-induced oxidative stress

Ecological risks of novel environmental crop technologies using phytoremediation as an example:

"Phytoremediation is the use of living plants, known as hyperaccumulators which absorb unusually large amounts of metals in comparison to other plants. The use of classical plant breeding and new molecular techniques offers great potential to develop crops with the ability to clean up polluted sites. While these technologies have gained widespread attention, prior to commercial development, there are risks that must be considered – only a few of which have received even modest examination. Therefore, the focus of this working paper is to explore specific risks associated with phytoremediation and suggest ways in which these risks can be managed so that new, novel, and innovative plant technologies may be applied to provide low cost and efficient environmental solutions. " Authors' AbstractPhytoextraction, Phytomining,

Long-term field metal extraction by pelargonium:phytoextraction efficiency in relation to plant maturity

The long length of periods required for effective soil remediation via phytoextraction constitutes a weak point that reduces its industrial use. However, these calculated periods are mainly based on short-term and/or hydroponic controlled experiments. Moreover, only a few studies concern more than one metal, although soils are scarcely polluted by only one element.In this scientific context, the phytoextraction of metals and metalloids (Pb, Cd, Zn, Cu,and As) by Pelargonium was measured after a long-term field experiment. Both bulk and rhizosphere soils were analyzed in order to determine the mechanisms involved in soil-root transfer. First, a strong increase in lead phytoextraction was observed with plant maturity, significantly reducing the length of the period required for remediation. Rhizosphere Pb, Zn, Cu, Cd, and As accumulation was observed (compared to bulk soil), indicating metal mobilization by the plant, perhaps in relation to root activity. Moreover, metal phytoextraction and translocation were found to be a function of the metals’ nature. These results, taken altogether, suggest that Pelargonium could be used as a multi-metal hyperaccumulator under multi-metal soil contamination conditions, and they also provide an interesting insight for improving field phytoextraction remediation in terms of the length of time required, promoting this biological technique

Cu2+ uptake by Chlorococcum hemicolum - A Xeric Chlorophycean Alga

Bioremediation of copper by xeric chlorophycean bioremediator, Chlorococcum hemicolum was investigated. The growth rates at various concentrations of Cu2+ were assessed in terms of protein level and 8 mg L-1 (37.67 % level in growth kinetics) is the tolerance limit. Absorption/adsorption kinetics was estimated after 240 hrs of Cu2+ treatments. Absorptions were higher than adsorption with maximum accumulation factor (AF) of 1.40. The Cu2+ concentration and absorption were linearly related (r = 0.99; p>0.01). Other biochemical parameters like total sugar, chlorophyll and carotenoids were also quantified to correlate the state of metabolism and these exhibited reduction due to heavy metal stress

Exploring the importance of sulfate transporters and ATP sulphurylases for selenium hyperaccumulation\u2014a comparison of Stanleya pinnata and Brassica juncea (Brassicaceae)

Selenium (Se) hyperaccumulation, the capacity of some species to concentrate Se to levels upwards of 0.1% of dry weight, is an intriguing phenomenon that is only partially understood. Questions that remain to be answered are: do hyperaccumulators have one or more Se-specific transporters? How are these regulated by Se and sulfur (S)? In this study, hyperaccumulator Stanleya pinnata was compared with related non-hyperaccumulator Brassica juncea with respect to S-dependent selenate uptake and translocation, as well as for the expression levels of three sulfate/selenate transporters (Sultr) and three ATP sulphurylases (APS). Selenium accumulation went down ~10-fold with increasing sulfate supply in B. juncea, while S. pinnata only had a 2\u20133-fold difference in Se uptake between the highest (5 mM) and lowest sulfate (0 mM) treatments. The Se/S ratio was generally higher in the hyperaccumulator than the non-hyperaccumulator, and while tissue Se/S ratio in B. juncea largely reflected the ratio in the growth medium, S. pinnata enriched itself up to 5-fold with Se relative to S. The transcript levels of Sultr1;2 and 2;1 and APS1, 2, and 4 were generally much higher in S. pinnata than B. juncea, and the species showed differential transcript responses to S and Se supply. These results indicate that S. pinnata has at least one transporter with significant selenate specificity over sulfate. Also, the hyperaccumulator has elevated expression levels of several sulfate/selenate transporters and APS enzymes, which likely contribute to the Se hyperaccumulation and hypertolerance phenotype

Uptake, sequestration and tolerance of cadmium at cellular levels in the hyperaccumulator plant species Sedum alfredii.

Sedum alfredii is one of a few plant species known to hyperaccumulate cadmium (Cd). Uptake, localization, and tolerance of Cd at cellular levels in shoots were compared in hyperaccumulating (HE) and non-hyperaccumulating (NHE) ecotypes of Sedum alfredii. X-ray fluorescence images of Cd in stems and leaves showed only a slight Cd signal restricted within vascular bundles in the NHEs, while enhanced localization of Cd, with significant tissue- and age-dependent variations, was detected in HEs. In contrast to the vascular-enriched Cd in young stems, parenchyma cells in leaf mesophyll, stem pith and cortex tissues served as terminal storage sites for Cd sequestration in HEs. Kinetics of Cd transport into individual leaf protoplasts of the two ecotypes showed little difference in Cd accumulation. However, far more efficient storage of Cd in vacuoles was apparent in HEs. Subsequent analysis of cell viability and hydrogen peroxide levels suggested that HE protoplasts exhibited higher resistance to Cd than those of NHE protoplasts. These results suggest that efficient sequestration into vacuoles, as opposed to rapid transport into parenchyma cells, is a pivotal process in Cd accumulation and homeostasis in shoots of HE S. alfredii. This is in addition to its efficient root-to-shoot translocation of Cd