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Search for plant species - prodigious in P use - is important for both P-sufficient and -deficient conditions. Gulf and Marshall ryegrass (Lolium multiflorum), grown in sterile media containing different organic P substrates (AMP, ATP, GMP, and IHP), exhibited high rates of growth and shoot P concentrations. Growth increase in Gulf was significantly greater on IHP relative to other sources of organic P substrates. Growth was also dependent on an increasing concentration of IHP (0-20 mM) in this cultivar. P accumulations in Gulf exceeded 1% shoot dry weight from IHP, AMP, and ATP-equivalent to the P accrual from equimolar Pi source. Plants supplied with IHP had phytase activity in root extracts comparable to that in Pi-fed plants or control (no P). The extracellular phytase, however, increased by about 100% relative to that observed in root extracts- for both ryegrass cultivars, but there were no significant differences (P < 0.05) between plant groups grown on different substrates (IHP, Pi or control). No significant differences in phosphomonoesterase activities were evident between plant groups supplied with organic P (IHP, G1P) and inorganic source or control. This study establishes the high P-use efficiency in ryegrass, irrespective of P source.

Growth of Sesbania seedlings in chloroaurate solution resulted in the accumulation of gold with the formation of stable gold nanoparticles in plant tissues. Transmission electron microscopy revealed the intracellular distribution of monodisperse nanospheres, possibly due to reduction of the metal ions by secondary metabolites present in cells. X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrated a high degree of efficiency for the biotransformation of Au(III) into Au(0) by planttissues. The catalytic function of the nanoparticle-rich biomass was substantiated by the reduction of aqueous 4-nitrophenol (4-NP). This is the first report of gold nanoparticle-bearing biomatrix directly reducing a toxic pollutant, 4-NP.

Deterioration in water quality caused by the movement of excessive soil P has created a condition necessary for the development of a sustainable P remediation technology. In this investigation, the phytoremediation potential of Gulf and Marshall ryegrass (Lolium multiflorum) grown in a greenhouse was determined under varying conditions of soil P concentration, pH, and temperature. Both genotypes demonstrated P accumulations > or =1% shoot dry weight depending on soil P concentrations (0-10 g of P/kg of soil), with higher shoot P in Gulf than Marshall ryegrass. An increase in plant biomass was proportional to the increasing concentrations of P up to a level of 10 g of P/kg of soil. The effect of soil pH on plant uptake of P was noticeable with a significant rise in shoot P in acidic soil (pH 5.6) as compared to soil with pH 7.8. Significant differences were observed in the biomass productivity and shoot P accumulation at varying temperatures in both grass types. The patterns of acid phosphomonoesterase and phytase activities in plant roots were interesting, activities being 2-fold higher in alkaline soil than acidic soil in both genotypes. The effect of P supply on the enzyme activity was also distinct, as plants growing in a high P concentration showed higher activity (nearly 30%) than those growing under P deficiency conditions (with no addition of P). These results indicate that Gulf and Marshall ryegrass can accumulate high P under optimal conditions and thus reduce soil P concentrations in successive cropping.

Agricultural and animal husbandry practices combined with soil composition have caused phosphate overloading of farmlands in different parts of the U.S. and Europe. Movement of soluble phosphates (Pi) from phosphorus enriched soils results in degradation of natural aquatic systems, triggering serious environmental problems. Remediation of such sites using plants that tolerate and accumulate high concentrations of Pi in their aerial parts may be an attractive remediation technology. In the present study, Pi transport and accumulation potential of Marshall and Gulf ryegrass (Lolium multiflorum cultivars) were determined using a solution culture of seedlings. Ryegrass seedlings accumulated phosphorus (P) in excess of 2% of dry weight in their aerial parts when supplied with 5 g/L KH2PO4 in medium. Phosphorus accumulation was positively correlated with the concentration of phosphate (0-5 g/L KH2PO4) in medium. Plants grew well on medium containing 5 g/L KH2PO4, but concentrations above 5 g/L caused symptoms of toxicity. Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed high P accumulation in different cell types of grass roots and shoots. Phosphate starvation and replenishment experiments point to the unique ability of these grasses to concentrate phosphate in the above-ground parts. It is hypothesized that the unique ability of these ryegrass cultivars may be due to the presence of efficient phosphate transport and sequestration mechanisms.

Lead phytoextraction can be economically feasible only when the developed systems employ high biomass plants that can accumulate greater than 1% Pb in their shoots. In this study Sesbania drummondii, a leguminous shrub occurring in the wild, was used to demonstrate its capability for greater than 1% Pb accumulation in shoots when grown in a Pb-contaminated nutrient solution. Shoot concentrations of >4% Pb were obtained from Sesbania plants grown on modified Hoagland's solution containing 1 g Pb(NO3)2/L. The accumulation of Pb in the tissue was found to be dependent on the concentration of Pb in the nutrient solution. Addition of EDTA (100 microM) in the medium containing 1 g Pb(NO3)2/L increased uptake by 21%. Lower pH also favored Pb translocation to shoot. Results also indicate the path of Pb transport through root tissues. Scanning electron microscopy revealed the distribution of Pb granules in the cells from epidermis to the central axis, indicating both apoplastic and symplastic modes of transport. Transmission electron microscopy and X-ray microanalysis of root sections demonstrated the localization of Pb granules in the plasma membrane and cell wall, and also in the vacuoles. This investigation shows that S. drummondii satisfies the prerequisites for a hyperaccumulator, and thus might be useful, particularly, in the restoration of disturbed vegetation.