Rhizosphere Organic Anions Play a Minor Role in Improving Crop Species' Ability to Take Up Residual Phosphorus (P) in Agricultural Soils Low in P Availability.

Many arable lands have accumulated large reserves of residual phosphorus (P) and a relatively large proportion of soil P is less available for uptake by plants. Root released organic anions are widely documented as a key physiological strategy to enhance P availability, while limited information has been generated on the contribution of rhizosphere organic anions to P utilization by crops grown in agricultural soils that are low in available P and high in extractable Ca, Al, and Fe. We studied the role of rhizosphere organic anions in P uptake from residual P in four common crops Triticum aestivum, Avena sativa, Solanum tuberosum, and Brassica napus in low- and high-P availability agricultural soils from long-term fertilization field trials in a mini-rhizotron experiment with four replications. Malate was generally the dominant organic anion. More rhizosphere citrate was detected in low P soils than in high P soil. B. napus showed 74-103% increase of malate in low P loam, compared with clay loam. A. sativa had the greatest rhizosphere citrate concentration in all soils (5.3-15.2 µmol g-1 root DW). A. sativa also showed the highest level of root colonization by arbuscular mycorrhizal fungi (AMF; 36 and 40%), the greatest root mass ratio (0.51 and 0.66) in the low-P clay loam and loam respectively, and the greatest total P uptake (5.92 mg P/mini-rhizotron) in the low-P loam. B. napus had 15-44% more rhizosphere acid phosphatase (APase) activity, ~0.1-0.4 units lower rhizosphere pH than other species, the greatest increase in rhizosphere water-soluble P in the low-P soils, and the greatest total P uptake in the low-P clay loam. Shoot P content was mainly explained by rhizosphere APase activity, water-soluble P and pH within low P soils across species. Within species, P uptake was mainly linked to rhizosphere water soluble P, APase, and pH in low P soils. The effects of rhizosphere organic anions varied among species and they appeared to play minor roles in improving P availability and uptake.

A novel chloroplast transformation vector compatible with the Gateway(®) recombination cloning technology.

To analyze the suitability of Gateway(®) vectors for transformation of chloroplasts, we converted a standard plastid transformation vector into a Gateway(®) destination vector containing the necessary recombination sites attR1 and attR2. Insertion of the green fluorescent protein (GFP) coding sequence with associated T7g10 ribosome binding site into this destination vector created the expression vector for transformation of tobacco chloroplasts with the biolistic method. Correct integration of the transgene into the plastid genome was verified by PCR and the homoplasmic nature of the transformed plants was confirmed by Southern Blot analysis. Expression of the GFP reporter protein was monitored by confocal laser scanning microscopy (CLSM) and quantification by western blot analysis showed a GFP accumulation level of 3% total soluble protein (TSP). The presented results clearly demonstrate that the Gateway(®) recombination sites are compatible with all steps of plastid transformation, from generation of transplastomic plants to expression of GFP. This is the first report of a plastid transformation vector made by the Gateway(®) recombinant cloning technology, which proves the suitability of this system for use in chloroplasts.

Conference scene: molecular pharming: manufacturing medicines in plants.

Within the expanding area of molecular pharming, the development of plants for manufacturing immunoglobulins, enzymes, virus-like particles and vaccines has become a major focus point. On 21 September 2012, the meeting 'Molecular Pharming - recent progress in manufacturing medicines in plants', hosted by EuroSciCon, was held at the Bioscience Catalyst campus, Stevenage, UK. The scientific program of this eventful meeting covered diverse highlights of biopharming: monoclonal antibodies, virus-like particles from transient and chloroplast expression systems, for example, for Dengue and HPV, apolipoproteins from safflower seeds, and new production platforms, such as potato or hydroponics by rhizosecretion. This report summarizes the stimulating scientific presentations and fruitful panel discussions on the current topics in this promising research field.