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Background and Aims Phosphorus (P) availability is often limiting for rice (Oryza sativa) production. Improving internal P-use efficiency (PUE) is crucial to sustainable food production, particularly in low-input systems. A critical aspect of PUE in plants, and one that remains poorly understood, is the investment of leaf P in different chemical P fractions (nucleic acid-P, lipid-P, inorganic-P, metabolite-P and residual-P). The overarching objective of this study was to understand how these key P fractions influence PUE. Methods Three high-PUE and two low-PUE rice genotypes were grown in hydroponics with contrasting P supplies. We measured PUE, total P, P fractions, photosynthesis and biomass. Key Results Low investment in lipid-P was strongly associated with increased photosynthetic PUE (PPUE), achieved by reducing total leaf P concentration while maintaining rapid photosynthetic rates. All low-P plants exhibited a low investment in inorganic-P and lipid-P, but not nucleic acid-P. In addition, whole-plant PUE was strongly associated with reduced total P concentration, increased biomass and increased preferential allocation of resources to the youngest mature leaves. Conclusions Lipid remodelling has been shown in rice before, but we show for the first time that reduced lipid-P investment improves PUE in rice without reducing photosynthesis. This presents a novel pathway for increasing PUE by targeting varieties with reduced lipid-P investment. This will benefit rice production in low-P soils and in areas where fertilizer use is limited, improving global food security by reducing P fertilizer demands and food production costs.

Potassium regulates a plethora of metabolic and developmental response in plants, and upon exposure to biotic and abiotic stresses a substantial K+ loss occurs from plant cells. The outward-rectifying potassium efflux GORK channels are central to this stress-induced K+ loss from the cytosol. In the mammalian systems, signaling molecules such as gamma-aminobutyric acid, G-proteins, ATP, inositol, and protein phosphatases were shown to operate as ligands controlling many K+ efflux channels. Here we present the evidence that the same molecules may also regulate GORK channels in plants. This mechanism enables operation of the GORK channels as a master switch of the cell metabolism, thus adjusting intracellular K+ homeostasis to altered environmental conditions, to maximize plant adaptive potential.

Acid rock drainage (ARD) is a major environmental problem that poses serious ecological risks during and after mining activities. To minimize the ecological risks and to lower remediation costs in the mining industry, ecological risk assessment is highly important in various phases of mining. In this study, a methodology for ecological risk assessment using probability bounds is presented. The methodology is demonstrated with a case study at a mine site. A fugacity-based model was employed to conduct the exposure characterization. Median lethal concentrations from toxicity studies were used to derive predicted no-effect concentrations (PNEC) and to characterize the effect of copper and zinc on the receptors. Probabilistic risk-quotient and overlaps between distributions of exposure and effect were employed to characterize risk. Data and parameter uncertainties in exposure, effect, and risk characterizations were propagated and quantified using a probability bounds approach. The exposure modeling results showed that the predicted concentrations of copper and zinc slightly exceeded the observed concentrations. The results of the effect characterization showed that the derived effect concentrations for copper and zinc are acceptable compared with guideline values. The risk characterization result indicated that a high probability of ecological risk may exist due to metals that are transported into a nearby lake. Moreover, the results showed that the methodology handles uncertainties due to imprecision and randomness in an integrated manner.

Salinity is one of the main causes of yield loss in agricultural crop production worldwide. Numerous attempts have been made to produce salinity tolerant crops by manipulating the expression of genes involved in ion transport; yet, the reported results are often rather controversial. In this work, Arabidopsis AtNHX1 gene encoding vacuolar Na+/H+ exchanger was introduced into barley (Horduem vulgare L. cv. Golden Promise) plants grown under saline conditions. Transgenic plants were compared to null segregants for biomass, water content, gas exchange, and Na+ and K+ content of the leaf. It was shown that most of the lines expressing AtNHX1 have no significant difference to null segregants, suggesting the lack of beneficial effect of expressing the AtNHX1 gene in barley, at least under our experimental conditions. The lack of phenotype might be explained by: (1) low level of activity of vacuolar H+-inorganic pyrophosphatase and vacuolar H+-ATPase resulting in an insufficient proton gradient required for the vacuolar Na+/H+ exchanger; (2) the inability of transgenic plants to prevent a passive leak of sodium via Na+ permeable slow activating and fast activating channels; (3) insufficient ATP pool to support H+ pumping activity; and (4) the fact that the AtNHX1 protein might not been properly folded, inactive or incorrectly targeted. Overall, this study suggests that, while targeting vacuolar Na+ sequestration, at least several genes need to be pyramided to ensure the efficiency of the above process.

Background Salinity tolerance is a physiologically multi-faceted trait attributed to multiple mechanisms. Three barley (Hordeum vulgare) varieties contrasting in their salinity tolerance were used to assess the relative contribution of ionic, osmotic and oxidative stress components towards overall salinity stress tolerance in this species, both at the whole-plant and cellular levels. In addition, transcriptional changes in the gene expression profile were studied for key genes mediating plant ionic and oxidative homeostasis (NHX; RBOH; SOD; AHA and GORK), to compare a contribution of transcriptional and post-translational factors towards the specific components of salinity tolerance. Results Our major findings are two-fold. First, plant tissue tolerance was a dominating component that has determined the overall plant responses to salinity, with root K+ retention ability and reduced sensitivity to stress-induced hydroxyl radical production being the main contributing tolerance mechanisms. Second, it was not possible to infer which cultivars were salinity tolerant based solely on expression profiling of candidate genes at one specific time point. For the genes studied and the time point selected that transcriptional changes in the expression of these specific genes had a small role for barley’s adaptive responses to salinity. Conclusions For better tissue tolerance, sodium sequestration, K+ retention and resistance to oxidative stress all appeared to be crucial. Because these traits are highly interrelated, it is suggested that a major progress in crop breeding for salinity tolerance can be achieved only if these complementary traits are targeted at the same time. This study also highlights the essentiality of post translational modifications in plant adaptive responses to salinity.

Salinity is a global problem affecting agriculture that results in an estimated US$27 billion loss in revenue per year. Overexpression of vacuolar ATPase subunits has been shown to be beneficial in improving plant performance under saline conditions. Most studies, however, have not shown whether overexpression of genes encoding ATPase subunits results in improvements in grain yield, and have not investigated the physiological mechanisms behind the improvement in plant growth. In this study, we constitutively expressed Arabidopsis Vacuolar ATPase subunit C (AtVHA-C) in barley. Transgenic plants were assessed for agronomical and physiological characteristics, such as fresh and dry biomass, leaf pigment content, stomatal conductance, grain yield, and leaf Na+ and K+ concentration, when grown in either 0 or 300 mM NaCl. When compared with non-transformed barley, AtVHA-C expressing barley lines had a smaller reduction in both biomass and grain yield under salinity stress. The transgenic lines accumulated Na+ and K+ in leaves for osmotic adjustment. This in turn saves energy consumed in the synthesis of organic osmolytes that otherwise would be needed for osmotic adjustment.