Arbuscular mycorrhiza influences carbon-use efficiency and grain yield of wheat grown under pre- and post-anthesis salinity stress.

Soil salinity severely affects and constrains crop production worldwide. Salinity causes osmotic and ionic stress, inhibiting gas exchange and photosynthesis, ultimately impairing plant growth and development. Arbuscular mycorrhiza (AM) have been shown to maintain light and carbon use efficiency under stress, possibly providing a tool to improve salinity tolerance of the host plants. Thus, it was hypothesized that AM will contribute to improved growth and yield under stress conditions. Wheat plants (Triticum aestivum L.) were grown with (AMF+) or without (AMF-) arbuscular mycorrhizal fungi (AMF) inoculation. Plants were subjected to salinity stress (200 mm NaCl) either at pre- or post-anthesis or at both stages. Growth and yield components, leaf chlorophyll content as well as gas exchange parameters and AMF colonization were analysed. AM plants exhibited a higher rate of net photosynthesis and stomatal conductance and lower intrinsic water use efficiency. Furthermore, AM wheat plants subjected to salinity stress at both pre-anthesis and post-anthesis maintained higher grain yield than non-AM salinity-stressed plants. These results suggest that AMF inoculation mitigates the negative effects of salinity stress by influencing carbon use efficiency and maintaining higher grain yield under stress.

Exploring abiotic stress on asynchronous protein metabolism in single kernels of wheat studied by NMR spectroscopy and chemometrics.

Extreme climate events are being recognized as important factors in the effects on crop growth and yield. Increased climatic variability leads to more frequent extreme conditions which may result in crops being exposed to more than one extreme event within a growing season. The aim of this study was to examine the implications of different drought treatments on the protein fractions in grains of winter wheat using (1)H nuclear magnetic resonance spectroscopy followed by chemometric analysis. Triticum aestivum L. cv. Vinjett was studied in a semi-field experiment and subjected to drought episodes either at terminal spikelet, during grain-filling or at both stages. Principal component trajectories of the total protein content and the protein fractions of flour as well as the (1)H NMR spectra of single wheat kernels, wheat flour, and wheat methanol extracts were analysed to elucidate the metabolic development during grain-filling. The results from both the (1)H NMR spectra of methanol extracts and the (1)H HR-MAS NMR of single kernels showed that a single drought event during the generative stage had as strong an influence on protein metabolism as two consecutive events of drought. By contrast, a drought event at the vegetative growth stage had little effect on the parameters investigated. For the first time, (1)H HR-MAS NMR spectra of grains taken during grain-filling were analysed by an advanced multiway model. In addition to the results from the chemical protein analysis and the (1)H HR-MAS NMR spectra of single kernels indicating that protein metabolism is influenced by multiple drought events, the (1)H NMR spectra of the methanol extracts of flour from mature grains revealed that the amount of fumaric acid is particularly sensitive to water deficits.

Modified plant plasma membrane H(+)-ATPase with improved transport coupling efficiency identified by mutant selection in yeast.

Transport across the plasma membrane is driven by an electrochemical gradient of H+ ions generated by the plasma membrane proton pump (H(+)-ATPase). Random mutants of Arabidopsis H(+)-ATPase AHA1 were isolated by phenotypic selection of growth of transformed yeast cells in the absence of endogenous yeast H(+)-ATPase (PMA1). A Trp-874-Leu substitution as well as a Trp-874 to Lys-935 deletion in the hydrophilic C-terminal domain of AHA1 conferred growth of yeast cells devoid of PMA1. A Trp-874-Phe substitution in AHA1 was produced gy site-directed mutagenesis. The modified enzymes hydrolyzed ATP at 200-500% of wild-type level, had a sixfold increase in affinity for ATP (from 1.2 to 0.2 mM; pH 7.0), and had the acidic pH optimum shifted towards neutral pH. AHA1 did not contribute significantly to H+ extrusion by transformed yeast cells. The different specifies of aha1, however, displayed marked differences in initial rates of net H+ extrusion and in their ability to sustain an electrochemical H+ gradient. These results provide evidence that Trp-874 plays an important role in auto-inhibition of the plant H(+)-ATPase and may be involved in controlling the degree of coupling between ATP hydrolysis and H+ pumping. Finally, these results demonstrate the usefulness of yeast as a generalized screening tool for isolating regulatory mutants of plant transporters.

Nitrate, nitrate reduction and organic nitrogen in plants from different ecological and taxonomic groups of Central Europe.

48 plant species of the families Asteraceae, Chenopodiaceae, Ericaceae, Fabaceae, Lamiaceae, Polygonaceae and Urticaceae were investigated in 14 natural habitats of Central Europe having different nitrate supplies, with respect to their nitrate content, nitrate reductase activity (NRA) and organic nitrogen content. Plants that were flowering were selected where possible for analysis. The plants were subdivided into flowers, laminae, petioles+shoot axes and below-ground organs. Each organ was analyzed separately. Differences among species were found for the three variables investigated. Apart from the Fabaceae, which had particularly high concentrations of organic N, these differences reflect mainly the ecological behaviour, i.e. high nitrate and organic N contents and NRA values per g dry weight were found in species on sites rich in nitrate, and vice versa. Nitrate content, NRA and organic N content were correlated with "nitrogen figures" of Central European vascular plants defined by Ellenberg (1979). By use of regression equations this correlation was tested with species from other systematic groups. Some species were attributed with calculated "N figures" for the first time.