Epicuticular Wax Load of Near-Isogenic Barley Lines Differing in Glaucousness

Scanning electron microscopy observations of epicuticular waxes on flag leaves (blades and sheaths) and ears were carried out on a pair of near-isogenic lines of two-row barley (Hordeum vulgare L. ), derived from cv. Troubadour, differing in their degree of glaucousness (wax bloom). Plants were grown under irrigated and rainfed mediterranean conditions. Wax bloom in flag leaves consisted mainly of thin wax deposits over the blade, and tubes over the sheath. Wax bloom in the blade was denser and more uniformly arranged on the adaxial than on the abaxial side. In the ears, tubular waxes predominated, forming dense patches on awns and lemmas, and becoming sparse on inner bracts such as the palea. Wax bloom increased under rainfed conditions in both lines. There were marked differences between the lines in the extent of deposition of crystallized epicuticular waxes in the leaf sheath and the ear, whereas differences in the leaf blade were less evident. Wax bloom was almost absent on the sheaths and ear of the non-glaucous line. These results suggest separate genetic control of epicuticular wax deposition on different parts of barley plants. The role of wax bloom in two related ecophysiological parameters, canopy reflectance and cuticular conductance to water diffusion, was also studied. Reflectance by the canopy in the 400 to 700 nm wavelengths was over 50% higher in the glaucous than in the non-glaucous line under rainfed conditions. Under irrigated conditions, flag leaf blades of the non-glaucous line showed the highest epidermal conductance. Ears showed no clear differences in epidermal conductance between lines or growth conditions

Zinc isotopic fractionation in Phragmites australis in response to toxic levels of zinc

Stable isotope signatures of Zn have shown great promise in elucidating changes in uptake and translocation mechanisms of this metal in plants during environmental changes. Here this potential was tested by investigating the effect of high Zn concentrations on the isotopic fractionation patterns of Phragmites australis (Cav.) Trin. ex Steud. Plants were grown for 40 d in a nutritive solution containing 3.2 μM (sufficient) or 2 mM (toxic) Zn. The Zn isotopic composition of roots, rhizomes, shoots, and leaves was analysed. Stems and leaves were sampled at different heights to evaluate the effect of long-distance transport on Zn fractionation. During Zn sufficiency, roots, rhizomes, and shoots were isotopically heavy (δ(66)Zn(JMC Lyon)=0.2‰) while the youngest leaves were isotopically light (–0.5‰). During Zn excess, roots were still isotopically heavier (δ(66)Zn=0.5‰) and the rest of the plant was isotopically light (up to –0.5‰). The enrichment of heavy isotopes at the roots was attributed to Zn uptake mediated by transporter proteins under Zn-sufficient conditions and to chelation and compartmentation in Zn excess. The isotopically lighter Zn in shoots and leaves is consistent with long-distance root to shoot transport. The tolerance response of P. australis increased the range of Zn fractionation within the plant and with respect to the environment

Comparative performance of the stable isotope signatures of carbon, nitrogen and oxygen in assessing early vigour and grain yield in durum wheat

The present paper studied the performance of the stable isotope signatures of carbon (δ13C), nitrogen (δ15N) and oxygen (δ18O) in plants when used to assess early vigour and grain yield (GY) in durum wheat growing under mild and moderate Mediterranean stress conditions. A collection of 114 recombinant inbred lines was grown under rainfed (RF) and supplementary irrigation (IR) conditions. Broad sense heritabilities (H2) for GY and harvest index (HI) were higher under RF conditions than under IR. Broad sense heritabilities for δ13C were always above 0·60, regardless of the plant part studied, with similar values for IR and RF trials. Some of the largest genetic correlations with GY were those shown by the δ13C content of the flag leaf blade and mature grains. Under both water treatments, mature grains showed the highest negative correlations between δ13C and GY across genotypes. Flag leaf δ13C was negatively correlated with GY only under RF conditions. The δ13C in seedlings was negatively correlated, under IR conditions only, with GY but also with early vigour. The sources of variation in early vigour were studied by stepwise analysis using the stable isotope signatures measured in seedlings. The δ13C was able to explain almost 0·20 of this variation under RF, but up to 0·30 under IR. In addition, nitrogen concentration in seedlings accounted for another 0·05 of variation, increasing the amount explained to 0·35. The sources of variation in GY were also studied through stable isotope signatures and biomass of different plant parts: δ13C was always the first parameter to appear in the models for both water conditions, explaining c. 0·20 of the variation. The second parameter (δ15N or N concentration of grain, or biomass at maturity) depended on the water conditions and the plant tissue being analysed. Oxygen isotope composition (δ18O) was only able to explain a small amount of the variation in GY. In this regard, despite the known and previously described value of δ13C as a tool in breeding, δ15N is confirmed as an additional tool in the present study. Oxygen isotope composition does not seem to offer any potential, at least under the conditions of the present study

Relationships between δ13C, δ18O and grain yield in bread wheat genotypes under favourable irrigated and rain-fed conditions

In previous investigations, carbon isotope composition (δ13C) has been used in C3 cereals to screen for genotypes with high transpiration efficiency and oxygen isotope composition (δ18O) has been shown to correlate with transpiration rate. We examined associations of δ13C of the grain and flag leaf and δ18O of the flag leaf with respect to grain yield in wheat cultivars in UK field conditions. Field experiments were carried out at University of Nottingham in 2009–10 and 2010–11 testing 17 wheat cultivars under fully irrigated and rain-fed conditions. Averaging across years grain yield was reduced by 1.69 t ha−1 (16.5%) in the rain-fed treatment (P < 0.001). There was a negative linear relationship between grain yield and grain δ13C amongst cultivars, under both irrigated (R2 = 0.47, P < 0.01) and rain-fed (R2 = 0.70, P < 0.001) conditions. Grain δ13C was negatively correlated with flag-leaf stomatal conductance (r = −0.94, P < 0.01) in a subset of six of the cultivars, indicating that higher transpiration efficiency was associated with lower stomatal conductance. The associations between grain yield and flag-leaf δ13C and flag-leaf δ18O amongst cultivars under irrigated and rain-fed conditions were not statistically significant. There was a positive linear relationship between flag-leaf δ18O and grain δ13C amongst cultivars under irrigated conditions (R2 = 0.38, P < 0.01), indicating a trade-off between transpiration and transpiration efficiency (TE). Genetic variation in grain yield under rain-fed conditions was also associated with delayed onset of flag-leaf senescence (R2 = 0.35, P < 0.05). The 17 wheat cultivars ranged in year of release (YoR) from 1964 to 2009 and grain yield increased linearly under irrigated conditions by 60.4 kg ha−1 yr−1 (0.72% yr−1) and under rain-fed conditions by 47.5 kg ha−1 yr−1 (0.66% yr−1) over the 45 year period and grain δ13C composition decreased by 0.0255 and 0.0304‰ yr−1, respectively, indicating genetic gains in wheat yield potential in the UK seem likely to have been achieved through a lower TE, higher water uptake and lesser limitation of stomatal conductance

Harvest index, a parameter conditioning responsiveness of wheat plants to elevated CO2

The expansion of the world’s population requires the development of high production agriculture. For this purpose, it is essential to identify target points conditioning crop responsiveness to predicted [CO2]. The aim of this study was to determine the relevance of ear sink strength in leaf protein and metabolomic profiles and its implications in photosynthetic activity and yield of durum wheat plants exposed to elevated [CO2]. For this purpose, a genotype with high harvest index (HI) (Triticum durum var. Sula) and another with low HI (Triticum durum var. Blanqueta) were exposed to elevated [CO2] (700 µmol mol–1 versus 400 µmol mol–1 CO2) in CO2 greenhouses. The obtained data highlighted that elevated [CO2] only increased plant growth in the genotype with the largest HI; Sula. Gas exchange analyses revealed that although exposure to 700 µmol mol–1 depleted Rubisco content, Sula was capable of increasing the light-saturated rate of CO2 assimilation (Asat) whereas, in Blanqueta, the carbohydrate imbalance induced the down-regulation of Asat. The specific depletion of Rubisco in both genotypes under elevated [CO2], together with the enhancement of other proteins in the Calvin cycle, revealed that there was a redistribution of N from Rubisco towards RuBP regeneration. Moreover, the down-regulation of N, NO3 –, amino acid, and organic acid content, together with the depletion of proteins involved in amino acid synthesis that was detected in Blanqueta grown at 700 µmol mol–1 CO2, revealed that inhibition of N assimilation was involved in the carbohydrate imbalance and consequently with the down-regulation of photosynthesis and growth in these plants

Carbon stable isotope analysis of cereal remains as a way to reconstruct water availability: preliminary results

Reconstructing past water availability, both as rainfall and irrigation, is important to answer questions about the way society reacts to climate and its changes and the role of irrigation in the development of social complexity. Carbon stable isotope analysis of archaeobotanical remains is a potentially valuable method for reconstructing water availability. To further define the relationship between water availability and plant carbon isotope composition and to set up baseline values for the Southern Levant, grains of experimentally grown barley and sorghum were studied. The cereal crops were grown at three stations under five different irrigation regimes in Jordan. Results indicate that a positive but weak relationship exists between irrigation regime and total water input of barley grains, but no relationship was found for sorghum. The relationship for barley is site-specific and inter-annual variation was present at Deir ‘Alla, but not at Ramtha and Khirbet as-Samra

Mapping adaptation of barley to droughted environments

Identifying barley genomic regions influencing the response of yield and its components to water deficits will aid in our understanding of the genetics of drought tolerance and the development of more drought tolerant cultivars. We assembled a population of 192 genotypes that represented landraces, old, and contemporary cultivars sampling key regions around the Mediterranean basin and the rest of Europe. The population was genotyped with a stratified set of 50 genomic and EST derived molecular markers, 49 of which were Simple Sequence Repeats (SSRs), which revealed an underlying population sub-structure that corresponded closely to the geographic regions in which the genotypes were grown. A more dense whole genome scan was generated by using Diversity Array Technology (DArT®) to generate 1130 biallelic markers for the population. The population was grown at two contrasting sites in each of seven Mediterranean countries for harvest 2004 and 2005 and grain yield data collected. Mean yield levels ranged from 0.3 to 6.2 t/ha, with highly significant genetic variation in low-yielding environments. Associations of yield with barley genomic regions were then detected by combining the DArT marker data with the yield data in mixed model analyses for the individual trials, followed by multiple regression of yield on markers to identify a multi-locus subset of significant markers/QTLs. QTLs exhibiting a pre-defined consistency across environments were detected in bins 4, 6, 6 and 7 on barley chromosomes 3H, 4H, 5H and 7H respectivel