Grain yield of wheat (Triticum aestivum L.) under long‐term heat stress is sink‐limited with stronger inhibition of kernel setting than grain filling

The aim of the study was to investigate source‐sink relations of wheat under continuous heat stress and to identify bottle necks of yield formation. A pot experiment was conducted in two climatic chambers exposing wheat plants (Triticum aestivum L. cv. Thasos) either to day/night temperatures of 20/20°C (control conditions) or of 30/25°C (heat stress) during the whole vegetation period in the absence of plant water deficit. Plants were harvested at four phenological stages: three‐node stage (DC 33), start of flowering (DC 61), grain filling (DC 75) and maturity (DC 94). Heat stress shortened the development phases of the plants and caused a significant decrease in total above‐ground biomass between 19% and 41%. At grain filling and at maturity, the reductions in total shoot biomass mainly resulted from grain yield depressions by 77% and 58%, respectively. The ear number per plant was significantly higher under heat stress in comparison with the control, at maturity it was more than doubled. On the contrary, under heat stress, the kernel number per ear was strongly decreased by 83% and 75% during grain filling and at maturity, respectively. The decrease in individual kernel weight was 23% at maturity. Thus, the heat‐stressed plants were able to strongly increase the number of ear‐bearing tillers which were able to set only a small number of kernels, yet these kernels showed good grain filling. The harvest index (HI) of heat‐stressed plants was significantly reduced by 36% (control: HI = 50.1% ± 0.4, heat: HI = 32.2% ± 0.9***). The plants in the stress treatment adapted to the adverse conditions by less biomass production which presumably allowed a higher transpiration without an increase in total water consumption. Nevertheless, under heat stress, the water use efficiency (WUE_grain) was strongly decreased by 62% as a result of a small grain yield. In ears and grains, the sucrose, glucose and fructose concentrations were not significantly different between control and heat stress at start of flowering and during grain filling. Thus, the supply of assimilates was not restricted (no source limitation). Sink capacity was reduced by heat stress, as lesser and smaller kernels were produced than in the control. Concerning sink activity, the sink‐limiting step during kernel set is probably the active transport of hexoses across the plasma membrane into the developing kernels, which could also affect grain filling. This needs to be investigated in more detail in further studies.     

Photoinhibition, carotenoid composition and the co-regulation of photochemical and non-photochemical quenching in neotropical savanna trees

Plants in the neotropical savannas of central Brazil are exposed to high irradiances, high air temperatures and low relative humidities. These conditions impose a selection pressure on plants for strong stomatal regulation of transpiration to maintain water balance. Diurnal adjustments of non-photochemical energy dissipation in photosystem II (PSII) provide a dynamic mechanism to reduce the risk of photoinhibitory damage during the middle of the day when irradiances and leaf temperatures are high and partial closure of the stomata results in considerable reductions in internal CO(2) concentration. At the end of the dry season, we measured diurnal changes in gas exchange, chlorophyll fluorescence parameters and carotenoid composition in two savanna tree species differing in photosynthetic capacity and in the duration and extent of the midday depression of photosynthesis. Non-photochemical quenching and its quantum yield were tightly correlated with zeaxanthin concentrations on a total chlorophyll basis, indicating that the reversible de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin within the xanthophyll cycle plays a key role in the regulation of thermal energy dissipation. In both cases, a single linear relationship fitted both species. Although efficient regulation of photochemical and non-photochemical quenching and adjustments in the partitioning of electron flow between assimilative and non-assimilative processes were operating, these trees could not fully cope with the rapid increase in irradiance after sunrise, suggesting high vulnerability to photoinhibitory damage in the morning. However, both species were able to recover quickly. The effects of photoinhibitory quenching were largely reversed by midday, and zeaxanthin rapidly converted back to violaxanthin as irradiance decreased in late afternoon, resulting in the maximal quantum yield of PSII of around 0.8 just before sunrise.     

Diagnostic determination of melamine and related compounds in kidney tissue by liquid chromatography/tandem mass spectrometry

In 2007, it was determined that melamine, ammeline, ammelide, and cyanuric acid (abbreviated as MARC for melamine and related contaminants) had been added to wheat gluten and rice protein that were subsequently incorporated into pet food. The consumption of food tainted by MARC compounds was implicated in numerous instances of renal failure in cats and dogs. A method for the analysis of MARC compounds in kidney tissue using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) has been developed. MARC analytes were extracted by homogenization of kidney tissue in 50/40/10 acetonitrile/water/diethylamine. The homogenate was centrifuged, and an aliquot of supernatant was diluted with acetonitrile, concentrated, and fortified with a stable isotope-labeled analogue of melamine. Analytes were detected using atmospheric pressure chemical ionization and multiple reaction monitoring. Quantitation of positive samples was performed using the internal standard method and five-point calibration curves ranging between 50 and 1000 ng/mL of each analyte. The method was validated by analysis of replicate kidney tissue samples fortified with the individual analytes and by analysis of kidney samples fortified with melamine cyanurate powder at two different concentrations. This method was successfully used for routine postmortem diagnosis of melamine toxicosis in animals. Melamine was also detected by this method in paraffin-embedded tissue from animals suspected to have died of melamine toxicosis.     

Cyanidadsorption an Sesquioxiden,Tonmineralen und Huminstoffen

Cyanide adsorption on sesquioxides, clay-minerals and humic substances The adsorption of cyanide (KCN) on sesquioxides, clay minerals, and humic substances at different pH-values was studied. Moreover we looked for the CN-adsorption on L-layers of the humus forms mull, moder and mor. Cyanide was only adsorbed by humic acid. The amount of CN adsorbed increased with increasing pH of the reaction solution. IR-spectroscopic investigations of CN treated humic acids revealed that the cyanide was adsorbed at low pH (<7) as HCN-molecules by formation of hydrogen bonds with COOH-, COH-, OH- and NH₂-groups of the humic acid. At pH > 7 the cyanide was mainly adsorbed as CN^? by charge transfer with acceptor-molecules such as chinones. The cyanide adsorption of L-layers of humus forms decreased in the order mor > mull > moder. It is surmised that the HCN-molecules were not only adsorbed by humic acids in these layers but also by oxidation products of lignin, pectin, protein, cellulose, and carbon-hydrates of fulvic acids. Solutions of K₂HPO₄ did not desorb cyanides from humic acids to any great extent.     

Determination of oleandrin in tissues and biological fluids by liquid chromatography-electrospray tandem mass spectrometry

A rapid LC-MS/MS method, using a triple-quadrupole/linear ion trap mass spectrometer, was developed for the quantitative determination of oleandrin in serum, urine, and tissue samples. Oleandrin, the major cardiac glycoside of oleander (Nerium oleander L.), was extracted from serum and urine samples with methylene chloride and from tissues with acetonitrile. The tissue extracts were cleaned up using Florisil solid-phase extraction columns. Six replicate fortifications of serum and urine at 0.001 microg/g (1 ppb) oleandrin gave average recoveries of 97% with 5% CV (relative standard deviation) and 107% with 7% CV, respectively. Six replicate fortifications of liver at 0.005 microg/g (5 ppb) oleandrin gave average recoveries of 98% with 6% CV. This is the first report of a positive mass spectrometric identification and quantitation of oleandrin in tissue samples from oleander intoxication cases. The sensitivity and specificity of the LC-MS/MS analysis enables it to be the method of choice for toxicological investigations of oleander poisoning.     

Specific polyphenol oxidase activity of red clover (Trifolium pratense) and its relation with forage quality in field experiments

Abstract

In feeding studies, red clover (RC) influenced positively the N utilization by ruminants. A relationship between polyphenol oxidase (PPO) activity and forage quality has not been established. Our objective was to investigate seasonal, site, genotype, and management effects on specific PPO activity in RC in three experiments under field conditions, and relate the activity to forage-quality parameters. In Experiment 1, six RC genotypes at two study sites were submitted to a 3-cut system. Specific PPO activity, forage quality, and vegetation stage were determined. PPO activity varied between harvest and study sites, with genotypes differing up to 3-fold in PPO activity within harvests. The specific PPO activity, forage quality, and vegetation stage in RC subjected to 5-cut system and grazing (Experiment 2) were determined. Additionally, in Experiment 3, cutting frequency in RC swards including mechanical stress (rolling) was investigated. The induction of PPO activity in RC by grazing or mechanical stress (Experiments 2 and 3) increased the activity up to 2.5-fold compared with RC at similar vegetation stage submitted to the 5-cut system. Mechanical stress induced by grazing or rolling, and seasonal differences, seem to have a larger influence on specific PPO activity than does the genotype effect observed in Experiment 1. For forage quality, an increased specific PPO activity explained 29–46% of the reduction in protein fraction ‘A’ content (non-protein N) in the cutting systems in Experiments 2 and 3. Other CP fractions achieved a lower relation. Furthermore, the precipitation-to-temperature ratio preceeding a harvest explained 63% of the variation in the specific PPO activity. In conclusion, the PPO activity in RC is induced by grazing and rolling. Whereas weather conditions preceeding a harvest showed a large influence, genotype influence had only minor relevance. These results may have implications for regional harvest management towards efficient N utilization by ruminants.