PHENOPSIS, an automated platform for reproducible phenotyping of plant responses to soil water deficit in Arabidopsis thaliana permitted the identification of an accession with low sensitivity to soil water deficit

The high-throughput phenotypic analysis of Arabidopsis thaliana collections requires methodological progress and automation. Methods to impose stable and reproducible soil water deficits are presented and were used to analyse plant responses to water stress. Several potential complications and methodological difficulties were identified, including the spatial and temporal variability of micrometeorological conditions within a growth chamber, the difference in soil water depletion rates between accessions and the differences in developmental stage of accessions the same time after sowing. Solutions were found. Nine accessions were grown in four experiments in a rigorously controlled growth-chamber equipped with an automated system to control soil water content and take pictures of individual plants. One accession, An1, was unaffected by water deficit in terms of leaf number, leaf area, root growth and transpiration rate per unit leaf area. Methods developed here will help identify quantitative trait loci and genes involved in plant tolerance to water deficit.     

Plasticity to soil water deficit in Arabidopsis thaliana: dissection of leaf development into underlying growth dynamic and cellular variables reveals invisible phenotypes

Genetic variability in the plasticity of leaf area expansion in response to water deficit has been reported in Arabidopsis thaliana. Here, the objective was to identify the underlying dynamic and cellular processes involved in this variability. Twenty-five accessions were subjected to identical soil water deficit treatments. In all accessions, the plasticity of leaf production was low compared with that of individual leaf expansion. A subset of accessions was selected for further dissection of individual leaf expansion into its underlying variables: the rate and duration of leaf expansion and epidermal cell number and area. In all accessions, water deficit had opposite effects on the rate and duration of leaf expansion. The accumulation of these effects was reflected in changes in final leaf area. At the cellular level, moderate water deficits had opposite effects on cell number and cell size, but more severe ones reduced both variables. The importance of these opposing effects is highlighted by the behaviour of the accession An-1, for which the compensation between the decrease in leaf expansion rate and the increase in the duration of expansion is total. This dynamic plasticity in response to water deficit is not detectable when only final measurements are done.     

Endogenous ascorbate restrains apoplastic peroxidase activity during sunflower leaf development

Several apoplastic enzymes have been implicated in the control of elongation growth of plant cells. Among them, peroxidases contribute to both loosening and stiffening of the cell wall. They appear to be regulated by various mechanisms, including the action of extracellular inhibitors. To obtain evidence of the role of the enzyme–inhibitor interaction during leaf development, the intercellular washing fluids from Helianthus annuus leaves of different ages were isolated using standard methods of vacuum infiltration and centrifugation. Peroxidase activities, assessed using tetramethylbenzidine as substrate, increased during leaf development, reaching a maximum value after the leaves were fully expanded. An inhibitor, chemically characterised as ascorbate, co‐localised with the enzyme in the apoplast. Moreover, there was a strong negative correlation between the action of peroxidase and the micromolar concentration of ascorbate in the apoplastic fluid. The results show that in growing leaves, the in planta ascorbate concentration is able to restrain peroxidase enzyme activity. Then, at the time of growth cessation, the loss of extracellular ascorbate relieves the inhibition on this enzyme that contributes to wall fixation.     

Survivability of Salmonella cells in popcorn after microwave oven and conventional cooking

The survivability of Salmonella cells in popcorn preparation was determined for two distinct cooking methods. The first method used a standard microwave oven. The second method used conventional cooking in a pan. Prior to thermal processing in independent experiments, 12 suspensions in a range between 1x10(3) and 8x10(6) colony-forming units (CFU) per gram of Salmonella cells were inoculated in both raw microwave popcorn and conventional corn kernels. The influence of the initial concentration of Salmonella cells in the raw products and the lethal effects on Salmonella by thermal treatments for cooking were studied. Survival of Salmonella cells was determined in the thermally processed material by pre-enrichment and enrichment in selective medium, in accordance with the legislation for expanded cereals and cereals in flakes. Viable experimental contaminants were recovered from the conventionally cooked popcorn with initial inoculation concentrations of 9x10(4)cells/g or greater. Salmonella cell viability was significantly reduced after microwave oven treatment, with recoveries only from initial concentrations of 2x10(6)cells/g or superior.     

An architectural analysis of the elongation of field-grown sunflower root systems. Elements for modelling the effects of temperature and intercepted radiation

The effects of photosynthetic photon flux density (PPFD) andsoil temperature on root system elongation rate have been analysedby using an architectural framework. Root elongation rate wasanalysed by considering three terms, (i) the branch appearancerate, (ii) the individual elongation rates of the taproot andbranches and (iii) the proportion of branches which stop elongating.Large ranges ofPPFD and soil temperature were obtained in aseries of field and growth chamber experiments. In the field,the growth of root systems experiencing day-to-day natural fluctuationof PPFD and temperature was followed, and some of the plantsunder study were shaded. In the growth chamber, plants experiencedcontrasting and constant PPFDs and root temperatures. The directeffect of apex temperature on individual root elongation ratewas surprisingly low in the range 13–25C, except forthe first days after germination. Root elongation rate was essentiallyrelated to intercepted PPFD and to distance to the source, bothin the field and in the growth chamber. Branch appearance ratesubstantially varied among days and environmental conditions.It was essentially linked to taproot elongation rate, as theprofile of branch density along the taproot was quite stable.The length of the taproot segment carrying newly appeared brancheson a given day was equal to taproot elongation on this day,plus a 'buffering term' which transiently increased if taprootelongation rate slowed down. The proportion of branches whichstopped elongating a short distance from the taproot rangedfrom 50–80% and was, therefore, a major architecturalvariable, although it is not taken into account in current architecturalmodels. A set of equations accounting for the variabilitiesin elongation rate, branch appearance rate and proportion ofbranches which stop elongating, as a function of interceptedPPFD and apex temperature is proposed. These equations applyfor both field and growth chamber experiments. Key words: Sunflower, root system, model, temperature, radiation