The effects of O2 on net photosynthesis at low temperature (5°C)

Abstract. It has been shown that atmospheric O₂ can either depress or stimulate the rate of apparent photosynthesis of white mustard depending on the environmental conditions: CO₂ concentration, light intensity and temperature. Stimulation by O₂ was observed only under high photon fluence rate and at high CO₂ concentrations. The critical CO₂ concentration below which O₂ was inhibiting and above which it was stimulating was dependent on the temperature of the assay: for plants grown at 12°C the critical CO₂ concentration was 13.35 mmol at 5° C and 21.92 mmol at 10° C. Stimulation by O₂ depended also on the growth temperature: for measurements at 26.31 mmol m^?3 CO₂, O₂ was stimulating at temperatures less than 12°C for plants grown at 12°C and less than 19°C for plants grown at 27°C. The efficiency of the O₂-dependent stimulation of net photosynthesis was maximum at 9.21 mol m^?3 O₂ at 26.31 mmol m^?3 CO₂. Oxygen-stimulation of net photosynthesis was detected in Nicotiana tabacum L. var Samsun, Lycopersicum esculentum L. and Chenopodium album L. At 5°C and under high photon fluence rate, O₂ increased the carboxylation capacity of the photosynthetic apparatus of mustard and decreased its affinity for CO₂. The O₂ inhibition of the net CO₂ uptake observed at low CO₂ concentrations was the result of a decrease in the affinity for carbon dioxide. The nature of the mechanism which causes the stimulation of photosynthesis is discussed.     

DETERMINATION OF SENSORY OIL-WATER PARTITION COEFFICIENTS OF SINGLE AROMA COMPOUNDS COMBINING PANELIST FREE INTENSITY RATING AND THEORETICAL MODELING OF ODOR INTENSITY

Using an intensity rating with no external calibration, experiments were designed to measure the sensory oil-water partition coefficients of four aroma molecules (benzaldehyde, ethyl butyrate, linalool and acetophenone) as the ratios of concentration producing stimuli of equivalent intensities. Flavored water and oil phases were successively assessed for odor intensity by 24 panelists who were given total freedom regarding scaling strategy. Each session combined five concentration levels of three out of the four studied aromas in a solvent (water or oil). A predominant concentration effect was found for each aroma in both solvents and concentration dependencies of perceived intensity above water and oil were similar. Experimental data were modeled with Fechner, Stevens and Hill equations. Combining results above water and oil solutions to feed a common model led to the evaluation of an overall sensory oil-water partition coefficient for each aroma compound. All three models produced similar partition coefficient values for each aroma that were lower than the related instrumental partition coefficients. Biases previously detected when external calibration had been used were reduced in a large proportion while suggested enhancement of odor intensity by water vapor could not be excluded.     

Comparative spatiotemporal analysis of root aerenchyma formation processes in maize due to sulphate, nitrate or phosphate deprivation

Nitrate (N), phosphate (P) or sulphate (S) deprivation causes aerenchyma formation in maize (Zea mays L.) nodal roots. The exact mechanisms that trigger the formation of aerenchyma under these circumstances are unclear. We have compared aerenchyma distribution across the nodal roots of first whorl (just emerging in 10-day-old seedlings), which were subject to S, N or P deprivation over a period of 10?days in connection with oxygen consumption, ATP concentration, cellulase and polygalacturonase activity in the whole root. The effect of deprivation on aerenchyma formation was examined using light and electron microscopy, along with in situ detection of calcium and of reactive oxygen species (ROS) by fluorescence microscopy. Aerenchyma was not found in the root base regardless of the deprivation. Programmed cell death (PCD) was observed near the root tip, either within the first two days (-N) or a few days later (-S, -P) of the treatment. Roots at day?6 under all three nutrient-deprived conditions showed signs of PCD 1?cm behind the cap, whereas only N-deprived root cells 0.5?cm behind the cap showed severe ultrastructural alterations, due to advanced PCD. The lower ATP concentration and the higher oxygen consumptions observed at day?2 in N-, P- and S-deprived roots compared to the control indicated that PCD may be triggered by perturbations in energy status of the root. The peaks of cellulase activity located between days?3 (-N) and 6 (-P), along with the respective alterations in polygalacturonase activity, indicated a coordination which preceded aerenchyma formation. ROS and calcium seemed to contribute to PCD initiation, with ROS possessing dual roles as signals and eliminators. All the examined parameters presented both common features and characteristic variations among the deprivations.     

Acclimation of isoprene emission and photosynthesis to growth temperature in hybrid aspen: resolving structural and physiological controls

Acclimation of foliage to growth temperature involves both structural and physiological modifications, but the relative importance of these two mechanisms of acclimation is poorly known, especially for isoprene emission responses. We grew hybrid aspen (Populus tremula x P. tremuloides) under control (day/night temperature of 25/20 °C) and high temperature conditions (35/27 °C) to gain insight into the structural and physiological acclimation controls. Growth at high temperature resulted in larger and thinner leaves with smaller and more densely packed chloroplasts and with lower leaf dry mass per area (M_A). High growth temperature also led to lower photosynthetic and respiration rates, isoprene emission rate and leaf pigment content and isoprene substrate dimethylallyl diphosphate pool size per unit area, but to greater stomatal conductance. However, all physiological characteristics were similar when expressed per unit dry mass, indicating that the area‐based differences were primarily driven by M_A. Acclimation to high temperature further increased heat stability of photosynthesis and increased activation energies for isoprene emission and isoprene synthase rate constant. This study demonstrates that temperature acclimation of photosynthetic and isoprene emission characteristics per unit leaf area were primarily driven by structural modifications, and we argue that future studies investigating acclimation to growth temperature must consider structural modifications.     

Dynamics of Aerenchyma distribution in the cortex of sulfate-deprived adventitious roots of maize

BACKGROUND AND AIMS: Aerenchyma formation in maize adventitious roots is induced in nutrient solution by the deprivation of sulfate (S) under well-oxygenated conditions. The aim of this research was to examine the extent of aerenchyma formation in the cortex of sulfate-deprived adventitious roots along the root axis, in correlation with the presence of reactive oxygen species (ROS), calcium levels and pH of cortex cells and root lignification. METHODS: The morphometry of the second whorl of adventitious (W2) roots, subject to S-deprivation conditions throughout development, was recorded in terms of root length and lateral root length and distribution. W2 roots divided into sectors according to the mean length of lateral roots, and cross-sections of each were examined for aerenchyma. In-situ detection of alterations in ROS presence, calcium levels and pH were performed by means of fluorescence microscopy using H(2)DCF-DA, fluo-3AM and BCECF, respectively. Lignification was detected using the Wiesner test. KEY RESULTS: S-deprivation reduced shoot growth and enhanced root proliferation. Aerenchyma was found in the cortex of 77 % of the root length, particularly in the region of emerging or developing lateral roots. The basal and apical sectors had no aerenchyma and no aerenchyma connection was found with the shoot. S-deprivation resulted in alterations of ROS, calcium levels and pH in aerenchymatous sectors compared with the basal non-aerenchymatous region. Lignified epidermal layers were located at the basal and the proximal sectors. S-deprivation resulted in shorter lateral roots in the upper sectors and in a limited extension of the lignified layers towards the next lateral root carrying sector. CONCLUSIONS: Lateral root proliferation is accompanied by spatially localized induced cell death in the cortex of developing young maize adventitious roots during S-deprivation.     

Different stomatal responses of maize leaves after blue or red illumination under anoxia

Abstract In normal air, illumination with a low level of blue or red light (40 μmol m^?2 s^?1) did not induce stomatal opening in maize plantlets. In CO₂-free air, 40 μmol m^?2 s^?1 of blue or red light promoted an enhancement in stomatal opening. At the same quantum flux, blue light was more efficient than red light and stomatal closure occurred more rapidly with a significantly shorter lag phase after blue light. Anoxia inhibited light-dependent stomatal opening, even under 320 μmol m^?2 s^?1 illumination. However, after 60 min of illumination with 40 μmol m^?2 s^?1 of blue light in anoxia, transient stomatal opening was observed when the plant was returned to darkness and normal air. This transient stomatal opening was weaker after pretreatment with red light. We conclude that a blue-light-dependent process induced under anoxia leads to stomatal opening provided oxygen is present. Possible mechanisms associated with blue-light-effect and the nature of the oxygen-consuming processes are discussed.     

Mating systems and territory in Lapwings Vanellus vanellus

In a population of Lapwings Vanellus vanellus studied for 5 years near Bergen, southwester Norway, 23–41% of the males were polygynous, having two and sometimes three mates, whereas 50–77% were monogamous and 0–21% remained unmated. Bachelors held territories in or immediately adjacent to the study area each of the years. As predicted from the Polygyny Threshold model, primary females generally laid eggs earlier than monogamous females, but the overlap in laying dates was substantial between these two classes. The number of females and start of breeding on the territories were analysed in relation to nine variables pertaining to safety from predation and to food. Of these, territory size correlated most consistently with number of females (positively) and the laying of first egg (negatively). Numbers of females observed were not significantly different from numbers expected from territory size in 4 out of 5 years; however, earlier start of breeding on large territories indicated that females did not settle according to the Neutral Mate Choice model. The Female-biased Sex Ratio hypothesis was refuted, unmated territorial males being available throughout the breeding seasons.