The changing sensitivity to auxin of the plasma-membrane H+-ATPase: Relationship between plant development and ATPase content of membranes

The auxin sensitivity of the plasma-membrane H⁺-ATPase from tobacco leaves (Nicotiana tabacum L. cv. Xanthi) depends on the physiological state of the plant (Santoni et al., 1990, Plant Sci. 68, 33–38). Results based on the study of auxin sensitivity according to culture conditions which accelerate or delay tobacco development demonstrate that the highest auxin sensitivity is always associated with the end of the period of induction to flowering. Auxin stimulation of H⁺-translocation activity corresponds to an increase of the apparent ATPase affinity for ATP. The plasma-membrane H⁺-ATPase content, measured with an enzyme-linked immunosorbent assay using a specific anti-H⁺-ATPase antibody, varies according to plant development, and was found to increase by 100% during floral induction. The specific molecular ATPase activity also changes according to plant development; more particularly, the decrease in molecular ATPase activity upto and during the floral-induction period parallels the increase of sensitivity to indole-3-acetic acid.Abbreviations ELISA enzyme-linked immunosorbent assay - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate Authors are grateful to Mrs. Grosclaude (Lab. Virologie, INRA, Jouy-en-Josas, France) and Mrs. Boudon (Lab. Mycoplasmes, INRA, Dijon, France) for support and advice in the preparation of antibodies. This work was supported by grants No. 89/512/6 from the E.P.R of Bourgogne and No. 89 C 0662 from M.R.T.     

Mass-spectrometric determination of O2 and CO2 gas exchange in illuminated higher-plant cells

In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO₂ and O₂ gas exchange were performed using ¹⁸O₂, ¹³CO₂ and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of O₂ and CO₂. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO₂), the rate of CO₂ influx represented 75±5% of the rate of gross O₂ evolution. After a dark-to-light transition, the rate of CO₂ efflux was inhibited by 50% whereas the O₂-uptake rate was little affected. The effect of a recycling of respiratory CO₂ through photosynthesis on the exchange of CO₂ gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO₂ recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO₂ efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO₂ efflux and O₂ uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO₂-uptake rate without involving cyclic transfer of electrons around PS I or mitochondrial supplementation.Abbreviations Chl chlorophyll - K_d permeability coefficient The authors thank Drs A. Vermeglio and P. Thibault, Dépt. de Biologie, CEN-Cadarache, St. Paul Lez Durance, France, for helpful discussions.     

Stimulation by auxin of phospholipase A in membrane vesicles from an auxin-sensitive tissue is mediated by an auxin receptor

Microsomal vesicles were prepared from zucchini (Cucurbita pepo L.) hypocotyls containing radioactive phosphatidylethanolamine or phosphatidylcholine, and these lipids were used as substrates by phospholipase A which is activated by auxins. Phospholipase D and phospholipase C hydrolysed the same substrates but were not influenced by auxin. Phospholipase A was activated by the auxins indolyl-3-acetic acid, 2,4-dichlorophenoxyacetic acid and, to a lesser extent, by -naphthaleneacetic acid whereas the weak auxins 2,3-dichlorophenoxyacetic acid and -naphthaleneacetic acid were almost inactive. This hormone specificity was also found in growth tests with etiolated zucchini hypocotyls. Phospholipase A activation by auxin was blocked by a polyclonal antibody against the maize auxin-binding protein. We propose that phospholipase A activation is a primary reaction in the signal transduction leading from hormone-binding to the growth response.Abbreviations IAA indolyl-3-acetic acid - 2,3-D, 2,4-D 2,3- and 2,4-dichlorophenoxyacetic acid - -NAA; -NAA - and -naphthaleneacetic acid This work was supported by the Deutsche Forchungsgemeinschaft. We thank D. Klämbt (Botanical Institute, University of Bonn, FRG) for a generous gift of polyclonal antibody (IgG fraction) against auxin-binding protein and U. Kutschera (Botanical Institute, University of Bonn, FRG) for advice with the growth tests.     

Electron trapping and reactions in rhamnose by ESR and ENDOR.

The main objective for a reinvestigation of rhamnose was to devise a mechanistic link between the trapped electron detected previously and the secondary radicals observed at 77 K and at room temperature. Single crystals of rhamnose were X-irradiated at temperatures between 15 and 300 K and examined using ESR, ENDOR, and field-swept ENDOR techniques. After low-temperature irradiation a C3 H-abstraction radical is formed following the visible light-induced decay of the trapped electron. This species was previously assigned erroneously to a C2 H-abstraction species. At temperatures above 120 K, this radical deprotonates at the C3 hydroxy group. Furthermore, a C2 H-abstraction radical is formed following the thermally induced decay of the trapped electron. The C2 and C3 H-abstraction radicals did not convert into each other. A third radical species formed at low temperatures is a C5 H-abstraction radical. It is unstable above 250 K and decays without any apparent successor. The C2 and C3 H-abstraction radicals are formed thermally and photochemically from the parent trapped electron. The conversions are mediated by hydrogen atoms formed intermediately or by elimination of hydride ions. The thermal decomposition pathway requires further studies, in particular with respect to the possible role of water. Recently, Box et al. analyzed the site of the trapped electron in rhamnose crystals. The present results support the results obtained by these authors (Radiat. Res. 121, 262 (1990)). In particular, trapped electron vs proton distances closely match the conversion mechanisms suggested.     

Progebiophilus bruscai (Isopoda:Bopyridae) parasitizing the shrimp Upogebia dawsoni (Thalassinoidea:Upogebiidae), in Baja California Sur, Mexico)]

Parasitism of the isopod Progebiophilus bruscai Salazar-Vallejo & Leija-Tristán over the common mud shrimp, Upogebia dawsoni Williams, was analysed in the Ensenada and Bahia de La Paz, Baja California Sur, Mexico. Mud-shrimps were collected in three similar sites that differ in grain size and in the anthropogenic organic matter enrichment. Four-hundred-nine mud-shrimps were collected; the largest abundance was registered in the organically enriched site, but they were significantly smaller and more heavily parasited than the animals from the site lacking such organic enrichment. The size of the parasite is clearly dependent on the size of the mud-shrimp. This is the first study of the upogebiid-bopyris relationship in Mexico.     

Calcium dependence of the contractile response of the aorta in the rat, rabbit and guinea pig and in the human uterine artery

The influence of extracellular Ca2+ on the contraction produced by noradrenaline (NA) (3 x 10(-6) M), KCl (60 mM) and BaCl2 (30 mM) on human uterine arteries (AUH) and aortic strips from rats, rabbits and guinea-pigs have been studied. The vessels were cut spirally and incubated in Krebs solution containing 2.5 mM Ca2+ (KN), 0 mM Ca2+ (K-0Ca) or 0 mM Ca2+ + 3 mM EDTA (K-EDTA). Both phases (fast and slow) of the response of aortic strips to NA and of the AUH to NA, KCl and BaCl2 were significantly smaller in solutions without Ca2+. Only in rabbit aortic strips the slow phase was significantly more reduced than the fast phase. Overall, the contractions of the rat aortic strips were most resistant to the absence of extracellular Ca2+. These results confirm the variability of the responses of blood vessels from different vascular beds and species to the removal of extracellular Ca2+.     

An integrated approach to oilseed rape cultivar selection using phenotypic stability

Summary Various methods of evaluating phenotypic stability have been proposed; however, no single method can adequately describe cultivar performance. The objectives of this study were to integrate a number of methods of evaluating stability and to use this approach for cultivar selection. These objectives were considered in the context of the broad-based oilseed rape cultivar (Brassica napus spp. oleifera) evaluation system currently used in western Canada. Regression analysis was used to assess cultivar response to environments. Cluster analysis was used to assemble cultivars into groups with similar regression coefficients (b _i ) and mean yield. Three parametric stability parameters, years within locations mean square (MS; Y/L), Shukla's stability variance ( _i ² ), and Francis and Kannenberg's coefficient of variability (CV _i ), were compared to determine which method would be most suitable for selection of oilseed rape cultivars from within clustered groups. Yield data from three cultivars and six breeding lines that had been tested for 2 years at 26 locations in the Western Canola Cooperative Test A were used for all calculations. The cluster analysis was successful in identifying commercially acceptable breeding lines. The parameter MS _i Y/L was considered to be more appropriate than either CV _i or _i ² , because it measured only the unpredictable portion of the genotype x environment interaction and was independent of the other cultivars in the test. The use of cluster analysis to group entries with similar b _i values and mean yields, followed by selection for stability within groups, was advocated.Contribution No. 846 of the Plant Science Department, University of Manitoba     

Respiratory response to chemical stimuli and exercise capacity under conditions of acute hypoxia in elite mountain climbers]

To investigate the factors that modulate exercise performance at extreme altitude, the role of the following variables was analyzed in 16 climbers: 1) ventilatory response to chemical stimuli (hypoxia and hypercapnia); and, 2) maximum exercise performance while breathing room air and during acute hypoxia (F1O2, 0.11). Seven climbers (elite climbers, AE) had previously ascended to 8,000 m or more above sea level, and 9 (A) had never achieved such extreme altitude. Then healthy sedentary subjects (C) of similar age (31.1 +/- 6.0 SD years) were used as control group. Elite climbers showed higher ventilatory responses to both transient hypoxia (-0.49 +/- 0.13 L x min-1 x %-1) (p less than 0.05) and progressive hypoxia (-0.47 +/- 0.13 L x min-1 x %-1) than C (-0.33 +/- 0.14 and -0.30 +/- 0.15 L x min-1 x %-1, respectively). By contrast, no differences were observed between the two groups of climbers. The ventilatory response to hypercapnia was higher in AE (3.04 +/- 1.03 L x min-1 mmHg-1) compared to A (1.85 +/- 0.73 L x min-1 mmHg-1) (p less than 0.05) but similar to that observed in C. Breathing 11% O2, maximum workload and oxyhemoglobin desaturation during maximum exercise were similar in both groups of climbers. Additionally, the ventilatory response to hypoxia did not correlate with maximum workload (F1O2, 0.11), maximal ventilation during exercise (F1O2, 0.11), nor with the altitude score. The present study supports previous reports that inform about the role of the ventilatory response to hypoxia in the exercise performance at high altitude.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence for a new biologic pathway of androstenedione synthesis from 11-deoxycortisol

17-Hydroxyprogesterone is a well-known precursor of androstenedione in adrenal biosynthesis. This study using sheep adrenal incubations demonstrates that 11-deoxycortisol, the precursor of cortisol synthesis, also can be a precursor of androstenedione. Indeed, our data show that androstenedione synthesis is negatively correlated to the synthesis of cortisol and cortisone. This fact allowed us to infer that this new pathway is closely related to the activity of the 11 beta-hydroxylase that is responsible for the synthesis of cortisol. Indeed, when the activity of this enzyme is impaired, 11-deoxycortisol follows the pathway that leads to androstenedione synthesis in the adrenals. This pathway could explain, at least in part, the marked increase of androstenedione observed in congenital adrenal hyperplasia due to 11 beta-hydroxylase deficiency.     

Cytology and morphology of the amphiploid Hordeum chilense (4x) × Aegilops squarrosa (4x)

Summary The intergeneric amphiploid Hordeum chilense × Aegilops squarrosa has been synthesized. The amphiploid plants have the expected chromosome number of 28. The average meiotic chromosome pairing was 12.48 bivalents + 3.04 univalents. The morphology of the amphiploid resembles that of the Aegilops parent. Nucleoli from both H. chilense and A. squarrosa are expressed in the amphiploid. Neither chromosome instability nor homoeologous pairing was found. The amphiploid is fertile and vigorous.