Homeostatic control of polyamine levels under long-term salt stress in Arabidopsis

Salt stress has been frequently studied in its first osmotic phase. Very often, data regarding the second ionic phase is missing. It has also been suggested that Putrescine or/and Spermine could be responsible for salt resistance. In order to test this hypothesis under long-term salt stress, we obtained Arabidopsis thaliana transgenic plants harboring pRD29A::oatADC or pRD29A::GUS construction. Although Putrescine was the only polyamine significantly increased after salt acclimation in pRD29A::oatADC transgenic lines, this rendered in no advantage to this kind of stress. The higher Spermine levels found in WT and transgenic lines when compared to control conditions along with no increment on Putrescine levels in WT plants under salt acclimation, leads us to analyze Spermine effect on pADC1 and pADC2 expression. Increasing levels of this polyamine inhibits these promoters expression while enhances pRD29A expression, making Spermine the polyamine responsible for salt acclimation, and the transgenic lines developed in this work suitable for studying Putrescine roles in conditions where its biosynthesis would be inhibited in the WT genotype

Efecto de la humedad del sustrato sobre el éxito en la incubación de los huevos de la Iguana Colorada (Tupinambis rufescens : Squamata, Teiidae)

Los huevos de Tupínambis rufescens “iguana colorada” no son estrictamente cleidoicos(permite el intercambio gaseoso y la menor pérdida o ganancia de agua) y el desarrollo del embrión depende de la temperatura, de la tensión de oxígeno y de la incorporación dinámica de agua (gaseosa y líquida) desde el medio exterior a través de la cáscara flexible. La hembra de T. rufescens aporta al embrión en cada huevo sólo una fracción del agua necesaria para el completo desarrollo, por ello la incorporación de agua desde el medio es de vital importancia. La etapa de incubación de los huevos es la más vulnerable del ciclo de vida de estos individuos, mayormente en ambientes inestables debido a la acción de los factores abióticos. Por medio de la incubación artificial de las posturas producidas por un plantel de lagartos en cautiverio en el MACN se pudo concretar el objetivo de conocer los efectos, a través de los parámetros asociados con el éxito de la incubación, de diferentes disponibilidades de agua en el sustrato (constantes a lo larga de toda la incubación) y cuando la temperatura permanecía fija en un valor óptimo (29il°C). Resultó notable el desarrollo a término de embriones en condiciones donde el potencial agua del substrato era extremadamente bajo. Aún cuando el huevo no incorporó agua desde el medio se completó la formación del embrión, a pesar de originar individuos de reducido tamaño. Por el contrario, cuando el potencial agua fue alto acarreaba problemas de contaminaciones fiíngicas, perforaciones en la superficie del huevo, casos en que no se completó la formación del embrión, un aumento de la mortalidad y una menor proporción de las eclosiones normales o espontáneas. Podemos decir entonces, que parece mas tolerable un valor medio a bajo de agua disponible que uno en exceso.Fil: Menéndez, Analía I.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Legacy of historic ozone exposure on plant community and food web structure.

Information on whole community responses is needed to predict direction and magnitude of changes in plant and animal abundance under global changes. This study quantifies the effect of past ozone exposure on a weed community structure and arthropod colonization. We used the soil seed bank resulting from a long-term ozone exposure to reestablish the plant community under a new low-pollution environment. Two separate experiments using the same original soil seed bank were conducted. Plant and arthropod richness and species abundance was assessed during two years. We predicted that exposure to episodic high concentrations of ozone during a series of growing cycles would result in plant assemblies with lower diversity (lower species richness and higher dominance), due to an increase in dominance of the stress tolerant species and the elimination of the ozone-sensitive species. As a consequence, arthropod-plant interactions would also be changed. Species richness of the recruited plant communities from different exposure histories was similar (≈ 15). However, the relative abundance of the dominant species varied according to history of exposure, with two annual species dominating ozone enriched plots (90 ppb: Spergula arvensis, and 120 ppb: Calandrinia ciliata). Being consistent both years, the proportion of carnivore species was significantly higher in plots with history of higher ozone concentration (≈3.4 and ≈7.7 fold higher in 90 ppb and 120 ppb plots, respectively). Our study provides evidence that, past history of pollution might be as relevant as management practices in structuring agroecosystems, since we show that an increase in tropospheric ozone may influence biotic communities even years after the exposure

Community structure of the experimental plots during ozone exposure at 0, 90 and 120 ppb and after transplanting under common ecological conditions.

<p>Community structure of the experimental plots during ozone exposure at 0, 90 and 120 ppb and after transplanting under common ecological conditions.</p

Means and statistics from analysis of variance of species richness (<i>S</i>), species diversity (Shannon-Weaver index, H´) and species evenness (<i>H</i>´/log_e (<i>S</i>)) for arthropod communities established from different historic exposure regimens.

<p>Means and statistics from analysis of variance of species richness (<i>S</i>), species diversity (Shannon-Weaver index, H´) and species evenness (<i>H</i>´/log_e (<i>S</i>)) for arthropod communities established from different historic exposure regimens.</p

Relative abundance of <i>Spergula arvensis</i>, <i>Calandrinia ciliata</i> and other species in plant communities selected under different episodic concentrations of tropospheric ozone.

<p>Ozone concentrations in the open top chambers during long-term exposure were 0 ppb (white bars), 90 ppb (grey bars) and 120 ppb (dark bars). Data represents species abundances during the first (a) and second (b) year of experiment after original soil seed bank was transplanted to a common natural field environment. Relative abundance for each plant species was calculated as the summed abundances of each plant species for a particular year/total number of seedlings recorded in the plot (n = 3). Error bars represent standard error. Year a ANOVA <i>P</i> _species < 0.01, <i>P</i>_ozone 0.016, <i>P</i>_{species x ozone} 0.034; year b ANOVA <i>P</i> _species < 0.01, <i>P</i>_ozone 0.024, <i>P</i>_{species x ozone} 0.042</p

Mean seedling density in 1 m² plots established from plant communities. selected under different episodic concentrations of tropospheric ozone (0, 90 and 120 ppb).

<p>Mean seedling density in 1 m² plots established from plant communities. selected under different episodic concentrations of tropospheric ozone (0, 90 and 120 ppb).</p