A synthetic oligonucleotide probe encoding for atrial natriuretic peptide detects specific mRNA transcripts in rat heart but not brain using in situ hybridization histochemistry

In situ hybridization histochemical techniques were used in an attempt to demonstrate atrial natriuretic peptide (ANP) messenger RNA (mRNA) in the rat brain. A synthetic oligonucleotide derived from previously reported ANF cDNA sequence was used as a probe. Northern blot analysis of total RNA isolated from rat heart demonstrated that the oligonucleotide recognized a single species of RNA (0.9 kb), a size consistent with previous reports. Rat heart sections revealed dense accumulations of ANF mRNA in the cardiac atria and lesser densities in the ventricles. Rat brain sections hybridized with the same oligonucleotide did not label ANF mRNA accumulations in any neuronal cell bodies. A possible explanation for this latter observation is either sparsely distributed expressing neurons or low expression and high turnover of ANF mRNA in brain.     

Photosynthetic capacity and temperature responses of photosynthesis of rubber trees (Hevea brasiliensis Müll. Arg.) acclimate to changes in ambient temperatures

The aim of this study was to assess the temperature response of photosynthesis in rubber trees (Hevea brasiliensis Müll. Arg.) to provide data for process-based growth modeling, and to test whether photosynthetic capacity and temperature response of photosynthesis acclimates to changes in ambient temperature. Net CO₂ assimilation rate (A) was measured in rubber saplings grown in a nursery or in growth chambers at 18 and 28°C. The temperature response of A was measured from 9 to 45°C and the data were fitted to an empirical model. Photosynthetic capacity (maximal carboxylation rate, V _cmax, and maximal light driven electron flux, J _max) of plants acclimated to 18 and 28°C were estimated by fitting a biochemical photosynthesis model to the CO₂ response curves (A–C _i curves) at six temperatures: 15, 22, 28, 32, 36 and 40°C. The optimal temperature for A (T _opt) was much lower in plants grown at 18°C compared to 28°C and nursery. Net CO₂ assimilation rate at optimal temperature (A _opt), V _cmax and J _max at a reference temperature of 25°C (V _cmax25 and J _max25) as well as activation energy of V _cmax and J _max (E _aV and E _aJ) decreased in individuals acclimated to 18°C. The optimal temperature for V _cmax and J _max could not be clearly defined from our response curves, as they always were above 36°C and not far from 40°C. The ratio J _max25/V _cmax25 was larger in plants acclimated to 18°C. Less nitrogen was present and photosynthetic nitrogen use efficiency (V _cmax25/N _a) was smaller in leaves acclimated to 18°C. These results indicate that rubber saplings acclimated their photosynthetic characteristics in response to growth temperature, and that higher temperatures resulted in an enhanced photosynthetic capacity in the leaves, as well as larger activation energy for photosynthesis.     

Ungulates increase forest plant species richness to the benefit of non‐forest specialists

Large wild ungulates are a major biotic factor shaping plant communities. They influence species abundance and occurrence directly by herbivory and plant dispersal, or indirectly by modifying plant‐plant interactions and through soil disturbance. In forest ecosystems, researchers’ attention has been mainly focused on deer overabundance. Far less is known about the effects on understory plant dynamics and diversity of wild ungulates where their abundance is maintained at lower levels to mitigate impacts on tree regeneration. We used vegetation data collected over 10 years on 82 pairs of exclosure (excluding ungulates) and control plots located in a nation‐wide forest monitoring network (Renecofor). We report the effects of ungulate exclusion on (i) plant species richness and ecological characteristics, (ii) and cover percentage of herbaceous and shrub layers. We also analyzed the response of these variables along gradients of ungulate abundance, based on hunting statistics, for wild boar (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Outside the exclosures, forest ungulates maintained higher species richness in the herbaceous layer (+15%), while the shrub layer was 17% less rich, and the plant communities became more light‐demanding. Inside the exclosures, shrub cover increased, often to the benefit of bramble (Rubus fruticosus agg.). Ungulates tend to favour ruderal, hemerobic, epizoochorous and non‐forest species. Among plots, the magnitude of vegetation changes was proportional to deer abundance. We conclude that ungulates, through the control of the shrub layer, indirectly increase herbaceous plant species richness by increasing light reaching the ground. However, this increase is detrimental to the peculiarity of forest plant communities and contributes to a landscape‐level biotic homogenization. Even at population density levels considered to be harmless for overall plant species richness, ungulates remain a conservation issue for plant community composition.     

Plasticity of morphological and physiological traits in response to different levels of irradiance in seedlings of silver fir (Abies alba Mill)

The ability of silver fir ( Abies alba Mill.) to acclimate to different levels of irradiance was tested with 3-year-old seedlings, grown for 2 years in a nursery close to Nancy (eastern France) under 100, 48, 18 and 8% of incident irradiance (neutral shade nets). Growth, total nutrients in needles, maximal carboxylation rate ( V _cmax), maximal light driven electron flow ( J _max) and the relative amount of nitrogen allocated to photosynthetic processes (carboxylation, bioenergetics, light harvesting) were investigated. The sensitivity to drought stress was assessed among the phenotypes resulting from light acclimation. Leader-shoot and branch elongation were greatest under 18% irradiance. Total seedling biomass, root-to-total biomass ratio, total leaf area, leaf mass-to-area ratio and needle-area based nitrogen content responded positively to increasing irradiance while leaf area ratio decreased. Both V _cmax and J _max increased by a factor of 1.6 and 1.8, respectively, from the lowest to the highest irradiance but the ratio J _max/ V _cmax remained stable. All these parameters, expressed on a projected needle area basis, remained within the lower range of values measured for broadleaved trees. Relative allocation of needle N to the different components of the photosynthetic apparatus was very low: 12, 3 and 7% of total nitrogen were invested in carboxylation, bioenergetics and light harvesting, respectively. The relative allocation of nitrogen to carboxylation and bioenergetics remained stable while that to light harvesting decreased with increasing irradiance. During drought, seedlings pre-acclimated to shade closed their stomata at higher predawn needle water potential than those which were grown under higher irradiance. Critical temperature for PSII photochemistry in needles was unaffected by irradiance and was close to 47°C. Drought significantly increased the critical temperature up to 51°C. In general, the amplitude of responses of silver fir to changing irradiance (phenotypic plasticity) was smaller than that recorded in broadleaved species.     

Season effects on leaf nitrogen partitioning and photosynthetic water use efficiency in mango

The key parameters of photosynthetic capacity (maximum carboxylation rate (V_cmax), electron transport capacity (J_max) and dark respiration rate (R_d)) and the slope (m) of the stomatal conductance model of Ball et al. [Progress in photosynthetic research, Martinus Nijhoff, Dordrecht, 1987] were measured for a whole growing season in fully expanded leaves of 12-year-old mango trees cv. Cogshall in La Réunion island. Leaf nitrogen partitioning into carboxylation (P_c) and bioenergetic (P_b) pools were computed according to the model of Niinemets and Tenhunen [Plant Cell Environ 1997;20: 845–66]. V_cmax, J_max, R_d, P_c and P_b remained relatively stable over the whole study period, with the exception of the period of linear fruit growth when J_max, R_d and P_b were slightly lower, and leaf non-structural carbohydrate content higher. During the pre-floral and floral periods, m decreased by more than 50%, indicating an increase in photosynthetic water use efficiency and m increased again during the period of linear fruit growth. Our results show that, in tropical orchard conditions characterized by mild seasonal climatic changes and non-limiting water supply, leaf nitrogen partitioning is rather stable. Our results also advocate for more studies on the effect of phenology on m and photosynthetic water use efficiency, which is of paramount importance for building coupled biochemical models of photosynthetic carbon assimilation.     

Temperature response of parameters of a biochemically based model of photosynthesis. II. A review of experimental data

The temperature dependence of C₃ photosynthesis is known to vary with growth environment and with species. In an attempt to quantify this variability, a commonly used biochemically based photosynthesis model was parameterized from 19 gas exchange studies on tree and crop species. The parameter values obtained described the shape and amplitude of the temperature responses of the maximum rate of Rubisco activity (V_cmax) and the potential rate of electron transport (J_max). Original data sets were used for this review, as it is shown that derived values of V_cmax and its temperature response depend strongly on assumptions made in derivation. Values of J_max and V_cmax at 25 °C varied considerably among species but were strongly correlated, with an average J_max : V_cmax ratio of 1·67. Two species grown in cold climates, however, had lower ratios. In all studies, the J_max : V_cmax ratio declined strongly with measurement temperature. The relative temperature responses of J_max and V_cmax were relatively constant among tree species. Activation energies averaged 50 kJ mol^?1 for J_max and 65 kJ mol^?1 for V_cmax, and for most species temperature optima averaged 33 °C for J_max and 40 °C for V_cmax. However, the cold climate tree species had low temperature optima for both J_max(19 °C) and V_cmax (29 °C), suggesting acclimation of both processes to growth temperature. Crop species had somewhat different temperature responses, with higher activation energies for both J_max and V_cmax, implying narrower peaks in the temperature response for these species. The results thus suggest that both growth environment and plant type can influence the photosynthetic response to temperature. Based on these results, several suggestions are made to improve modelling of temperature responses.     

Regional Distribution of the GABAA/Benzodiazepine Receptor (α Subunit) mRNA in Rat Brain

A human cDNA clone containing the 5' coding region of the GABAA/benzodiazepine receptor alpha subunit was used to quantify and visualize receptor mRNA in various regions of the rat brain. Using a [32P]CTP-labelled antisense RNA probe (860 bases) prepared from the alpha subunit cDNA, multiple mRNA species were detected in Northern blots using total and poly A rat brain RNA. In all brain regions, mRNAs of 4.4 and 4.8 kb were observed, and an additional mRNA of 3.0 kb was detected in the cerebellum and hippocampus. The level of GABAA/benzodiazepine receptor mRNA was highest in the cerebellum followed by the thalamus = frontal cortex = hippocampus = parietal cortex = hypothalamus much greater than pons = striatum = medulla. In situ hybridization revealed high levels of alpha subunit mRNA in cerebellar gray matter, olfactory bulb, thalamus, hippocampus/dentate gyrus, and the arcuate nucleus of the hypothalamus. These data suggest the presence of multiple GABAA/benzodiazepine receptor alpha subunit mRNAs in rat brain and demonstrate the feasibility of studying the expression of genes encoding the GABAA/benzodiazepine receptor after pharmacological and/or environmental manipulation.     

20-Hydroxyecdysone induces the expression of one beta-tubulin gene in Drosophila Kc cells

The expression of 56D and 60C beta-tubulin genes has been examined in Drosophila melanogaster Kc cells in response to the insect moulting hormone, 20-hydroxyecdysone (20-OH-E). Northern blots probed with beta-tubulin subclones show that the 56D beta-tubulin gene encodes a 1.8 kb mRNA whose abundance is not affected by 20-OH-E. The 60C gene probe detects two mRNAs: one of 1.8 kb present in untreated and 20-OH-E-treated cells, and one of 2.6 kb present only in 20-OH-E-treated cells; using a 60C 3'-specific probe, only the 2.6 kb is revealed. Hybrid selection translation experiment demonstrates that a 20-OH-E-inducible mRNA homologous to the 60C gene encodes a beta-tubulin subunit (P4); this subunit is the so-called beta 3-tubulin. Translation of size-fractionated mRNA shows that the 20-OH-E-induced beta 3-tubulin subunit is encoded, in treated cells, by the 2.6 kb mRNA.