Bird communities of dry forests and oak woodland of western Mexico

Bird species-richness and densities were studied in spring and autumn of 1991 and 1992 in dry forest and oak woodland in western Mexico. Classification of the vegetation resulted in the identification of six dry forest types: from thorn forests, dominated by Acacia , through broad-leaved tree forest (typical dry forest of western Mexico) and small-leaved tree forest to Ipomoea forest. Oak woodland and mixed woodland, which are a transition between dry forest and the more mesic oak woodland, formed two further forest types. In the study area as a whole, bird densities were higher in autumn, following the rainy season, than in spring, which is the dry season, and the beginning of the breeding season. Densities in the two autumns were very similar (mean 93 ± 7.8 birds per 2.8 ha) but differed significantly between spring 1991 (57 ± 2.2 per 2.8 ha) and spring 1992 (70 ± 3.2 per 2.8 ha), possibly due to unseasonal rain in 1992. In autumn, bird densities were highest in thorn forests and lowest in broad-leaved tree forests and oak woodland. In spring 1991, bird densities were highest in Prosopis thorn forest and mixed woodland, and lowest in oak woodland. Bird species-richness was low in oak woodland, in both seasons, and high in mixed woodland and Ipomoea forest in spring. Bird species composition between forest types was more similar in the spring than autumn. The spring similarity in species composition is explained by the presence of generalist species in times of food scarcity during the dry season, and by the homogeneity of the predominantly leafless vegetation. Comparison with the bird species composition of a dry forest in Venezuela and the Pacific coast of Mexico indicates that the sites in the present study have an intermediate number of species. Although the present study recorded a smaller number of bird species than on the Pacific coast, 16 were different, expanding the total for Mexican dry forest by 14% from 118 to 134.     

Validation of a UHPLC-FLD analytical method for the simultaneous quantification of aflatoxin B1 and ochratoxin a in rat plasma, liver and kidney

A rapid and simple method for the simultaneous quantification of AFB1 and OTA in rat plasma, liver and kidney by UHPLC-FLD has been successfully validated according to the following criteria: selectivity, stability, linearity, precision, accuracy, recovery, robustness and limits of quantification and detection. The extraction method, calibration curves and chromatographic conditions are common for the three matrices. Plasma and homogenized tissue samples (100 μL) were extracted with acetonitrile:formic acid mixture (99:1) (300 μL). Chromatographic separation was performed with a mixture of water and acetonitrile:methanol (50:50), both acidified with 0.5% of formic acid using a gradient profile. The method avoids the use of immunoaffinity columns and allows reduction of sample and solvent volumes as well as toxic wastes. The detection is based on a photochemical reaction which enhances the AFB1 response without affecting the OTA signal before reaching the fluorescent detector. The mycotoxin recovery for each matrix was very efficient, between 93% and 96% for AFB1 and between 94% and 96% for OTA. For both mycotoxins the LOQs were 2μg/L in plasma and 8μg/kg in liver and kidney. The method has successfully been applied to rat samples after a single oral administration of a mixture of AFB1 and OTA and it could be a useful tool in toxicokinetic and toxicological studies.     

Deschampsia antarctica Desv. primary photochemistry performs differently in plants grown in the field and laboratory

Primary photochemistry of photosystem II (F _v/F _m) of the Antarctic hair grass Deschampsia antarctica growing in the field (Robert Island, Maritime Antarctic) and in the laboratory was studied. Laboratory plants were grown at a photosynthetic photon flux density (PPFD) of 180 μmol m⁻² s⁻¹ and an optimal temperature (13 ± 1.5°C) for net photosynthesis. Subsequently, two groups of plants were exposed to low temperature (4 ± 1.5°C day/night) under two levels of PPFD (180 and 800 μmol m⁻² s⁻¹) and a control group was kept at 13 ± 1.5°C and PPFD of 800 μmol m⁻² s⁻¹. Chlorophyll fluorescence was measured during several days in field plants and weekly in the laboratory plants. Statistically significant differences were found in F _v/F _m (=0.75–0.83), F ₀ and F _m values of field plants over the measurement period between days with contrasting irradiances and temperature levels, suggesting that plants in the field show high photosynthetic efficiency. Laboratory plants under controlled conditions and exposed to low temperature under two light conditions showed significantly lower F _v/F _m and F _m. Moreover, they presented significantly less chlorophyll and carotenoid content than field plants. The differences in the performance of the photosynthetic apparatus between field- and laboratory-grown plants indicate that measurements performed in ex situ plants should be interpreted with caution.     

Differences in light usage among three fern species of genus <Emphasis Type="Italic">Blechnum</Emphasis> of contrasting ecological breadth in a forest light gradient

In Chilean evergreen temperate forest, fern species of the genus Blechnum occur in diverse microhabitats in a light gradient. We hypothesized that differences in the habitat preferences of three co-occurring Blechnum species would be associated with differences in the magnitude of responses of light capture [chlorophyll (Chl) content] and use (photosynthetic capacity and performance) to light availability. We measured the abundance, chlorophyll content, photosynthetic capacity (A), and photosynthetic performance (chlorophyll fluorescence of photosystems I and II) of juvenile individuals of each species growing in different light levels in the field. While Blechnum magellanicum covers a broad light environments range, B. mochaenum is restricted to shade, and B. penna-marina occupies full sun sites. Despite significant interspecific differences in average total chlorophyll content, this trait did not differ among species along the light gradient. There was significant interspecific variation in both the mean value and the plasticity of Chl a:Chl b ratio and A to light availability. While B. penna-marina showed a flatter reaction norm (lower response) of Chl a:Chl b ratio to light availability than its two congeners, B. mochaenum showed a lower response of A to light availability. B. penna-marina and B. magellanicum individuals from open sites had higher light saturation points of the electron transport rate (ETR) of both photosystems (ETR_LSP I and II) and photochemical quenching (qL and NA) than the shade restricted B. mochaenum. Additionally, non-photochemical quenching values for both photosystems (NPQ and ND) were higher in ferns species occurring in shaded sites. The adjustment of the photosynthetic capacity and performance to light availability appears to be an important mechanism of acclimation in these three Blechnum species that differ in their habitat preferences across a light gradient.     

Effects of Hydroxamic Acids Isolated from Gramineae on Adenosine 5'-triphosphate Synthesis in Chloroplasts

Two hydroxamic acids isolated from maize extracts, 2,4-dihydroxy-7-methoxy-1,4-(2H)-benzoxazin-3(4H)-one (DIMBOA) and the 2-O-beta-d-glucopyranoside of DIMBOA, inhibit photophosphorylation by spinach chloroplasts. Both cyclic and noncyclic photophosphorylations were inhibited to the same extent. The concentrations producing 50% inhibition for DIMBOA and its glucoside were about 1 and 4 millimolar, respectively. These compounds inhibit coupled electron transport but do not affect basal or uncoupled electron transport. Both acids inhibit the ATPase activities of membrane-bound coupling factor 1 (CF(1)) and of purified CF(1). On the basis of these results, it is concluded that DIMBOA and its glucoside act as energy transfer inhibitors of photophosphorylation.     

2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one, an Inhibitor from Zea mays with Differential Activity against Soft Rotting Erwinia Species

[2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one] DIMBOA was extracted with ethyl acetate from acidified water homogenates of corn (Zea mays L.) seedlings. Pure DIMBOA or ethyl acetate extracts of corn tissue were added to bacterial growth medium at five concentrations (measured as hydroxamates). DIMBOA and corn extracts were more inhibitory to soft rot bacteria (Erwinia spp.) that are nonpathogenic to corn than to soft rot bacteria that are corn pathogens. The inhibitory activity of DIMBOA was similar to that of the ethyl acetate extracts. Both corn extracts and DIMBOA prolonged the lag phase of bacterial growth without significantly changing log phase growth rates. At various concentrations of the inhibitor, 50 to 100% of the activity of corn extracts inhibitory to different bacterial isolates was attributable to DIMBOA. Extracts of DIMBOA-deficient plants (genotype bxbx) were not inhibitory to Erwinia spp. It was concluded that DIMBOA is the major active component in those corn extracts which are inhibitory to soft rot Erwinia species.     

Decomposition of 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one in Aqueous Solutions

Cyclic hydroxamic acids present in some species of Gramineae have been reported to be important in resistance of these plants to fungi and insects. Since the nonglucosylated forms of these acids are unstable in aqueous solution, in vitro methods for the measurement of their antibiotic properties have been difficult. Kinetics of the decomposition of 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), the major hydroxamate in corn (Zea mays L.) extracts, were studied in buffered aqueous solutions from pH 5 to 7.5 at temperatures from 20 to 80 C. Kinetics were apparently first order under all conditions tested; energies of activation (24 to 28 kcal/mol) were nearly pH-independent. DIMBOA decomposed rapidly (half-life = 5.3 hours at 28 C, pH 6.75) relative to the time required for many procedures which have been used to demonstrate the biological activity of DIMBOA. The rate of disappearance of inhibitory activity of DIMBOA toward Erwinia carotovora was indistinguishable from the rate of decomposition of DIMBOA. Contrary to reports, yields of 6-methoxy-2-benzoxazolinone (MBOA) were not quantitative. Gas-liquid chromatography analytical procedures were developed for quantitation of trimethylsilyl and acetyl derivatives of MBOA. As measured by ultraviolet spectroscopy and/or gas-liquid chromatography, conversion of DIMBOA to MBOA ranged from 40 to 75% of theoretical in aqueous buffers, bacterial growth medium, and ethyl acetate extracts of corn tissue resuspended in buffer. Yields varied with temperature, pH, and constituents in the medium.     

Differential accumulation of dehydrin-like proteins by abiotic stresses in Deschampsia antarctica Desv.

Dehydrins are proteins that accumulate during environmental stresses leading to cell dehydration. Deschampsia antarctica is one of the two vascular plants that have colonized the Maritime Antarctic. This plant is usually exposed to cold, salt and desiccating winds in the field. We proposed that among the factors that allow D. antarctica to survive the harsh environmental conditions is the presence of dehydrins. We studied the accumulation of dehydrins by abscisic acid (ABA), dehydration, NaCl and low osmotic potential. Western blots using an anti-dehydrin antibody revealed a complex pattern of dehydrin-like proteins (DLPs) accumulation in the different treatments. DLPs with apparent molecular weight of 58, 57, 55, 53, 48, 42, 32, 30, 28 and 25 kDa were detected in the different treatments. DLPs accumulation was associated with a decrease in the relative water content (RWC) of the plants. These results suggest that DLPs accumulation could contribute to explain how D. antarctica can survive under adverse Antarctic conditions.     

Ki-67 immunolabeling in pre-malignant lesions and carcinoma of the prostate. Histological correlation and prognostic evaluation

The antigen Ki-67, which is associated with cell proliferation, has been demonstrated to be useful in predicting the development of human tumors. The objective of this study was to evaluate the prognostic utility of this biomarker in pre-malignant and malignant lesions of the prostate. A total of 162 prostate biopsies taken from patients diagnosed for benign prostatic hyperplasia (BPH, n=49), low grade prostatic intraepithelial neoplasia (LGPIN, n=53), high grade prostatic intraepithelial neoplasia (HGPIN, n=25) and carcinoma (CAR, n=35), were studied. Immunohistochemistry for Ki-67 was carried out on all the samples and the number of labeled cells was semi-quantitatively evaluated (weak, moderate or intense). In the non-invasive lesions, the presence of Ki-67-positive cells in the luminal layer of the epithelium was evaluated qualitatively as positive or negative. The correlation between the immunolabeling for Ki-67 and the histological diagnosis showed highly significant differences between BPH and CAR, LGPIN and CAR and HGPIN and CAR, with no significant differences being found among the other groups. Analysis of the immunolabeling in luminal cells of non-invasive lesions showed an increase in accordance with the increase in the degree of histological lesion, the greatest percentage being obtained in the HGPIN lesions (88.0%), with significant differences among all the groups. Bearing in mind that Ki-67 is a prognostic biomarker for cell proliferation, our results demonstrating the immunolabeling of Ki-67 in the luminal compartment of non-invasive lesions having the potential to evolve to malignancy, may have prognostic implications.