Héctor Espinosa Pérez

The Aberrant Cell Walls of Boron-Deficient Bean Root Nodules Have No Covalently Bound Hydroxyproline-/Proline-Rich Proteins

B-deficient bean (Phaseolus vulgaris L.) nodules examined by light microscopy showed dramatic anatomical changes, mainly in the parenchyma region. Western analysis of total nodule extracts examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that one 116-kD polypeptide was recognized by antibodies raised against hydroxyproline-rich glycoproteins (HRGPs) from the soybean (Glycine max) seed coat. A protein with a comparable molecular mass of 116 kD was purified from the cell walls of soybean root nodules. The amino acid composition of this protein is similar to the early nodulin (ENOD2) gene. Immunoprecipitation of the soybean ENOD2 in vitro translation product showed that the soybean seed coat anti-HRGP antibodies recognized this early nodulin. Furthermore, we used these antibodies to localize the ENOD2 homolog in bean nodules. Immunocytochemistry revealed that in B-deficient nodules ENOD2 was absent in the walls of the nodule parenchyma. The absence of ENOD2 in B-deficient nodules was corroborated by performing hydroxyproline assays. Northern analysis showed that ENOD2 mRNA is present in B-deficient nodules; therefore, the accumulation of ENOD2 is not affected by B deficiency, but its assembly into the cell wall is. B-deficient nodules fix much less N2 than control nodules, probably because the nodule parenchyma is no longer an effective O2 barrier.

Purification, characterization, and cDNA cloning of profilin from Phaseolus vulgaris.

Profilin from common bean (Phaseolus vulgaris L.) was purified to homogeneity by poly-L-Pro affinity chromatography and gel filtration. The hypocotyl and symbiotic root nodule protein was detected as a single isoform with a 14.4-kD molecular mass and an isoelectric point of 5.3. Partial amino acid and DNA sequencing of a full-length cDNA clone confirmed its identity as profilin. An antibody generated against the purified protein binds to a protein with the same molecular mass in leaves and nodules. Immunolocalization of the protein showed a diffuse distribution in the cytoplasm of hypocotyls and nodules but enhanced staining at the vascular bundles. The strong identity of the sequence among the profilins of birch, maize, and bean suggests that it may play an important role in the signal transduction mechanism of plant cells and plant-bacterial symbioses.

A new blind cave fish population of genus Astyanax: geography, morphology and behavior

A new population of blind, cave dwelling tetra fish of the genus Astyanax was discovered in Granadas Cave, in the Balsas drainage, southern Mexico. All blind Mexican tetras previously described are from Tampico and San Luis Potosi, northern Mexico. The discovery of a new blind morph thus represents an independent colonization and convergent adaptation to the cave environment by this fish. Individuals of this population display variability of their troglomorphic features. Some individuals presented asymmetrical degeneration of the eyes, where one was normal, but the other somewhat reduced in size and complexity. Loss of pigmentation and eye reduction, although sometimes correlated, were not always linked; reduced eyes were found on pigmented fish and unpigmented fish often possessed normal eyes. Some individuals had reduced lens size or an absence of lens altogether. Retina is highly modified with photoreceptors sometimes absent. Eye reduction was correlated with a diminished size of the optic lobes and an increase of the prosencephalon. Modifications of the skull involve closing in of the circumorbital series of bones. Certain aspects of behavior are also modified.

Mexican native trouts: a review of their history and current systematic and conservation status

While biologists have been aware of theexistence of native Mexican trouts for over acentury, they have received little study. Thefew early studies that did much more thanmention their existence began in the 1930s andcontinued into the early 1960s, focusingprimarily on distributional surveys andtaxonomic analyses. Starting in the 1980s theBaja California rainbow trout became thesubject of more detailed studies, but verylittle remains known of mainland trouts of theSierra Madre Occidental. We review earlierstudies and report on our own collections andobservations made between 1975 and 2000. Wepresent newly discovered historical evidencethat leads us to conclude that a “lost”cutthroat trout, a lineage not previously knownfrom Mexico, was collected more than a centuryago from headwaters of the Río Conchos (amajor tributary of the Rio Grande (= RíoBravo)), a basin not previously considered toharbor a native trout. We review the lastcentury of regional natural resource managementand discuss our own observations of trouthabitats. Impacts of logging, road building andovergrazing are widespread and expanding. Manystreams suffer from heavy erosion, siltationand contamination, and though long-termhydrologic data are generally not available,there is evidence of decreased discharge inmany streams. These problems appear related toregion-wide land management practices as wellas recent regional drought. Trout cultureoperations using exotic rainbow trout haverapidly proliferated throughout the region,threatening genetic introgression and/orcompetition with native forms and predation onthem. Knowledge of distribution, abundance,relationships and taxonomy, not to mentionecology and population biology, of nativetrouts of the Sierra Madre Occidental remainsinadequate. Vast areas of most mainlanddrainages are still unexplored by fishcollectors, and even rudimentary informationregarding basic biology, ecology and populationstructure of stocks remains lacking.Concentrated exploration, research andmanagement of this long overlooked andundervalued resource are all urgently needed.The history of natural resources exploitationthat placed so many native trouts of thewestern United States on threatened andendangered species lists is repeating itself inthe Sierra Madre Occidental. Without concertedaction and development of region-widesocio-economic solutions for current, largelynon-sustainable resource management practices,native Mexican trout gene pools will soon be ingrave danger of extinction.

Actin isoforms in non-infected roots and symbiotic root nodules of Phaseolus vulgaris L.

The present report describes an initial characterization of actin from non-infected roots and symbiotic nodules of Phaseolus vulgaris L. cv. Negro damapa. Using anti-actin monoclonal antibodies, a 42-kDa polypeptide was identified in plant extracts. After two-dimensional SDS-PAGE analysis and Western blotting of actin fractions enriched using diethylaminoethyl-resin, the presence of one major isoform of actin in symbiotic nodules and two main isoforms in non-infected roots was revealed. Possible implications of this finding are discussed.

Exotic and invasive fishes in Mexico

This paper presents a list of the exotic fish species introduced in Mexican aquatic systems. This list is the result of the systematized information contained in several databases of ichthyological collections around the world and different publications. A total of 104 species were found, distributed in 19 families and 51 genera. The most species-rich were Cyprinidae with 22 species, Poeciliidae (19 species), Cichlidae (15 species) and Centrarchidae (13 species). A map and an electronic database were created based on the knowledge of the species, showing the known introductions of exotic fishes in the country. The information was obtained from a database stored in the Coleccion Nacional de Peces IBUNAM, which can be accessed online. This study has a high importance for the knowledge of the exotic fish fauna of Mexico and its current status.

The effect of boron deficiency on development in determinate nodules: changes in cell wall pectin contents and nodule polypeptide expression

The effect of boron (B) deficiency on nodule development and nitrogen fixation in bean (Phaseolus vulgaris) was studied. Nodules from plants grown without B in the nutrient solution were smaller in size and had a weight lower than the controls. In addition, B starvation resulted in a severe decrease in acetylene reduction activity after two weeks of treatment. Light microscopy examination of B deficient nodules showed dramatic changes in cell shape, amyloplast number, and cell wall structure, mainly in those cells located in the middle of the central zone. The use of the tissue-printing technique indicated that pectins are decreased in B-deficient nodules. Finally, one and two dimensional analysis of the nodule polypeptides showed the premature expression of a 116 kDa polypeptide in B-deficient compared to control nodules. These data suggest that B is an obligatory requirement for normal determinate nodule development and functioning.

Molecular systematics of the New World clingfish genus Gobiesox (Teleostei: Gobiesocidae) and the origin of a freshwater clade

The phylogenetic relationships between marine and freshwater members of the New World clingfish genus Gobiesox are investigated using both mitochondrial and nuclear sequence data. Phylogenetic hypotheses are derived from Bayesian and maximum parsimony analyses of a six-gene concatenated data set (2 mitochondrial and 4 nuclear markers; 4098bp). Gobiesox is paraphyletic, due to the inclusion of Pherallodiscus, in phylogenetic hypotheses resulting from all analyses and its two included species are reassigned to Gobiesox. Within the expanded genus Gobiesox, the freshwater species (G. cephalus, G. juradoensis, G. mexicanus and G. potamius) represent a monophyletic group that is nested inside of a paraphyletic marine group. Based on the monophyly of the freshwater clingfishes, a habitat transition from marine to freshwater is inferred to have occurred only once in the evolutionary history of the group (potentially in the mid-Miocene). Gobiesox is obtained as part of a larger clade of New World clingfishes, including also members of Acyrtops, Acyrtus, Arcos, Rimicola, Sicyases and Tomicodon equivalent to the subfamily Gobiesocinae. The phylogenetic hypotheses obtained are discussed briefly in relation to the two alternative classifications currently in use simultaneously for the Gobiesocidae. A rediagnosis and list of included species is provided for Gobiesox.

Rhizobium Nodulation Signals Induce Calcium Changes and Actin Cytoskeleton Rearrangements in Plant Root Hair Cells

In the first stages of root nodule morphogenesis, there is evidence that the actin cytoskeleton participates in the formation of preinfection threads and induction of cortical cell divisions (Bakhuizen, 1988). It has been reported that actin becomes fragmented in curled root hairs fromViciae hirsuta when infected with Rhizobium (Ridge et al. 1992). Although Allen et al., (1994) have reported that in curled root hairs actin foci were observed close to the tip, when exposed to Nod factors, the question of how actin cytoskeleton responded to Nod factors, during the first minutes of exposure, remains unanswered. We are interested in analyzing this response using as a model, the symbiosis P. vulgaris-R. etli. On the other hand, it is a known fact that Ca2+ is indispensable for the infection process as suggested by the use of aureomycin. The increased fluorescence normally found at the root hair tip due to the presence of Ca2+ has suggested its possible role in the formation and growth of the infection thread (Sethi and Reporter 1981). Recent studies have explored ion movement as an indicator of root hair activity related to signal perception. It has been found that alfalfa root hairs displayed a depolarization of the cytoplasmic membrane in response to R. meliloti Nod factors (Ehrhardt et al., 1992; Felle et al., 1995; Kurkdjian, 1995). Albeit the ionic basis for this behaviour is unknown, there is some evidence that variable currents of H+ and Ca++ ions, are present outside root hairs from alfalfa (legume forming indeterminate nodules) which had been exposed to Nod factors (Allen et al., 1994). In alfalfa root hair cells, a calcium spiking response around the nucleus, that initiated 10 min after Nod factor exposure and remained up to 60 min has been reported (Ehrhardt et al., (1996). To elucidate the calcium response in root hair cells from a legume forming determinate nodules, P. vulgaris, we isolated and purified Nod factors from R. etli (Cardenas et al., 1995), and studied their effect on intracellular and extracellular Ca2+ current influxes in this legume. We used two approaches, dextran-linked calcium selective dyes injected directly into P. vulgaris root hairs, and an ion selective vibrating probe.

Intracellular and Extracellular Calcium Changes in Plant Root Hair Cells Responding to Nodulation Signals

There is evidence that Ca2+ participates in multiple signal transduction pathways in stimulus-response coupling in plants in general. Increases in cytosolic free Ca2+ have been observed in different cell types in response to a number of stimuli, including plant hormones, mechanical stimuli, high and low temperatures, salt stress, among others (Bush, 1993; Gilroy et al., 1993; Poovaiah and Reddy, 1993).