Vol.26 - Issue 3- 2002

Water relations and leaf growth rate of three Agropyron genotypes
under water stress

Departamento de Agronomía y CERZOS (CONICET), Universidad Nacional del Sur. (8000) Bahía Blanca, Argentina.

Key words: Agropyron scabrifolium (Döell) Parodi, Agropyron elongatum (Host) Beauv., water stress, water relations, leaf growth rate.

ABSTRACT: The effects of water stress on leaf water relations and growth are reported for three perennial tussock grass genotypes under glasshouse conditions. Studies were performed in genotypes El Palmar INTA and Selección Anguil of Agropyron scabrifolium (Döell) Parodi, and El Vizcachero of A. elongatum (Host) Beauv. Agropyron scabrifolium El Palmar INTA is native to a region with warm-temperate and humid climate without a dry season, and an average annual precipitation of 900 mm. Agropyron scabrifolium Selección Anguil comes from a region with a sub-humid, dry to semiarid climate and a mean annual precipitation of 600 mm. Agropyron elongatum is a widespread forage in semiarid Argentina with well-known water stress resistance. A mild water stress treatment was imposed slowly; plants reached a minimum pre-dawn leaf water potential of about -1.83 MPa by day 21 after watering was withheld. In all genotypes, water stress led to a reduction of leaf growth. There was a tendency for a greater epicuticular wax accumulation on water-stressed plants of A. scabrifolium Selección Anguil and A. elongatum than on those of A. scabrifolium El Palmar INTA. This may have contributed to obtain greater turgor pressures and relative water contents in the first two than in the later genotype. In turn, this may have contributed to determine smaller leaf growth rate reductions in A. scabrifolium Selección Anguil and A. elongatum than in A. scabrifolium El Palmar INTA under water stress. This study demonstrated variation in water stress resistance between genotypes in A. scabrifolium, and between A. scabrifolium Selección Anguil and A. elongatum versus A. scabrifolium El Palmar INTA, which was related to their differential responses in water relations.

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In vitro propagation of Opuntia ellisiana Griff. and acclimatization
to field conditions

1. Centro Regional de Investigaciones Científicas y Tecnológicas (CRICYT), Instituto Argentino de Investigaciones de las
Zonas Áridas (IADIZA). C.C. 507, 5500 Mendoza, Argentina. E-mail: mcjuarez@lab.cricyt.edu.ar
2. Facultad de Ciencias Agrarias, Universidad Nacional de Cuyo. C.C. 7, 5505 Chacras de Coria, Mendoza, Argentina. Email:
cpassera@lab.cricyt.edu.ar; cpassera@fca.uncu.edu.ar

Key words: micropropagation, areole culture, cold hardy forage, arid forage resources

ABSTRACT: The genus Opuntia is a valuable forage resource in arid and semiarid lands during periods of drought and shortage of herbaceous plants. However, absolute minimum temperatures in the plains of Mendoza represent a limiting factor to cultivate several species. Opuntia ellisiana is a cold hardy species, so the goals of this study were to massively propagate it using in vitro culture techniques, and then to acclimatize plantlets obtained to field conditions. Different sterilization protocols were tested. Areoles were isolated in laminar airflow cabinet, and cultured on Murashige-Skoog medium, supplemented with sucrose and different BAP and IBA combinations. Explants
were grown at 27±2ºC, under a 16-h photoperiod. The shoots produced were used in the rooting assay using different auxin combinations. In the most eff icient growth treatment, plantlets reached 100% shooting after 35 days of culture, and a mean length of 10.2 mm after 49 days of culture. A 100% rooted plantlets was obtained on a medium containing 5 mg L-1 IBA, after 12 days of culture. Acclimatization was achieved under greenhouse conditions, showing 100% plantlet survival. This study suggests that O. ellisiana can be successfully micropropagated by areoles, and easily acclimatizated to field conditions.

Abbreviations: benzylaminopurine (BAP); indole-3-butyric acid (IBA); basal medium (BM).

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Oogenesis in the swamp eel Synbranchus marmoratus (Bloch,
1795) (Teleostei; synbranchidae). Ovarian anatomy, stages of
oocyte development and micropyle structure

Laboratorio de Embriología Animal. Departamento de Biología, Facultad de Ciencias Exactas y Naturales, Universidad de
Buenos Aires, Buenos Aires – ARGENTINA.

Keywords: Synbranchidae, ovarian anatomy, oogenesis, micropyle.

ABSTRACT: Synbranchus marmoratus (Synbranchidae), commonly known as the swamp eel, is a protogynous diandric teleost fish widely distributed throughout South America. The purpose of this work was to study the ovarian anatomy and to describe oocyte developmental stages in the swamp eel, Synbranchus marmoratus. S. marmoratus has a unique sacular ovary. It is covered by a conspicuous muscular wall, probably involved in an egg-releasing system acting as a peristaltic-like mechanism. The internal ovarian anatomy shows a Ushaped ovarian lamella delimiting a dorsal ovarian lumen. The microscopic study shows evidence of the existence of a germinal epithelium in the inner surface of the lamella, which contains germinal cells, prefollicular cells and epithelial cells. The complete oogenesis process is divided into four stages: oogonia, primary growth, cortical alveoli and vitellogenesis. Besides, the ovulated oocytes, and atretic structures were described. The structure of the micropyle was studied by scanning electron microscopy (MEB). Near the animal pole the vitelline envelope forms crests that fuse together becoming furrow-like structures with a slightly spiraled direction that converge into the micropyle pit where is located the micropylar canal. Although the sex reversal process of Synbranchids has been subject of many studies, this is the first complete description of the ovarian anatomy and oogenesis.

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Effects of high molybdenum intake on 1,2-dimethylhydrazineinduced
intestinal tumors in rats

* Faculty of Veterinary Sciences, National University of Norwest-UNNE- Argentina.
** Institute of Pathology, Faculty of Veterinary Sciences, National University of La Plata, Argentina.
E.J. Gimeno is a research career member from CONICET.

Key words: Intestinal cancer, Molybdenum, 1,2-dimethylhydrazine, rats.

ABSTRACT: Wistar male rats, 3 months of age were given ad-libitum a nutritionally adequate diet and demineralized drinking water. The Molybdenum (Mo) and Tungsten (W) were provided in the drinking water at 200 ppm concentration. Intestinal tumors were induced by 1,2-dimethylhydrazine (DMH) given subcutaneously as 16 weekly doses at 20 mg/kg body weight. Mo in the form of (NH4)6 Mo7O24 4H2O or W in the form of (Na2WO4) were provided in the drinking water two months before the first DMH treatment and were continued during 4 months more until the last DMH treatment. Three months after the last carcinogen injection, all animals were sacrificed and examined for intestinal tumors. The number, size and location of the tumors were recorded and the pathology was examined. The addition of Mo to the drinking water induced an increase of hepatic Mo content. At the end of the second month, the hepatic content of Mo was 5.61 ppm, compared with control and W groups (2.18 and 0.96 ppm, respectively). A significantly lower incidence of tumors was observed in the Mo group (47), compared with the control group given DMH alone (105) and W
group (113). On the other hand, the Mo group showed a significant decrease in the numbers of multiple tumors per rat.

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Ultrastructural characteristics of the lung of Melanophryniscus
stelzneri stelzneri (Weyenberg, 1875) (Anura, Bufonidae)

Laboratorio Histología Animal, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y
Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, Argentina.

Key words: lung ultrastructure, respiratory epithelium, electronic microscopic, toad, amphibian.

ABSTRACT: The lung of the toad, Melanophryniscus stelzneri stelzneri was studied using scanning and transmission electron microscopy. In M.s.stelzneri the parenchyma forms a polygonal network arrangement, therefore the parenchyma is edicular. These spaces are delimited by the interconnection of third order septa which are covered by respiratory epithelium. Small patches of ciliated epithelium without goblet cells appear irregularly distributed on the septa. The respiratory epithelium consists of one type of pneumocyte, which shows characteristics of both type I and type II alveolar cells of higher vertebrates. The pneumocytes are irregular in shape and possess attenuated cytoplasmic processes, which spread around the capillaries to form the outer layer of the air-blood barrier. These cells contain different types of cytoplasmic bodies: electron dense bodies, multivesicular bodies and lamellar bodies. Dense bodies are probably the precursors of lamellar bodies and the multivesicular bodies are incorporated into the latter. Neuroepithelial bodies appear randomly distributed over the septa. These bodies are separated from the lumen of the lung by thin cytoplasmic
processes of neighbouring pneumocytes. The air-blood barrier consists of three layers: epithelium, interstitial space and endothelium. The relatively simple pulmonary structure of M.s.stelzneri is due to a lower degree of partitioning of the pulmonary lumen in comparison to the lung of other bufonid anurans, could be correlated with a well developed cutaneous and buccopharingeal respiration. The testing of this hypothesis awaits further studies.

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Microanatomical Characteristics of Marginal Ommatidia in
Three Different Size-Classes of the Semi-Terrestrial Isopod
Ligia exotica (Crustacea; Isopoda)

1. Department of Biology, University of Oulu, P.O. Box 3000, SF-90014 Oulu, Finland.
2. Department of Developmental Genetics, National Institute of Genetics, Mishima 411- 8540, Japan.
3. School of Engineering and Science, International University Bremen, D-28725 Bremen, Germany.
4. Department of Biology, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu, 431-3192, Japan.

Key words: Crustaceans, eye, retina, vision, growth, moulting, ultrastructure.

ABSTRACT: The aims of this paper have been (a) to characterize marginal ommatidia from different eye regions through a detailed description of their distinct ultrastructural features in three different size-classes of L. exotica, and (b) to compare microanatomical characteristics of the marginal ommatidia with those of ommatidia of the same eye, but located further centrally. On the basis of transverse as well as longitudinal sections we conclude that new ommatidia are added from a crescentic dorso-anterio-ventral edge of the eye and that maturing ommatidia go through a sequence in which originally the nuclei of cone -, pigment-, and retinula cells are arranged in three separate layers. At the beginning of the microvillar development, the organization of the corresponding rhabdomeres is still quite different (much less regular) from that of those rhabdomeres that make up the mature rhabdom. Marginal ommatidia always possess smaller diameters than more centrally located ones and retinal screening pigment granules are most apparent in the retinula cells only after the first microvilli have appeared. The diameters of rhabdom microvilli (approx. 55 nm) do not differ in ommatidia from the five investigated eye regions in small specimens (< 1.5 cm body length), but show a tendency to be slightly wider in the anterior (=frontal or rostral) regions of the eye (approx. 65 nm) in larger specimens (> 2.0 cm body length).

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Brief Note

Stimulation of jasmonic acid production in Zea Mays L. infected
by the maize rough dwarf virus - Río Cuarto. Reversion of
symptoms by salicylic acid

* Facultad de Ciencias Exactas, U.N.R.C, 5800-Río Cuarto, Argentina.
** Leibniz-Institut für Pflanzenbiochemie, Weinberg 3, 06120-Halle, Germany.

Key words: maize, virus disease, jasmonic and salicylic acids

ABSTRACT: In the present paper we study the possible biological relevance of endogenous jasmonic acid (JA) and exogenous salicylic acid (SA) in a plant-microbial system maize-virus. The virus disease "Mal de Río Cuarto" is caused by the maize rough dwarf virus - Río Cuarto. The characteristic symptoms are the appearance of galls or "enations" in leaves, shortening of the stem internodes, poor radical system and general stunting. Changes in JA and protein pattern in maize control and infected plants of a virus-tolerant cultivar were investigated. Healthy and infected-leaf discs were collected for JA measurement at different post-infection times (20, 40, 60 and 68 days). JA was also measured in roots on day 60 after infection. For SDS-PAGE protein analysis, leaf discs were also harvested on day 60 after infection. Infected leaves showed higher levels of JA than healthy leaves, and the rise in endogenous JA coincided with the enation formation. The soluble protein amount did not show differences between infected and healthy leaves; moreover, no difference in the expression of soluble protein was revealed by SDS-PAGE. Our results show that the octadecanoid pathway was stimulated in leaves and roots of the tolerant maize cultivar when infected by this virus. This finding, together with fewer plants with the disease symptoms, suggest that higher foliar and roots JA content may be related to disease tolerance. SA exogenous treatment caused the reversion of the dwarfism symptom.

Abbreviations: AcOH, acetic acid; GC-MS, gas chromatography-mass spectrometry; JA, jasmonic acid; JIP, jasmonate induced protein; MeOH, methanol; MeJA, methy-jasmonate; PR, pathogenesis-related; SA, salicylic acid; SAR, systemic acquired resistance; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

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