Insolubilization of potassium chloride crystals in Tradescantia pallida

Summary. Calcium oxalate crystals are by far the most prevalent and widely distributed mineral deposits in higher plants. In Tradescantia pallida, an evergreen perennial plant widely used as an ornamental plant, calcium oxalate crystals occur in the parenchymal tissues of stem, leaf, and root, as well as in flower organs, in the form of either raphides or tetragonal prismatic crystals or both. Energy-dispersive X-ray analysis revealed that C, O, and Ca were the main elements; and K, Cl, and Si, the minor elements. Infrared and X-ray analyses of crystals collected from these tissues detected the coexistence of two calcium oxalate chemical forms, i.e., whewellite and weddellite, as well as calcite, opal, and sylvite. Here, we show for the first time the occurrence of epitaxy in mineral crystals of plants. Epitaxy, which involves the oriented overgrowth of one crystal onto a second crystalline substrate, might explain how potassium chloride (sylvite) – one of the most water-soluble salts – stays insoluble in crystal form when coated with a calcium oxalate epilayer. The results indicate the potential role of crystals in regulating the ionic equilibrium of both calcium and potassium ions. Correspondence and reprints: Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EGA, Ciudad de Buenos Aires, Argentina.     

Mucor rouxii ultrastructure: cyclic AMP and actin cytoskeleton

Summary. A comparative analysis of the effect of two compounds, dibutyryl–cyclic-AMP (dbcAMP) and latrunculin B, on the morphology and ultrastructure of the dimorphic fungus Mucor rouxii under aerobic growth conditions is presented. dbcAMP acts through the sustained activation of protein kinase A, and latrunculin B through the disruption of the actin cytoskeleton. Upon addition of these compounds to the growth medium at any stage of the germination process, cells lost polarised growth and switched to isodiametric growth. The effect was reversible. The morphologies, visualised by light microscopy or scanning electron microscopy (SEM), were alike. A switch from a rough to a smooth surface was observed by SEM when cells were repolarised by removal of the added compound. Ultrastructural changes under both conditions, as observed by transmission electron microscopy, were similar, the main feature being the enlargement of the cell wall, with irregular depositions, and detachment from the cell membrane. dbcAMP-treated cells showed a decrease in the number of glycogen granules compared with control and latrunculin B-treated cells. F-actin staining with fluorescein isothiocyanate–phalloidin showed that both dbcAMP- and latrunculin B-treated cells displayed a much lower fluorescence than control cells, with only a few pale plaques. The results suggest that the sustained activation of protein kinase A, which impairs polarised growth, might exert its effect through a modification of actin cytoskeleton organisation, very probably also involving an integrinlike pathway, as judged by the cell wall detachment and loss of cell adhesiveness of the dbcAMP-treated isodiametric cells. Correspondence and reprints: Departamento de Química Biológica, Pabellón 2, Piso 4, Ciudad Universitaria, Universidad de Buenos Aires, 1428 Buenos Aires, Argentina.     

Semi-viviparous embryo development and dehydrin expression in the mangrove Rhizophora mucronata Lam.

Rhizophora mucronata Lam. is a tropical mangrove with semi-viviparous (cotyledon body protrusion before shedding), non-quiescent and non-desiccating (recalcitrant) seeds. As recalcitrance has been thought to relate to the absence of desiccation-related proteins such as dehydrins, we for the first time systematically described and classified embryogenesis in R. mucronata and assessed the presence of dehydrin-like proteins. Embryogenesis largely follows the classic pattern till stage eight, the torpedo stage, with the formation of a cotyledonary body. Ovule and embryo express radical adaptations to semi-vivipary in the saline environment: (1) A large, highly vacuolated and persistent endosperm without noticeable food reserves that envelopes the developing embryo. (2) Absence of vascular tissue connections between embryo and maternal tissue, but, instead, transfer layers in between endosperm and integument and endosperm and embryo. Dehydrin-like proteins (55–65 kDa) were detected by the Western analysis, in the ovules till stage 10 when the integuments are dehisced. An additional 50 kDa band was detected at stages 6–8. Together these results suggest a continuous flow of water with nutrients from the integument via the endosperm to the embryo, circumventing the vascular route and probably suppressing the initially induced dehydrin expression.     

The recalcitrant plant species, Castanospermum australe and Trichilia dregeana, differ in their ability to produce dehydrin-related polypeptides during seed maturation and in response to ABA or water-deficit-related stresses

In constrast to seeds of orthodox species, those of recalcitrantspecies do not acquire desiccation tolerance during their developmentand are shed from the parent plant at high water contents. Dehydrinproduction in seeds of recalcitrant species was examined duringdevelopment and germination, in response to abscisic acid (ABA),and following the imposition of various water-deficit-relatedstresses, including desiccation, water stress, high salt, highosmolarity, and low temperature. Two tropical species exhibiteda differential capacity to produce dehydrin-related proteinsduring seed maturation. Dehydrins were present in axes and cotyledonsof Castanospermum australe seeds during mid-maturation and atmaturity. In Trichilia dregeana, no dehydrin-related polypeptideswere detected in the mature seed. During the development ofC. australe seeds, the nature of the dehydrin related polypeptidesaccumulated in the cotyledons and axis changed and new polypeptideswere detected in the mature seeds that were not present duringmid-maturation. The dehydrins present in cotyledons of matureseeds (31, 37 and 40 kDa) were still detectable after germination(i.e. in untreated seedlings). These dehydrins became less abundantin the cotyledons of C. australe seedlings following ABA andall stress treatments except cold, although most of the dehydrinswere still detectable. An exception was the desiccation-treatedseedlings, in which no dehydrins were detected. In the rootsof C. australe seedlings, no dehydrins were found after germinationnor were they induced in the root by ABA or any of the stresstreatments imposed on seedlings. Seedlings of Trichilia dregeanadid not produce dehydrins in the roots or cotyledons when exposedto ABA or water-deficit-related stresses. Key words: Dehydrin, ABA, desiccation, recalcitrant, seed     

Economic Botany ofSphenostylis (Leguminosae)

Sphenostylis, a genus of seven species in tropical and southern Africa, includes three taxa that are used by humans. Flowers and seeds of S. schweinfurthii Harms are occasionally eaten in West Africa, and this species has potential value as a forage crop. Flowers and seeds of Sphenostylis erecta (E. G. Baker) E. G. Baker subsp. erecta are eaten in parts of Central Africa, while the roots are used medicinally and as a source of dye and fish poison. The edible tubers of S. stenocarpa (Hochst, ex A. Rich.) Harms, the African yam bean, are collected from the wild in Central and East Africa. This species is cultivated for its edible seeds in west tropical Africa and for its edible tubers in Zaire. Cultivated races of S. stenocarpa may be considered domesticated forms, since they differ from wild plants of the species in a number of morphological characteristics that are evidently the result of human selection. A list of common names for the three taxa, from throughout their ranges, is presented. Sphenostylis, un género con siete especies de las regiones sur y tropical de Africa, incluye tres taxa utilizados por humanos. Las flores y semillas deS. schweinfurthii Harms son alimento ocasional en el oeste de Africa, y la especie tiene, ademas, valor potencial como forraje. Las flores y semillas de Sphenostylis erecta (E. G. Baker) E. G. Baker subsp. erecta se comen en regiones del centro de Africa, mientras que las raíces tienen usos medicinales y son fuente de colorantes y embarbascantes. Los tubérculos comestibles de S. stenocarpa (Hochst, ex A. Rich.) Harms, la jícama Africana, se colectan de plantas silvestres en el centro y este de Africa. Esta especie se cultiva por sus semillas comestibles en el oeste de Africa tropical, y por sus tubérculos comestibles en Zaire. Las razas cultivadas deS. stenocarpa pueden ser consideradas como formas domesticadas, puesto que difieren de las plantas silvestres en muchas características morfológicas que son, evidentemente, el resultado de la selección humana. Se presenta una lista de los nombres comunes para los tres taxa a lo largo de sus rangos de distribución.     

Genetic diversity of Cryptosporidium identified in clinical samples from cities in Brazil and Argentina

The identification and characterisation of Cryptosporidiumgenotypes and subtypes are fundamental to the study of cryptosporidiosis epidemiology, aiding in prevention and control strategies. The objective was to determine the genetic diversity ofCryptosporidium in samples obtained from hospitals of Rio de Janeiro, Brazil, and Buenos Aires, Argentina. Samples were analysed by microscopy and TaqMan polymerase chain reaction (PCR) assays forCryptosporidium detection, genotyped by nested-PCR-restriction fragment length polymorphism (RFLP) analysis of the 18S rRNA gene and subtyped by DNA sequencing of the gp60 gene. Among the 89 samples from Rio de Janeiro, Cryptosporidium spp were detected in 26 by microscopy/TaqMan PCR. In samples from Buenos Aires,Cryptosporidium was diagnosed in 15 patients of the 132 studied. The TaqMan PCR and the nested-PCR-RFLP detected Cryptosporidium parvum, Cryptosporidium hominis, and co-infections of both species. In Brazilian samples, the subtypes IbA10G2 and IIcA5G3 were observed. The subtypes found in Argentinean samples were IbA10G2, IaA10G1R4, IaA11G1R4, and IeA11G3T3, and mixed subtypes of Ia and IIa families were detected in the co-infections. C. hominis was the species more frequently detected, and subtype family Ib was reported in both countries. Subtype diversity was higher in Buenos Aires than in Rio de Janeiro and two new subtypes were described for the first time.     

Immunoanalysis of dehydrins in Araucaria angustifolia embryos

The aim of this study was to describe the dehydrin content of mature Araucaria angustifolia embryos, a species of endangered and economically important conifers, native to southern Brazil, northeastern Argentina, and eastern Paraguay. The A. angustifolia seeds have been categorized as recalcitrant. Dehydrins were studied by western blot analysis and in situ immunolocalization microscopy using antibodies raised against the K segment, a highly conserved lysine-rich 15-amino acid sequence extensively used to recognize proteins immunologically related to the dehydrin family. Western blot analysis of the heat-stable protein fraction, as estimated by 15 % SDS-PAGE, revealed three main bands of approximately 20-, 26-, and 29-kDa; when 17.5 % SDS-PAGE was used, each band resolved into two other bands. Two thermosensitive dehydrin bands of around 16 and 35 kDa were common to the axis and cotyledons, and another thermosensitive band, with molecular mass of approximately 10 kDa, was present in the cotyledons only. Following alkaline phosphatase (AP) treatment, a gel mobility shift was detected for each one of the four main bands that can be due to phosphorylation. Dehydrins were detected in all axis and cotyledon tissues using in situ immunolocalization microscopy. At the subcellular level, dehydrins were immunolocalized in the nuclei, protein bodies, and microbodies. In the nucleus, dehydrins were found to be associated with chromatin. We concluded that the gel mobility shift for the four main bands (probably due to phosphorylation), the presence of thermosensitive bands, and the specific localizations in nuclei and protein bodies provide key starting points to understand the function of dehydrins in the embryo cells of this species.     

Alkaloid diversity in eleven species of Ormosia and in Clathrotropis macrocarpa (Leguminosae-Papilionoideae)

Quinolizidine alkaloids were surveyed using gas chromatography (GC) and combined mass spectroscopy (MS) in bark or leaves of eleven species ofOrmosia Jackson as well as inClathrotropis macrocarpa Ducke from tropical forests in Latin America. A list of detected alkaloids, with their MS fragmentation patterns and GC retention indices, is given, as are the distribution of alkaloids among the samples and their detected concentrations. Alkaloid diversity inOrmosia was high, and the taxonomic distribution of specific alkaloids was not congruent with morphological taxonomic criteria: Of 143 alkaloids apparent in 14 samples, 65 were observed in only one sample, and no single alkaloid was common to all samples. Within a species, alkaloid concentrations were inconsistent and therefore cannot be used as a taxonomic character. This was shown for leaf alkaloid concentrations of two neighboring conspecific trees in the same habitat. Hemos analizado mediante cromatografia de gases (CG) y espectrometría de masas (EM) la composición en alcaloides quinolizidínicos de muestras de corteza y hojas de once especies deOrmosia Jackson y deClathrotropis macrocarpa Ducke, procedentes de las selvas de Latinoamérica. Presentamos una lista completa de los alcaloides detectados incluyendo sus fragmentos en EM y su índice de retención en CG. También presentamos la distribución de los alcaloides en las muestras y su concentración. La variedad de alcaloides era alta y su distribución por especies no se ajustó con criterios taxonómicos morfológicos: De los 143 alcaloides detectados en 14 muestras, 65 alcaloides estaban presentes en una sola muestra y ningún en todas las muestras. La concentración de los alcaloides en una especie no fue consistente y por lo tanto no puede utilizarse como carácter taxonómico. Esta conclusión proviene del análisis de la concentración de alcaloides en hojas de dos árboles de la misma especie en el mismo hábitat.     

An interpretation of genomic balance in seed formation in interspecific hybrids of Solanum

Summary To investigate the mechanisms of seed failure in intraspecific and interspecific crosses of Solanum two diploid, S. commersonii and Group Phureja, and one tetraploid species, S. acaule, species were crossed and the seeds were analyzed for embryo and endosperm development. Many seeds of certain crosses observed seven days after pollinations were found to contain abnormal embryos and degenerating endosperms. In some cases seeds contained an embryo with no endosperm, or an endosperm with no embryo. Other interspecific crosses which were predicted to fail actually produced seeds with normally developed embryos and endosperms. To further characterize the intra- and interspecific embryos and endosperms the nuclear DNA was measured. There are several ways to explain the ploidy levels of embryos and endosperms among the crosses, the occurrence of unreduced gametes in some cases and genomic instability in other cases. The latter resulted in chromosome loss at meiotic and mitotic divisions. Genomic balance in interspecific seeds is critical to both embryo and endosperm development.Scientific Journal Series Article No. 14636 of the Minnesota Experiment Station     

Predation upon the subterranean rodent Ctenomys talarum (tuco-tucos) by Buteo polyosoma (red-backed hawks) in coastal grasslands of Argentina

Differential predation upon tuco-tucos (Ctenomys talarum) by red-backed hawks (Buteo polyosoma) is reported, considering the characteristics that could lead to prey vulnerability and to predator selectivity. Predation was evaluated through analysis of 100 pellets and 20 prey remains collected in coastal grasslands at Mar de Cobo (Buenos Aires, Argentina) during winter (May to August) 2003–2004. The tuco-tucos represented the main component in the diet of red-backed hawks, registering a high consumption of sub-adult individuals (49.3%). Juvenile individuals (42.0%) were overrepresented and adults (8.7%) were underrepresented in relation to their field frequencies (14.4 and 43.1%, respectively), whereas sub-adults did not show significant differences. This high consumption of smaller tuco-tucos would be based on the higher vulnerability of young individuals to predation rather than raptor's handling constraints on bigger individuals. Our results indicate that a strong predator–prey relationship between tuco-tucos and red-backed hawks is established at the study area, and that tuco-tucos represent a key component for the survival of wintering hawks.

Reportamos la depredación diferencial sobre el tuco-tuco (Ctenomys talarum) por el aguilucho común (Buteo polyosoma), considerando las características que podrían determinar la vulnerabilidad de la presa y la selectividad del predador. La depredación fue evaluada mediante el análisis de 100 egagrópilas y 20 restos presa recolectados en pastizales costeros de la localidad de Mar de Cobo (Buenos Aires, Argentina) durante el periodo invernal Mayo–Agosto de 2003–2004. El tuco-tuco representó el principal componente en la dieta del aguilucho común, registrándose un alto consumo de individuos subadultos (49.3%). Los individuos juveniles (42.0%) fueron sobrerrepresentados y los adultos (8.7%) fueron subrepresentados en la dieta en relación a sus frecuencias en el campo (14.4 y 43.1%, respectivamente), mientras que los subadultos no mostraron diferencias significativas. Este elevado consumo de individuos más pequeños radicaría en una mayor vulnerabilidad a la depredación de los juveniles más que en restricciones de manipuleo del predador sobre las presas más grandes. Nuestros resultados indican que existe una estrecha relación predador–presa entre el tuco-tuco y el aguilucho común, y que los tuco-tucos representan un componente clave para la supervivencia invernal de los aguiluchos.     

Detection and subcellular localization of dehydrin-like proteins in quinoa (Chenopodium quinoa Willd.) embryos

The aim of this study was to characterize the dehydrin content in mature embryos of two quinoa cultivars, Sajama and Baer La Unión. Cultivar Sajama grows at 3600-4000 m altitude and is adapted to the very arid conditions characteristic of the salty soils of the Bolivian Altiplano, with less than 250 mm of annual rain and a minimum temperature of -1 degrees C. Cultivar Baer La Unión grows at sea-level regions of central Chile and is adapted to more humid conditions (800 to 1500 mm of annual rain), fertile soils, and temperatures above 5 degrees C. Western blot analysis of embryo tissues from plants growing under controlled greenhouse conditions clearly revealed the presence of several dehydrin bands (at molecular masses of approximately 30, 32, 50, and 55 kDa), which were common to both cultivars, although the amount of the 30 and 32 kDa bands differed. Nevertheless, when grains originated from their respective natural environments, three extra bands (at molecular masses of approximately 34, 38, and 40 kDa), which were hardly visible in Sajama, and another weak band (at a molecular mass of approximately 28 kDa) were evident in Baer La Unión. In situ immunolocalization microscopy detected dehydrin-like proteins in all axis and cotyledon tissues. At the subcellular level, dehydrins were detected in the plasma membrane, cytoplasm and nucleus. In the cytoplasm, dehydrins were found associated with mitochondria, rough endoplasmic reticulum cisternae, and proplastid membranes. The presence of dehydrins was also recognized in the matrix of protein bodies. In the nucleus, dehydrins were associated with the euchromatin. Upon examining dehydrin composition and subcellular localization in two quinoa cultivars belonging to highly contrasting environments, we conclude that most dehydrins detected here were constitutive components of the quinoa seed developmental program, but some of them (specially the 34, 38, and 40 kDa bands) may reflect quantitative molecular differences associated with the adaptation of both cultivars to contrasting environmental conditions.     

Chemical composition and current distribution of “Azafr’an de Bolita”(Ditaxis heterantha Zucc; Euphorbiaceae): A food pigment producing plant

Ditaxis heterantha Zucc. (azafrán de bolita), a plant of the Euphorbiaceae family, grows wild in the semiarid regions of Mexico. Its seeds are used by the inhabitants of the regions where it grows to give color and to enhance the flavor of food. It has been recently cultivated locally, however, the plant has not been cultivated extensively, and it is considered that this crop could have an economic potential. The purpose of this work is to validate the reported geographical distribution of the plant and its chemical composition. The endosperm of the seeds has an intense yellow color, indicating the presence of pigments of the carotenoid family. The pigment was extracted using hexane, and seven fractions were obtained by HPLC. The spectra of the fractions produce three maxima, λ_max characteristic of carotenoids. Chemical composition of the seed showed average oil content of 39.4% and 18.8% of protein. The oil and protein content are similar to that of cottonseed and sunflower seed, respectively. Its composition allows the seed to be used as a source of natural pigment, vegetable oil, and protein. The seed has a competitive price and a promising profit margin in local markets, and its cultivation requires little care, growing especially well under limited water conditions

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Résumé  Ditaxis heterantha Zucc. (azafrán de bolita) es una planta que pertenece a la familia de las Euphorbiáceas, se encuentra en las regiones semiáridas de México en forma silvestre. Sus semillas son utilizadas por los habitantes de las regiones donde crece, para dar color y sabor en la preparatión de sus alimentos. Recientemente se ha iniciado su cultivo en forma local, sin embargo, la planta no ha sido cultivada extensivamente pero puede ser un cultivo económicamente potential. El objetivo de este trabajo es validar la distribución geográfica de la planta y determinar su composición química. El endospermo de las semillas es de color amarillo intenso indicando la presencia de pigmentos de la familia de los carotenoides. La extractión del pigmento se llevó a cabo con hexano, y se lograron identificar 7 fracciones por HPLC. El espectro de estas fracciones presentó un espectro con 3 absorbancias máximas, lo cual es característico de los carotenoides. Los análisis de la composición química de la semilla, mostraron que el contenido de grasa en promedio es del 39.4%, mientras que de proteína es del 18.8%. El contenido de grasa y proteína es semejante a las semillas de algodón y girasol respectivamente. Su compositión puede permitir la utilización de la semilla como fuente pigmentos naturales, aceite vegetal y proteína. La semilla alcanza precios competitivos en los mercados locales y tienen una promisoria rentabilidad económica debido a que su cultivo requiere pocos cuidados específicamente baja demanda de agua

     

The expression of dehydrin proteins in desiccation-sensitive (recalcitrant) seeds of temperate trees

Proteins that have homology with dehydrins have been identified immunologically in the desiccationsensitive (recalcitrant) seeds of English oak (Quercus robur L.), European chestnut (Castanea sativa L.), horse chestnut (Aesculus hippocastanum L.), sycamore (Acer psuedoplatanus L.) and silver maple (Acer saccharinum L.), and in the desiccation-tolerant seeds of Norway maple (Acer platanoides L.). The mRNA for a late embryogenesis abundant (LEA) protein (dehydrin) was also detected by Northern blotting, using a cDNA clone (D11) from cotton embryos, in the recalcitrant and orthodox seeds. Medium-stringency washing was required to detect this hybridization. InQ. robur the amount of dehydrin protein increased during seed development, andLEA mRNA was induced by limited desiccation and by abscisic acid. Confirmation of the presence of dehydrin mRNA in matureQ. robur andC. sativa seeds was obtained by in-vitro translation of the extracted polyadenylated RNA followed by analysis of the immunoprecipitation products. Thus the presence of dehydrin proteins is not sufficient to confer desiccation tolerance on truly recalcitrant seeds, nor can their presence or absence be used as clear criteria for identification of recalcitrant seeds.     

Endophytic fungi in leaves of Lycopersicon esculentum Mill

Endophytic fungi were isolated from healthy tomato leaves from field-grown plants. Several surface-sterilization techniques were assayed for removing and killing epiphytes on tomato leaves. Surface-sterilization with an undiluted commercial solution of sodium hypochlorite was employed. To determine the spectrum of endophytes, samples were collected in February 1998 and 1999 from tomato plants (cultivar Tommy) cultivated in the experimental fields of Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, Buenos Aires, Argentina. In general, different spectra of species were isolated in 1998 and 1999.Alternaria alternata was the fungus most frequently isolated from tomato leaves in 1999, but it was the second most common species in 1998. In contrast, Colletotrichum gloeosporioides was the fungus most frequently isolated in 1998, but it was not found in 1999. Species of other genera, such as Cladosporium and Penicillium, were isolated in both years.     

RGD-containing peptides and cyclic AMP have antagonistic roles in the morphology of Mucor rouxii

Summary. The tripeptide Arg-Gly-Asp (RGD) (1 mM) as well as the polymer ProNectin F (20 nM) added to culture medium of the fungus Mucor rouxii (defined medium) produced a delay in the switch from isodiametric growth to tip growth; at the time of germination the mother cell had a 4.6 times larger volume with 3.6 times more germ tubes per cell than control germinating sporangiospores. Disruption of the actin network with 2 µg of cytochalasin A per ml blocked the switch to tip growth; the effect was analogous to the one of 150 µM dibutyryl–cyclic AMP (cAMP), which we previously described to promote isodiametric growth via protein kinase A. 150 µM dibutyryl-cAMP antagonises partially the effect of 1 mM RGD; the cells still emit several germ tubes per mother cell but their number is smaller and the volume of the cell at germ tube emission is larger than with RGD alone. At higher concentrations the dibutyryl-cAMP overrides completely the effect of RGD. Our results suggest that M. rouxii has an RGD recognition system and demonstrate that RGD-containing peptides have a profound effect on the isotropic stage of growth and on the establishment of cell polarity and that cAMP analogues can override this effect.Correspondence and reprints: Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Pabell'n 2, Ciudad Universitaria, Universidad de Buenos Aires, 1428 Buenos Aires, ArgentinaReceived January 29, 2003; accepted March 10, 2003; published online September 23, 2003     

Plant communities and phytogeographical position of a large depression in the Great Chaco,Argentina

A survey is presented of the vegetation of the central region of the Santafesinian Chaco (Argentina), a scarcely populated flat area of 20 000 km², with seasonal flooding. Soils have a strong halo-hydromorphic character and vegetation is basically halophilous. Trees are scarce and most communities are savannas, grasslands or swampy vegetation. Twenty-three communities are described, some of them with several variants. The most widespread communities areSpartina argentinensis grasslands,Elyonurus muticus savannas and a complex of hygrophilous communities. The most important communities are distributed in relation to a topographical gradient, and their structure is shaped by recurrent flooding and fire disturbance. Most of the area is virgin land with very little human interference. The phytogeographical position of the area is discussed. Nomenclature: Burkart, A. 1969, 1974, 1979. Flora ilustrada de Entre Rios, INTA, Buenos Aires, and Cabrera, 1963, 1965a, b, 1967, 1968, 1970. Flora de la Provincia de Buenos Aires, INTA, Buenos Aires.     

Identification and characterization of dehydrins in horse chestnut recalcitrant seeds

The fraction of heat-stable dehydrins cytosolic proteins from mature recalcitrant seeds of horse chestnut (Aesculus hippocastanum L.) was studied in the period of their dormancy and germination in order to identify and characterize stress-induced dehydrin-like polypeptides. In our experiments, in tissues of dormant seeds, dehydrin was identifies by immunoblotting as a single bright band with a mol wt of about 50 kD. Low-molecular-weight heat-stable proteins with mol wts of 25 kD and below 16 kD, which were abundant in this fraction, did not cross-react with the antibody. Dehydrin was detected in all parts of the embryo: in the cells of axial organs, cotyledon storage parenchyma, and petioles of cotyledonary leaves. This indicates the absence of tissue-specificity in distribution of these proteins in the horse chestnut seeds. Dehydrins were detected among heat-stable proteins during the entire period of stratification and also radicle emersion. During radicle emergence, not only the fraction of heat-stable proteins was reduced but also the proportion of dehydrins in it decreased. In vitro germination of axes excised at different terms of stratification also resulted in dehydrin disappearance. When growth of excised axes was retarded by treatments with ABA, cycloheximide, or α-amanitin, dehydrins did not disappeared from the fraction of heat-stable proteins. When excised axes were germinated in vitro in the presence of compounds, which did not affect their growth or stimulated it (dehydrozeatin, glucose), this resulted in dehydrin disappearance. This means that dehydrin metabolism is closely related to the process of germination. Dehydrin in the horse chestnut seeds could cross-react with the antibody against ubiquitin, which can indicate the involvement of ubiquitination in the process of dehydrin degradation during germination via the proteasome system. The analysis of total proteins of the homogenate from horse chestnut seeds revealed, along with a 50-kD heat-stable dehydrin, one more component with a mol wt of 80 kD, which was located in the fraction of heat-sensitive proteins and was named as a dehydrin-like protein. It was demonstrated that dehydrins in horse chestnut seeds represented only a very small fraction of heat-stable cytosolic proteins. The role and function of major heat-stable proteins in horse chestnut seeds are yet to be studied.