Nurse plants vs. nurse objects: effects of woody plants and rocky cavities on the recruitment of the Pilosocereus leucocephalus columnar cactus.

BACKGROUND AND AIMS: Most studies on cactus recruitment have focused on the role of woody plants as seedling facilitators. Although the spatial association of cacti with objects had been described, the mechanisms underlying this association remain unknown. The aims of this study were to identify which mechanisms facilitate the establishment of a columnar cactus under the shade and protection of objects and to compare these mechanisms with those involved in plant-plant facilitation. METHODS: Three split-split-plot field experiments were conducted to compare the effects of two microhabitats (inside rocky cavities and beneath plant canopies) on seed removal, germination, seedling survivorship and dry weight. Flat, open spaces were used as the control. For each microhabitat, the effect of seed or seedling protection and substrate limitation were explored; aboveground microclimate and some soil properties were also characterized. KEY RESULTS: The permanence of superficial seeds was greater inside rocky cavities than beneath woody plant canopies or on flat, open areas. Germination was similar in cavities and beneath plant canopies, but significantly higher than on flat, open areas. Seedling survivorship was greater beneath plant canopies than inside cavities or on flat, open spaces. CONCLUSIONS: The mechanisms of plant facilitation are different from those of object facilitation. There are seed-seedling conflicts involved in the recruitment of P. leucocephalus: nurse plants favour mainly seedling survivorship by providing a suitable microenvironment, while nurse objects mainly favour seed permanence, by protecting them from predators.

Synthesis and cardiovascular activity of metoprolol analogues.

The synthesis of four novel analogues of metoprolol, a well-known beta1-blocker used to reduce arterial blood pressure, is described. The preparation of (2S,2'S)-7, (2R,2'S)-7, (2R,2'R)-8, and (2S,2'R)-8 was based on the reaction of racemic 2-[4-(2'-methoxyethyl)-phenoxymethyl]-oxirane (4) with (R)- or (S)-2-amino-1-butanol. Salient characteristics of analogues 7 and 8 relative to metoprolol are the incorporation of an additional stereogenic center, as well as a methyl group and a hydroxyl function on the nitrogen-containing chain. These novel derivatives present significant hypotensive and bradycardiac activity, although no blocking action toward beta1 and beta2 adrenergic receptor.

Reactividad cutánea en conjuntivitis alérgica / Cutaneous reactivity in allergic conjunctivitis

Debido a la frecuencia con que se presenta la conjuntivitis alérgica en nuestro medio, se buscó la forma de determinar la afección ocular más frecuente y la sensibilidad específica a diferentes aeroalergenos. Se publican los resultados de un estudio prospectivo longitudinal en 20 pacientes, que acudieron a la consulta externa de alergia e inmunología y oftalmología del Hospital Infantil de México Federico Gómez de mayo a julio de 1990, con diagnóstico de conjuntivitis alérgica, determinándose la afección ocular y la sensibilidad a diversos aeroalergenos por medio de pruebas cutáneas. Se encontró predominio del sexo masculino (17 vs 7), en la edad escolar, cuyos síntomas principales en orden de frecuencia fueron: plurito, ardor, lagrimeo y fotofobia. La conjuntivitis vernal en su variedad límbica y tarsal ocupó el primer lugar con 45 por ciento (9/20), siguiendo la conjuntivitis folicular en ocho pacientes y el resto con flictenular. Las pruebas cutáneas fueron negativas en ocho de los 20 pacientes. El alergeno principalmente relacionado fue el Amaranthus palmeri (siete pacientes), siguiendo el Rumex crispus y los ácaros del polvo casero (seis individuos).