I. New species of Cuban Senecioneae. II. Diagnoses of new species and notes on other spermatophytes, chiefly from Mexico and Central America. By Jesse More Greenman.

v.2:no.8(1912)

I. New species of Cuban Senecioneae. II. Diagnoses of new species and notes on other spermatophytes, chiefly from Mexico and Central America. By Jesse More Greenman.

v.2:no.8(1912)

A Ca2+/H+ antiport system driven by the tonoplast pyrophosphate-dependent proton pump from maize roots.

Calcium uptake by tonoplast enriched membrane vesicles from maize (Zea mays L. cv. LG 11) primary roots was studied. A pH gradient, measured by the fluorescence quenching of quinacrine, was generated across sealed vesicles driven by the pyrophosphate-dependent proton pump. The fluorescence quenching was strongly inhibited by Ca2+; moreover, when increasing Ca2+ concentrations were added to vesicles at steady-state, a concomitant decrease in the proton gradient was observed. Ca2+ uptake using Ca-45(2+) was linear from 10 min when oxalate (10 mM) was present, while Ca2+ uptake was completely inhibited with proton ionophores (FCCP and monensin), indicating a Ca2+/H+ antiport. Membranes were further fractionated using a linear sucrose density gradient (10-45%) and were identified with marker enzymes. Ca2+ uptake co-migrated with the tonoplast pyrophosphate-dependent proton pumping, pyrophosphatase and ATPase activities: the Ca2+/H+ antiport is consequently located at the tonoplast.

Does the generalist parasitic plant Cuscuta campestris selectively forage in heterogeneous plant communities?

Cuscuta spp. are holoparasitic plants that can simultaneously parasitise several host plants. It has been suggested that Cuscuta has evolved a foraging strategy based on a positive relationship between preuptake investment and subsequent reward on different host species. Here we establish reliable parasite size measures and show that parasitism on individuals of different host species alters the biomass of C. campestris but that within host species size and age also contributes to the heterogeneous resource landscape. We then performed two additional experiments to test whether C. campestris achieves greater resource acquisition by parasitising two host species rather than one and whether C. campestris forages in communities of hosts offering different rewards (a choice experiment). There was no evidence in either experiment for direct benefits of a mixed host diet. Cuscuta campestris foraged by parasitising the most rewarding hosts the fastest and then investing the most on them. We conclude that our data present strong evidence for foraging in the parasitic plant C. campestris.

Evaluacion del estado trofico de tres cuencas interiores de Catalu��a (Foix, Besos y Llobregat) mediante la vegetacion acuatica: Aplicacion de un indice trofico de resolucion generica (IVAM)

Durante abril de 2005 se realiz�� una campa��a de muestreo de la vegetaci��n acu��tica macrosc��pica en las cuencas de los r��os Foix, Bes��s y Llobregat, sumando un total de 68 estaciones de muestreo. El objetivo principal fue evaluar el estado tr��fico de dichas cuencas mediante el ��ndice tr��fico generado en Espa��a denominado IVAM (��ndice de Vegetaci��n Acu��tica Macrosc��pica). Se identificaron un total de 44 t��xones, 8 g��neros de Cyanophyta, 5 de Rodophyta, 2 de Xantophyceae, 3 de Bacillariophyceae, 15 de Clorophyta, 8 de Spermatophyta, 1 liquen y 2 bri��fitos (musgos y hep��ticas). La cuenca del Llobregat fue la m��s diversa (37 t��axones), seguida del Bes��s (33) y el Foix (25). Los t��xones m��s frecuentes fueron Cladophora, Vaucheria, Oedogonium, Apium, Rorippa y Oscillatoria, adem��s de los musgos. Las faner��gamas fueron escasas, destacando los g��eneros Ranunculus, Zannichellia y Potamogeton. Los t��xones que alcanzaron una mayor puntuaci��n del IVAM (valor de tolerancia, vt = 8), aunque poco frecuentes, fueron Ranunculus, Cymbella, Rivularia, Nostoc, Tolypothrix, Chroococcus y Lemanea, todos indicadores de aguas oligotr��oficas. En aguas de buena calidad pero algo eutrofizadas (aguas mesotr��ficas, vt = 6), los t��xones m��s frecuentes fueron Chara, Monostroma y Hildenbrandia, adem��s de las hep��ticas y un liquen. Seg��n la calificaci��n de los tramos en clases de estado tr��fico realizada por el IVAM, el 38.2% de los tramos presentaron una buena calidad (clases I y II) mientras que el 61.8% presentaron un estado tr��fico alterado (clases III, IV y V). La respuesta del IVAM a la concentraci��n de nutrientes (fosfato, amonio, nitrito y nitrato) fue siempre significativa, destacando la alta correlaci��n alcanzada con el i��n fosfato (r = 0.71, p < 0.001), superior a la alcanzada por otros ��ndices de diatomeas y macr��fitos de resoluci��n taxon��mica espec��fica. Este hecho confirma la ventaja de utilizar el IVAM en la evaluaci��n del estado tr��fico de los r��os, ya que sin necesidad de alcanzar un nivel taxon��mico de especie se obtiene una respuesta adecuada a dicha perturbaci��n.