Induction of metabolic shocks in source and sink of two cucurbits by molybdenum stress.

Different concentrations of ammonium molybdate (10(-7) to 10(-4)M) affected the levels of metabolites in the source and sink organs of the seedlings of C. melo and C. vulgaris and data were recorded at 7, 14 and 21 days after treatment (DAT) of molybdenum (Mo). Reducing and non reducing sugars declined with an increase in concentration of ammonium molybdate from 10(-7) to 10(-4) M. Soluble protein and dry weight of seedlings increased in source at lower concentration (10(-7) M) and gradually decreased in all other concentrations (10(-6), 10(-5) and 10(-4) M). Starch was slightly accumulated in hypocotyl and fresh weight constantly declined with an increase in ammonium molybdate concentration from 10(-7) to 10(-4) M in all the parts of seedlings viz. cotyledon, hypocotyl and roots. Thus molybdenum at higher concentration induced decline in the metabolite levels in source and sink as well as in transporting organs.

Modelo experimental para el estudio de la molibdenosis y de la deficiencia primaria de cobre en ratas / Experimental model for the study of molybdenosis in the primary copper deficiency in rats

Con el objetivo de diferenciar los efectos producidos por la deficiencia primaria cobre y los provocados por el excesso de molibdeno se evaluó un modelo experimental en ratas. Sesenta ratas de destete (30 machos y 30 hembras) recibieron una dieta compuesta por 70 por ciento de leche entera en polvo (1 ppm Cu) y 30 por ciento de harina de maíz (0.8 - 1.5 ppm Cu). Los animales se dividieron en tres grupos conforme a la suplementación mineral recibida: deficiencia primaria de cobre (40 ppm Fe), molibdenosis (40 ppm Fe + 40 ppm Cu + 500 ppm Mo) y controles (40 ppm Fe + 40 ppm Cu). Se pesaron cada 14 días. Al cabo de 70 días de tratamiento se obtuvieron muestras de sangre para determinación de hematocrito y actividad sérica de ceruloplasmina y se sacrificaron para medir concentraciones hepáticas de Cu y Mo. El grupo deficiente en Cu tuvo valores significativamente inferiores en la actividad de ceruloplasmina. Las concentraciones hepáticas de Cu y Mo fueron superiores significativamente en los animales con molibdenosis. Se concluye que con niveles de Cu por encima de los requerimientos mínimos, la alimentación con alto contenido de Mo, no afecta la actividad sérica de ceruloplasmina. Esto sumado a la concentración hepática de Mo lograda, permitirá identificar efectos "per se" de la molibdenosis.

Action of K-crown ether on photosystem II electron transport: characterization of the site of action.

We have investigated the inhibitory effect of K-crown (18-crown-6 potassium picrate) on photosystem II (PSII)-enriched membrane fragments and O2-evolving core complexes. K-crown at 2-4 microM inhibits about half the control level of O2-evolution activity in both types of PSII samples. Oxygen-evolution studies demonstrated that the ether works by inactivating the centres and not by interfering with antenna function or energy transfer to the reaction centre. K-crown does not disrupt binding of the extrinsic proteins associated with O2 evolution nor complex with bound Ca2+ or Cl- cofactors, but rather it directly inhibits electron transfer after the tetrameric Mn cluster. Fluorescence studies on active and Tris-treated samples showed that K-crown does not prevent artificial donors from transferring electrons to PSII but like DCMU inhibits on the acceptor side after QA, the primary quinone acceptor. However, the ether is a leaky inhibitor and may also act as a weak donor when the Mn cluster is not present. Oxygen-production experiments using silicomolybdate as an artificial acceptor (which accepts from both pheophytin and QB in PSII membranes) demonstrated that the inhibition is at or near the DCMU site.