No abstract

Changes in root morphology and acid phosphatase activity (APA) were followed during the developent of P-deficiency in tomato plants grown for 7, 14, and 21 days in 0.16 P well aereated nutrient solutions, followed by a period of sufficiency (recovery) in 1 mM P. Plants were harvested weekly for APA, dry weight, and P concentration in roots, stems and leaves, and every 2 weeks for root morphology determinations. APA was highly correlated to development and recovery from P stress. Mixmium values were attained during growth under deficiency and decreased to that of the control plants after a period of recovery in 1 mM P nutrient solutions. Total root weight and average root diameter decreased under P-stress and root surface area per unit dry weight increased. Efficiency of P utilization (g dry weight/mg absorbed P) was much higher at the end of the stress period but approached that of the controls as P-supply was restored to sufficiency levels. The implications of these results in developing rapid and reliable screening technigues to detect successful plant performance under P-stress is discussed.

No abstract

The response of apoplastic antioxidant systems in root and leaf tissues from two onion genotypes (‘Texas 502’, salt-sensitive and ‘Granex 429’, salt-resistant) in response to salinity was studied. Electrolyte leakage data indicated the membrane integrity impairing by the effect of salts, especially in ‘Texas 502’. We detected superoxide dismutase (SOD) and peroxidase (POX) activity in the root and leaf apoplastic fractions from onion plants. Salinity increased SOD activity in the root symplast of ‘Texas 502’ and in ‘Granex 429’ leaves. In contrast, salinity reduced SOD activity in the leaf and root apoplastic fractions from ‘Texas 502’. In ‘Granex 429’, salt-stress increased leaf apoplastic POX activity and symplastic catalase (CAT) activity of both organs, but a decline in root apoplastic POX from ‘Texas 502’ took place. Salt-stress increased monodehydroascorbate reductase (MDHAR) in root and leaf symplast and in root glutathione reductase GR, mainly in ‘Granex 429’, but only in this genotype, leaf dehydroascorbate reductase (DHAR) activity increased. In contrast, a decline in leaf GR was produced only in ‘Texas 502’. Salinity increased leaf ASC levels, and no accumulation of dehydroascorbate (DHA) was observed in roots in both cases. These responses increased the redox state of ascorbate, especially in roots. In contrast, salinity declined reduced glutathione (GSH), but oxidised glutathione (GSSG) was accumulated in leaves, decreasing the redox state of glutathione. Salinity slightly increased root GSH concentration in the salt-tolerant genotype and was unchanged in the salt-sensitive genotype, but no accumulation of GSSG was produced, favoring the rise and/or maintenance of the redox state of the glutathione. These results suggest that the lower sensitivity to salt in ‘Granex 429’ could be related to a better performance of the antioxidant machinery under salinity conditions.

Resumen Las siguientes cuatro especies: Balliella pseudocorticata, Perikladosporon percurrens, Monosporus indicus y Seirospora occidentalis, constituyen las primeras citas para la costa venezolana. Se mencionan sus caracteres diagnóstico y se establecen comparaciones con especies cercanas. Todas estas han sido mencionadas en arrecifes coralinos de aguas tropicales y se consideran comunes en el Mar Caribe.

Following pathogen infection, plants have developed diverse mechanisms that direct their immune systems towards more robust induction of defense responses against recurrent environmental stresses. The induced resistances could be inherited by the progenies, rendering them more tolerant to stressful events. Although within-generational induction of tolerance to abiotic stress is a well-documented phenomenon in virus-infected plants, the transgenerational inheritance of tolerance to abiotic stresses in their progenies has not been explored. Here, we show that infection of Nicotiana benthamiana plants by Potato virus X (PVX) and by a chimeric Plum pox virus (PPV) expressing the P25 pathogenicity protein of PVX (PPV-P25), but not by PPV, conferred tolerance to both salt and osmotic stresses to the progeny, which correlated with the level of virulence of the pathogen. This transgenerational tolerance to abiotic stresses in the progeny was partially sustained even if the plants experience a virus-free generation. Moreover, progenies from a Dicer-like3 mutant mimicked the enhanced tolerance to abiotic stress observed in progenies of PVX-infected wild-type plants. This phenotype was shown irrespective of whether Dicer-like3 parents were infected, suggesting the involvement of 24-nt small interfering RNAs in the transgenerational tolerance to abiotic stress induced by virus infection. RNAseq analysis supported the upregulation of genes related to protein folding and response to stress in the progeny of PVX-infected plants. From an environmental point of view, the significance of virus-induced transgenerational tolerance to abiotic stress could be questionable, as its induction was offset by major reproductive costs arising from a detrimental effect on seed production.

El presente trabajo agrupa la información de las colecciones venezolanas de musgos (Bryophyta) presentes en el Herbario Nacional de Venezuela (VEN). Esta se encuentra constituida por 5282 especímenes de musgos en base de datos, de los cuales 4099 especímenes son venezolanos. La colección cuenta con 54 familias, 174 géneros y 546 especies identificadas. Como resultado se obtuvo un listado el cual ubica alfabéticamente las especies por familia, género y especie según la clasificación de Buck & Goffinett (2000), esta información se complementa además con datos de localidad, colector con número colecta, fecha de colección y datos de la determinación.

Se realizó un inventario de las macroalgas de la zona submareal, entre 5 y 17 m de profundidad para las localidades de Puerto Maya, en el estado Aragua, Puerto Cruz, en el estado Vargas, Madrizquí y Boca de Cote, Parque Nacional Archipiélago Los Roques, Dependencias Federales. Como resultado se reportan cuatro nuevos registros de especies de algas rojas (Rhodophyta) para la costa de Venezuela: Apoglossum gregarium, Platysiphonia caribaea, Gloiocladia iyoensis y Botryocladia monoica. De las cuales, A. gregarium y G. iyoensis se registran también por primera vez en el Mar Caribe. Se establecen sus principales caracteres diagnósticos, resumidos como: hábito y dimensiones del talo, morfología de las estructuras reproductivas, presencia o ausencia de corticación y presencia o ausencia de células glandulares. Además se realizan comparaciones con sus especies morfológicamente cercanas.