Importance of N source on heat stress tolerance due to the accumulation of proline and quaternary ammonium compounds in tomato plants.

Proline and quaternary ammonium compounds (QAC), in addition to being N-rich, are known to accumulate in plants under different environmental stress conditions. The accumulation of N-rich compounds in plants has been shown to confer stress resistance. The aim of our work is two-fold: first, to study the influence of temperature on proline, QAC, and choline metabolism in tomato leaves; and second, to investigate the relationship between N source applied (NO3- or NH4+) and thermal stress resistance in these plants. To do this, experiments were conducted at three different temperatures (10 degrees C, 25 degrees C, 35 degrees C); at each temperature half of the plants received NO3-, and the other half received NH4+. At 35 degrees C the plants had the lowest biomass production with respect to 25 degrees C (optimal temperature) and 10 degrees C (cold stress), suggesting that tomato plants were most affected by heat stress. At 35 degrees C, there were also high levels of choline and proline due to the activation of Delta1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT), and simultaneous inhibition of proline dehydrogenase (PDH) and proline oxidase (PO). However, plants with NH4+ as the N source exhibited reduced growth with respect to the plants fed with NO3-. This is interesting because, under heat stress (35 degrees C), biomass production, as well as proline and choline accumulation, in NH4+ fed plants was higher than in NO3- fed plants. From this, we concluded that tomato plants fed with NH4+ as the N source show higher tolerance to heat stress (35 degrees C) than plants fed with NO3-.

Direct action of the biocide carbendazim on phenolic metabolism in tobacco plants.

In view of the essential role of phenolic compounds in the development of pathogen resistance in plants, and given the influence that fungicides exert over phenolic metabolism, the aim of the present study was to determine the effect of the application of different rates of fungicide on the metabolism of phenolic compounds in tobacco plants (Nicotiana tabacum L. cv. Tennessee 86). The fungicide applied was carbendazim, with a purity of 100%, at three different rates: 1.3 mM (carb(1)), 2.6 mM (this being the recommended concentration, carb(2)), and 5.2 mM (carb(3)). The control treatment was without carbendazim. The results in relation to control plants indicate that the application of carb(1) in tobacco plants not afflicted by damaging biotic and abiotic agents boosts phenolic accumulation. Therefore, in the case of carbendazim, the application of 50% less (carb(1), 1.3 mM) than the recommended dosage (carb(2), 2.6 mM) of this fungicide could be more effective, because the foliar accumulation of phenolics presented at carb(1) may imply an increased resistance of plants to pathogen infection. On the other hand, we found an inhibition of the phenolic oxidation by the application of carbendazim, principally at carb(3). These results suggest that the excessive application of carbendazim (5.2 mM) could be harmful for healthy plants, because, on inhibiting phenolic metabolism (biosynthesis and oxidation), such treatment would also sharply reduce the capacity of these plants to respond against pathogen attack.

Resistance to cold and heat stress: accumulation of phenolic compounds in tomato and watermelon plants.

Tomato plants, Lycopersicon esculentum L. cv. Tmknvf(2), and watermelon plants, Citrullus lanatus [Thomb.] Mansf. cv. Dulce maravilla, were grown for 30 days at different temperatures (15, 25 and 35 degrees C). We analysed soluble phenolics, enzymatic activities (phenylalanine ammonia-lyase, polyphenol oxidase and peroxidase), and dry weight. The impact of the three temperatures was different in tomato and watermelon. Our results indicate that heat stress in tomato plants occurred at 35 degrees C, while chilling stress occurred in watermelon plants at 15 degrees C. Thermal stress in both plants caused: (1) decreased shoot weight; (2) accumulation of soluble phenolics; (3) highest phenylalanine ammonia-lyase activity; and (4) lowest peroxidase and polyphenol oxidase activity. These results indicate that thermal stress induces the accumulation of phenolics in the plant by activating their biosynthesis as well as inhibiting their oxidation. This could be considered an acclimation mechanism of the plant against thermal stress.

Leishmaniasis americana en zonas de desmontes de la Provincia de Salta. / Leishmaniasis americana in zones with clearing of trees of the Salta province

Desde 1972 a Junio de 1982 hemos observado 104 enfermos de leishmaniasis americana.En los ultimos tres anos hubo un aumento notorio de la enfermedad con pacientes provenientes de zonas de desmonte de la provincia de Salta. Las manifestaciones clinicas se clasifican en: a. cutaneas puras o de primo-infeccion; b. latentes; c.reactivacion o cutaneo-mucosas. Para el tratamiento se utilizo derivados antimoniales pentavalentes (glucantime), de buena tolerancia y gran eficacia en las manifestaciones cutaneas puras

Leishmaniasis americana en zonas de desmontes de la Provincia de Salta. / Leishmaniasis americana in zones with clearing of trees of the Salta province

Desde 1972 a Junio de 1982 hemos observado 104 enfermos de leishmaniasis americana.En los ultimos tres anos hubo un aumento notorio de la enfermedad con pacientes provenientes de zonas de desmonte de la provincia de Salta. Las manifestaciones clinicas se clasifican en: a. cutaneas puras o de primo-infeccion; b. latentes; c.reactivacion o cutaneo-mucosas. Para el tratamiento se utilizo derivados antimoniales pentavalentes (glucantime), de buena tolerancia y gran eficacia en las manifestaciones cutaneas puras