Showing papers in "Revista Brasileira De Fisiologia Vegetal in 1999"

Measurements of leaf relative water content in Araucaria angustifolia.

Abstract: Measurements of relative water content (RWC) in leaf tissues are commonly used to assess the water status of plants. Despite its simplicity, this technique needs to be adjusted for each plant material. Adjustments are mainly related to the length and environmental conditions of the imbibition period, needed to obtain the turgid mass. In this study, the effects of light, temperature and leaf position, during imbibition, on measurements of RWC in Araucaria angustifolia (Bert.) O. Ktze leaves were tested. Additionally, we compared the patterns of water absorption between hydrated and water-stressed leaves. The results indicate that, similar to other conifer species, leaves of A. angustifolia require longer periods of imbibition than broadleaf species. Also, leaves that develop under drought conditions require longer periods of imbibition than those that develop under conditions of high water availability, a fact that is probably related to drought-induced structural changes in the leaf tissue. RWC estimates in leaves from fully rehydrated shoots were slightly below the expected value of 100%. No advantage of imbibing the leaves at a low temperature was found and the measured effects of light were very small within the 0 to 50 μmol m -2 s -1 range. The small temperature and light effects reflect the maturity of the leaves used in this study. Floating and standing the leaves in water generated the same estimates of RWC, despite the greater absorption area in the former situation. A 24-hour imbibition period is suggested for mature leaves of A. angustifolia and limitations of the method are discussed. Additional index terms: Brazilian pine, conifers, water relations, water status.

Aluminum effects on lipid peroxidation and on the activities of enzymes of oxidative metabolism in sorghum.

Abstract: Seedlings of two sorghum (Sorghum bicolor (L.) Moench) cultivars with differential tolerance to Al were exposed to 0 and 185 µM of Al, in a pH 4.0 nutrient solution, for 10 days and, then, lipid peroxidation and the activity of enzymes of the oxidative metabolism were determined. Lipid peroxidation increased in the root system of the two cultivars, especially in the sensitive one. In the presence of Al, superoxide dismutase and cinnamyl alcohol dehydrogenase activities increased only in the Al-tolerant cultivar. In this cultivar the largest reduction in phenylalanine ammonia lyase activity also occurred. So, this cultivar probably accumulated less amounts of reactive oxygen species and of toxic phenolic compounds and, consequently, showed smaller lipid peroxidation. On the other hand, largest increases in peroxidase and polyphenoloxidase activities were observed in the Al-sensitive cultivar in the presence of Al. In this cultivar a greater accumulation of peroxides and phenolic compounds probably occurred resulting in more lipid peroxidation. The changes in ascorbate peroxidase and catalase activities in both cultivars suggest a reduced contribution of these enzymes in the mechanism of peroxide decomposition. The results indicate that the Al-tolerant cultivar produces smaller concentrations of reactive oxygen species and/or it possesses more efficient enzymatic mechanisms of removal and/or neutralization of these radicals than the Al-sensitive cultivar. Additional index terms: Al toxicity, free oxygen radicals, peroxides, Sorghum bicolor. EFEITOS DO ALUMINIO SOBRE A PEROXIDACAO DE LIPIDIOS E A ATIVIDADE DE ENZIMAS DO METABOLISMO OXIDATIVO EM SORGO

Carbon isotope discrimination and gas exchange in Coffea species grown under different irradiance regimes

Abstract: Two coffee species (Coffea arabica L. cv. Catuai Vermelho and Coffea canephora L. cv. Apoata) were grown in pots placed outdoor under three irradiance regimes, full sunlight (S), 50% of shade (50% S) and 80% of shade (80% S), and evaluated for stable carbon isotope discrimination (Δ), photosynthetic gas exchange, and growth. The rate of CO 2 assimilation in S and 50% S plants was higher in C. arabica than in C. canephora, but there was no difference between the two species in 80% S. Both species showed similar response to the irradiance regimes. CO 2 assimilation rate at 80% S was 0.49 and 0.58 of CO 2 assimilation in full sunlight, respectively, for C. arabica and C. canephora. There was no significant difference in CO 2 assimilation between S and 50% S plants for either species. Stomatal conductance in C. arabica increased with the irradiance level, but the increase was less evident than that observed for CO 2 assimilation. Consequently, the CO 2 assimilation/stomatal conductance ratio (A/g), expressing intrinsic water use efficiency, was greater in the S plants and 50% S plants than in the 80% S plants. Irradiance regimes did not affect stomatal conductance in C. canephora, which had a lower A/g ratio than C. arabica for the same irradiance regime. Leaf Δ values were lower in S plants than in 80% S plants for both species, but there was no difference between S and 50% S treatments. The decrease in Δ was associated with a greater increase in the CO 2 assimilation rate (106%) than in the stomatal conductance (54%) in C. arabica. In C. canephora the decrease in Δ was associated with an increase in CO 2 assimilation (73%), because stomatal conductance values were not influenced by the irradiance regime. Leaf tissue Δ was negatively correlated with instantaneous measurements of CO 2 assimilation (r = - 0.92; P = 0.0109) and with stomatal conductance (r = - 0.80; P = 0.0570). Full sunlight grown plants exhibited higher leaf nitrogen content than 80% S plants. The increase in leaf nitrogen content with increasing irradiance levels was strongly correlated with CO 2 assimilation rate (r = 0.99, P = 0.0007) and negatively with Δ (r = - 0.94, P = 0.0071). Additional index terms: CO 2 assimilation rate, growth, leaf N, stomatal conductance.

Plant response to motor exhaust emissions from gasoline and alcohol.

Abstract: Plants of Ricinus communis L. were fumigated with different dilutions of exhaust gases from gasoline or ethanol from sugar cane commonly used in Brazil. Alcohol proved less toxic than gasoline in terms of visual injuries produced by acute toxic concentrations. Exhaust gases first attacked leaf palisade parenchyma resulting in necrotic spots with reduced chlorophyll content and led to a decrease in peroxidase and nitrate reductase activities. Non-lesion-producing exhaust gas concentrations from both fuel types stimulated peroxidase and nitrate reductase activities, but reduced soluble protein content in the leaves. Levels of nitrate and nitrite were higher after fumigation and chlorophyll content not altered. It was concluded that from an environmental standpoint, alcohol fuel from sugar cane is a reasonable alternative energy source to fossil gasoline. Additional index terms: chlorophyll, fossil fuel, fumigation experiments, nitrate reductase, nitrogen metabolism, peroxidase, soluble protein, sugar cane.

Ethylene and the inhibition of nodulation and nodule activity by nitrate in soybean 1

Abstract: The aim of this study was to verify the involvement of ethylene in the inhibitory process of nitrate on nodulation and nodule activity in soybean (Glycine max L.). Plants were inoculated with Bradyrhizobium elkanii and cultivated in water-culture with nutrient solution containing Co, AVG or IAA, with or without nitrate. Plants were harvested during reproductive development (R4 stage) when xylem sap was collected and plant growth and nodulation evaluated. Nitrate produced the expected inhibition of nodulation. Neither Co nor AVG were effective in reverting the inhibitory effect of nitrate on nodulation, suggesting that ethylene is not involved. However, IAA (an inducer of ACC synthese) at 0.01 and 1 μM did afford partial protection against the inhibitory effect of nitrate on nodulation. Nitrate also reduced xylem ureide transport more than nodulation, consistent with its inhibitory action on nodule activity. Again, no clear ethylene-related effects on this phenomenon could be found. Although total amino acid transport was little or inconsistently affected by any treatment, marked changes in the composition occurred. Nitrate treatment led to higher Asn and lower Gln levels. Asp levels in general were increased dramatically in hydroponics, being further stimulated by AVG in the absence of nitrate and by IAA both in the presence and absence of nitrate. IAA also prevented the increase in Asn associated with nitrate. The significance of these changes in terms of N assimilation efficiency is discussed. Additional index terms: amino acids, AVG, Co, Glycine max, IAA, nitrogen fixation, ureides, water- culture