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In this study, the effects of nitrate (NO3-), ammonium (NH4+) and of the absence of nitrogen (N) in photosynthesis, photorespiration and antioxidant metabolism of young rubber plants were evaluated. Plants were grown in sand irrigated with Bolle-Jones's nutrient solution, with the nitrogen final concentration (8mM) added in the following NO3-/NH4+ proportions: 8/0, 0/8 and 0/0, respectively. The gas exchange, chlorophyll a fluorescence, photorespiration and antioxidant enzyme activities (SOD, CAT and APX) in leaves were evaluated. The net CO2 assimilation rate (A) and the electron transport rate (ETR) were higher in NO3- treated plants. Lowest ETR and higher photorespiratory activity were observed in plants treated with NH4+. SOD activity was higher in leaves of plants treated with both N sources. Lower CAT and higher APX activities were found in NO3- treated plants. Plants grown in the absence of N showed lowest values of A. We observed that the different N sources significantly affected the photosynthetic process and that NH4+ favored photorespiratory process in rubber plants. [ABSTRACT FROM AUTHOR]

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This study aimed to evaluate the effect of agents inducing water and saline stress on the seed germination and early growth and antioxidant activity in sunflower seedlings. Sunflower seeds, cv. M735, were germinated on moistened paper in solutions with osmotic potentials of 0.0,-0.2, -0.4 and -0.8 MPa induced by PEG 6000 and NaCl. The germination test was conducted with four samples of 100 seeds and four replicates per treatment, in a germination chamber at 25 °C without light. We evaluated the final percentage and speed of germination index, and the initial growth and activity of antioxidant enzymes in sunflower seedlings. Water stress induced by PEG 6000 increased the percentage of seeds germinated in the potential of -0.2 MPa, on the other hand, for NaCl in the potential of -0.8 MPa, there was a significant reduction. For this same potential, there was also a reduction in the rate of seed germination speed index in both conditioning agents. For the parameters of growth, shoot length decreased linearly with increasing concentrations of PEG 6000 and NaCl. As for the dry mass of leaves and roots and root length, this effect was more significant only in the potential of -0.8 MPa. The enzymes SOD, APX and CAT activity tended to be lower in seedlings originating from seeds in PEG 6000. In the presence of NaCl, the activity of SOD in the leaves increased significantly in the three tested for potential witnesses. For APX and CAT increase was observed at potentials of -0.2 and -0.4 MPa. In the roots there was no significant difference. An analysis of the evaluated parameters indicates that sunflower cv M735, under the conditions tested, showed tolerance to drought stress and salt until the potential of -0.4 MPa. [ABSTRACT FROM AUTHOR]