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Relationship between CO2 Assimilation, Photosynthetic Electron Transport, and Active O2 Metabolism in Leaves of Maize in the Field during Periods of Low Temperature1

Fryer, Michael J.; Andrews, James R.; Oxborough, Kevin; Blowers, David A.; Baker, Neil R.
Fonte: American Society of Plant Physiologists Publicador: American Society of Plant Physiologists
Tipo: Artigo de Revista Científica
Publicado em /02/1998 Português
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16.06%
Measurements of the quantum efficiencies of photosynthetic electron transport through photosystem II (φPSII) and CO2 assimilation (φCO2) were made simultaneously on leaves of maize (Zea mays) crops in the United Kingdom during the early growing season, when chilling conditions were experienced. The activities of a range of enzymes involved with scavenging active O2 species and the levels of key antioxidants were also measured. When leaves were exposed to low temperatures during development, the ratio of φPSII/φCO2 was elevated, indicating the operation of an alternative sink to CO2 for photosynthetic reducing equivalents. The activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, and superoxide dismutase and the levels of ascorbate and α-tocopherol were also elevated during chilling periods. This supports the hypothesis that the relative flux of photosynthetic reducing equivalents to O2 via the Mehler reaction is higher when leaves develop under chilling conditions. Lipoxygenase activity and lipid peroxidation were also increased during low temperatures, suggesting that lipoxygenase-mediated peroxidation of membrane lipids contributes to the oxidative damage occurring in chill-stressed leaves.

Cold-Resistant and Cold-Sensitive Maize Lines Differ in the Phosphorylation of the Photosystem II Subunit, CP29.

Mauro, S.; Dainese, P.; Lannoye, R.; Bassi, R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1997 Português
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The effects of low temperature on the relative contributions of the reaction center and the antenna activities to photosystem II (PSII) electron transport were estimated by chlorophyll fluorescence. The inhibition of PSII photochemistry resulted from photo-damage to the reaction center and/or a reduced probability of excitation energy trapping by the reaction center. Although chill treatment did not modify the proportion of the dimeric to monomeric PSII, it destabilized its main light-harvesting complex. Full protection of the reaction center was achieved only in the presence of the phosphorylated PSII subunit, CP29. In a nonphosphorylating genotype the chill treatment led to photoinhibitory damage. The phosphorylation of CP29 modified neither its binding to the PSII core nor its pigment content. Phosphorylated CP29 was isolated by flat-bed isoelectric focusing. Its spectral characteristics indicated a depletion of the chlorophyll spectral forms with the highest excitation transfer efficiency to the reaction center. It is suggested that phosphorylated CP29 performs its regulatory function by an yet undescribed mechanism based on a shift of the equilibrium for the excitation energy toward the antenna.

Chilling Injury Induces Lipid Phase Changes in Membranes of Tomato Fruit.

Sharom, M.; Willemot, C.; Thompson, J. E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1994 Português
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16.06%
Wide-angle x-ray diffraction has provided evidence for lipid phase separations in microsomal membranes from chill-injured tomato (Lycopersicon esculentum Mill. cv Caruso) fruit. Mature-green fruit stored for 20 d at 5[deg]C had not begun to ripen and were essentially free of chilling injury symptoms. Within 4 d of being returned to 25[deg]C, however, the fruit displayed characteristic symptoms of chilling injury, including translucent water-soaked patches, surface pitting, and irregular pigmentation. Membrane damage measured as electrolyte leakage from pericarp discs intensified after the fruit were returned to ambient temperature. Wide-angle x-ray diffraction patterns recorded at 25[deg]C for microsomal membranes isolated from untreated, mature-green fruit indicated that the membrane bilayers were exclusively liquid-crystalline. Diffraction patterns for microsomal membranes from fruit stored for 20 d at 5[deg]C showed only trace amounts of gel phase lipid, but within 4 d of subsequent exposure of the fruit to ambient temperature, there was evidence for a pronounced lateral phase separation of lipids within the membranes that would render them leaky. Inas-much as the phase separations were detectable at 25[deg]C and became pronounced only subsequent to the chilling episode...

Chilling Sensitivity of Cucumber Cotyledon Protoplasts and Seedlings 1

Pomeroy, M. Keith; Mudd, J. Brian
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1987 Português
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16.6%
Cucumber (Cucumis sativus L.) seedlings are more sensitive to chilling stress when transferred to low temperature from the night cycle than from the day cycle. However, greater damage occurs when chilling is carried out in light than in dark. Freshly isolated protoplasts are extremely sensitive to damage when chilled at 4°C in light, but suffer significantly less injury when chilled in dark. If freshly isolated protoplasts are pre-chill conditioned at 27°C in either light or dark for a few hours prior to exposure to various chilling stresses, subsequent chilling damage is markedly reduced. Damage to chilled protoplasts also is reduced if cultures are placed in dark instead of light immediately following removal from low temperature. Experiments utilizing the cell wall synthesis inhibitor, dichlorobenzonitrile, showed that cell wall regeneration during the pre-chill conditioning period at 27°C does not appear to be associated with the enhanced chilling tolerance observed in these cultures. The results obtained in this investigation suggest that the physiological properties of cucumber cotyledon protoplasts accurately reflect those of intact seedlings, and hence provide a good system for studies into the mechanism of chilling damage in plants.

A Porous Convection Model for Grass Patterns

Thompson, Sally E.; Daniels, Karen
Fonte: The American Naturalist Publicador: The American Naturalist
Tipo: Artigo de Revista Científica
Publicado em /01/2010 Português
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46.46%
Spatial ecological patterns are usually ascribed to Turingtype reaction-diffusion or scale-dependent feedback processes, but morphologically indistinguishable patterns can be produced by instabilities in fluid flow. We present a new hypothesis that suggests that fluid convection and chill damage to plants could form vegetation patterns with wavelengths ≈1–2 times the plant height. Previous hypotheses for small-scale vegetation pattern formation relied on a Turing process driven by competition for water, which is thought to occur in large vegetation patterns. Predictions of the new hypothesis were consistent with properties of natural grass patterns in North Carolina, contradicting the Turing hypothesis. These results indicate that similarities in pattern morphology should not be interpreted as implying similarities in the pattern-forming processes, that small-wavelength vegetation patterns may arise from mechanisms that are distinct from those generating long-wavelength vegetation patterns, and that fluid instabilities should be recognized as a cause of ecological patterns.