Peñuelas J, Munné-Bosch S, Llusià J, Filella I (2004) Leaf reflectance and photo- and antioxidant protection in field-grown summer-stressed Phillyrea angustifolia. Optical signals of oxidative stress? New Phytologist 162:115-124.
Munné-Bosch S., Peñuelas J., Asensio D., Llusià J. (2004) Airborne ethylene may alter antioxidant protection and reduce tolerance of holm oak to heat and drought stress. Plant Physiology. 136: 2937-2947.LinkDoi: 10.1104/pp.104.050005
Plant-emitted ethylene has received considerable attention as a stress hormone and is considered to play a major role at low concentrations in the tolerance of several species to biotic and abiotic stresses. However, airborne ethylene at high concentrations, such as those found in polluted areas (20-100 nL L -1) for several days, has received far less attention in studies of plant stress tolerance, though it has been shown to alter photosynthesis and reproductive stages (seed germination, flowering, and fruit ripening) in some species. To assess the potential effects of airborne ethylene on plant stress tolerance in polluted areas, the extent of oxidative stress, photo- and antioxidant protection, and visual leaf area damage were evaluated in ethylene-treated (approximately 100 nL L -1 in air) and control (without ethylene fumigation) holm oak (Quercus ilex) plants exposed to heat stress or to a combination of heat and drought stress. Control plants displayed tolerance to temperatures as high as 50°C, which might be attributed, at least in part, to enhanced xanthophyll de-epoxidation and 2-fold increases in α-tocopherol, and they suffered oxidative stress only when water deficit was superimposed on temperatures above 45°C. By contrast, ethylene-treated plants showed symptoms of oxidative stress at lower temperatures (35°C) than the controls in drought, as indicated by enhanced malondialdehyde levels, lower α-tocopherol and ascorbate concentrations, and a shift of the redox state of ascorbate to its oxidized form. In addition, ethylene-treated plants showed higher visual leaf area damage and greater reductions in the maximum efficiency of the PSII photochemistry than controls in response to heat stress or to a combination of heat and drought stress. These results demonstrate for the first time that airborne ethylene at concentrations similar to those found in polluted areas may reduce plant stress tolerance by altering, among other possible mechanisms, antioxidant defenses. © 2004 American Society of Plant Biologists.
Peñuelas J., Llusià J. (2004) Plant VOC emissions: Making use of the unavoidable. Trends in Ecology and Evolution. 19: 402-404.LinkDoi: 10.1016/j.tree.2004.06.002
All plants emit substantial amounts of phytogenic volatile organic compounds (PVOCs), which include alkanes, alkenes, alcohols, aldehydes, eters, esters and carboxylic acids. Defence, communication and/or protection against extreme conditions have been proposed as reasons for these emissions. However, Rosenstiel and colleagues have recently proposed that emission of PVOCs represents a metabolic 'safety valve' by preventing the unnecessary sequestration of phosphates. Additionally, Niinemets and colleagues suggest that the emission rates of some PVOCs are determined by the principal physicochemical characteristics of the emitted compounds, such as their solubility, volatility and diffusivity, rather than by physiological mechanisms, such as their synthesis rates. These two new studies lead to the hypothesis that there is not necessarily a specific role for every PVOC emitted, given that their emission is unavoidable as result of their volatility. However, in some cases, natural selection has worked to take advantage of this volatility.
Peñuelas J., Llusià J., Martínez B., Fontcuberta J. (2004) Diamagnetic susceptibility and root growth responses to magnetic fields in Lens culinaris, Glycine soja, and Triticum aestivum. Electromagnetic Biology and Medicine. 23: 97-112.LinkDoi: 10.1081/LEBM-200032772
We studied the response of root growth to different magnetic fields and forces. We submitted the seeds of three plant species, Lens culinaris L., Glycine soja Siebold & Zucc., and Triticum aestivum L., which differ in concentrations of paramagnetic (e.g., Fe or Co) and diamagnetic materials (e.g., starchy amyloplasts), to different static magnetic fields and forces. A magnetic field of 176 G reduced root growth of L. culinaris, G. soja, and T. aestivum, 37, 31, and 15%, respectively. A weaker magnetic field of 21 G reduced root growth of L. culinaris and G. soja only 13 and 21%, respectively, whereas it had no significant effect on the cereal T. aestivum. The germinating seeds of L. culinaris and G. soja were less diamagnetic than T. aestivum, and the latter had a smaller paramagnetic component. Since at room temperature, the paramagnetic component was much smaller than the diamagnetic one, the magnetic inhibition of root growth may be linked to the diamagnetic susceptibility, the inhibition being greater for the less diamagnetic materials and for the stronger magnetic forces. These results provide new examples of possible species-specific effects of moderate magnetic fields on plant growth, especially when growth is rapid, such as root growth after germination. We propose a simple hypothesis to relate root growth inhibition with magnetic fields and with the different responses found among species, seasons, and physiological and environmental conditions reported here and in the literature. It is based on a reduced magnetic force acting on the cell biological substances and on the cellular organelles such as amyloplasts, rather than on the cytoplasmic matrix where they are immersed as a consequence of their lower diamagnetic susceptibility. As a result, a nonuniform magnetic field exerts a ponderomotive force on the biological components in the opposite direction to the growing tip. This can result in intracellular magnetophoresis, and can account for inhibition of the root growth rate downwards. This inhibition would be stronger the lower the diamagnetic susceptibility.
Ogaya R, Peñuelas J, Asensio D, Llusià J, Sardans J, Serrano L, Lloret F, Terradas J (2004) Efectes ecofisiològics d'una sequera experimental sobre l'alzinar de Prades. In Vallvey A, Grau JMT (eds) Actes de les Primeres Jornades sobre el Bosc de Poblet. Paratge Natural d'Interès Nacional de Poblet, Departament de Medi Ambient i Habitatge, Generalitat de Catalunya, pp.183-191.
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