Airborne limonene confers limited thermotolerance to Quercus ilex

Llusià J., Peñuelas J., Asensio D., Munné-Bosch S. (2005) Airborne limonene confers limited thermotolerance to Quercus ilex. Physiologia Plantarum. 123: 40-48.
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Doi: 10.1111/j.1399-3054.2004.00426.x

Resum:

The purpose of the study was to test the possible and controversial thermotolerance role of monoterpene production and emission and the related responses of antioxidants. Quercus ilex seedlings were exposed to a ramp of temperatures of 5°C steps from 25 to 50°C growing with and without limonene fumigation (7.5 μll-1). Net photosynthetic rates, maximal photochemical efficiency of PSII (Fv/Fm), oxidation state of ascorbic acid, and lipid peroxidation estimated by malondialdehyde concentrations of limonene-fumigated (LF) plants did not significantly differ from control (C) plants. No consistent changes in emissions of the other monoterpenes, α-pinene, β-phellandrene, β-pinene or β-myrcene were found. However, slight differences were found in the concentration of antioxidants. The amounts of α-tocopherol did not change or even tended to decrease at high temperatures in LF plants whereas they tended to increase by approximately 60% at 45 and 50°C relative to 25°C in C plants. Ascorbic acid reached its maximum concentration only at 45°C in LF plants whereas it reached its maximum at 35°C in C plants. β-Carotene did not decrease at high temperatures in LF plants whereas it decreased by approximately 15% at 45-50°C in C plants. Brown pigment index (BPI), an optical indicator of tissue oxidative processes, was lower in LF plants than in C plants. The photochemical reflectance index (PRI), an optical indicator of photosynthetic light use efficiency, was higher for LF plants than for C plants at elevated temperatures. Visual leaf damage (browning) tended to be less in LF plants than in C plans although not significantly (26.5 ± 8.5 versus 16.2 ± 4.8%). These results show that limonene does not confer clear and strong thermotolerance but might have some minor role. These results are in agreement with previous indications of weaker thermotolerance effect of monoterpenes than of isoprene.

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Linking isoprene with plant thermotolerance, antioxidants and monoterpene emissions

Peñuelas J., Llusià J., Asensio D., Munné-Bosch S. (2005) Linking isoprene with plant thermotolerance, antioxidants and monoterpene emissions. Plant, Cell and Environment. 28: 278-286.
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Doi: 10.1111/j.1365-3040.2004.01250.x

Resum:

The purpose of the present study was to test the possible plant thermotolerance role of isoprene and to study its relationship with non-enzymatic antioxidants and terpene emissions. The gas exchange, chlorophyll fluorescence, extent of photo- and oxidative stress, leaf damage, mechanisms of photo- and antioxidant protection, and terpene emission were measured in leaves of Quercus ilex seedlings exposed to a ramp of temperatures of 5°C steps from 25 to 50°C growing with and without isoprene (10 μL L-1) fumigation. The results showed that isoprene actually conferred thermotolerance (shifted the decrease of net photosynthetic rates from 35 to 45°C, increased Fv/Fm at 50°C from 0.38 to 0.65, and decreased the leaf area damaged from 27 to 15%), that it precluded or delayed the enhancement of the antioxidant non-enzymatic defence conferred by α-tocopherol, ascorbic acid or β-carotene consumption in response to increasing temperatures, and that it decreased by approximately 70% the emissions of monoterpenes at the highest temperatures. This suggests that there are inducible mechanisms triggered by the initial stages of thermal damage that up-regulate these antioxidant compounds at high temperatures and that these mechanisms are somehow suppressed in the presence of exogenous isoprene, which seems to already exert an antioxidant-like behaviour. © 2004 Blackwell Publishing Ltd.

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