On the monoterpene emission under heat stress and on the increased thermotolerance of leaves of Quercus ilex L. fumigated with selected monoterpenes

Abstract

Leaves of the monoterpene emitter Quercus ilex were exposed to a temperature ramp with 5°C steps from 30 to 55°C while maintained under conditions in which endogenous emission of monoterpenes was allowed or suppressed, or under fumigation with selected exogenous monoterpenes. Fumigation with monoterpenes reduced the decline of photosynthesis, photorespiration and monoterpene emission found in non-fumigated leaves exposed to high temperatures. It also substantially increased respiration when photosynthesis and photorespiration were inhibited by low O 2 and CO 2 -free air. These results indicate that, as previously reported for isoprene, monoterpenes may help plants cope with heat stress. Monoterpenes may enhance membrane stability, thus providing a rather non-specific protection of photosynthetic and respiratory processes. Monoterpene emission was maximal at a temperature of 35°C and was inhibited at higher temperatures. This is likely to be the result of the temperature dependency of the enzymes involved in monoterpene synthesis. In contrast to other monoterpenes, cis-and trans-β-ocimene did not respond to exposure to high temperatures. Cis-β-ocimene also did not respond to low O 2 or to fumigation. These results indicate that cis and trans-β-ocimene may have a different pathway of formation that probably does not involve enzymatic synthesis.

Fumigation with exogenous monoterpenes of a non‐isoprenoid‐emitting oak (Quercus suber): monoterpene acquisition, translocation, and effect on the photosynthetic properties at high temperatures

“…One of the most interesting hypothesis is that isoprenoids protect leaves against thermal stresses. Monoterpene fumigation increases thermotolerance of the monoterpene emitting oak Quercus ilex (Loreto et al, 1998c). Isoprene fumigation also increases the thermotolerance of intact leaves of isoprene emitting species (Sharkey & Singsaas, 1995), though it did not increase thermotolerance of leaf discs (Logan & Monson, 1999).…”

Strong correlation between isoprene emission and gross photosynthetic capacity during leaf phenology of the tropical tree species Hymenaea courbaril with fundamental changes in volatile organic compounds emission composition during early leaf development

“…For monoterpenes similar physiological functions as for isoprene were postulated, namely the protection of the photosynthetic apparatus against high temperatures episodes (Sharkey & Singsaas 1995;Loreto et al 1998;Delfine et al 2000) and against oxidative damage (O 3 , OH, H 2 O 2 , HO 2 ) Loreto & Velikova 2001). In extension to the hypothesis of Rosenstiel et al (2002), stating that the availability of DMAPP may explain part of the ontogenetic delay of isoprene emission versus photosynthesis (which could not be shown for H. courbaril), low DMAPP availability may also confer a reasonable explanation for the observed change between monoterpene and isoprene biosynthesis/emission in H. courbaril.…”

BVOCs: plant defense against climate warming?

“…Later, thermotolerance was also observed in monoterpene emissions from Quercus ilex, a Mediterranean oak species [9]. Further studies have not always been able to reproduce these results and the mechanism for this protection against high-temperature damage has yet to be shown [10].…”