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

We tested if fumigation with exogenous monoterpenes might induce thermotole rance in leaves of an oak species (Quercus suber) which does not form and e mit isoprenoids. To understand if exogenous monoterpene fumigation results in internal accumulation of monoterpenes, a physical method of monoterpene extraction was used. The internal content of monoterpenes increased in conc ert with increasing fumigation doses. This unambiguously demonstrated acqui sition of exogenous monoterpenes. We exposed fumigated Q. suber leaves to t wo cycles of increasing temperatures from 35 to 55 degrees C at 5 degrees C steps. When leaves were exposed to a low dose of exogenous monoterpenes, y ielding an internal content similar to that endogenously formed in the leav es of the monoterpene-emitter Q. ilex, no clear improvement in thermotolera nce was found. When leaves were exposed to a high dose of exogenous monoter penes, yielding an internal content of about five fold the endogenous pool of Q. ilex, but comparable with the expected content following stress-induc ed stomatal closure, photosynthesis inhibition at high temperatures was att enuated. This effect was observed only at temperatures < 45 degrees C durin g the first cycle, but at all temperatures between 35 and 55 degrees C when plants were exposed to two cycles of high temperatures. Monoterpenes were still found in the leaves of Q. suber 12 h after ending the fumigation. Mon oterpenes mere also found in non-fumigated leaves distant up to 45 cm from the fumigated leaves. If monoterpenes make the photosynthetic apparatus mor e resistant to high temperatures, the effect might not be limited to the fu migated leaves and might be persistent after fumigation.