Methanol as a signal triggering isoprenoid emissions and photosynthetic performance in Quercus ilex
Several volatile organic compounds (VOCs) have been reported as having a communication role between plants and also between plants and animals. We aimed to test whether methanol, a short-chain oxygenated VOC, could also have a signalling role between plants. We monitored photosynthetic performance and VOC exchange rates of Quercus ilex L. saplings before and after two different treatments: (a) clipping of some leaves to simulate an attack by herbivores and (b) fumigation with gaseous methanol for 5 h to simulate the amount of methanol a plant could receive from surrounding plants if those had been already attacked by herbivores. The clipping treatment enhanced the photosynthetic rates, the chlorophyll a to b ratio and the carotenoid to chlorophyll ratio of non-clipped leaves, suggesting an activation of plant protective metabolism. Also, a small but interesting systemic (in non-clipped leaves) increase in methanol emission rates was observed, which agrees with the possibility that methanol may act as a signalling cue. The methanol fumigation treatment induced an increase in the actual photochemical efficiency of PSII and also in the carotenoid to chlorophyll ratio. Methanol fumigation also promoted a 14% increase in the monoterpene emission rate, 1 day after the treatment, a similar response to the ones induced by other signalling VOCs. The enhanced monoterpene emissions could add to the blend of VOCs emitted after stress and be part of further signalling pathways, thus forwarding the message started by methanol. This study suggests that clipping and methanol fumigation at natural concentrations elicit significant neighbour plant physiological responses and further BVOC emissions.