De novo post-illumination monoterpene burst in Quercus ilex (holm oak)

Main conclusion Explicit proof for de novo origin of a rare post-illumination monoterpene burst and its con- sistency under low O2, shows interaction of photores- piration, photosynthesis, and isoprenoid biosynthesis during light-dark transitions. Quercus ilex L (holm oak) constitutively emits foliar monoterpenes in an isoprene-like fashion via the methyl erythritol phosphate (MEP) pathway located in chloro- plasts. Isoprene-emitting plants are known to exhibit post- illumination isoprene burst, a transient emission of iso- prene in darkness. An analogous post-illumination monoterpene burst (PiMB) had remained elusive and is reported here for the first time in Q. ilex. Using 13CO2 (50%) O2, and becomes consistent in leaves exposed to low (2%) O2. PiMB is stronger and occurs earlier at higher temperatures. We also show that primary and secondary post-illumination CO2 bursts (PiCO2B) are sensitive to O2 in Q. ilex. The primary photorespiratory PiCO2B is absent under both ambient and low O2, but is induced under high ([50%) O2, while the secondary PiCO2B (of unknown origin) is absent under ambient, but present at low and high O2. We propose that post-illumination recycling of pho- torespired CO2 competes with the MEP pathway for pho- tosynthetic carbon and energy, making PiMB rare under ambient O2 and absent at high O2. PiMB becomes con- sistent when photorespiration is suppressed in Q. ilex.