De novo post-illumination monoterpene burst in Quercus ilex (holm oak)
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Explicit proof for de novo origin of a rare post-illumination monoterpene burst and its consistency under low O 2 , shows interaction of photorespiration, 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 chloroplasts. Isoprene-emitting plants are known to exhibit post-illumination isoprene burst, a transient emission of isoprene 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 labelling, we show that PiMB is made from freshly fixed carbon. PiMB is rare at ambient (20%) O2, absent at high (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 CO 2 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 photorespired CO2 competes with the MEP pathway for photosynthetic carbon and energy, making PiMB rare under ambient O2 and absent at high O2. PiMB becomes consistent when photorespiration is suppressed in Q. ilex.
Keywords13CO2 labelling Light–dark transition MEP pathway Monoterpene emission Post-illumination bursts Photosynthesis Photorespiratory CO2 recycling
Research and travel grants to KGSD from the National Council of Research of Italy (STM-N.0040285), Prof. Mark Westoby and Macquarie University are gratefully acknowledged. KGSD and GM also thank Dr. Tsonko Tsonev and Dr. Camilla Pandolfi for technical assistance. This study was funded by the EU-FP7 project WATBIO (No. 311929).
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