Srikanta Dani K G, Marino Giovanni, Taiti Cosimo, Mancuso Stefano, Atwell Brian J, Loreto Francesco, Centritto Mauro
Institute of Ecosystem Studies, National Research Council of Italy, via Madonna del Piano 10, 50019, Sesto Fiorentino (FI), Italy.
Department of Biological Sciences, Macquarie University, North Ryde, Sydney, NSW 2109, Australia.
Planta. 2017 Feb;245(2):459-465. doi: 10.1007/s00425-016-2636-x. Epub 2016 Dec 18.
Explicit proof for de novo origin of a rare post-illumination monoterpene burst and its consistency under low O , 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 CO labelling, we show that PiMB is made from freshly fixed carbon. PiMB is rare at ambient (20%) O, absent at high (50%) O, and becomes consistent in leaves exposed to low (2%) O. PiMB is stronger and occurs earlier at higher temperatures. We also show that primary and secondary post-illumination CO bursts (PiCOB) are sensitive to O in Q. ilex. The primary photorespiratory PiCOB is absent under both ambient and low O, but is induced under high (>50%) O, while the secondary PiCOB (of unknown origin) is absent under ambient, but present at low and high O. We propose that post-illumination recycling of photorespired CO competes with the MEP pathway for photosynthetic carbon and energy, making PiMB rare under ambient O and absent at high O. PiMB becomes consistent when photorespiration is suppressed in Q. ilex.
对一种罕见的光照后单萜类物质爆发的从头起源及其在低氧条件下的一致性的明确证据，表明了光呼吸、光合作用和类异戊二烯生物合成在明暗转换过程中的相互作用。冬青栎（Quercus ilex L）通过位于叶绿体中的甲基赤藓糖醇磷酸（MEP）途径，以类似异戊二烯的方式持续释放叶单萜类物质。已知释放异戊二烯的植物会表现出光照后异戊二烯爆发，即在黑暗中短暂释放异戊二烯。一种类似的光照后单萜类物质爆发（PiMB）一直难以捉摸，本文首次在冬青栎中报道。通过二氧化碳标记，我们表明PiMB是由新固定的碳形成的。PiMB在环境氧浓度（20%）下很罕见，在高氧（50%）下不存在，而在暴露于低氧（2%）的叶片中变得一致。PiMB在较高温度下更强且出现得更早。我们还表明，光照后初级和次级二氧化碳爆发（PiCOB）在冬青栎中对氧敏感。初级光呼吸PiCOB在环境氧和低氧条件下均不存在，但在高氧（>50%）条件下被诱导，而次级PiCOB（来源不明）在环境氧条件下不存在，但在低氧和高氧条件下存在。我们提出，光呼吸产生的二氧化碳的光照后再循环与MEP途径竞争光合碳和能量，使得PiMB在环境氧条件下罕见，在高氧条件下不存在。当冬青栎中的光呼吸受到抑制时，PiMB变得一致。
