Heat- and ozone-resilient grapevines
As part of the Marie Skłodowska-Curie Individual Fellowships grant, the EU-funded Horizon 2020 OVOC project investigated a general mechanism for plant protection from abiotic stresses. This is exerted by compounds known as volatile isoprenoids (VIPs), the simplest of which is isoprene (C5H8). VIPs are an important class of secondary metabolites produced by plants and they are believed to have an antioxidant role, but the underlying mechanism is still not known. Some crops, such as grapevine do not emit C5H8 but emit other isoprenoids such as monoterpenes. Despite 60 years of research, the role of VIPs is still not fully understood, although the presence of C5H8 is linked to increased tolerance to oxidative stresses, like thermal stress. “However, it is not clear if the massive carbon investment that plants commit to isoprene emission is consistent with this role. Also, the mechanism by which isoprene, and possibly other isoprenoids, acts as antioxidant within plants is still not known,” says project coordinator Dr Francesco Loreto. Researchers first assessed an antioxidant mechanism for C5H8 in plants. Specifically, they investigated if C5H8 is oxidised within plants, thus acting as scavenger of oxidants. Scientists also aimed to prove that VIPs have an antioxidant role in grapevine, the most economically important fruit crop in Europe. In addition, they investigated whether mechanisms similar to the one tested for C5H8 takes place for other isoprenoids in grapevine. Important insights The research team used high sensitivity proton transfer reaction – time of flight – mass spectrometry (PTR-TOF-MS) to measure VIPs, their putative oxidation products, and possible volatile transformation products by plant metabolism. This work was carried out in real-time with very high sensitivity, separating isotopically labelled compounds in carbon-tracking experiments. Findings showed some VIPs in the form of monoterpenes have an antioxidant role in grapevine. A new transformation mechanism for the oxidation products of plants was also proposed and proven. Finally, the emission of putative C5H8 oxidation products and their transformation products upon abiotic stress was linked to within-leaves C5H8 oxidation. For the atmospheric science community, the transformation mechanism of methyl vinyl ketone into methyl ethyl ketone is also significant, as the origin of biogenic methyl ethyl ketone – which is an important compound in atmospheric chemistry - was previously unknown. A key finding according to Dr Loreto is that “some volatile monoterpenes protect grapevine against heat shocks, which are more likely to happen in a scenario featuring extreme events linked to climatic changes.” Wider benefits The atmospheric science community will gain from the discovery of a new transformation mechanism of the oxidation products of C5H8 by plants. “Isoprene and the oxidative products of isoprene by plants are key molecules in determining the oxidative properties of the atmosphere, including ozone and particle formation,” Dr Loreto points out. OVOC findings will support the plant science community by advancing knowledge in this field and opening up new research pathways and enquiries. Furthermore, the project is now developing a screening technique for determining increased resistance in grapevine varieties. This will help a wide range of stakeholders involved in agricultural science as well as plant breeders, who will benefit from OVOC in the long term.
Keywords
OVOC, isoprene (C5H8), grapevine, stress, volatile isoprenoids (VIPs), monoterpene, methyl ethyl ketone, atmospheric science, oxidative stress, proton transfer reaction – time of flight – mass spectrometry (PTR-TOF-MS)