Leaf monoterpene emission limits photosynthetic downregulation under heat stress in field-grown grapevine

Rising temperature is among the most remarkably stressful phenomena induced by globalclimate changes with negative impacts on crop productivity and quality. It has been previouslyshown that volatiles belonging to the isoprenoid family can confer protection against abiotic stresses.In this work, twoVitis viniferacv. ‘Chardonnay’ clones (SMA130 and INRA809) differing dueto a mutation (S272P) of the DXS gene encoding for 1-deoxy-D-xylulose-5-phosphate (the firstdedicated enzyme of the 2C-methyl-D-erythritol-4-phosphate (MEP) pathway) and involved in theregulation of isoprenoids biosynthesis were investigated in field trials and laboratory experiments.Leaf monoterpene emission, chlorophyll fluorescence and gas-exchange measurements were assessedover three seasons at different phenological stages and either carried out inin vivoor controlledconditions under contrasting temperatures. A significant (p< 0.001) increase in leaf monoterpeneemission was observed in INRA809 when plants were experiencing high temperatures and over twoexperiments, while no differences were recorded for SMA130. Significant variation was observed forthe rate of leaf CO2assimilation under heat stress, with INRA809 maintaining higher photosyntheticrates and stomatal conductance values than SMA130 (p= 0.003) when leaf temperature increasedabove 30◦C. At the same time, the maximum photochemical quantum yield of PSII (Fv/Fm) wasaffected by heat stress in the non-emitting clone (SMA130), while the INRA809 showed a significantresilience of PSII under elevated temperature conditions. Consistent data were recorded betweenfield seasons and temperature treatments in controlled environment conditions, suggesting a stronginfluence of monoterpene emission on heat tolerance under high temperatures. This work providesfurther insights on the photoprotective role of isoprenoids in heat-stressed its vinifera, and additionalstudies should focus on unraveling the mechanisms underlying heat tolerance on the monoterpene-emitter grapevine clone.