Isoprene and nitric oxide reduce damages in leaves exposed to oxidative stress

Isoprene and nitric oxide (NO) are two volatile moleculesthat are produced in leaves. Both compounds were sug-gested to have an important protective role against stresses.We tested, in two isoprene-emitting species, Populusnigra and Phragmites australis, whether: (1) NO emissionoutside leaves is measurable and is affected by oxidativestresses; and (2) isoprene and NO protect leaves againstoxidative stresses, both singularly and in combination. Theemission of NO was undetectable, and the compensationpoint was very low in control poplar leaves. Both emissionand compensation point increased dramatically in stressedleaves. NO emission was inversely associated with stomatalconductance. More NO was emitted in leaves that wereisoprene-inhibited, and more isoprene was emitted whenNO was reduced by NO scavenger c-PTIO. Both isopreneand NO reduced oxidative damages. Isoprene-emittingleaves which were also fumigated with NO, or treated withNO donor, showed low damage to photosynthesis, areduced accumulation of H2O2 and a reduced membranedenaturation. We conclude that measurable amounts of NOare only produced and emitted by stressed leaves, that bothisoprene and NO are effective antioxidant molecules andthat an additional protection is achieved when both mol-ecules are released