A potential ozone defense in intercellular air space: Clues from intercellular BVOC concentrations and stomatal conductance.

Ozone (O) enters plants through the stomata, passes into the intercellular air space and is decomposed in cell walls. Two factors that affect the O level in the intercellular air space are the stomatal conductance and the concentration of biogenic volatile organic compounds (BVOCs). Stomatal conductance controls the O flux into the air space and the intercellular BVOCs react with the O. Therefore, the intercellular air space serves as a place where O defense can occur, but it has received relatively little attention. This study aimed to explore potential plant-defense against O in the intercellular air space by measuring the stomatal conductance and intercellular BVOC concentrations of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Seedlings of both species were exposed to two levels of O, ambient (15 nmol mol) and 80 nmol mol (dropping to an ambient level at night), in plant growth chambers for five days in both spring and summer. We found that O decreased stomatal conductance in both species and in both seasons, which can lower the O flux into the intercellular air space. Intercellular BVOC concentrations were decreased in spring while increased in summer for both species in response to O. This suggests that the BVOC protection in the intercellular air space is only of consequence in summer. These results demonstrate the potential for BVOCs to provide intercellular O defense in both species, but with seasonal variation.