Text by Shuai Li
Two papers studying how plants cope with ozone stress were recently published in the journal Plant Cell & Environment.
The first paper estimates the possible protective role of non-glandular and glandular trichomes on the leaf surface against ozone stress. This study analyzes ozone stress resistance of photosynthesis and induction of stress volatiles in 24 species with widely varying trichome characteristics and taxonomy, and demonstrated that the presence of glandular trichomes strongly reduced stomatal ozone uptake and ozone-dependent damage. The results indicate that leaf surface glandular trichomes constitute a major factor in reducing ozone toxicity and function as a chemical barrier which neutralizes the ozone before it enters the leaf. Once ozone enters plants mainly through the stomata, it leads to the onset of cell damage and elicitation of volatile emissions.
The second paper studies the key role of stomatal conductance in controlling ozone uptake, leaf injury and volatile release. This study investigates photosynthetic characteristics and VOC emissions in Phaseolus vulgaris leaves following acute ozone exposure under illumination and in darkness. The study also analyzes the key quantitative emission characteristics of volatile release and demonstrates different stress volatiles scale differently with ozone dose. This highlights stomatal closure due to darkness and pre-exposure to low-level ozone (priming) protected leaves against high-level ozone-induced injury.
Citation 1: Li, S., Tosens, T., Harley, P. C., Jiang, Y., Kanagendran, A., Grosberg, M., Jaamets, K. & Niinemets, Ü. (2018). Glandular trichomes as a barrier against atmospheric oxidative stress: relationships with ozone uptake, leaf damage and emission of LOX products across a diverse set of species. Plant, Cell & Environment, doi:10.1111/pce.13128 (link to full text)
There is a spectacular variability in trichome types and densities and trichome metabolites across species, but the functional implications of this variability in protection from atmospheric oxidative stresses remain poorly understood. The aim of the present study was to evaluate the possible protective role of glandular and non-glandular trichomes against ozone stress. We investigated the interspecific variation in types and density of trichomes and how these traits were associated with elevated impacts on visible leaf damage, net assimilation rate, stomatal conductance, chlorophyll fluorescence and emissions of lipoxygenase (LOX) pathway products in 24 species with widely varying trichome characteristics and taxonomy. Both peltate and capitate glandular trichomes played a critical role in reducing leaf ozone uptake, but no impact of non-glandular trichomes was observed. Across species, the visible ozone damage varied 10.1-fold, reduction in net assimilation 3.3-fold and release of LOX compounds 14.4-fold, and species with lower glandular trichome density were more sensitive to ozone stress and more vulnerable to ozone damage compared to species with high glandular trichome density. These results demonstrate that leaf surface glandular trichomes constitute a major factor in reducing ozone toxicity and function as a chemical barrier which neutralizes the ozone before it enters the leaf.
Citation 2: Li, S., Harley, P.C. & Niinemets, Ü. (2017) Ozone-induced foliar damage and release of stress volatiles is highly dependent on stomatal openness and priming by low-level ozone exposure in Phaseolus vulgaris. Plant Cell & Environment 40, 1984–2003. (link to full text)
Acute ozone exposure triggers major emissions of volatile organic compounds (VOC), but quantitatively, it is unclear how different ozone doses alter the start and the total amount of these emissions, and the induction rate of different stress volatiles. It is also unclear whether priming (i.e., pre-exposure to lower O3 concentrations) can modify the magnitude and kinetics of volatile emissions. We investigated photosynthetic characteristics and VOC emissions in Phaseolus vulgaris following acute ozone exposure (600 nmol mol-1 for 30 min) under illumination and in darkness and after priming with 200 nmol mol-1 O3 for 30 min. Methanol and lipoxygenase (LOX) pathway product emissions were induced rapidly, followed by moderate emissions of methyl salicylate (MeSA). Stomatal conductance prior to acute exposure was lower in darkness and after low O3 priming than in light and without priming. After low O3 priming, no MeSA and lower LOX emissions were detected under acute exposure. Overall, maximum emission rates and the total amount of emitted LOX products and methanol were quantitatively correlated with total stomatal ozone uptake. These results indicate that different stress volatiles scale differently with ozone dose and highlight the key role of stomatal conductance in controlling ozone uptake, leaf injury and volatile release.