Study led by scientists from the Estonian University of Life Sciences indicate that many crops with hairier leaves tolerate ground-level ozone better. The relative content of ground-level ozone in the air has significantly increased since the beginning of the 20th century. It seems that this trend will continue in the future. However, this gas is an environmental poison and harmful to living organisms. Compared to the beginning of the current century, large-scale ozone damage to forest trees as well as on crops has been recorded all over the world.

In a recently-published paper, an international working group, which was led by Estonian plant physiologist from EMÜ, looked at how the gland-tipped hairs of plants protect against the harmful effects of ozone. Plant epidermis has about ten different types of these hairs. Their density also varies between species with some species lacking these hairs altogether. So far, the gland-tipped hairs were primarily associated with a plant’s ability to fight against herbivory.

This time, the scientists limited their focus to agriculturally important plants, such as pumpkins, cucumbers, lavender, rosemary, etc. The research group found that the gland-tipped hairs excrete compounds which have an ozone-neutralising effect. Plants with hairier leaves were significantly more resistant to a high concentration of ozone. Their leaves developed the brown spots marking ozone damage later than less-hairy species.

This paper is significant because, for the first time in history, the  gland-tipped hairs have assumed an important function as neutralisers of ozone.

Citation: 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.org/10.1111/pce.13128 (link to full text).

Gravitational life-history effects on male trichomes. So far probably not tested in plants… (pic from here)

Abstract:

There is a spectacular variability in trichome types and densities and trichome metabolites across species, but the functional implications of this variability in protecting from atmospheric oxidative stresses remain poorly understood. The aim of this 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 ozone impacts on visible leaf damage, net assimilation rate, stomatal conductance, chlorophyll fluorescence, and emissions of lipoxygenase 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 rate 3.3‐fold, and release of lipoxygenase 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 that neutralizes the ozone before it enters the leaf.