Thiourea can Mitigate the Adverse Effect of Ozone on Crop Productivity

Ozone, a short-lived climate pollutant, has emerged as a new environmental challenge causing crop stress and potential risk to global food security. Tropospheric ozone exceeding a threshold concentration of 40 ppb often reduces plant photosynthesis, assimilate partitioning and development of reproductive organs, besides causing premature leaf senescence. All such effects eventually result in reductions in crop yield. Ground level ozone concentrations have been increasing at 1–2% per year in industrialized countries of the Northern Hemisphere and are projected to increase by 20–25% by 2050. Acute ozone exposures cause cell death and visible foliar injury, whereas chronic ozone exposures result in physiological dysfunction and reduced plant performance. It has been reported that ethylene signalling pathway is involved in plant damage due to ozone stress, and nitric oxide signalling has a role in stress mitigation. Several chemicals have been tried to alleviate ozone stress in plants, and ethylene diurea has proven effective in a consistent manner so far. Ethylene diurea improves ascorbate–glutathione pathway probably by nitrate reductase-induced nitric oxide signalling and synthesis. In view of such observation, it appears likely that thiol compounds can also play a role in reducing the harmful effects of ozone stress in crops. Thiourea is one such thiol compound and a bioregulator for use as an ozone protectant. Thiourea, a NO and H2S donor, has shown effects in improving glutathione reductase activity and improving salt tolerance which possibly mimics ozone tolerance at physiological and metabolic levels. Both thiourea and H2S have been reported to reduce the detrimental effects of ozone in animal studies, and therefore, thiourea holds considerable promise for mitigating ozone stress in crops. But systematic controlled experiments as well as field evaluations should be made to validate the efficacy of thiourea as a potential ozone protectant.