The potential of proline as a key metabolite to design real-time plant water deficit and low-light stress detector in ornamental plants

Nowadays, people are interested to use plants, especially air-purifying plants, in residential and other indoor settings to purify indoor air and increase the green area in the building. In this study, we investigated the effect of water deficit and low light intensity on the physiology and biochemistry of popular ornamental plants, including Sansevieria trifasciata, Episcia cupreata and Epipremnum aureum. Plants were grown under low light intensity in the range of 10–15 μmol quantum m−2 s−1 and 3 days of water deficit. The results showed that these three ornamental plants responded to water deficit with different pathways. Metabolomic analysis indicated that water deficit affected Episcia cupreata and Epipremnum aureum by inducing a 1.5- to 3-fold increase of proline and a 1.1- to 1.6-fold increase in abscisic acid compared to well-watered conditions, which led to hydrogen peroxide accumulation. This resulted in a reduction of stomatal conductance, photosynthesis rate and transpiration. Sansevieria trifasciata responded to water deficit by significantly increasing gibberellin by around 2.8-fold compared to well-watered plants and proline contents by around 4-fold, while stomatal conductance, photosynthesis rate and transpiration were maintained. Notably, proline accumulation under water deficit stress could be attributed to both gibberellic acid and abscisic acid, depending on plant species. Therefore, the enhancement of proline accumulation in ornamental plants under water deficit could be detected early from day 3 after water deficit conditions, and this compound can be used as a key compound for real-time biosensor development in detecting plant stress under water deficit in a future study.