Abstract

Ultraviolet-B radiation (UV-BR) is a significant factor affecting plant growth and function. The present study was conducted to examine the effect of UV-BR on the oxidative metabolism, glandular trichomes, mesophyll cells, and the production of phytochemicals in leaf tissues of water mint (Mentha aquatica) at two vegetative (early and late) growth stages. With this aim, the plants were exposed to prolonged periods of UV-BR (2 h or 4 h daily) for three weeks at these growth stages. Physiological, biochemical, morphological, ultrastructural, and molecular investigations showed that UV-BR had divergent consequences on water mint. Biomass and photosynthetic pigments were reduced in the UV-BR-exposed plants compared with the unexposed plants. Conversely, UV-BR improved the oxidative metabolism, quantity of glandular trichomes, production of phytochemicals, and expression level of the candidate genes involved in terpene biosynthesis process at both the growth stages. In addition to these, UV-BR modified the chemical composition of volatile oils and the chloroplast ultrastructure in mesophyll cells. However, the rate of alterations in the surveyed parameters differed between the early and late vegetative stages. Plants were more sensitive to UV-BR at the early vegetative stage than at the late vegetative stage. The considered variables were found to be correlated under the UV-BR treatments at the different growth stages. Hence, it can be concluded that the UV-BR affects the production of phytochemicals, as well as the biosynthetic pathways involved, in water mint at the growth stages studied.

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