Ultraviolet-B radiation induces physiological, biochemical, and structural changes in Viola odorata

Ultraviolet (UV) radiation is a common environmental factor that affects the growth and productivity of plants. However, many plants have evolved structural, physiological, and biochemical mechanisms to cope with UV radiation. Viola odorata, is exposed to extended daily sunlight and acclimatization mechanisms have been developed in response to natural UV radiations. The purpose of this study was to assess the changes in the morphology and abundance of mucilaginous structures besides the physiological and biochemical changes of V. odorata plants under exposure to UV-B radiation (2 h and 4 h daily). After 4 weeks of treatments, the obtained results showed that the V. odorata plants responded to UV-B radiation anatomically and physiologically through changes in thickening of the cuticle, production of mucilage and enzymatic and non-enzymatic antioxidants; also, the content of malondialdehyde (MDA) and hydrogen peroxide (H2O2) was increased. The investigation showed that the duration of exposure to UV-B radiation had a negative correlation with the content of carotenoids, chlorophyll a, chlorophyll b, and soluble carbohydrates, whereas it had a positive correlation with the content of mucilage, anthocyanins, flavonoids, MDA, H2O2, and activity of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) enzymes. These findings display the different defense mechanisms in V. odorata plants against UV-B radiation.