Physiological Responses of Melissa officinalis seedling to Different Bands of Ultraviolet (UV) Radiation

Ultraviolet (UV) rays are part of solar radiation, which induces physiological processes mediated by photoreceptors. This research investigated the effect of short-term exposure to different bands of UV rays (UV-A, UV-B, and UV-C) with the wavelengths of ۳۶۵, ۳۱۲, and ۲۵۴ nm on Melissa officinalis L. seedlings, respectively.  The amount of Chl. a, b, total, carotenoids, anthocyanin, UV absorbing compounds, and proteins in the leaves were measured. The control group was not treated with any UV rays. The total chlorophyll content decreased under UV-A (۱۹%), UV-B (۲۳%), and UV-C (۴۹%) treatments. The lowest amount of Chl. a, b, and total chlorophyll belonged to UV-C with about ۵۰, ۴۶, and ۴۹%, respectively. The carotenoid contents significantly decreased under UV-A and UV-C treatments. The ratio of carotenoids to total chlorophyll increased under UV-B (۱۷%), and UV-C (۴۵%) treatments compared with the control. The reduction of carotenoids content under UV treatment was less than that of the chlorophyll. The amount of anthocyanin and UV-absorbing compounds increased under different bands of UV radiation. The UV-A and UV-B increased protein contents, while UV-C treatment decreased protein content. This research indicated that the UV-B ray stimulate plant antioxidant system helping to plant survival under UV stress.

Keywords:

lemon balm , photosynthesis pigments , protein , UV