Intermittent UV-B irradiation optimizes secondary metabolite production and growth in red rubin basil

Abstract

Understanding the plant growth responses and secondary metabolite synthesis to artificial ultraviolet-B irradiation (UV-B) is important for selecting the crop, UV-B doses, wavelength, and exposure time for the application. Red rubin basil was grown in a glasshouse under supplemental LED lights and periodically irradiated with artificial 4 W UV-B lamp at a single wavelength of 315 nm, in an indoor UV-B chamber for 3 h and 6 h. These treatments resulted in cumulative UV-B of 43.2 kJ m−2 and 86.4 kJ m−2 respectively. Both UV-Bs improved the overall production, indicating a significant potential of artificial UV-B in development and improvement of red rubin basil. A thiobarbituric acid reactive substance (TBARS) assay was carried out to assess the membrane oxidative damage to basil plants after the UV-B treatments. The results showed significant higher lipid peroxidation in UV-B treated basil in relation to control plants. Significantly increased concentrations of carotenoids was found for 43.2 kJ m−2 UV-B compared to 86.4 kJ m−2 while similar chlorophyll a and b concentrations were observed for 43.2 kJ m−2 UV-B compared to both 86.4 kJ m−2 and control. In vivo analysis revealed an increase of flavanols under post 86.4 kJ m−2 UV-B while the overall leaf performance index significantly reduced under this UV-B. The maximum quantum efficiency of photosystem II declined for both UV-B treatments compared to the control while a significant increment was seen in terms of absorption and dissipation of heat on active reaction centers in post UV-B 86.4 kJ m−2 compared to post 43.2 kJ m−2 UV-B. Similarly, significant increment in phenolic index and total anthocyanins concentrations was seen for 86.4 kJ m−2 UV-B treated plants. The UV-B of 86.4 kJ m−2 exhibited a significant higher nitrate concentration compared to the control. Furthermore, the basil under 43.2 kJ m−2 UV-B significantly outperformed other treatments in terms of reducing sugars and sucrose while 86.4 kJ m−2 treated plants yielded lower total sugars between the treatments. The present findings provided an insight into how artificial UV-B could potentially affect the accumulation of phytochemical compounds.