Effect of UV-B and humic acid on the physiological properties of Nepeta crispa

Nepeta crispa is a perennial plant in the mint family. The present study aimed to study the effect of the combined application of humic acid and UV-B radiation on the growth and some phytochemical responses of this plant. The experiment was conducted as a factorial (two-factor) in a completely randomized design with three replications. The first factor was humic acid at 4 levels (0, 2, 4 and 8 g .L-1) and the second factor, UV-B radiation at 3 levels (0, 1 and 3 hours of irradiation per day). Based on the results, in contrast to the UV-B irradiation treatment, the effect of humic acid application significantly increased stem height compared to the control treatment. Also, the highest amount of total phenol, flavonoids, and antioxidant capacity and the lowest amount of total tannin were all obtained in 3 hours of UV-B irradiation treatment without the application of humic acid. The highest amount of total tannin and the lowest antioxidant capacity were observed in the treatment of 8 g .L-1 humic acid. The results of HPLC analysis of leaf extract showed that the highest amount of rosmarinic acid and salvanoic acid was produced in 3 hours of UV-B irradiation treatment per day. Among the studied phenolic acids, the highest amount of chlorogenic acid was obtained in the treatment of 3 hours of UV-B radiation + 8 g .L-1 of humic acid. The highest amount of caffeic acid was observed in 1 hour of radiation treatment + 4 g .L-1 of humic acid. In all, the combined use (interaction) of humic acid and UV-B were significant for total phenol, total flavonoid, caffeic acid and chlorogenic acid. The use of humic acid (simple effect) in this plant had a significant effect on the total tannin, antioxidant capacity and rosmarinic acid at a level of 1% and increased tannin while decreasing antioxidant activity and rosmarinic acid in Nepeta crispa leaves. Humic acid also reduced the levels of antioxidant capacity and rosmarinic acid, and the only trait that had an increasing effect on it was the amount of total tannin. The results of this study can be considered for the cultivation of this plant under greenhouse-field conditions.

Effect of UV-B and humic acid on the physiological properties of Nepeta crispa Keywords:

Antioxidant capacity , Optical stress , Phenolic compounds , Rosemaryic acid , Stress reducing agents , اسید رزمارینیک , ترکیبات فنلی , تنش نوری , ظرفیت آنتی اکسیدانی , عوامل کاهنده تنش