Determination of UV-B tolerance and humic acid effects on some gen characteristics, biochemical and physiological parameters in lettuce (Lactuca sativa L.)

In this study, some genes involved in the phenylpropanoid pathway ]phenylalanine ammonia lyase (PAL) and γ-tocopherol methyltransferase (γ-TMT)[ were detected in the lettuce (L.) seedling of ultraviolet B (UV-B) stress pretreatment of a growth regulator, (γ-TMT)] and the effects on some biochemical were investigated on physiological parameters. Additionally, effect of pretreatment of humic acid (HA) as a growth regulator on changes in expressions of some phenylpropanoid pathway's genes [phenylalanine ammonia lyase (PAL) and γ-tocopherol methyltransferase (γ-TMT)] and also some biochemical and physiological parameters was investigated in lettuce (Lactuca sativa L.) plant exposed to ultraviolet B (UVB) radiation stress. For this purpose, amount of 10 mg/kg (HA I), 20 mg/kg (HA II) and 30 mg/kg (HA III) HA solution were given to the 30-day lettuce seedlings, then lettuces were exposed to 3.3 Wm-2 UV-B radiation, for a period of 12 h, and some molecular, biochemical and physiological changes in harvested lettuce leaves were investigated. UV-B application in compared to control conditions increased the amount of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide radical (O2.-), the activities of some antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)], ascorbic acid, tocopherol, total phenolic substance, total flavonoid content and antioxidant capacity. Additionally, the concentrations of phenolic compounds such as chlorogenic acid, cichoric acid, and caffeic acid were increased by UV-B application. When results of UV-B application were compared parameters like PAL and γ-TMT gene expression, activities of antioxidant enzymes, ascorbic acid, tocopherol, total phenolic substance, total flavonoid amount and antioxidant capacity were significantly increased (P <0.05) in lettuce esexposed to UV-B stress after HA treatment at different concentrations, while the amount of MDA, H2O2 and O2- were decreased significantly (P <0.05). In conclusion, the protective role of humic acid in plants against the destructive effects of UV-B radiation has been determined by decreasing oxidative damage caused by UVB radiation in lettuce seedlings via increases in the accumulation of enzymatic and non-enzymatic antioxidant substances.