The Role Of Flavonol In Salt Resistance

Abiotic and biotic stresses often induce ROS overproduction in plants, which brings about serious oxidative damage. Plants possess diverse adaptive mechanisms to reduce such oxidative damage by synthesizing large amount of enzymatic and non-enzymatic ROS scavengers. Flavonoids are secondary metabolites with low molecular weight, and act as a kind of -enzymatic ROS scavengers, so their synthesis is often promoted when exposed to abiotic stress. Flavonoids are classified as six classes, including flavonols, anthocyanins, and so on. The antioxidant capacity and in planta distribution are differential among six classes, of which flavonols exhibit the strongest antioxidant capacity. To date, the studies concerning the role of flavonoids mostly focus on the total flavonoids and anthocyanins. Howeverr, the specific contribution of flavonols to the stress tolerane has not been well addressed.Flavonol was produced by the catalysis of flavonol synthase (FLS). In Arabidopsis, there have six FLSes, of which FLS1 possess superior enzymatic activity, FLS3 has weak activity, but the other have no activity. The previous study indicated that FLS1 mutant fls1-3 produces lower flavonols, but FLS1 overexpression Arabidopsis lines do not accumulate more flavonols. In our lab, a wheat FLS gene TaFLS1 was isolated from a wheat introgression cultivar SR3 with high salt and drought resistance, and its overexpression in Arabidopsis obviously promoted the accumulation of flavonols. In this study, we studied the role of flavonols in salt tolerance using fls1-3 and TaFLS1 overexpression lines.1. Flavonols offered salt tolerance in ArabidopsisIn comparison with the wildtype, the salt tolerance of flsl-3 seedlings was reduced, but that of the TaFLS1 overexpression lines was enhanced. When plants in soils were irrigated with salt solution, the growth of wildtype and flsl-3 were seriously restricted with a more restriction strength in fls1-3, but the TaFLS1 overexpression lines exhibited more vigorous growth ability. Exogenous application of flavonol also enhanced the salt tolerance of the wildtype and flsl-3. At germination stage, the germination rate of TaFLS1 overexpression lines was higher than the wildtype under saline stress, and exogenous application of flavonols phenocopied this effect. Interestingly, however, flsl-3 also had higher germination rate than the wildtype and was near to TaFLS1 overexpression lines after exposure to salt stressTo know the association of salt tolerance by flavonols with their antioxidant capacity, we measured the content of O2- and H2O2, two major classes of ROS, by NBT and DAB staining, respectively. When treated with NaCl, ROS level in TaFLS1 overexpression lines was lower than widetype, but an opposite result was found in flsl-3. Meanwhile, exogenous flavonols also lowered ROS level under salt stress. All these results fully indicated that flavonols offered salt resistance in Arabidopsis via acting as ROS scavengers to lowering ROS level under salt stress2. Flaovols enhanced the resistance to Oxidative stressTo further confirm the association between flavonols and antioxidation, we analyzed the resistance capacity of plants to exogenous H2O2. At seeding and plant stage, in comparison with the wildtype, fls1-3 had lower H2O2 resistance, but TaFLS1 overexpression lines showed more vigorous growth ability. Exogenous flavonols also presented the wildtype and flsl-3 the capacity. However, at germination stage, alike the finding under salt treatment, the germination rate of flsl-3 was higher than wildtype and was close to TaFLS1 overexpression lines.When dyed by DAB and NBT, the staining signal in overexpression lines was weaker than widetype and fls1-3.3. Flavonols reduced the sensitivity to ABAABA is a stress responsive phytohormone, so we further analyzed the effect of flavonols on ABA sensitivity. When treated with ABA, at seedling stage, in comparison with the wildtype, flsl-3 had higher ABA sensitivity, but TaFLSl overexpression lines showed an opposite phenotype. Exogenous flavonols also decreased the sensitivity to ABA. At germination period, the similar response of flsl-3 and TaFLS overexpression lines was also found, and notably, the germination rate of fls1-3 was even higher than TaFLS overexpression lines when exposed to ABA.In combination with all these results, we conclude that flavonols enhanced salt tolerance by improving ROS scavenging capacity, and TaFLSl is a candidate gene for crop molecular breading...