Gibberellic Acid-Priming Promotes Fluoride Tolerance in a Susceptible Indica Rice Cultivar by Regulating the Antioxidant and Phytohormone Homeostasis

Abstract

Excessive utilization of groundwater for anthropogenic purposes has led to severe depletion of the water table, resulting in contamination of fluorides from the mineral bed. Irrigation of rice seedlings with such fluoride-infested water leads to high fluoride bioaccumulation and compromised growth physiology. In the present study, we showed that the priming of seeds with gibberellic acid 3 (GA) alleviated prolonged fluoride-induced toxicity in the fluoride-susceptible indica rice cultivar, IR-64 (grown in soil) by reducing the accumulation of the xenobiotic within the seedling biomass. The primed seeds showed improved percentage of germination during fluoride stress compared to the non-primed seeds. The stressed seedlings grown from the GA-primed seeds exhibited increased endogenous accumulation of GA and the auxin, indole-3-acetic acid which stimulated shoot and root growth and relative water content, compared to the stressed seedlings germinated from the non-primed seeds. GA-priming reduced the chlorophyll degradation, affected the homeostasis of the accessory pigments and lowered the electrolyte leakage during stress. Upon GA-priming, the fluoride-induced oxidative stress was ameliorated by an increase in proline, anthocyanin, flavonoid and total phenolic contents, reducing power, total antioxidant capacity and DPPH-radical scavenging activity. The altered activity of the antioxidative enzymes like catalase, ascorbate peroxidase and guaiacol peroxidase also enabled efficient H2O2 scavenging in the stressed plants germinated from the primed seeds. Thus, seed pre-treatment with GA promoted fluoride tolerance by activating the antioxidant machinery and elevating the endogenous level of the two most important classes of plant growth regulators, gibberellic acid and auxin.