Study of phytohormones effects on UV-B stress seeds of thyme species

Thymus vulgaris L. and Thymus daenensis Celak (Thyme), members of the family Lamiaceae, are widely used in Iranian folk medicine. The aim of this research was to study how salicylic acid (SA), gibberellin (GA), and indole acetic acid (IAA)-seed priming affect UV-B radiation in seeds of Thyme (T. vulgaris, T. daenensis Celak) under both laboratory and outdoor conditions. The effects of phytohormones (200, 400, 600 ppm) and irradiation performed in a 60 Co Gamma cell 220 source at a dose of 3 kGy (10, 20 and 30 min) on seeds of Thyme species were studied. Seeds were tested under in vitro and outdoor conditions in a complete randomized factorial layout with 4 and 3 replications, respectively. The characters measured under in vitro condition were seed germination percentage, mean time of germination, root and stem length. On the field, the characters evaluated were number of leaf, length of plant, root and shoot dry matter and essential oil. SA treatment was better under in vitro conditions. No significant effects were obtained from GA and IAA. The most destructive effects and the best beneficial phytohormones were UV 30 min and SA (200 and 400 ppm), respectively. The effects of foliar application of hormones were determined on growth and essential oil production in medicinal plants in two consecutive years. Shoot dry matter increased in both years with SA applications but IAA and GA had no beneficial effects on germination characters after UV radiation. SA-priming of seeds protects thyme seedlings against UV-B radiation. The results of this study also showed that elevation of free SA levels in plants, either by exogenous feeding or genetically may enhance their tolerance to abiotic stress.