LAUSR

Abstract Seed germination and root development are vital phases of the plant growth process; however, these steps are strongly influenced by the seed characteristics and environmental conditions. Seed priming provides a condition for uniform and rapid germination and plant establishment. Limited studies are available on the effect of seed priming to ameliorate cadmium (Cd) stress in thyme plants. Hence, the effect of seed hormopriming (salicylic acid and jasmonic acid, 100 mg.l-1) was evaluated. Hydropriming was done using double distilled water. Seed priming significantly increased the seed germination percentage (GP) and germination rate (GR) at all stress levels of Cd contamination. SA-primed seed showed the greatest increase in GP and GR at 30 mg.l-1 Cd by 26 and 37%, respectively, compared with the control. Salicylic acid (SA) increased plumule and radicle length 29 and 43%, respectively, at 30 mg.l-1 of Cd concentration compared with the control seeds. SA pretreatment increased plumule dry weight more than radicle dry weight. The leaf antioxidant enzyme activity was increased with increasing Cd concentration. Seed priming with SA increased superoxide dismutase (SOD) and peroxidase (POX) activity by 14 and 15%, respectively. Leaf malondialdehyde (MDA) content was increased 15% at 30 mg.l-1 Cd concentration compared with the control plants, but SA priming reduced leaf MDA content 18% compared with the control seeds. The greatest leaf proline content was observed at 30 mg.l-1 Cd concentration and SA priming. Regardless of the priming treatment, the greatest leaf protein content was observed at 10 mg.l-1 Cd concentration compared with the control. Seed priming with SA diminished the adverse effects of Cd on germination process via enhancing the antioxidant activities and accumulation of osmolytes. Therefore, hormopriming of thyme seeds by SA can enhance the resistance of this valuable medicinal herb to cadmium stress.