Abstract

This study evaluated the effects of the best priming treatment on germination responses of milkthistle (Silybum marianum) seeds. Seeds of S. marianum are two ecotypes namely (Amol and Majar) primed with KNO₃ in -2, -4, -6, -8 and -10 bar for 6, 12 and 18 h at 25°C, followed by air-drying to their initial moisture level. Then, based on germination percentage, germination rate, mean germination time (MGT) and seed vigor, the best priming treatment was selected. Antioxidant enzymes activity of S. marianum were determined in primed (-2 bar 6 and 18 h in Amol and Majar, respectively) and non-primed seeds in 24 and 96 h after sowing during germination. Results indicated that osmo-priming increased germination percentage, germination rate and seed vigor and shortened MGT than non-primed. The best priming treatment in Amol and Majar was -2 bar 6 and 18 h, respectively. Moreover, priming also enhanced the anti-oxidative enzymes of peroxidase (POX) and ascorbate POX (APX) and soluble proteins level of treated seeds but catalase (CAT) activity decreased in primed seeds than non-primed control. Majar had greater activity of APX enzyme and soluble proteins level than Amol. As a result, Majar had higher germination percentage and seed vigor and faster germination rate as compared to that of Amol. Activity of POX was higher in Amol than Majar. The soluble proteins levels in 24 h after sowing was greater than 96 h after sowing and in 96 h after sowing decreased but activities of APX  and POX were greater in 96 h after sowing than 24 h after sowing. The enhanced anti-oxidative enzyme activities of APX and POX and soluble proteins levels might explain in part why primed milk thistle seeds germinated better than non-primed seeds.

Key words: Seed priming, antioxidative enzymes, germination, Silybum marianum.