Mannitol Stress Changes The Antioxidant and Sulforaphane Contents of Broccoli Sprout in Different Varieties

To assess the effect of drought stress induced by mannitol at two levels (88 and 176 mM) on some biochemical, growth related, and polyphenolic traits of six F1 broccoli varieties (Castle Dome, Green Magic, Heraklion, Marathon, Matsuri and Sacora),a factorial experiment based on completely randomized design in three replications was implemented. The overall results of this study showed that the application of mannitol as a compound that lowers the osmotic potential among cells is a suitable compound for being used to induce the simulated drought stress in laboratory experiment; and it robustly induced the drought stress changes in measured parameters. The activity of all enzymatic antioxidant were significantly higher under mannitol application condition. The response of Marathon to mannitol application related to these parameters was higher. Also, results showed that sulforaphane content of the different varieties under different stress levels was different, but mannitol stress totally increased the content of sulforaphane. Marathon showed the highest content of sulforaphane among all varieties under both normal and stressful conditions. Considering all these results together, put us in touch with a suggestion that Marathon is the most proper varieties for both cultivation and breeding aims among all employed varieties. Heraklion variety showed high content of some parameters specially sulforaphane while showed low content for some others, so that it could be used as complementary variety with Marathon in breeding programs. Furthermore, since the content of sulforaphane along with antioxidant actives were higher under stressful condition, and also moderate stress (88 mM concentration of Mannitol) showed more slight changes measured antioxidant enzymes, using low concentration of mannitol (up to 88 mM) as representative of moderate drought stress might increase the content of suitable compounds as sulforaphane in broccoli could be a proper management approach to be more considered.