Seed germination on standard media (a) and media supplemented with mannitol (b), KCl (c), nitrate (d), H2O2 (e), α-NAA (f), 2,4-D (g), ABA (h) and 3.5 % sucrose (i). Gray symbols, air 12; black symbols, control. Data presented are the mean of three independent replicates consisting of at least 10 seedlings each. Error bars represent standard error