Differences in the Improvement of Regeneration Ability of Wheat Calli by Ascorbate and H2O2 Through Modulation of Their Hormone and Metabolite Profile

Successful plant regeneration from calli is important during transformation and micropropagation of plants. In order to increase its efficiency, the redox environment of the wheat calli was modified. Calli were treated with 0, 10, 20 and 40 mM ascorbate (Asc) or H 2 O 2 for one week to compare their influence on shoot regeneration and the redox and hormonal regulatory mechanisms. Both compounds increased shoot formation in 10 mM concentration which could be the consequence of the mild oxidative stress indicated by increased H 2 O 2 levels. However, only 20 mM H 2 O 2 improved regeneration, while 20 mM Asc and both compounds at 40 mM levels had no such effect. Asc in 20 mM concentration was already very harmful based on the low survival of calli which could be the result of much larger increase in the ratio of oxidised glutathione compared to 20 mM H 2 O 2 . This change could contribute to the great reduction in the level of oxo-indole-3-acetic acid glucose-ester, trans- zeatin-glucosides and in isopentenyladenosine and its 9-glucoside in the more oxidising redox environment after 20 mM Asc treatment. These redox and hormonal changes after 20 mM Asc addition might also lead to much greater decrease of polyamine levels compared to 20 mM H 2 O 2 . In 10 mM concentration, both compounds improved shoot regeneration through their influence on metabolism, but at 20 mM level only H 2 O 2 exhibited such positive effect, and Asc was harmful. Thus, H 2 O 2 seems to be more appropriate for the induction of shoot formation during plant transformation and micropropagation.