engleski

Endogenous phytohormones and cellular redox status in ammonium-induced embryogenic culture of C. pepo

Ammonium, when supplied as the sole source of nitrogen, may trigger somatic embryogenesis induction in some plant species including pumpkin. To get an insight in the involvement of phytohormones in this adaptive developmental response, status of endogenous ABA, IAA, CKs and their conjugates was analyzed. Results were compared with phytohormone status in an embryogenic culture induced by exogenously supplied 2, 4-D. Endogenous ABA peaked after 7 days of cultivation in 2, 4-D-medium while in NH4+- medium maximum of ABA is measured after 21 days of cultivation, what suggested the involvement of different stress response mechanisms. Furthermore, NH4+-induced embryogenic cultures accumulated endogenous IAA to a level similar or higher than the level induced by exogenously supplied 2, 4-D. Transfer from NH4+- medium into the medium containing both ammonium and nitrate decreased free IAA content. A significant decrease in endogenous IAA was also observed when the acidification of NH4+-medium during cultivation was prevented by 25 mM MES. On the other side, buffering of the culture medium increased endogenous ABA and CKs. Ammonium nutrition was also found to decrease total ascorbate and glutathione content as well as peroxidase activity what coincided with low mitotic index and growth retention of the NH4+- induced culture, probably caused by unfavorable growth conditions. Results demonstrate that the high endogenous auxin content and the dominancy of reduced forms of ascorbate and glutathione are key factors involved in the acquisition of embryogenic competence in ammonium- induced somatic embryogenesis in pumpkin. Interplay between ammonium nutrition, pH and hormone signaling during somatic embryogenesis induction in pumpkin is discussed.

abscisic acid; ammonium; citokinins; indole-3-acetic acid; somatic embryogenesis; stress response

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