engleski

ANTIOXIDATIVE AND DEVELOPMENTAL RESPONSE IN AMMONIUM-INDUCED SOMATIC EMBRYOGENESIS OF PUMPKIN

Somatic embryogenesis in pumpkin can be induced on auxin-containing medium but also on hormone-free medium containing 1 mM ammonium (NH4+) as the sole source of nitrogen. Growth of ammonium-induced embryogenic tissue was slow and caused considerable acidification of the culture medium. In order to distinguish NH4+ effects from pH effects, the NH4-only medium was buffered with MES but no further differentiation was observed. Proembryogenic cell clusters, consisted of small spherical cells with dense cytoplasma, could develop into late stage embryos only after the re-supply of nitrogen in form of nitrate or L-glutamine. Suboptimal supply of nitrogen starvation led to a marked decline in protein biosynthesis, whereas it induced an increase in the level of lipid peroxidation, as estimated by malondialdehyde (MDA). The activities of antioxidative enzymes superoxide dismutase (SOD) and soluble peroxidase (POD) were high in tissues growing into NH4+ medium, and decreased after re-supply of nitrogen what indicated oxidative stress in the tissue assimilating only NH4+. In addition, ammonium-induced embryogenic tissue was characterized by elevated activity of esterase, the early marker of somatic embryogenesis, what was in accordance with highly proembryogenic state of the culture. Together, results show that the induction and development of embryogenic competence in pumpkin is associated with the oxidative stress as induced by nitrogen limitation.

Cucurbita pepo; lipid peroxidation; nitrogen supply; oxidative stress; soluble peroxidase; somatic embryogenesis; superoxide dismutase

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