engleski

The involvement of oxidative stress response in ammonium-induced somatic embryogenesis of pumpkin

Plant cells are able to form adventitious or somatic embryos by a process similar to zygotic embryogenesis. This process is known as somatic embryogenesis and is suitable for studying molecular mechanisms underlying plant embryo development. As presumed, different stress treatments may be the effectors of phytohormones production and thus regulate content and enzyme activity, leading to embryo development. Somatic embryogenesis in pumpkin (Cucurbita pepo L.) can be induced by exogenously applied phytohormone 2, 4-D, but also by a suboptimal supply of nitrogen in form of 1 mM NH4Cl as the sole source of nitrogen. The cultures established without hormones are characterized with a high embryogenic rate and developmental arrest in early proembryogenic stage. To investigate the involvement of stress responses in the NH4+-induced somatic embryogenesis, changes in specific activity of antioxidative enzymes superoxide dismutase (SOD) and soluble peroxidase (POD) were analyzed. Besides its role in the stress response, peroxidase also participates in the metabolism of phytohormone auxin and physiological processes of cell wall modification. Results have shown increased activity of both SOD and POD in tissue induced and maintained in NH4+-only medium. This up-regulation coincided with low level of protein synthesis, and high lipid peroxidation, as estimated by malondialdehyde (MDA) content. The enzymes activity and MDA content decreased after additional supply of nitrogen, in relation to the type (NO3- or Gln) and concentration (1-20 mM) of nitrogen sources. Moreover, re-supply of nitrogen triggered late stage embryo development. These results suggest the involvement of oxidative stress response in induction of somatic embryogenesis, although further studies are required to elucidate regulatory role of reactive oxygen species in the activation of enzymatic activity and developmental changes during somatic embryogenesis, in relation to changes in nitrogen supply.

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

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