Ammonium-related metabolic changes affect somatic embryogenesis in pumpkin ( Cucurbita pepo L.)

Somatic embryogenesis in pumpkin can be induced on auxin-containing medium and also on hormone-free medium containing 1 mM ammonium (NH 4 +) as the sole source of nitrogen. Growth of NH 4 +-induced embryogenic tissue was slow and caused considerable acidification of the culture medium. Small spheric...

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Bibliographic Details
Published in:Journal of plant physiology 2011-11, Vol.168 (16), p.1943-1951
Main Authors: Mihaljević, Snježana, Radić, Sandra, Bauer, Nataša, Garić, Rade, Mihaljević, Branka, Horvat, Gordana, Leljak-Levanić, Dunja, Jelaska, Sibila
Format: Article
Language:English
Subjects:
Antioxidative enzymes
Biological and medical sciences
Cucurbita - drug effects
Cucurbita - embryology
Cucurbita - enzymology
Cucurbita - metabolism
Cucurbita pepo
Esterases - metabolism
Fundamental and applied biological sciences. Psychology
Glucans - metabolism
Glutamate-Ammonia Ligase - drug effects
Glutamate-Ammonia Ligase - metabolism
Glutamine synthetase
Hydrogen-Ion Concentration
Indoleacetic Acids - pharmacology
Nitrates - metabolism
Nitrates - pharmacology
Nitrogen - metabolism
Nitrogen - pharmacology
Nitrogen supply
Oxidative Stress
Peroxidase - metabolism
Phenylalanine ammonia-lyase
Phenylalanine Ammonia-Lyase - drug effects
Phenylalanine Ammonia-Lyase - metabolism
Plant physiology and development
Plant Somatic Embryogenesis Techniques
Quaternary Ammonium Compounds - pharmacology
Stress, Physiological
Superoxide Dismutase - metabolism
Time Factors
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Summary:Somatic embryogenesis in pumpkin can be induced on auxin-containing medium and also on hormone-free medium containing 1 mM ammonium (NH 4 +) as the sole source of nitrogen. Growth of NH 4 +-induced embryogenic tissue was slow and caused considerable acidification of the culture medium. Small spherical cells with dense cytoplasma formed proembryogenic cell clusters that could not develop into late stage embryos. Buffering of NH 4 + medium with 25 mM 2-(N-morpholino)-ethane-sulfonic acid enhanced tissue proliferation, but no further differentiation was observed. Later stage embryos developed only after re-supply of nitrogen in form of nitrate or l-glutamine. Effects of nitrogen status and pH of culture media on ammonium assimilation were analyzed by following the activity of glutamine synthetase (GS) in relation to phenylalanine ammonia-lyase (PAL). Increased activity of GS and PAL in NH 4 + induced tissue coincided with significantly higher activity of stress-related enzymes superoxide dismutase (SOD) and soluble peroxidase (POD), indicating oxidative stress response of embryogenic tissue to NH 4 + as the sole source of nitrogen. In addition, considerable increase was observed in callose accumulation and esterase activity, the early markers of somatic embryogenesis. Activity of stress-related enzymes decreased after the re-supply of nitrate (20 mM) or Gln (10 mM) in combination with NH 4 + (1 mM), which subsequently triggered globular embryo development. Together, these results suggest that stress responses, as affected by nitrogen supply, contribute to the regulation of embryogenic competence in pumpkin.
ISSN:0176-1617
1618-1328
DOI:10.1016/j.jplph.2011.05.025