engleski

Effect of nitrogen supply on somatic embryo development and phenolic metabolism in pumpkin (Cucurbita pepo L.)

In pumpkin, sustained subculturing of embryogenic tissues in a medium containing NH4Cl as the sole source of nitrogen permitted the establishment of highly uniform cultures in which preglobular and globular embryos comprised more than 70% of tissue mass. Growth parameters were measured over a 15-day culture period and related to glucose uptake and pH changes in the medium. In order to distinguish NH4+ effects from pH effects, the NH4-only medium was buffered with MES. The addition of this buffer enhanced tissue proliferation and facilitated protein excretion, but no further differentiation was observed. Globular embryos proceeded to maturity only when both NH4+ and NO3- were provided in the medium. The NO3-supply noticeably reflected on increased tissue growth, glucose uptake, and the excretion of proteins and phenolics into the culture medium. Phenylalanine ammonia-lyase (PAL) activities were higher in tissue grown in NH4+-containing medium than in medium supplemented with both NH4+ and NO3-. The results show that the developmental transition of pumpkin somatic embryos is regulated, in part, in response to nitrate availability.

nitrogen; pumpkin; phenolics; PAL; somatic embryogenesis

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