Influence of Nitrogen and Sucrose in the Medium and of Irradiance of the Stock Plants on Root Formation in Pelargonium Petioles Grown in vitro.

In vitro root formation was studied in petiole explants from Pelargonium × hortorum Bailey cv. Radio exposed to different irradiance (2.5. 11.6 or 23.0 W/m²). Optimal root formation was found when stock plants were subjected to 2.5 W/mm² and explants were grown on a medium with 20 g/1 of sucrose and 5.0 mM of nitrogen. The number of roots per explant decreased with increasing nitrogen or sucrose concentrations in the growth medium and with increasing irradiance applied to the stock plants. Variation in temperature (17, 21 or 25°C) did not affect root formation. The number of roots per explant was higher in explants from young petioles than in explants from older petioles. The initial nitrogen content of the explants was highest at the lowest irradiance. The content of reducing sugars and sucrose increased with increasing irradiance. The endogenous levels of lysine. arginine and ornithine were highest at 2.5 W/mm² and the levels of proline. alanine, γ-aminobutyric acid, glutamic acid, glutamine. aspartic acid and asparagine were highest at 23.0 W/mm². With rising nitrogen concentration in the medium, the final endogenous content of nitrogen in the explants increased, whereas the content of reducing sugars decreased. When the sucrose concentration in the medium increased, the endogenous content of reducing sugars rose, and the nitrogen level was lowered. Variations in the nitrogen concentration in the growth medium influenced the final level of free amino acids in the explants. [ABSTRACT FROM AUTHOR]