Influence of nitrogen and phosphorus on induction embryogenic callus of sorghum

Abstract

Fragments of young panicles and immature embryos of different cultivars of grain sorghum were cultured on modified MS and N6 media supplemented with L-asparagine (6.7 mM), L-proline (17.4 mM) and different concentrations of NO ^-₃ , NH ⁺₄ and PO ^3-₄ . The panicle-derived cultures were used in experiments with different nitrogen sources; the influence of PO ^3-₄ level was studied in embryo-derived and panicle-derived cultures. An increase of the NO ^-₃ and NH ⁺₄ levels in the media with amino acids significantly increased induction and growth of embryogenic callus (EC) and its regeneration ability. A new M2 medium, which contained 62.5 mM NH ⁺₄ and 72.4 mM NO ^-₃ , exceeded other media which were previously effective for obtaining EC of sorghum. The level of NO ^-₃ and NO ^-₃ /NH ⁺₄ ratio in the media supplemented with L-asparagine and L-proline were established to be the critical factors of friable EC formation in sorghum. High level of NH ⁺₄ with low level of NO ^-₃ resulted in formation of compact EC, while increase of NO ^-₃ concentration (39.9–82.4 mM) in MS or N6 media favoured proliferation of friable EC in some genotypes. Formation of compact EC in the NH ⁺₄ -rich media was accompanied by strong pigmentation of the medium, which was never observed in cultures with friable EC. An increase of the PO ^3-₄ level (up to 8.8–14.2 mM) was shown to increase the frequency of somatic embryogenesis by 3–4 times, the EC mass by 1.5–2.0 times and its regeneration ability. Media with increased nitrogen or phosphorus could be used for maintenance of sorghum EC for 4–5 passages; for a more prolonged maintenance, their level in the medium should be decreased.