Influence of nitrogen and phosphorus on induction embryogenic callus of sorghum

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 NO3-, NH4+ and PO43-. The panicle-derived cultures were used in experiments with different nitrogen sources; the influence of PO43- level was studied in embryo-derived and panicle-derived cultures. An increase of the NO3- and NH4+ 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 NH4+ and 72.4 mM NO3-, exceeded other media which were previously effective for obtaining EC of sorghum. The level of NO3- and NO3-/NH4+ 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 NH4+ with low level of NO3- resulted in formation of compact EC, while increase of NO3- 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 NH4+-rich media was accompanied by strong pigmentation of the medium, which was never observed in cultures with friable EC. An increase of the PO43- 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.