Nitrogen source, concentration, and NH4 +:NO3 − ratio influence shoot regeneration and hyperhydricity in tissue cultured Aloe polyphylla

Abstract

The role of nitrogen (N) supplied as inorganic ammonium (NH4+) and nitrate (NO3−), and organic glutamine on shoot regeneration, incidence of hyperhydricity and production of good quality shoots in Aloe polyphylla explants was investigated. The omission of total N from the culture medium resulted in low proliferation and hindered shoot growth. Ammonium as the sole source of N depressed shoot regeneration and growth and escalated the frequency of hyperhydricity to ca. 50%. When NO3− was used as the sole N source, shoots of good quality were produced and hyperhydricity was completely eliminated. Overall, the MS N combination was superior to any single N source for proliferation and growth of shoots, suggesting a synergistic effect between NH4+ and NO3− on shoot regeneration. Moreover, the relative amounts of NH4+ and NO3− also influenced the parameters tested. The highest regeneration was obtained with NH4+:NO3− ratios (mM) of 20:40, 30:30 and 40:20. Decreasing the ratio of NH4+:NO3− lowered the incidence of hyperhydricity. This study also demonstrates the potential of glutamine as the sole source of N, since its application resulted in the production of good quality shoots and almost no hyperhydricity.