Leaf bases of pineapple cultured on a shoot induction medium (SIM) produced protuberances followed by shoot-buds via direct organogenesis at a frequency of 46 %. When 8 mM glutamine (gln) was a supplement to SIM (SIM8gln), the regeneration rate increased to 70 %, thus suggesting that 8mM gln increased explant competence for organogenesis. Besides this, shoot vigor was strongly enhanced in SIM8gln. Other gln concentrations (16 or 32 mM) evoked a lower frequency of shoot-bud induction and number of regenerated shoots per explant when compared to SIM8gln. In this study, it was defined that explant organogenic commitment to form shoot-buds occurred in the first 7 days of culture on SIM8gln. Thereafter, endogenous indole-3-acetic acid (IAA) and cytokinin (4 types) measurements were carried out during this period, that is, during the induction phase of shoot-bud formation. The IAA content increased greatly until the 5th day in the leaf bases cultured on SIM8gln. No such change in IAA concentration was observed in the explants cultivated on SIM or in the presence of the highest gln concentration (32 mM), this being inhibitory to the organogenic process. The only natural cytokinin detected was isopentenyladenine. An increase of 50 % in the level of this phytohormone occurred in leaf bases cultured on SIM8gln at the 5th day, when compared to SIM or of 170% compared to SIM32gln. These results suggest that 8 mM gln favorably influenced the organogenic process through changes in IAA and iP concentrations in pineapple leaves.
Ananas comosus; amino acids; auxin, Bromeliaceae; cytokinins; phytohormones; shoot regeneration
