Auxin-induced high-frequency shoot organogenesis in diverse plant species

High-frequency regeneration through shoot organogenesis and/or somatic embryogenesis is a prerequisite for genetic transformation of plants. Cytokinins have been mainly implicated in shoot organogenesis. The present work is focused on the effect of auxins alone on shoot organogenesis in two elite clones (‘CE2’ and ‘Y8’) of Eucalyptus tereticornis, cultivars of Solanum tuberosum, Chlorophytum borivilianum, and Gladiolus hybridus. Leaf segments taken from microshoots of these plants showed differential shoot organogenesis on medium supplemented with only auxins except in case of S. tuberosum where leaves were unable to regenerate. In S. tuberosum shoot organogenesis was induced on medium supplemented with auxins only from internodal explants. Out of the three different auxins tried (NAA, IAA, and 2, 4-D), the highest frequency of shoot organogenesis (66.67%) was observed on MS medium supplemented with 25.0 μM NAA in E. tereticornis (‘CE2’) after 6 weeks of inoculation. In case of S. tuberosum, a maximum of 33.33% shoot organogenesis was observed from the internodal segments on medium containing 10.0 μM NAA after 4 weeks of inoculation. Incorporation of IAA at 25.0 μM was found to be more effective for generating the highest shoot organogenesis (58.89%) from the leaf segments of C. borivilianum. Shoot organogenesis was also observed from the leaf segments of G. hybridus, but the frequency was significantly lower than the other plants used. Histological observations revealed that shoot organogenesis was initiated from tightly packed, nucleus dense meristematic cells of calli. The emergence of shoot buds from the meristematic pockets was observed after development of shoot primordia. Random amplified polymorphic DNA (RAPD) marker confirmed clonal fidelity of the regenerated plants to that of mother plant. The present study concluded that auxins at particular concentrations were found to be effective for inducing shoot organogenesis from both dicots as well as monocot plants.