An efficient system for plant regeneration of Senna occidentalis from hypocotyl-derived callus was developed. Callus was induced from leaf and hypocotyl explants on MS medium amended with 9.04 μM 2,4-D + 2.22 μM BAP and 10.74 μM NAA + 2.22 μM BAP. Medium browning due to leaching of compounds from callus was encountered and ameliorated through incorporation of 2.84 μM ascorbic acid. Leaf-derived callus showed no shoot induction ability, while hypocotyl-derived callus produced shoots in all cytokinin-amended treatments and also in combination with 2.68 μM NAA. For shoot formation, BAP-augmented treatments were better than medium with Kin added. Rhizogenesis was better on 1/2 MS basal medium with IBA than in the NAA and IAA treatments. Regenerated plants were acclimatized with 94% survival and showed similar morphology to field-grown plants.
Abstract Plant tissue culture techniques have become an integral part of progress in plant science research due to the opportunity offered for close study of detailed plant development with applications in food production through crop improvement, secondary metabolites production and conservation of species. Because the techniques involve growing plants under controlled conditions different from their natural outdoor environment, the plants need adjustments in physiology, anatomy and metabolism for successful in vitro propagation. Therefore, the protocol has to be optimized for a given species or genotype due to the variability in physiological and growth requirement. Developing the protocol is hampered by several physiological and developmental aberrations in the anatomy and physiology of the plantlets, attributed to in vitro culture conditions of high humidity, low light levels and hetero- or mixotrophic conditions. Some of the culture-induced anomalies become genetic, and the phenotype is inherited by clonal progenies while others are temporary and can be corrected at a later stage of protocol development through changes in anatomy, physiology and metabolism. The success of protocols relies on the transfer of plantlets to field conditions which has been achieved with many species through stages of acclimatization, while with others it remains a challenging task. This review discusses various adjustments in nutrition, physiology and anatomy of micro-propagated plants and field grown ones, as well as anomalies induced by the in vitro culture conditions.