Induction of somatic embryogenesis and biochemical characterization of Cordyline australis (G. Forst.) Endl. ‘Red Star’ callus

Abstract

The current study presents a method for the plant regeneration from stem segments of Cordyline australis (G. Forst.) Endl. ‘Red Star’ through somatic embryogenesis. We tested the effect of 3 kinds of auxin 4-amino-3,5,6-trichloropicolinic acid (picloram), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2-methoxy-3,6-dichlorobenzoic acid (dicamba), with a combination of 2 kinds of cytokinin, 6-benzyladenine (BA) and thidiazuron (TDZ), on the induction of embryogenic callus and its capacity to induce somatic embryogenesis under dark culture condition. The highest percentage of explants forming callus (nodular and friable) was observed on medium containing 25μM picloram and 0.5μM BA. The embryogenic callus, with white-yellowish nodular structures, was proliferated in the initial media and finally produced somatic embryos on all media with picloram and 2,4-D. Somatic globular embryos were obtained with a higher frequency from explants cultured on MS medium supplemented with 25μM picloram and 0.5μM BA. On this medium, a mean number of 23.0 embryos developed per gram of callus. Globular embryos developed most efficiently into cotyledonary stage on MS medium supplemented with 5μM picloram and 1μM BA. The addition of zeatin (5 and 2.5μM) and NAA (0.5 and 0.25μM) to the medium was found to be essential for the highest conversion of somatic embryos into plants. Plantlets were successfully acclimatized in the greenhouse with 90% survival rate. Callus was tested for phenolic compounds, sugars, peroxidase activity and protein contents in order to find if these compounds might be the indicators of further embryos development. The embryogenic callus of C. australis with various stages of embryo development had higher level of protein than the non-regenerable one, whereas level of sugars increased only in callus with embryos in cotyledonary stage. Callus with globular embryos contained high concentration of phenolics and low activity of peroxidase, comparing to other types of callus.