Exogenous polyamines enhance somatic embryogenesis and Agrobacterium tumefaciens-mediated transformation efficiency in sugarcane (Saccharum spp. hybrid)

The influence of exogenous polyamines (PAs) on somatic embryogenesis from immature leaf roll explants and Agrobacterium tumefaciens-mediated transformation of embryogenic callus of Saccharum spp. (sugarcane) 'Co 86032' was examined. Immature leaf roll-derived embryogenic callus was obtained on Murashige and Skoog with Gamborg B5 vitamins (MSB5) medium containing 3 mg L-1 2,4-dichlorophenoxyacetic acid (2,4-D). Various concentrations of PAs along with 2 mg L-1 2,4-D and 0.5 mg L-1 kinetin (Kin) were tested for somatic embryo induction. A total of 106 somatic embryos per 250 mg of callus (96.3% responsive explants) were obtained on medium supplemented with 20 mg L-1 putrescine (PUT) and 92.0% of the somatic embryos matured and produced 98 shoots per 250 mg of callus. Somatic embryo induction and maturation was increased more than two- and threefold, respectively, on PUT-supplemented medium compared to control cultures. Histomorphological analyses of various developmental stages verified somatic embryogenesis from immature leaf roll explants. The rooted plantlets were successfully hardened and exhibited normal growth. The efficiency of A. tumefaciens-mediated transformation of embryogenic callus using various concentrations of PAs in the infection, co-cultivation, and regeneration media was also assessed. Putrescine at 20 mg L-1 showed the highest regeneration (54.4%) and transformation (35.8%) efficiencies, which were more than twofold higher than the control treatment. These results demonstrate that exogenously supplied PAs improve plant regeneration using somatic embryogenesis and A. tumefaciens-mediated transformation of embryogenic callus of sugarcane 'Co 86032'.