The effect of ABA (abscisic acid) on embryogenesis and growth was studied on ovular callus of the «Shamouti» orange (Citrus sinensis). Embryogenesis was considerably stimulated by 0.04–20.0 μM, with maximal response at 2–4 μM of ABA. A great stimulation of embryogenesis was also observed when low concentrations (0.01–1.0 mg/l) of 2-chloroethyl-phosphonic acid (ethephon) were added to the culture medium. Higher concentrations were strongly inhibitory.
GA3 (gibberellic acid) suppressed embryogenesis while two inhibitors of GA3 biosynthesis, CCC (2-chloroethyl trimethylammonium chloride) and Alar (succinic acid 2,2-methylhydrazide) significantly stimulated this process when added to the culture medium in the range of 0.01–10.0 mg/l.
