PJB-2020-398
Establishment of somatic embryogenesis and plant regeneration from immature zygotic embryos of Catalpa bungei C. A. Mey
Hongwei Liang
Abstract
Catalpa bungei is a rare and high quality timber species and unique to China. Herein, immature zygotic embryos of C. bungei were used as explants to investigate the effects of different concentrations and combinations of plant growth regulators (PGRs) on the induction and proliferation of initial callus and embryogenic callus, the development of somatic embryos and plant regeneration. After 15 days, the highest frequency of initial calli (90 %) was obtained on 1/2 MS medium with 1.0 mg·L-1 2,4-D (2,4-Dichlorophenoxyacetic acid) and 0.1 mg·L-1 BA (6-benzyladenine) by culturing immature zygotic embryos. The initial calli converted into black and compact granular callus when they were proliferated in the 1/2 MS medium containing 1.0 mg·L-1 BA and 0.01 mg·L-1 NAA (1-Naphthaleneacetic acid), and light yellow embryogenic callus could be induced from black callus after secondary culture. The highest frequency (59.82 %) of somatic embryos induction was achieved on 1/2 MS medium supplemented with 0.2 mg·L-1 BA and 0.05 mg·L-1 NAA for a subculture lasting two and a half months. Gradually, these converted into globular-, heart-, torpedo- and cotyledonary-stage somatic embryos following subsequent subculture on the same medium. Cotyledonary-stage embryos, appearing with two leaves, were transferred into a hormone-free plant regeneration medium and which, in the end, developed into complete plantlets. The rooting rate reached to 92.31 % when the stems deriving from somatic seedlings were cultured at the 1/2MS medium supplemented 1.0 mg·L-1 IBA. Based on the histocytological analysis, the development of somatic embryos was similar to that of zygotic embryos. Starch accumulation occurred only in the process of transformation from callus to embryogenic callus, which closely related to the energy supply of somatic embryogenesis. This somatic embryogenesis system is of great significance to large-scale propagation, genetic improvement and germplasm conservation of C. bungei.
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