Submitted to: In Vitro Cellular and Developmental Biology - Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2006
Publication Date: 2/1/2007
Citation: Ahn, Y., Vang, L., Mckeon, T.A., Chen, G.Q. 2007. High-frequency plant regeneration through adventitious shoot formation in castor (ricinus communis l.). In Vitro Cellular and Developmental Biology - Plants. 43: 9-15. Interpretive Summary: Castor (Ricinus communis L.) is an important oil crop containing approximately 60% oil in its seeds. This highly versatile oil and its derivatives have a number of industrial uses, including high-quality lubricants, paints, plastics and coatings. However, despite of the high industrial demand, the United States no longer grows castor; its cultivation poses serious health concerns due to the presence of toxin ricin and hyper-allergenic 2S albumins in its seeds. Genetic engineering appears to be an effective approach to reduce the levels of these hazardous proteins. Therefore, a reliable plant regeneration protocol is needed for the transgenic manipulation of castor.
Technical Abstract: An efficient plant regeneration protocol was established for castor (Ricinus communis L.). Hypocotyl explants dissected from mature seeds produced adventitious shoots when treated with either thidiazuron (TDZ, 1 'M) or 6-benzylaminopurine (BA, 20 'M). TDZ induced adventitious shoots at a higher rate; the number of shoots per explant was more than 3 fold higher with TDZ (24.2 shoots), compared to the number of shoots induced by BA (6.8 shoots). Our results also showed that the pre-treatment of explants in the dark increased the average number of shoots. With TDZ, the explants pre-incubated in the dark for 7 d produced an average of 24.2 shoots, which was a 1.8 fold increase, compared with the number of shoots (13.3 shoots) regenerated from the controls, which were cultured without the pre-treatment. The elongation of hypocotyl explants in the dark might be the primary cause of the increase. Comparable rates of rooting were achieved on the both media supplemented with indole-3-butyric acid (IBA, 84.3%) or 1-naphthaleneacetic acid (NAA, 87.4%) at the concentration of 5 'M. However, IBA was more efficient in root growth and shoot development leading to the higher rate of acclimation (93.5 %) in the soil, compared to the rate with NAA (39.5%). Histological analysis revealed the presence of the two meristematic entities, meristemoid and shoot apical meristem, and their spatial and timely development to form adventitious shoot buds. To our knowledge, this is the first study reporting adventitious shoot formation from hypocotyl explants in castor, an important oil crop.