| Medicinal dendrobium is a kind of rare precious Chinese herb with long history, which is active against many diseases, especially cataract, throat inflammation, peripheral vascular obstruction and chronic superficial gastritis. However, it has fallen into serious danger of extinction because of its excessive collection for growing medicinal demands. Technology of clonal propagation in vitro is one of the most effective means to improve it. In this paper, establishment of the clone system of Dendrobium densiflorum and Dendrobium exile in vitro and effect of rare earth elements (REE) on roots regeneration of D. densiflorum have been studied.Plant hormone is a kind of physiological activity substance adjusting plant growth effectively. Effects of plant hormones (IBA, NAA, IAA, BA and KT) on PLBs inducement, stems and roots regeneration of D. densiflorum and D. exile were studied. PLBs could be induced from stem-segment both in light and dark at a temperature of 25±1℃, 16 h photoperiods of 2000 1x intensity of illumination. In light, the optimal hormone combinations of inducing PLBs from stem-segment of D. densiflorum is 1.0 mg/L IBA+2.0 mg/L BA, the maximum inducement ratio is 80.4%, and for D. exile, is 1.0 mg/L IBA+5.0 mg/L BA, reached 85.7%. In dark, the most optimal combinations are 1.0 mg/L IBA+2.0 mg/L BA (D. densiflorum) ,2.0 mg/L IBA+5.0 mg/L BA (D. exile), and the inducement ratios are 76.9% and 79.4%, respectively.Two modes, direct stems regeneration which means the stems regenerated from the stem-segment directly and indirect stems regeneration which means the stems regenerated via PLBs induced from the stem-segment in light, were observed in this research. In the former mode, under the combinations, 0.5 mg/L IBA, 2.0 mg/L BA and 1.0 mg/L NAA+2.0 mg/L BA, the corresponding maximum induction ratio is 70.8%, 80.0%, 84.3%. In the latter one, the most optimal combinations are 0.5 mg/L IBA+ (1.0~2.0) mg/L BA, 2.0mg/L IBA, 2.0 mg/L BA;0.5 mg/L IBA+2 mg/L KT, 1.0 mg/L IBA+1.0mg/L KT, and all of the maximum regeneration ratio is 100.0%.Effect of MS or 1/2MS medium supplemented with potato water on roots regeneration is obvious. The optimal basic medium type of inducing regenerated roots from D. densiflorum and D. exile is MS medium. The optimal hormone is IBA, which is more effective than NAA, IAA and the maximum regeneration ratio is 66.4% (D. densiflorum) and 66.0% (D. exile). Adding additional 0.5% activated charcoal (AC) and plant hormone in MS medium, the root regeneration ratio is much higher than that on AC used independently.Rare earth elements (REE) have important biological effect even though they are not the essential elements for the organism. The effect of La3+, Ce3+ and Nd3+ on inducing roots regeneration of the tube plants from D. densiflorum was studied. The result showed the optimal REE of inducing root-regeneration is Nd3+, and the regeneration ratio of roots is 100.0% and the mean number of regenerated roots from per seedling is 23.9 under Nd3+of 4.0 mg/L The effect of combinations of REE and plant hormone on inducing regenated roots is worse than that of REE used independently. |
