Abstract：Cremastra appendiculata is a perennial rare medicinal plant. Under natural conditions, it's hard to reproduce sexually, and the vegetative reproduction cannot effectively branch development to increase the number of pseudobulb due to apical inhibition of newborn pseudobulb. These factors lead to a very low breeding coefficient. Therefore, to explore internal mechanism of pseudobulbs growth in cluster, the pseudobulbs of C. appendiculata were treated by decapitation, auxin transport inhibitors N-1-naphthylphthalamic acid (NPA) and 2, 3, 5-triiodibenzoic acid (TIBA). In this way, endogenous plant hormone levels might be changed to promote the growth of lateral buds of C. appendiculata. After decapitation and application of auxin transport inhibitors (NPA and TIBA) treated the pseudobulb of C. appendiculata for 6 days, the results showed that auxin levels in the lateral buds were significantly reduced (P＜0.05), and cytokinin levels were obviously increased (P＜0.05). The results of qRT-PCR showed that cytokinin levels increased because of rapidly up-regulated key genes of cytokinin synthetase (isopentenyl transferase, IPT) after treatments. After the decapitation, NPA and TIBA treating for 40 d, the germination rate of the biennial pseudobulbs in pseudobulbs string were increased from 0% to 95%, 85% and 90%, respectively, and the triennial pseudobulbs were increased from 0% to 15%, 76% and 75%, respectively. For the treatments of decapitation, NPA and TIBA, the number of seedlings per plant could reach to 2.20, 3.13 and 3.05 times of the control after 90 d, respectively. The application of zeatin promoted the germination of lateral buds of C. appendiculata in a certain extent (biennial: 51%; triennial: 35%), but did not increase the rate of seedling emergence, which indicated that cytokinin promoted the germination of lateral buds, but could not promote to continued growth. The change of auxin levels was necessary for the continued growth of lateral buds. The results of this study indicated that auxin might regulate transcriptional level of IPT gene to control cytokinin level, and indirectly regulated lateral buds development and growth of C. appendiculata. This research increases the propagation coefficient of C. appendiculata, and provides a reference for the apical dominance theory of underground stems.
