Tissue development of culm in Dendrocalamus sinicus from shoot to young culm stage

Dendrocalamus sinicus Chia et J. L. Sun, a rare bamboo species endemic to Yunnan Province in China, is one of the strongest woody bamboo species in the world. It occurs as two variants, i.e., straight-culmed variant (SC) and bent-culmed variant (BC). To reveal the anatomical basis of SC and BC, we collected data on culm height and morphological characteristics of shoots and young culms (emerged from ground for 0-49 d) from six clumps of D. sinicus . In addition, shoot and young culm development (0-45 d) were observed using comparative anatomy based on paraffin sectioning. Results showed that culm-height growth exhibited a "slow-fast" pattern, and the BC morphological character clearly appeared at 21-35 d, which was distinct from that of SC. The development of vascular bundles occurred earlier in BC (5-30 d) than in SC. Within BC, compared with the outer vascular bundles, the inner vascular bundles possessed smaller diameters and more fibrocytes in the fibrous sheath. Parenchyma cell differentiation occurred earlier in BC than in SC. Nuclei dyed with Safranine and Fast Green appeared in the parenchyma cells, which became regularly arranged from 20 d in BC. The parenchyma cells in the inner culm of BC were slightly smaller than those in the outer culm, whereas there was a greater number of parenchyma cells with dyed nuclei in the inner culm than in the outer culm. These results showed that the bent culm shape in BC can be identified by culm morphology during 21-35 d. The development of vascular bundles and differentiation of parenchyma cells occurred earlier in BC than in SC. Furthermore, compared with the outer culm in BC at the corresponding period, cell divisions in the inner culm were more vigorous and the degree of vascular bundle lignification was also higher.