Chitosan effects on floral production, gene expression, and anatomical changes in the Dendrobium orchid

Six types of chitosan molecules, P-70, O-70, P-80, O-80, P-90, and O-90, were used to determine the effects on Dendrobium ‘Eiskul’ floral production. According to analysis of variance (ANOVA) followed by Duncan's multiple range test (DMRT), chitosan O-80 at all concentrations tested, 1, 10, 50, and 100 ppm could induce early flowering and increase the accumulative inflorescence number during the 68 weeks of the experimental period, when compared to the non-chitosan-treated controls. Therefore, chitosan O-80 was selected for further investigation of chitosan effects on the Dendrobium orchid. With the foliar anatomical study, chloroplasts in the young leaves of the plants treated with chitosan O-80 at 10 and 50 ppm were found to be significantly larger than those of the non-chitosan-treated ones. Enlarged chloroplasts were also detected in the old leaves treated with 50 ppm chitosan O-80. Differential display showed that the ycf2 gene (accession no. DQ268736) in chloroplasts was affected after 24 h of chitosan O-80 treatment. The reduction of ycf2 gene expression was detected in the young leaves after 12–48 h of chitosan O-80 application using the reverse transcription-polymerase chain reaction (RT-PCR) method. This indicated that chloroplast was one of the target sites for chitosan action in Dendrobium. Moreover, chitosan O-80 also significantly increased the number of vascular bundles containing silica cells in both old and young leaves, suggesting chitosan effects on silica metabolism and/or silica uptake in orchids.