Cell wall modifications regulate flower development in dendrobium crumenatum

Abstract

The involvement of cell wall modifications, in particular, changes in cell wall components and activities of cell wall-based enzymes, in regulating flower development in a sympodial orchid, Dendrobium crumenatum, were investigated. Plants were subjected to cold treatments to release floral buds from dormancy, and various parameters were investigated from young floral bud stage till flower senescence. Anatomical studies demonstrated structural disorganization in sepals and petals in developing floral buds. The packing and arrangement of the cells were observed to become increasingly disorganized during flower opening and flower senescence. Subsequent analysis of cell wall composition showed that the cell walls of sepals and petals were modified extensively during floral bud development, flower opening and flower senescence, as observed by the changes in the amounts of cellulose, hemicelluloses and total pectins. Pectin solubilisation was also observed to commence during early floral bud development. Of the tested cell wall-based enzymes, N2-glucosidase demonstrated the highest specific activity, followed by pectin methylesterase and N2-galactosidase. Significant changes in the activities of the enzymes were also observed during floral bud and flower development. The results indicated that cell wall modifications began early in young floral buds, and regulated flower development. A model for cell wall modifications, which involved loosening of the cellulose/hemicellulose and pectin networks, in D. crumenatum was proposed. Furthermore, comparisons of the cell wall modifications in D. crumenatum floral buds/ flowers to those in other species suggested the presence of species-specific changes. Throughout the development of D. crumenatum floral buds up till flower opening, senescence hallmarks, such as the decrease in membrane stability, were observed. Attempts were made to generate floral buds that exhibited abnormal patterns of flowering for future studies. This would allow comparisons of cell wall modifications (and other physiological factors) between the normal and abnormal floral buds. Exogenous application of the plant growth regulator, benzyladenine, was found to suppress flower opening and caused floral buds to abort.