Achene mucilage formation process and extrusion from hydrated pericarp of Mirabilis himalaica

Myxospermy is an important feature of achenes of the alpine plant Mirabilis himalaica, and the achene mucilage increases the germination rate and early seedling growth during exposure to abiotic stresses, which has important functions that allow M. himalaica to survive the extreme climate of the Tibet Plateau. However, achene formation and mucilage extrusion are poorly understood. In the present study, comprehensive analyses were performed on mucilage production during achene development and mucilage release from hydrated achene pericarp in M. himalaica. First, fertilization initiated the development of M. himalaica achenes, during which their color, size and texture were altered dramatically. Second, using a metachromatic staining procedure, cytological events, the establishment of mucilage secretory cells in the inner epicarp layer were observed. The hydration of mature achenes led to the rapid bursting of mucilage secretory cells, which released a hydrophilic gel that surrounded the achenes. Finally, enzymatic digestion indicated that major components of the mucilage were pectins; glucose (41.40%), rhamnose (26.58%), galactose (18.33%), trehalose (12.12%), and mannose (1.57%) were found to be the components of achene by using ion-exchange chromatography.