Outer cell wall structure and the secretion mechanism of colleters of Bathysa nicholsonii K. Schum. (Rubiaceae)

Abstract

Secretory structures are formed by many types of plants and are present on numerous diff erent organs. Among the many types of known secretory structures, colleters are predominant on plants of the Rubiaceae. One remarkable characteristic of secretory tissues is the export of exudates; however, the precise mechanism involved in this process is still unclear. To better understand the mechanisms of exudate externalization it is necessary to understand the ultrastructure and dynamics of the outer cell wall of the secretory structures during the secretory process, and so we investigated these aspects of the colleters of Bathysa nicholsonii. Th e outer cell wall (OCW) exhibits multiple layers: a basal polysaccharide rich layer; a cuticular membrane, which is subdivided into arborescent and reticulated layers; and a thin cuticle proper. Th e structural organization of the OCW is changed during secretion passage, which is mainly related to the development of a secretion accumulation site on the polysaccharide rich layer. Secretion dynamics is driven by the organization and disruption of the secretion accumulation site. Th e results show that the OCW of the colleters of B. nicholsonii is a dynamic structure with an active role in secretion externalization via constant structural reorganization directly related to secretion passage.