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

Emilio De Castro Miguel,Claudia Franca Barros,Maura Da Cunha,Saulo Pireda,Valdirene Moreira Gomes,Flavio Costa Miguens,Umberto Zottich

doi:10.1590/0102-33062016abb0420

Abstract

ABSTRACT Secretory structures are formed by many types of plants and are present on numerous different 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. The 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. The 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. The 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.

Highlights

Secretory structures and tissues occur on numerous different plant organs and are characterized by their distinct forms (Dickinson 2000)
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
The results show that the outer cell wall (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

Summary

Introduction

Secretory structures and tissues occur on numerous different plant organs and are characterized by their distinct forms (Dickinson 2000). The classification of secretory structures is based mainly on morphology or exudate composition This classification is questionable since secretory tissues, generally, experience transformations over a short period of time. In this manner, the structure, ultrastructure and biochemical composition of secretory cells can be modified quickly, making classification difficult because similar tissues may appear different because they were analyzed at different life cycle phases (Fahn 1979). Colleters are secretory structures consisting of a parenchymatous middle axis surrounded by a layer of secretory palisade-like epidermal cells.

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