Cytochemical and Morphological Evidence for the Involvement of the Plasma Membrane and Plastids in Mucilage Secretion in Aloe arborescens

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Abstract
Most of the volume of Aloe arborescens leaves (volumetric density = 0.68±0.08) is occupied by a mucilage tissue. The mucilages of Aloe species are glucomannans of great medical and pharmaceutical importance. An electron microscopical and histochemical study was carried out, following the development of the tissue and secretion processes. In contrast to other reports on polysaccharide secretion in plants, no observable activity was found in the Golgi apparatus. In the young stages of leaf development, positive histochemical staining for polysaccharides and structural changes were found mainly in the plastids. In the mature leaves the mucilage cells remain alive and intact and secretory activity appears to be centered in the plasma membrane.