Structural Analysis of Water-Storage Tissue in Leaves of Sansevieria (Agavaceae)

Abstract

Leaves in 49 species of Sansevieria contain water-storage (WS) tissue in their central mesophyll region consisting of two cell types: a three-dimensional network of living cells and interspersed dead WS cells. In 28 species, WS cells have secondary cell wall bands. In this study, 15 species were examined to determine variations in density, width, and amount and type of branching of wall bands. In cross section, wall bands in WS cells surrounding vascular and fiber bundles are oriented concentrically around the bundles. In thick flat leaves, wall bands are oriented mostly parallel to the surface of the leaf blade. Wall bands are aligned at corners but not across faces of adjacent WS cells and provide structural support during desiccation, either reducing the collapse of WS cells or restricting the direction in which the WS cells shrink. In cell wall replicas, wall bands appear as massive aggregations of microfibrils. Secondary wall material, as a very thin continuous layer between wall bands, is also deposited. Three species without WS cell wall bands were also examined. WS cells in these species also deposit a secondary wall but without localized thickenings.