The chloroplasts and unlignified parenchyma of two tropical pioneer forest tree species (urticaceae)

Abstract

The influence of light on chloroplast density and formation of unlignified parenchyma was determined in stems of Myriocarpa longipes and Urera glabriuscula, two woody pioneer species from the Mexican tropics, growing either under the shade or under sunny conditions. The goals of the present study were: (1) to quantify and characterize chloroplasts in this tissue and (2) to determine the influence of two light conditions in chloroplast number and unlignified parenchyma formation. Sunshine increases the presence of chloroplasts and the area of unlignified parenchyma in M. longipes stems, whereas in U. glabriuscula it occurs the opposite. Differences in the presence of some features in the pioneer species studied, such as the abundance of mucilaginous ducts (M. longipes), type of cystolith (U. glabriuscula), and the area occupied by the pith in stem cross sections, occur as a response to canopy gaps in this tropical forest.