TUBULAR STRUCTURES IN THE PLASTIDS OF <i>ECHINOMASTUS INTERTEXTUS</i> BRIT. &amp; ROSE (CACTACEAE)

Abstract

SUMMARY Tubules in hexagonal packing arrays were found in the stroma of proplastids as well as in mature chloroplasts of Echinomastus intertextus Brit. &amp; Rose. The morphology of the proplastids in the shoot meristem was variable. These organelles were found as ovoids, cup shapes and long meandering cylinders. Within the plastids, the tubules were oriented at right angles to the plastidial envelope. Usually, the tubules were contained between the inner membrane of the plastid envelope and a stromal lamella. Sometimes, arrays of tubules alternated with sheets of stromal thylakoids forming several layers of tubules which occupied a large volume of the proplastids. Phytoferritin and lipid droplets were common inclusions of proplastids. Grana were extensive and composed a large portion of the volume of mature chloroplasts. In chloroplasts the tubules were restricted to the periphery, often between the plastid envelope and a sheet of stromal lamella. Frequently, round bulges with tubular components were found at the periphery of the chloroplasts. Starch and lipids were found in chloroplasts.