Ultrastructure of Verdigellas peltata (Palmellaceae, Chlorophyta), a deep-water, palmelloid alga with ferritin and trilaminar sheaths

Abstract

The palmelloid green alga Verdigellas peltata D.L. Ballantine et J.N. Norris was collected from depths of 70 to 110 meters in the Bahamas and studied by light microscopy and transmission electron microscopy. Most of the cell was filled by a cup-shaped chloroplast that contained scattered starch grains but no pyrenoid. Some chloroplasts had clusters of granular inclusions that were identified as ferritin based on their particle size, native electron density, and iron content; the last was detected by energy-dispersive X-ray microanalysis. A nucleus, dictyosome, mitochondrion, and large vacuole occupied a pocket mostly surrounded by the chloroplast. Centrioles and basal bodies were absent. The nuclear envelope was continuous with the endoplasmic reticulum, and some cells had one or two spherical, glycoprotein inclusions, c. 1–2 μm in diameter, within the confluent lumen. The Golgi vesicles contributed fibrillar material to the vacuole, but most of the vacuolar contents consisted of appressed sheets of trilaminar material. Trilaminar sheets were also present between the plasmalemma and cell wall. Preparation of specimens without osmium postfixation resulted in the loss of membrane contrast, but the trilaminar sheets were unaffected. The cell walls apparently thicken by the addition of trilaminar sheets to their inner surface. The part of the thin cell wall overlying the cytoplasmic pocket was often perforated by pores. The palmelloid colonies contained an abundance of acetolysis-resistant material.