Variation in extracellular coverings of green algae.

<p>(A) <i>Mesostigma viride</i> (CGA) and many members of the Prasinophyceae (Chlorophyta) have a very distinct extracellular matrix (ECM; arrow). DIC image. Scale bar = 5 µm. (B) Close examination of the <i>Mesostigma</i> ECM reveals regular repeating units (arrow). DIC image. Scale bar = 175 nm. (C) The repeating units of the ECM represent the large body scales aligned upon the outer surface. TEM image. Scale bar = 100 nm. (D) In addition to the large outer body scales, two other body scale layers (arrow) are part of the inner regions of the ECM. TEM image. Scale bar = 50 nm. (E) In <i>Chlorokybus</i> (CGA), the ECM consists of a gel-like wall that holds cells together in sarcinoid packets (arrow). DIC image. Scale bar = 25µm. (F) The <i>Chlorokybus</i> sheath labels with JIM13 (arrow), a mAb with specificity toward arabinogalactan protein epitopes of land plants. Fluorescence microscopy. Scale bar = 30 µm. (G) In desmids like <i>Penium</i> (CGA), the ECM consists of a cell wall and extracellular polymeric substance or EPS. DIC image. Scale bar = 8 µm. (H) <i>Penium</i>’s cell wall is highlighted by a pectin-rich outer wall layer (arrow) as highlighted by JIM5 labeling. Fluorescence image. Scale bar = 4.5 µm. (I) The EPS of <i>Penium</i> is extensive as it covers the surface of cells after they stop gliding (arrow). The EPS was labeled with an anti-EPS antibody. Fluorescence image. Scale bar = 17 µm. (J) Thalloid CGA like <i>Coleochaete</i> have cell walls. DIC image. Scale bar = 25 µm. (K) The cell wall of <i>Coleochaete</i> also contains epitopes of wall polysaccharides that are similar to those found in land plants. Here, JIM5, with specificity toward pectin, labels the junction zone of three cells (arrow). Scale bar = 75 nm.