in vivo

Descrição:

Portrait of the trebouxiophyte,Microthamnion strictissimum (Rabenhorst). The thalli of this filamentous alga are uniseriate (cells in a single row) and have a more distinguishable main axis than the similar M. kuetzingianum. Branches originate as lateral outgrowths from cells. Thalli are attached to the substrate by a basal cell with a small bulbous holdfast. Cells are cylindrical and of the same diameter. Terminal cells taper to a blunt tip. The single parietal plate-like chloroplast lacks a pyrenoid. Reproduction is by biflagellate zoospores which escape from the parent cell through a lateral rupture of the cell wall. One of the distinguishing features of trebouxiophytes is metacentric mitosis in which centrioles are located near the metaphase plate of the chromosomes rather than at the spindle poles. Other characteristics include formation of microtubules parallel to the dividing cell wall during cytokinesis (phycoplast)and a cruciate arrangement of flagellar roots with the basal bodies offset in a counterclockwise fashion on electron microscopy. Collected from a freshwater dredge pond near Idaho City, Idaho. June 2005.Phase contrast.