Postdoctoral Research Fellow Skidmore College Saratoga Springs, New York
Body of Abstract: Penium margaritaceum is a unicellular streptophyte green alga that contains a homogalacturonan (HG)-rich cell wall. Wall expansion occurs at a narrow 1-2 µm ring that encircles the cell center. Newly deposited wall components assemble at the ring and displace pre-existing cell wall toward the two cell poles. The expansion ring is underlain by cortical bands of microtubules and actin filaments.
When the microtubule band at the expansion ring is disrupted by incubation in 1 µM of the microtubule-targeting agent, APM, secretion of new CW material occurs over a broad rather than narrow ring at the center of the cell. As a result, the cell swells/bends at the cell center and the arrangement of HG in the wall is notably altered. When incubated in 4U of the Aspergillus-derived pectate lyase (PL), the isthmus and two satellite regions of the HG architecture are noticeably degraded. After several days of incubation cell size is notably reduced. New HG secretion that normally occurs in a thin band in the expansion ring, is dispersed irregularly at the cell surface.
When Penium is incubated in both PL and APM, the plastids displace into the polar regions leaving a cytoplasm-rich cell center. This zone is highlighted by layers of ER, clusters of Golgi bodies, elongate vacuoles and a distinct cell wall ingrowth that incompletely “bisects” the cell. The location of cell expansion changes to polar satellite zone(s), resulting in swellings at one or both poles. These changes resemble subcellular reorganization that occurs during programmed cell modulations caused by environmental stress. One possible explanation is that PL-induced HG-fragments (e.g. oligogalacturonides) are recognized by the cell that then induces the activation of new expansion centers at the polar zones. This reorganization would provide a means for rapid cell expansion/division at the cell periphery.