The effects of applied electric fields onMicrasterias: II. the distributions of cytoplasmic and plasma membrane components

Abstract

The accompanying paper describes the effects of applied electric fields on the morphogenesis and patterns of wall deposition of growing cells of Micrasterias denticulata. This paper details the effects of electric fields (approximately 14 V cm-1) on the subcellular components of Micrasterias, including a description of the plasma membrane of growing semi-cells as visualized by freeze-fracturing. There are no gross cytoplasmic abnormalities or asymmetrics in the distributions of cytoplasmic organelles caused by the fields. In particular, neither the Large Vesicles nor Dark Vesicles are concentrated in the cathode-facing (CF) halves of lobes oriented perpendicular to the fields, where extra deposition of wall material has been shown to occur. In freeze-fracture replicas, there are about twice as many plasma membrane particles near the tips of growing lobes as there are in proximal regions of the lobes. Additionally, rosettes, consisting of 6 membrane particles, are seen predominantly in the distal parts of the lobes, and these rosettes are believed to be important in the synthesis of cell wall microfibrils. The applied fields cause a large asymmetry in the distributions of membrane particles, with larger numbers being found on the CF sides of lobes oriented perpendicular to the fields. We were not able to detect a specific effect on any class of particles. Taken all together, the data support the hypothesis that some of the factors responsible for growth localization in Micrasterias reside in the plasma membrane.

Electrochemical Control of Cell and Tissue Polarity

“…In these experiments, electric fields (EFs) of magnitudes similar to those measured in vivo have been shown to direct polarity in living cells and tissues. There is now a large body of evidence that most cells-ranging from bacteria, fungi, and amoebas to animal cells-are electrotactic and robustly orient polarity, migration, or division planes to applied EFs (Figure 2a) (Brower & Giddings 1980;Hinkle et al 1981;Korohoda et al 2000;Lin et al 2008;Minc & Chang 2010;Nishimura et al 1996;Patel & Poo 1982;Pu et al 2007;Pullar et al 2006;Rajnicek et al 1992Rajnicek et al , 1994Soong et al 1990;Zhang et al 2000;Zhao et al 1999Zhao et al , 2006. Similarly, EFs also affect cellular behaviors in multicellular tissues in the context of wound Dictyostelium amoeba migrates toward the cathode of an applied EF and to the anode when both PI3K and cGMP are inhibited (adapted from Sato et al 2009).…”