title: Wound-healing motility in the green alga Ernodesmis: calcium ions and metabolic energy are required.
abstract: Wounding a giant cell of the marine alga Ernodesmis verticillata (Kützing) Børgesen (Chlorophyta) induces two concomitant motility phenomena: longitudinal contraction of the protoplasm away from the wound site, and centripetal contraction of the cut end around the central vacuole. Healing is complete within 30 min of wounding. Mechanical extrusion of the protoplasm into the medium with a teasing needle is followed by contraction of the protoplasm into numerous spherical protoplasts within 60 min. Utilizing a simple defined medium, it is shown that motility is almost completely inhibited by the absence of exogenous free Ca(2+), with 5.0 mM ethylene glycol bis-(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid present. This inhibition is reversible by rinsing the cells with Ca(2+)-containing medium. Similarly, extruded cytoplasm fails to exhibit motility in Ca(2+)-free medium. The threshold concentration of exogenous free Ca(2+) is approx. 10(-7) M for wound-induced contraction. The ions Ba(2+), Cd(2+) and Sr(2+) will substitute for Ca(2+), but the rate of contraction is one-half that with Ca(2+) present. Although darkness has no inhibitory effect, lower temperature (15°C), cyanide, or micromolar amounts of phosphorylation uncouplers reversibly slow protoplasmic motility in wounded cells and extruded cytoplasm. Carbonylcyanide m-chlorophenylhydrazone and carbonylcyanide p-trifluoromethoxyphenylhydrazone are especially potent inhibitors. These results indicate that cellular wound healing utilizes metabolic energy and requires exogenous free Ca(2+), implying that motility in Ernodesmis is a true contractile process. Since 1.0 mM La(3+) completely and reversibly prevents contraction, it is postulated that Ca(2+) fluxes may actually trigger motility.
authors.affiliation: Department of Botany, University of Texas, 78712, Austin, TX, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: La Claire