Effects of nifedipine, verapamil, and diltiazem on tip growth inFunaria hygrometrica

Abstract

Protonemata ofFunaria hygrometrica Sibth. were treated with nifedipine, verapamil, or diltiazem. Responses to each of the drugs were, on the one hand, reduction of growth rate and tip cell length and, on the other hand, formation of apical swellings in caulonema tip cells and of anomalously oriented separation walls between main filaments and young side branches. The first effect is regarded as a more general expression of inhibition while the second complex of effects is attributed to perturbations in directed vesicle transport. Replacement of drug-containing media by normal Knop agar demonstrated the reversibility of inhibitor action: growth parameters were comparable to those of control protonemata within a few hours. A fast reaction, the formation of subapical vacoules, occurred within minutes of drug application and was only observed with verapamil and diltiazem. In connection with this process, rapid migrations of chloroplasts took place, but examination of the microtubule cytoskeleton in such cells by indirect immunofluorescence with a monoclonal antibody against tubulin showed an intact microtubule network. callose deposits in tip cells treated with verapamil. They were polarly distributed and started to appear in cell apices about 2h after the beginning of verapamil application. Two mechanisms of action for the tested inhibitors are discussed: (i) perturbations of membrane permeability by interference with one or more of the cell's Ca(2+)-transport systems, and (ii) a more indirect mechanism affecting vesicle transport via the microfilament system.

Calcium Antagonists Inhibit Sustained Gibberellic Acid-Induced Growth of Avena (Oat) Stem Segments

“…1, 2A, 3, 6, 7). Although these millimolar concentrations are generally at least an order of magnitude greater than the levels found to be effective with animal cells (Underwood and Riches, 1992), lower plants (Conrad and Hepler, 1988;Kataoka, 1990;Wacker and Schnepf, 1990), plant cell cultures (Roberts and Haigler, 1990), or protoplasts (Graziana et al, 1988), they are comparable to the concentrations that inhibit the growth of pea stem sections (Cunninghame and Hall, 1986;Brummell and Machlachlan, 1989) and maize roots (Perdue et al, 1988). None of the antagonists, except lanthanum at a very high concentration of 100 mM, was found to inhibit the relatively small amount of growth in nonhormone-treated segments.…”

A cytochalasin-sensitive actin filament meshwork is a prerequisite for local wound wall deposition inNitella internodal cells

“…Delicate actin filament meshworks responsible for vesicle transport are characteristic of sites of intense exocytosis in plant cells as, for instance, the tips of elongating hyphae, rhizoids, and zygotes (e.g., Wacker and Schnepf 1990, Sievers et al 1991, Henry et al 1996) and cytochalasin markedly reduces or inhibits tip growth (e.g., Herth et al 1972). In contrast to these studies, the presence of an actin meshwork in pollen tube tips is under dispute in view of recent findings (Doris andSteer 1996, Miller et al 1996).…”

The cytoskeleton in plant and fungal cell tip growth

“…The presence of MTs in the apex has been reported in hyphae (Åström et al ., 1994; Bourett et al ., 1998; Torralba et al ., 1998a), root hairs (light microscopy, Lloyd, 1983; Lloyd & Wells, 1985; Traas et al ., 1985: electron microscopy, Emons, 1989) and moss protonemata (Doonan et al ., 1985, 1988; Schwuchow et al ., 1990; Wacker & Schnepf, 1990) (Fig. 11).…”

“…In the cytoplasm, MTs are mostly associated with particular structures such as the nucleus. Moss protonemata are an exception to this pattern; in these cells MTs are abundant both in the central cytoplasm as well as in cortical locations (Schwuchow et al ., 1990; Wacker & Schnepf, 1990; Goode et al ., 1993).…”

“…MT helices of varying pitch and predominant longitudinal orientation cross each other and seemingly form a meshwork (Fig. 10a; hyphae, Roberson & Vargas, 1994: root hairs, Emons & Wolters‐Arts, 1983; Traas et al ., 1985; Emons, 1989: moss protonemata, Doonan et al ., 1985, 1988; Schwuchow et al ., 1990; Wacker & Schnepf, 1990: algal rhizoids (subapical zone), Braun & Sievers, 1994).…”