Cytokinin activation and redistribution of plasma-membrane ion channels in Funaria

Mj, Saunders

doi:10.1007/bf00391346

Cited by 61 publications

(22 citation statements)

References 28 publications

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“…Cytokinin stimulation of Ca2+ influx into moss protoplasts indicates that cytokinins regulate the channel. This is in agreement with whole-plant studies where cytokinin treatment increased the inward current 2-fold along the length of moss cells (41). Within minutes, current decreased in the nuclear zone and at the proximal end, while increasing at the distal end of target cells at the site of future bud formation.…”

Section: Resultssupporting

confidence: 91%

“…Within minutes, current decreased in the nuclear zone and at the proximal end, while increasing at the distal end of target cells at the site of future bud formation. These results led to the conclusion that cytokinin may activate plasma-membrane Ca2+ channels, which are subsequently redistributed to the distal ends of the target cells by a microfilament-dependent process (41).…”

Section: Resultsmentioning

confidence: 99%

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Cytokinin stimulates dihydropyridine-sensitive calcium uptake in moss protoplasts.

Schumaker

Gizinski

1993

Proc. Natl. Acad. Sci. U.S.A.

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Ca2 influx through dihydropyridine (DHP)-sensitive Ca2+ channels is thought to be an early event in cytokinin-induced bud formation in moss protonema because DHP antagonists inhibit bud formation in the presence of cytokinin and DHP agonists stimulate bud formation in the absence of cytokinin [Conrad, P. A. & Hepler, P. K. (1988) Plant Physiol. 86, 684-687]. In the present study, we established the presence of a DHP-sensitive Ca2+ transport system by measuring 4-Ca2+ influx into moss protoplasts. Ca2+ influx was stimulated by external KCI (up to 5 mM), indicating that transport is voltage-dependent. K+-induced Ca2+ influx was DHP-sensitive with >50% inhibition at 500 nM nifedipine. Ca2+ influx was stimulated by increasing concentrations of the DHP Ca2+ channel agonist Bay K8644 with half-maximal effects at 25 nM; this stimulation was seen only in the absence of K+, suggesting that the agonist works preferentially on polarized membranes. Ca2+ influx was also inhibited by phenylalkylamines (verapamil) and benzothiazepines (diltiazem). The phytohormone 6-benzylaminopurine consistently stimulated Ca2+ influx with a Km value of 1 nM, whereas adenine, indoleacetic acid, and gibberellic acid had no effect on Ca2+ transport. The cytokinins kinetin and trans-zeatin caused a greater stimulation of Ca2+ influx and induced more bud formation than did 6-benzylaminopurine. These results indicate that Ca2+ is taken up into moss protoplasts through voltage-dependent DHP-sensitive Ca2+ channels on the plasma membrane and that one of the cytokinin effects in the induction of bud formation is regulation of this plasma membrane Ca2+ channel. an adenine-type cytokinin (8), and subsequently, a small initial cell is formed (6). Asymmetric division of the initial cell leads to bud formation and a change from the twodimensional filamentous protonemata to the three-dimensional "leafy" gametophore.Cytokinin applied to caulonema cells causes profuse premature bud formation (6), and localized increases in Ca2+ precede this cytokinin-induced cell division (9-13). Wholeplant studies indicate that cytokinin-modulated Ca2+ entry takes place via dihydropyridine (DHP)-sensitive channels on the plasma membrane (13). DHPs are organic compounds that modulate Ca2+ movement through voltage-dependent Ca2+ channels in the plasma membrane of animal cells (14) by fluorescent tubes. Petri dishes containing appropriately supplemented basal medium overlaid with sterile cellophane were inoculated with spore suspensions. To prepare spore suspensions, mature sporophytes were harvested, and capsules were sterilized by soaking in 3% (wt/vol) sodium hypochlorite/0.1% Triton X-100 for 10 min followed by five rinses in sterile distilled water. Capsules were opened with sterile forceps, and the spores were dispersed in sterile distilled water; plates were inoculated with 1 ml of spore suspension (104 viable spores per ml).To isolate protoplasts, protonemata were incubated with 2% (wt/vol) driselase (laminarinase, xylanase and cellulase,

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Cytokinin stimulates dihydropyridine-sensitive calcium uptake in moss protoplasts.

Schumaker

Gizinski

1993

Proc. Natl. Acad. Sci. U.S.A.

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“…This alteration in the cell's polarity is manifested in a reorganization of the organelles into distinct zones in the bud site and the activation of tip growth perpendicular to the main axis of the filament (1). These gradients in Ca2l and organelle distribution are dissipated prior to the division cutting off the bud initial, as evidenced by the vibrating probe experiments of Saunders (18) and our ultrastructural data (1), and diffuse growth is established. Since Ca2+ channel openers stimulate initial formation and these DHPinduced initials rarely, if ever, produce complete buds, we further stipulate that cytokinin activation of Ca2 + channels is the hormone's immediate action and that subsequent cytokinin-induced mechanisms are operating to maintain bud formation.…”

Section: Discussionmentioning

confidence: 87%

The Effect of 1,4-Dihydropyridines on the Initiation and Development of Gametophore Buds in the Moss Funaria

Conrad¹,

Hepler²

1988

Plant Physiol.

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The plant hormone cytokinin stimulates target caulonemata of Funaria to form buds that develop into the leafy gametophyte. Previous reports have shown that increases in intracellular Ca2+ occur during hormoneactivated budding concomitant with an alteration in the polarity of the organelles in the bud site. In order to ascertain the involvement of voltagedependent Ca2+ channels in this phenomenon, we have employed dihydropyridines (DHP), compounds noted for their ability to alter Ca2l flux through potential-sensitive channels. Addition of the DHP agonists (+ )2(2-791 and CGP 28392 (100 micromolar) induces bud initials on every target cell including the tip cell. Application of the DHP antagonist (-)202-791, in the presence of cytokinin (1 micromolar benzyladenine), inhibits budding 96%. Similarly, nifedipine blocks cytokinin-induced budding 87% and its effect on budding can be inactivated with a pulse of ultraviolet light. These results are consistent with the idea that cytokinin induces the budding response by increasing Ca2+ entry through voltage-operated channels. We suggest that cytokinin activation of Ca2l channels is the first action of the hormone and that subsequent cytokinin-induced mechanisms are operating to maintain budding, since DHP-induced initials rarely develop into complete buds.The plant hormone cytokinin stimulates target caulonemata of Funaria to form buds leading to the leafy gametophyte. Previous reports (1,19)

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“…Lanthanum is a very strong inhibitor of Ca2+ channel activity in animal cells (Kusaka and Matsushita, 1987;Reed and Bygrave, 1974) and has been shown to block plasma membrane Ca2+ fluxes in plants (Rincon and Hanson, 1986;Siebers etal., 1990). Gadolinium is an inhibitor of stretch-activated Ca2+ channels in animals (Yang and Sachs, 1989) and inhibits cytokinin-evoked Ca2+ currents at the plasma membrane of Funaria (Saunders, 1986). Recently it has been shown to inhibit a voltage-gated Ca2+ channel at the tonoplast of higher plants (Johannes etal., 1991).…”

Section: Discussionmentioning

confidence: 99%

Membrane potential‐dependent calcium transport in right‐side‐out plasma membrane vesicles from Zea mays L. roots

et al. 1994

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SummaryRight-side-out plasma membrane vesicles isolated from Zea mays roots were used to study membrane potential (Av)-dependent Ca2+ transport. Membrane potentials were imposed on the vesicles using either K+ concentration gradients and valinomycin or SCNconcentration gradients, and the size of the imposed A v was measured with ['4C]tetraphenylphosphonium. Uptake of 45Ca2+ into the vesicles was stimulated by inside-negative Ay. The rate of transport increased to a maximum at a A y of about -80 mV and then declined at more negative Av. When extravesicular Ca2+ concentration was varied, uptake was maximal in the range 100-200 pM Ca2+. Neither dihydropyridine nor phenylalkylamine Ca2+ channel blockers had any effect on Ca2+ uptake but 30 pM ruthenium red was completely inhibitory with half maximal inhibition at 10-15 pM ruthenium red. Calcium transport was also inhibited by inorganic cations. Zn2+, Gd3+ and Mg2+ inhibited by a maximum of 30% while La3+, Nd3+ and Mn2+ inhibited by 70%. The inhibitory effects of La3+ and Gd3+ were additive. Lanthanum-insensitive Ca2+ tive Ca2+ transport was totally inhibited by 80 pM Gd3+ and showed maximum activity at a A~J of -60 mV, with less uptake at both higher and lower Av. Lanthanum and Gd3+ also inhibited Ca2+ uptake into protoplasts isolated from Zea roots and their individual and combined effects were similar in extent to those observed with plasma membrane vesicles. It is concluded that

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Cytokinin activation and redistribution of plasma-membrane ion channels in Funaria

Cited by 61 publications

References 28 publications

Cytokinin stimulates dihydropyridine-sensitive calcium uptake in moss protoplasts.

Cytokinin stimulates dihydropyridine-sensitive calcium uptake in moss protoplasts.

The Effect of 1,4-Dihydropyridines on the Initiation and Development of Gametophore Buds in the Moss Funaria

Membrane potential‐dependent calcium transport in right‐side‐out plasma membrane vesicles from Zea mays L. roots

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