Calcium Activates an Electrogenic Proton Pump in <i>Neurospora</i> Plasma Membrane

Lew, Roger R.

doi:10.1104/pp.91.1.213

Cited by 27 publications

(10 citation statements)

References 23 publications

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“…In its absence, the filamentous fungus is unable to response normally to either lower or higher Ca 2ϩ levels. The Ca 2ϩ in turn may regulate ion transport activity, possibly modulating H ϩ -ATPase activity (16). In the absence of normal ion transport activity, turgor is lower, causing the slower growth and poor vigor of the mid-1 mutant.…”

Section: Vol 7 2008mentioning

confidence: 99%

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Phenotype of a Mechanosensitive Channel Mutant, mid - 1 , in a Filamentous Fungus, Neurospora crassa

et al. 2008

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In the yeast Saccharomyces cerevisiae, the MID1 (mating-induced death) gene encodes a stretch-activated channel which is required for successful mating; the mutant phenotype is rescued by elevated extracellular calcium. Homologs of the MID1 gene are found in fungi that are morphologically complex compared to yeast, both Basidiomycetes and Ascomycetes. We explored the phenotype of a mid-1 knockout mutant in the filamentous ascomycete Neurospora crassa. The mutant exhibits lower growth vigor than the wild type (which is not rescued by replete calcium) and mates successfully. Thus, the role of the MID-1 protein differs from that of the homologous gene product in yeast. Hyphal cytology, growth on diverse carbon sources, turgor regulation, and circadian rhythms of the mid-1 mutant are all similar to those of the wild type. However, basal turgor is lower than wild type, as is the activity of the plasma membrane H ؉ -ATPase (measured by cyanide [CN ؊ ]-induced depolarization of the energy-dependent component of the membrane potential). In addition, the mutant is unable to grow at low extracellular Ca 2؉ levels or when cytoplasmic Ca 2؉ is elevated with the Ca 2؉ ionophore A23187. We conclude that the MID-1 protein plays a role in regulation of ion transport via Ca 2؉ homeostasis and signaling. In the absence of normal ion transport activity, the mutant exhibits poorer growth.

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Section: Vol 7 2008mentioning

confidence: 99%

“…Fresh-weight comparisons were performed by growing colonies on cellophane in larger (15 by 150 mm) petri dishes, measuring colony diameter, and harvesting the mycelium for fresh-weight measurements after 16,23, and 36 h of incubation. For growth in agar of various hardnesses, conidia were placed in the center of the petri dish and covered with dialysis tubing.…”

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Phenotype of a Mechanosensitive Channel Mutant, mid - 1 , in a Filamentous Fungus, Neurospora crassa

et al. 2008

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“…The increase in cytosolic calcium activates the potassium channel, causing calcium entry from the extracellular solution. Increased cytosolic calcium may also activate the plasma membrane proton pump (7) and vacuolar channels (6). It is not known how increased calcium levels cause chloroplast rotation, but it is unlikely that channel activation is a part of the mechanism leading to chloroplast rotation since TMB-8 inhibits channel activation but not chloroplast rotation.…”

Section: Red Light Stimulates Channel Activity In the Absence Of Extrmentioning

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Calcium Activation of Mougeotia Potassium Channels

Lew

Serlin²,

Schauf³

et al. 1990

Plant Physiol.

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Phytochrome mediates chloroplast movement in the alga Mougeotia, possibly via changes in cytosolic calcium. It is known to regulate a calcium-activated potassium channel in the algal plasma membrane. As part of a characterization of the potassium channel, we examined the properties of calcium activation. The alga Mougeotia is a classic system for the study of phytochrome since photoactivation of phytochrome regulates the positioning of its single large chloroplast, which is easily monitored (5). It is known that calcium plays a role in the movement of the chloroplast (1-3, 13). Phytochrome may cause cytosolic calcium to increase either by calcium release from internal calcium stores (2) or entry of external calcium into the cell (1), and this in turn results in chloroplast repositioning (13).We recently discovered a phytochrome-activated potassium channel in Mougeotia which is also activated by the calcium ionophore A23 187 (8). It is not known what function, if any, the potassium channel has in chloroplast positioning, though we hypothesize that it allows entry of extracellular calcium into the cell. In this paper, we study calcium-activation of the channel, and present evidence that it is activated by internal calcium stores.

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“…This process may rely upon properties of the expanding tip, for example, the high Ca 2+ gradient in the tip (Silverman-Gavrila & Lew, 2003). Ca 2+ activates the H + pump (Lew, 1989), which may function in osmotic adjustment by generating the driving force for influx of co-transported solutes. However, it remains likely that pressure-driven cytoplasm flow is an integral and normal component of fungal tip growth, and represents an example of what could be described as 'growth from behind', distinct from the vesicle-dense tip-region of the hypha.…”

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Mass flow and pressure-driven hyphal extension in Neurospora crassa

Lew

2005

Microbiology

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Mass flow of cytoplasm in Neurospora crassa trunk hyphae was directly confirmed by injecting oil droplets into the hyphae. The droplets move in a manner similar to cytoplasmic particles and vacuoles within the hyphae. The direction of mass flow is towards the growing hyphal tips at the colony edge. Based on flow velocities (about 5 μm s−1), hyphal radius and estimates of cytoplasm viscosity, the Reynolds number is about 10−4, indicating that mass flow is laminar. Therefore, the Poiseulle equation can be used to calculate the pressure gradient required for mass flow: 0·0005–0·1 bar cm−1 (depending on the values used for septal pore radius and cytoplasmic viscosity). These values are very small compared to the normal hydrostatic pressure of the hyphae (4–5 bar). Mass flow stops after respiratory inhibition with cyanide, or creation of an extracellular osmotic gradient. The flow is probably caused by internal osmotic gradients created by differential ion transport along the hyphae. Apical cytoplasm migrates at the same rate as tip extension, as do oil droplets injected near the tip. Thus, in addition to organelle positioning mediated by molecular motors, pressure-driven mass flow may be an integral part of hyphal extension.

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Calcium Activates an Electrogenic Proton Pump in Neurospora Plasma Membrane

Cited by 27 publications

References 23 publications

Phenotype of a Mechanosensitive Channel Mutant, mid - 1 , in a Filamentous Fungus, Neurospora crassa

Phenotype of a Mechanosensitive Channel Mutant, mid - 1 , in a Filamentous Fungus, Neurospora crassa

Calcium Activation of Mougeotia Potassium Channels

Mass flow and pressure-driven hyphal extension in Neurospora crassa

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