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Regulation of callose synthase activity in situ in alamethicin-permeabilized Arabidopsis and tobacco suspension cells.

Aidemark M, Andersson CJ, Rasmusson AG, Widell S - BMC Plant Biol. (2009)

Bottom Line: In the presence of alamethicin, Ca2+ addition was required for callose synthase activity, and the activity was further stimulated by Mg2+ Cells pretreated with oryzalin to destabilize the microtubules prior to alamethicin permeabilization showed significantly lower callose synthase activity as compared to non-treated cells.This pattern was unaffected by oryzalin pretreatment, showing a quantitative rather than a qualitative effect of polymerized tubulin on callose synthase activity.The results also suggest that alamethicin permeabilization induces a defense response mimicking the natural physical separation of cells (for example when intercellulars are formed), during which plasmodesmata are transiently left open.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cell and Organism Biology, Lund University, Lund, Sweden. mari.Aidemark@cob.lu.se

ABSTRACT

Background: The cell wall component callose is mainly synthesized at certain developmental stages and after wounding or pathogen attack. Callose synthases are membrane-bound enzymes that have been relatively well characterized in vitro using isolated membrane fractions or purified enzyme. However, little is known about their functional properties in situ, under conditions when the cell wall is intact. To allow in situ investigations of the regulation of callose synthesis, cell suspensions of Arabidopsis thaliana (Col-0), and tobacco (BY-2), were permeabilized with the channel-forming peptide alamethicin.

Results: Nucleic acid-binding dyes and marker enzymes demonstrated alamethicin permeabilization of plasma membrane, mitochondria and plastids, also allowing callose synthase measurements. In the presence of alamethicin, Ca2+ addition was required for callose synthase activity, and the activity was further stimulated by Mg2+ Cells pretreated with oryzalin to destabilize the microtubules prior to alamethicin permeabilization showed significantly lower callose synthase activity as compared to non-treated cells. As judged by aniline blue staining, the callose formed was deposited both at the cell walls joining adjacent cells and at discrete punctate locations earlier described as half plasmodesmata on the outer walls. This pattern was unaffected by oryzalin pretreatment, showing a quantitative rather than a qualitative effect of polymerized tubulin on callose synthase activity. No callose was deposited unless alamethicin, Ca2+ and UDP-glucose were present. Tubulin and callose synthase were furthermore part of the same plasma membrane protein complex, as judged by two-dimensional blue native SDS-PAGE.

Conclusion: Alamethicin permeabilization allowed determination of callose synthase regulation and tubulin interaction in the natural crowded cellular environment and under conditions where contacts between the cell wall, the plasma membrane and cytoskeletal macromolecules remained. The results also suggest that alamethicin permeabilization induces a defense response mimicking the natural physical separation of cells (for example when intercellulars are formed), during which plasmodesmata are transiently left open.

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Alamethicin permeabilization of Col-0 cells. (A) Oxygen consumption in Col-0 and BY-2 cells after addition of 20 μg ml-1 alamethicin. Points represent the rate of oxygen consumption relative to the control rate prior to alamethicin addition. (B-F) Visualization of alamethicin permeabilization of Col-0 cells by Yo-Pro staining. Bright field microscopy images of untreated (B) and alamethicin-permeabilized (C) cells as well as fluorescent images showing Yo-Pro staining of untreated (D) and alamethicin-permeabilized (E-F) cells. (F) shows a close up of (E).
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Figure 1: Alamethicin permeabilization of Col-0 cells. (A) Oxygen consumption in Col-0 and BY-2 cells after addition of 20 μg ml-1 alamethicin. Points represent the rate of oxygen consumption relative to the control rate prior to alamethicin addition. (B-F) Visualization of alamethicin permeabilization of Col-0 cells by Yo-Pro staining. Bright field microscopy images of untreated (B) and alamethicin-permeabilized (C) cells as well as fluorescent images showing Yo-Pro staining of untreated (D) and alamethicin-permeabilized (E-F) cells. (F) shows a close up of (E).

Mentions: It was previously shown that alamethicin could be used to permeabilize BY-2 cells [47]. To enable the use of A. thaliana cells in addition to BY-2 and to investigate the regulation of callose synthesis, we wished to establish if Col-0 suspension cultured cells were similarly permeabilized by alamethicin. A decrease in respiration (oxygen consumption) by metabolite depletion was found also with Col-0, and the time required to abolish respiration was around 10 min for both BY-2 and Col-0 cells (Fig. 1A). Treatment of Col-0 cells with alamethicin for 10 min also allowed the membrane-impermeable nucleic acid stain Yo-Pro to mark nuclei and organelles with uniform staining of the whole cell population (Fig. 1B–F). A virtually identical staining was produced by the membrane-impermeable nucleic acid stain propidium iodide, as observed by perfectly overlapping double staining (results not shown).


Regulation of callose synthase activity in situ in alamethicin-permeabilized Arabidopsis and tobacco suspension cells.

Aidemark M, Andersson CJ, Rasmusson AG, Widell S - BMC Plant Biol. (2009)

Alamethicin permeabilization of Col-0 cells. (A) Oxygen consumption in Col-0 and BY-2 cells after addition of 20 μg ml-1 alamethicin. Points represent the rate of oxygen consumption relative to the control rate prior to alamethicin addition. (B-F) Visualization of alamethicin permeabilization of Col-0 cells by Yo-Pro staining. Bright field microscopy images of untreated (B) and alamethicin-permeabilized (C) cells as well as fluorescent images showing Yo-Pro staining of untreated (D) and alamethicin-permeabilized (E-F) cells. (F) shows a close up of (E).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2667179&req=5

Figure 1: Alamethicin permeabilization of Col-0 cells. (A) Oxygen consumption in Col-0 and BY-2 cells after addition of 20 μg ml-1 alamethicin. Points represent the rate of oxygen consumption relative to the control rate prior to alamethicin addition. (B-F) Visualization of alamethicin permeabilization of Col-0 cells by Yo-Pro staining. Bright field microscopy images of untreated (B) and alamethicin-permeabilized (C) cells as well as fluorescent images showing Yo-Pro staining of untreated (D) and alamethicin-permeabilized (E-F) cells. (F) shows a close up of (E).
Mentions: It was previously shown that alamethicin could be used to permeabilize BY-2 cells [47]. To enable the use of A. thaliana cells in addition to BY-2 and to investigate the regulation of callose synthesis, we wished to establish if Col-0 suspension cultured cells were similarly permeabilized by alamethicin. A decrease in respiration (oxygen consumption) by metabolite depletion was found also with Col-0, and the time required to abolish respiration was around 10 min for both BY-2 and Col-0 cells (Fig. 1A). Treatment of Col-0 cells with alamethicin for 10 min also allowed the membrane-impermeable nucleic acid stain Yo-Pro to mark nuclei and organelles with uniform staining of the whole cell population (Fig. 1B–F). A virtually identical staining was produced by the membrane-impermeable nucleic acid stain propidium iodide, as observed by perfectly overlapping double staining (results not shown).

Bottom Line: In the presence of alamethicin, Ca2+ addition was required for callose synthase activity, and the activity was further stimulated by Mg2+ Cells pretreated with oryzalin to destabilize the microtubules prior to alamethicin permeabilization showed significantly lower callose synthase activity as compared to non-treated cells.This pattern was unaffected by oryzalin pretreatment, showing a quantitative rather than a qualitative effect of polymerized tubulin on callose synthase activity.The results also suggest that alamethicin permeabilization induces a defense response mimicking the natural physical separation of cells (for example when intercellulars are formed), during which plasmodesmata are transiently left open.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cell and Organism Biology, Lund University, Lund, Sweden. mari.Aidemark@cob.lu.se

ABSTRACT

Background: The cell wall component callose is mainly synthesized at certain developmental stages and after wounding or pathogen attack. Callose synthases are membrane-bound enzymes that have been relatively well characterized in vitro using isolated membrane fractions or purified enzyme. However, little is known about their functional properties in situ, under conditions when the cell wall is intact. To allow in situ investigations of the regulation of callose synthesis, cell suspensions of Arabidopsis thaliana (Col-0), and tobacco (BY-2), were permeabilized with the channel-forming peptide alamethicin.

Results: Nucleic acid-binding dyes and marker enzymes demonstrated alamethicin permeabilization of plasma membrane, mitochondria and plastids, also allowing callose synthase measurements. In the presence of alamethicin, Ca2+ addition was required for callose synthase activity, and the activity was further stimulated by Mg2+ Cells pretreated with oryzalin to destabilize the microtubules prior to alamethicin permeabilization showed significantly lower callose synthase activity as compared to non-treated cells. As judged by aniline blue staining, the callose formed was deposited both at the cell walls joining adjacent cells and at discrete punctate locations earlier described as half plasmodesmata on the outer walls. This pattern was unaffected by oryzalin pretreatment, showing a quantitative rather than a qualitative effect of polymerized tubulin on callose synthase activity. No callose was deposited unless alamethicin, Ca2+ and UDP-glucose were present. Tubulin and callose synthase were furthermore part of the same plasma membrane protein complex, as judged by two-dimensional blue native SDS-PAGE.

Conclusion: Alamethicin permeabilization allowed determination of callose synthase regulation and tubulin interaction in the natural crowded cellular environment and under conditions where contacts between the cell wall, the plasma membrane and cytoskeletal macromolecules remained. The results also suggest that alamethicin permeabilization induces a defense response mimicking the natural physical separation of cells (for example when intercellulars are formed), during which plasmodesmata are transiently left open.

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