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Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima.

Furch AC, Zimmermann MR, Will T, Hafke JB, van Bel AJ - J. Exp. Bot. (2010)

Bottom Line: A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring approximately 10 min after burning.This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids.Mass flow resumed 30-40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities.

View Article: PubMed Central - PubMed

Affiliation: Plant Cell Biology Research Group, Institute of General Botany, Justus-Liebig-University, Senckenbergstrasse 17, D-35390 Giessen, Germany. Alexandra.C.Furch@bot1.bio.uni-giessen.de

ABSTRACT
The relationships between damage-induced electropotential waves (EPWs), sieve tube occlusion, and stop of mass flow were investigated in intact Cucurbita maxima plants. After burning leaf tips, EPWs propagating along the phloem of the main vein were recorded by extra- and intracellular microelectrodes. The respective EPW profiles (a steep hyperpolarization/depolarization peak followed by a prolonged hyperpolarization/depolarization) probably reflect merged action and variation potentials. A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring approximately 10 min after burning. Early stop of mass flow, well before completion of callose deposition, pointed to an occlusion mechanism preceding callose deposition. This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids. The early occlusion is probably due to proteins, as indicated by a dramatic drop in soluble sieve element proteins and a simultaneous coagulation of sieve element proteins shortly after the burning stimulus. Mass flow resumed 30-40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities. Stop of mass flow by Ca(2+)-dependent occlusion mechanisms is attributed to Ca(2+) influx during EPW passage; the reversibility of the occlusion is explained by removal of Ca(2+) ions.

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Stop of mass flow in sieve tubes of Cucurbita maxima induced by leaf tip burning (at a distance of 9 cm from the observation window) as recorded using a CLSM in intact plants (n=3). The direction of mass flow is from top (leaf tip) to bottom (leaf base). (A) Observation of carboxyfluorescein mass flow. CFDA was applied to a loading window (red circle), 3.5 cm upstream of the observation window (blue circle). (B) The membrane-impermeant carboxyfluorescein (CF) was transported by mass flow. (C) After burning of the leaf tip at t=0 s, carboxyfluorescein was photobleached at the observation window. Fluorescence did not emerge during the next 40 min probably due to sieve tube occlusion. The sieve tube at the other end of the SP is bending downwards and is therefore out of focus. Carboxyfluorescein transport through the SP was optically checked, but is not presented here. (D–F) Increasing fluorescence between 45 min and 90 min demonstrated recovery of carboxyfluorescein supply from the upstream loading window which inferred the lifting of the sieve tube blockage. (G–I) Repeated photobleaching of carboxyfluorescein at each observation revealed a second sieve tube occlusion after ∼90 min. The leaf tip is towards the top and the leaf base is towards the bottom in all photomicrographs. (J) Quantification of CF fluorescence (given on an arbitrary scale) in a sieve tube (yellow box) after burning the leaf tip. Each replicate was executed with different plants. SE, sieve element; CC, companion cell; SP, sieve plate.
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fig2: Stop of mass flow in sieve tubes of Cucurbita maxima induced by leaf tip burning (at a distance of 9 cm from the observation window) as recorded using a CLSM in intact plants (n=3). The direction of mass flow is from top (leaf tip) to bottom (leaf base). (A) Observation of carboxyfluorescein mass flow. CFDA was applied to a loading window (red circle), 3.5 cm upstream of the observation window (blue circle). (B) The membrane-impermeant carboxyfluorescein (CF) was transported by mass flow. (C) After burning of the leaf tip at t=0 s, carboxyfluorescein was photobleached at the observation window. Fluorescence did not emerge during the next 40 min probably due to sieve tube occlusion. The sieve tube at the other end of the SP is bending downwards and is therefore out of focus. Carboxyfluorescein transport through the SP was optically checked, but is not presented here. (D–F) Increasing fluorescence between 45 min and 90 min demonstrated recovery of carboxyfluorescein supply from the upstream loading window which inferred the lifting of the sieve tube blockage. (G–I) Repeated photobleaching of carboxyfluorescein at each observation revealed a second sieve tube occlusion after ∼90 min. The leaf tip is towards the top and the leaf base is towards the bottom in all photomicrographs. (J) Quantification of CF fluorescence (given on an arbitrary scale) in a sieve tube (yellow box) after burning the leaf tip. Each replicate was executed with different plants. SE, sieve element; CC, companion cell; SP, sieve plate.

Mentions: Stop of mass flow in sieve tubes of C. maxima induced by leaf tip burning (at a distance of 9 cm from the observation window) was observed using CFDA, as recorded using CLSM (Fig. 2).


Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima.

Furch AC, Zimmermann MR, Will T, Hafke JB, van Bel AJ - J. Exp. Bot. (2010)

Stop of mass flow in sieve tubes of Cucurbita maxima induced by leaf tip burning (at a distance of 9 cm from the observation window) as recorded using a CLSM in intact plants (n=3). The direction of mass flow is from top (leaf tip) to bottom (leaf base). (A) Observation of carboxyfluorescein mass flow. CFDA was applied to a loading window (red circle), 3.5 cm upstream of the observation window (blue circle). (B) The membrane-impermeant carboxyfluorescein (CF) was transported by mass flow. (C) After burning of the leaf tip at t=0 s, carboxyfluorescein was photobleached at the observation window. Fluorescence did not emerge during the next 40 min probably due to sieve tube occlusion. The sieve tube at the other end of the SP is bending downwards and is therefore out of focus. Carboxyfluorescein transport through the SP was optically checked, but is not presented here. (D–F) Increasing fluorescence between 45 min and 90 min demonstrated recovery of carboxyfluorescein supply from the upstream loading window which inferred the lifting of the sieve tube blockage. (G–I) Repeated photobleaching of carboxyfluorescein at each observation revealed a second sieve tube occlusion after ∼90 min. The leaf tip is towards the top and the leaf base is towards the bottom in all photomicrographs. (J) Quantification of CF fluorescence (given on an arbitrary scale) in a sieve tube (yellow box) after burning the leaf tip. Each replicate was executed with different plants. SE, sieve element; CC, companion cell; SP, sieve plate.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2921205&req=5

fig2: Stop of mass flow in sieve tubes of Cucurbita maxima induced by leaf tip burning (at a distance of 9 cm from the observation window) as recorded using a CLSM in intact plants (n=3). The direction of mass flow is from top (leaf tip) to bottom (leaf base). (A) Observation of carboxyfluorescein mass flow. CFDA was applied to a loading window (red circle), 3.5 cm upstream of the observation window (blue circle). (B) The membrane-impermeant carboxyfluorescein (CF) was transported by mass flow. (C) After burning of the leaf tip at t=0 s, carboxyfluorescein was photobleached at the observation window. Fluorescence did not emerge during the next 40 min probably due to sieve tube occlusion. The sieve tube at the other end of the SP is bending downwards and is therefore out of focus. Carboxyfluorescein transport through the SP was optically checked, but is not presented here. (D–F) Increasing fluorescence between 45 min and 90 min demonstrated recovery of carboxyfluorescein supply from the upstream loading window which inferred the lifting of the sieve tube blockage. (G–I) Repeated photobleaching of carboxyfluorescein at each observation revealed a second sieve tube occlusion after ∼90 min. The leaf tip is towards the top and the leaf base is towards the bottom in all photomicrographs. (J) Quantification of CF fluorescence (given on an arbitrary scale) in a sieve tube (yellow box) after burning the leaf tip. Each replicate was executed with different plants. SE, sieve element; CC, companion cell; SP, sieve plate.
Mentions: Stop of mass flow in sieve tubes of C. maxima induced by leaf tip burning (at a distance of 9 cm from the observation window) was observed using CFDA, as recorded using CLSM (Fig. 2).

Bottom Line: A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring approximately 10 min after burning.This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids.Mass flow resumed 30-40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities.

View Article: PubMed Central - PubMed

Affiliation: Plant Cell Biology Research Group, Institute of General Botany, Justus-Liebig-University, Senckenbergstrasse 17, D-35390 Giessen, Germany. Alexandra.C.Furch@bot1.bio.uni-giessen.de

ABSTRACT
The relationships between damage-induced electropotential waves (EPWs), sieve tube occlusion, and stop of mass flow were investigated in intact Cucurbita maxima plants. After burning leaf tips, EPWs propagating along the phloem of the main vein were recorded by extra- and intracellular microelectrodes. The respective EPW profiles (a steep hyperpolarization/depolarization peak followed by a prolonged hyperpolarization/depolarization) probably reflect merged action and variation potentials. A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring approximately 10 min after burning. Early stop of mass flow, well before completion of callose deposition, pointed to an occlusion mechanism preceding callose deposition. This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids. The early occlusion is probably due to proteins, as indicated by a dramatic drop in soluble sieve element proteins and a simultaneous coagulation of sieve element proteins shortly after the burning stimulus. Mass flow resumed 30-40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities. Stop of mass flow by Ca(2+)-dependent occlusion mechanisms is attributed to Ca(2+) influx during EPW passage; the reversibility of the occlusion is explained by removal of Ca(2+) ions.

Show MeSH
Related in: MedlinePlus