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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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Related in: MedlinePlus

Graphic overlay of EPWs measured by independent methods and their impact on sieve tube occlusion and mass flow after burning the leaf tip. The black solid line shows extracellular electrical potentials, the grey solid line the membrane potentials of SEs, the black dashed line sieve tube occlusion as indicated by carboxyfluorescein fluorescence, the grey vertical line the time point of protein plug formation at the SP, the black vertical line the time point of sieve tube occlusion indicated by aphid behaviour change, and the grey dashed line callose deposition and degradation.
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fig7: Graphic overlay of EPWs measured by independent methods and their impact on sieve tube occlusion and mass flow after burning the leaf tip. The black solid line shows extracellular electrical potentials, the grey solid line the membrane potentials of SEs, the black dashed line sieve tube occlusion as indicated by carboxyfluorescein fluorescence, the grey vertical line the time point of protein plug formation at the SP, the black vertical line the time point of sieve tube occlusion indicated by aphid behaviour change, and the grey dashed line callose deposition and degradation.

Mentions: Like carboxyfluorescein (Fig. 2), aphids provide compelling physiological evidence in favour of a stop of mass flow due to occlusion in response to remote damage. However, the time delay between stop of mass flow and callose deposition is difficult to interpret. Aphids feeding on the main vein showed an abrupt change in behaviour (Fig. 4) well after the time point when mass flow had stopped (Fig. 7). It may take some time before sieve tube occlusion is perceived by aphids as a loss of pressure (Will et al., 2008). If the aphid response indeed presents a delayed reaction to sieve tube occlusion, aphid behaviour could reflect stoppage of mass flow long before callose deposition is being completed (Fig. 7). Similarly, carboxyfluorescein movement stops (Fig. 2) well before callose deposition is completed (Fig. 3). That stoppage of mass flow does not need maximal deposition of callose could explain this time-incongruence, but the following alternative may be attractive.


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)

Graphic overlay of EPWs measured by independent methods and their impact on sieve tube occlusion and mass flow after burning the leaf tip. The black solid line shows extracellular electrical potentials, the grey solid line the membrane potentials of SEs, the black dashed line sieve tube occlusion as indicated by carboxyfluorescein fluorescence, the grey vertical line the time point of protein plug formation at the SP, the black vertical line the time point of sieve tube occlusion indicated by aphid behaviour change, and the grey dashed line callose deposition and degradation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig7: Graphic overlay of EPWs measured by independent methods and their impact on sieve tube occlusion and mass flow after burning the leaf tip. The black solid line shows extracellular electrical potentials, the grey solid line the membrane potentials of SEs, the black dashed line sieve tube occlusion as indicated by carboxyfluorescein fluorescence, the grey vertical line the time point of protein plug formation at the SP, the black vertical line the time point of sieve tube occlusion indicated by aphid behaviour change, and the grey dashed line callose deposition and degradation.
Mentions: Like carboxyfluorescein (Fig. 2), aphids provide compelling physiological evidence in favour of a stop of mass flow due to occlusion in response to remote damage. However, the time delay between stop of mass flow and callose deposition is difficult to interpret. Aphids feeding on the main vein showed an abrupt change in behaviour (Fig. 4) well after the time point when mass flow had stopped (Fig. 7). It may take some time before sieve tube occlusion is perceived by aphids as a loss of pressure (Will et al., 2008). If the aphid response indeed presents a delayed reaction to sieve tube occlusion, aphid behaviour could reflect stoppage of mass flow long before callose deposition is being completed (Fig. 7). Similarly, carboxyfluorescein movement stops (Fig. 2) well before callose deposition is completed (Fig. 3). That stoppage of mass flow does not need maximal deposition of callose could explain this time-incongruence, but the following alternative may be attractive.

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