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Growing pollen tubes possess a constitutive alkaline band in the clear zone and a growth-dependent acidic tip.

Feijó JA, Sainhas J, Hackett GR, Kunkel JG, Hepler PK - J. Cell Biol. (1999)

Bottom Line: Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 microM or greater, will dissipate the gradient, possibly through shuttle buffering.The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins.These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.

View Article: PubMed Central - PubMed

Affiliation: Department Biologia Vegetal, Faculdade de Ciências, Universidade de Lisboa, P-1749-016 Lisboa, Portugal. jose.feijo@fc.ul.pt

ABSTRACT
Using both the proton selective vibrating electrode to probe the extracellular currents and ratiometric wide-field fluorescence microscopy with the indicator 2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran to image the intracellular pH, we have examined the distribution and activity of protons (H+) associated with pollen tube growth. The intracellular images reveal that lily pollen tubes possess a constitutive alkaline band at the base of the clear zone and an acidic domain at the extreme apex. The extracellular observations, in close agreement, show a proton influx at the extreme apex of the pollen tube and an efflux in the region that corresponds to the position of the alkaline band. The ability to detect the intracellular pH gradient is strongly dependent on the concentration of exogenous buffers in the cytoplasm. Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 microM or greater, will dissipate the gradient, possibly through shuttle buffering. The apical acidic domain correlates closely with the process of growth, and thus may play a direct role, possibly in facilitating vesicle movement and exocytosis. The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins. These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.

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A model for proton gradients in pollen tubes. The geometry of the tube has been simplified to a two-dimensional rectangular section and the pivotal assumptions have been based on  the pattern described for extracellular fluxes. A and B represent  the intracellular and extracellular buffers, and C the metabolic irreversible proton formation (see text and also Appendix for  mathematical details).
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Figure 13: A model for proton gradients in pollen tubes. The geometry of the tube has been simplified to a two-dimensional rectangular section and the pivotal assumptions have been based on the pattern described for extracellular fluxes. A and B represent the intracellular and extracellular buffers, and C the metabolic irreversible proton formation (see text and also Appendix for mathematical details).

Mentions: A more realistic model is one typified by a reaction-diffusion system that incorporates kinetic terms related to metabolism and transport processes, and diffusion terms imposed by the differential localization of membrane fluxes; when taken together these factors can amplify anisotropy in ion distribution, and possibly account for the formation of pH gradients in pollen tubes. We summarize our thinking in Fig. 13 where, for the sake of simplicity we reduce the problem to a two-dimensional space and simplify the geometry of the pollen tube to a rectangular shape. The model considers two compartments, the intracellular and extracellular spaces, separated by an interface with heterogeneous permeability properties. In the tip, proton influx exhibits saturation kinetics imposed by the transport limitations of the specific carriers; we suggest that within this area the spatial distribution of ionic channels is uniform. We also define nonapical areas rich in active ATPase systems that actively extrude protons. We stress that these biological conjectures are supported by the results obtained with proton selective vibrating electrodes reported herein.


Growing pollen tubes possess a constitutive alkaline band in the clear zone and a growth-dependent acidic tip.

Feijó JA, Sainhas J, Hackett GR, Kunkel JG, Hepler PK - J. Cell Biol. (1999)

A model for proton gradients in pollen tubes. The geometry of the tube has been simplified to a two-dimensional rectangular section and the pivotal assumptions have been based on  the pattern described for extracellular fluxes. A and B represent  the intracellular and extracellular buffers, and C the metabolic irreversible proton formation (see text and also Appendix for  mathematical details).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132912&req=5

Figure 13: A model for proton gradients in pollen tubes. The geometry of the tube has been simplified to a two-dimensional rectangular section and the pivotal assumptions have been based on the pattern described for extracellular fluxes. A and B represent the intracellular and extracellular buffers, and C the metabolic irreversible proton formation (see text and also Appendix for mathematical details).
Mentions: A more realistic model is one typified by a reaction-diffusion system that incorporates kinetic terms related to metabolism and transport processes, and diffusion terms imposed by the differential localization of membrane fluxes; when taken together these factors can amplify anisotropy in ion distribution, and possibly account for the formation of pH gradients in pollen tubes. We summarize our thinking in Fig. 13 where, for the sake of simplicity we reduce the problem to a two-dimensional space and simplify the geometry of the pollen tube to a rectangular shape. The model considers two compartments, the intracellular and extracellular spaces, separated by an interface with heterogeneous permeability properties. In the tip, proton influx exhibits saturation kinetics imposed by the transport limitations of the specific carriers; we suggest that within this area the spatial distribution of ionic channels is uniform. We also define nonapical areas rich in active ATPase systems that actively extrude protons. We stress that these biological conjectures are supported by the results obtained with proton selective vibrating electrodes reported herein.

Bottom Line: Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 microM or greater, will dissipate the gradient, possibly through shuttle buffering.The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins.These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.

View Article: PubMed Central - PubMed

Affiliation: Department Biologia Vegetal, Faculdade de Ciências, Universidade de Lisboa, P-1749-016 Lisboa, Portugal. jose.feijo@fc.ul.pt

ABSTRACT
Using both the proton selective vibrating electrode to probe the extracellular currents and ratiometric wide-field fluorescence microscopy with the indicator 2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran to image the intracellular pH, we have examined the distribution and activity of protons (H+) associated with pollen tube growth. The intracellular images reveal that lily pollen tubes possess a constitutive alkaline band at the base of the clear zone and an acidic domain at the extreme apex. The extracellular observations, in close agreement, show a proton influx at the extreme apex of the pollen tube and an efflux in the region that corresponds to the position of the alkaline band. The ability to detect the intracellular pH gradient is strongly dependent on the concentration of exogenous buffers in the cytoplasm. Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 microM or greater, will dissipate the gradient, possibly through shuttle buffering. The apical acidic domain correlates closely with the process of growth, and thus may play a direct role, possibly in facilitating vesicle movement and exocytosis. The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins. These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.

Show MeSH
Related in: MedlinePlus