Dietmar Tietz - Academia.edu (original) (raw)
Papers by Dietmar Tietz
Journal of Plant Physiology, 1985
Changes in the abscisic acid (ABA) content of epidermis and mesophyll of isolated Commelina commu... more Changes in the abscisic acid (ABA) content of epidermis and mesophyll of isolated Commelina communis L. leaves were followed and compared to changes in diffusion resistance during a water stress treatment. Diffusion resistance increased within 15 min before a rise in the ABA content of the epidermis could be determined. By application of (14)C-labelled ABA to isolated leaves via the transpiration stream it was found that the minimal amount of ABA to induce stomatal closure was in the range of 0.4 fmol per stomatal complex. Isolated epidermis was treated with tritiated ABA and subjected to microautoradiography. The stomatal complexes showed an accumulation of radioactive material. This accumulation was observable in living as well as in non-living, heat- or cold-treated epidermis. The results are discussed in relation to the hypothesis that ABA regulates stomatal closure in water-stressed leaves.
Springer eBooks, 1980
It is well known that abscisic acid (ABA) was discovered in investigations on bud dormancy and ab... more It is well known that abscisic acid (ABA) was discovered in investigations on bud dormancy and abscission. Numerous attempts have been undertaken to establish a regulatory role of ABA in both of these processes. However, so far we have only little evidence that ABA functions as a dormancy hormone or as a regulator of abscission (1).
Planta, 1974
When pea seedlings lose about 5% of their water content the abscisic acid ((+)-ABA) level of the ... more When pea seedlings lose about 5% of their water content the abscisic acid ((+)-ABA) level of the shoots increases ca. 20 times and the level of bound ABA, in all probability ABA-glucose, ca.7-10 times. After watering both ABA and bound ABA contents decrease within 24-48 h to the level in the control plants.After application of (±)-[2-(14)C] ABA to wilted pea shoots at the time of watering radioactive substances appear in the water-soluble, ether-insoluble fraction of ethanolic extracts and increase with time whereas radioactivity in the acidic ether fraction decreases. The neutral ether fraction remains free of radioactivity. Three radioactive zones, A, B, and C, are seen on chromatograms of the water-soluble fraction. A increases considerably within the entire experimental time, whereas B increases in the first 4-8 h after application and subsequently decreases. The third substance, C, which releases free ABA after hydrolytic treatment, does not change during the experiment. Chromatograms of the acidic ether fraction yield ABA and a substance staying at the origin, possibly phaseic acid and/or dihydrophaseic acid. Only the activity of ABA decreases during the experiment.
Progress in Botany / Fortschritte der Botanik, 1982
PubMed, 1995
Significantly more information can be obtained if sample mobilities are measured at several gel c... more Significantly more information can be obtained if sample mobilities are measured at several gel concentrations (%T) and evaluated on the basis of a mathematical-physical model. This allows one to exploit differences in particle size, charge and shape, and results in the following advantages: (i) Charge and size isomers of proteins can be detected. It is possible to separate components of similar size, but different surface net charge density. (ii) Samples yielding patterns with no discernible peaks can be evaluated to produce size and charge distribution profiles, as shown for protein-conjugated meningitis vaccines. Particle distributions are calculated from 2-D Serwer-type gels. (iii) Different DNA conformations are recognized and reasonable size estimates are available for anomalously migrating DNA species (e.g., bent kinetoplast DNA) or DNA complexes (nucleosome core particles).
Electrophoresis, 1995
The extended Ogston model has frequently been applied to characterize particles in biological sam... more The extended Ogston model has frequently been applied to characterize particles in biological samples according to size and free mobility (surface net charge density). The analysis rests on the computer-assisted evaluation of the semi-logarithmic plot of mobility, µ, vs. gel concen- tration, T [g/lOO mL] (Ferguson plot). The model originates from the work of Chrambach and Rodbard and is based on experimental observations of Morris and mathematical rationales of Ogston. Recently, this model was challenged in a short communication by Slater and Guo.This letter is a preliminary response to that article stating that Slater and Guo’s objections appear not sufficiently substantiated as explained in the following.
ZAMM - Z. angew. Math. Mech., 1996
Gel electrophoresis is a frequently used analytical method in molecular biology and medicine for ... more Gel electrophoresis is a frequently used analytical method in molecular biology and medicine for the separation and characterization of macromolecules (proteins and nucleic acids) and subcellular-sized particles (e.g. viruses and small cell organelles). Significantly more information can be obtained if electrophoretic mobilities of samples are measured at several gel concentrations and evaluated on the basis of a mathematical-physical model. The rationales of the model and three computer-assisted applications are briefly described.
Electrophoresis, Mar 1, 1995
The extended Ogston model has frequently been applied to characterize particles in biological sam... more The extended Ogston model has frequently been applied to characterize particles in biological samples according to size and free mobility (surface net charge density). The analysis rests on the computer-assisted evaluation of the semi-logarithmic plot of mobility, µ, vs. gel concen- tration, T [g/lOO mL] (Ferguson plot). The model originates from the work of Chrambach and Rodbard and is based on experimental observations of Morris and mathematical rationales of Ogston. Recently, this model was challenged in a short communication by Slater and Guo.This letter is a preliminary response to that article stating that Slater and Guo’s objections appear not sufficiently substantiated as explained in the following.
Electrophoresis, Mar 1, 1995
Protein-conjugated meningitis vaccines have been developed by John Robbins, Rachel Schneerson and... more Protein-conjugated meningitis vaccines have been developed by John Robbins, Rachel Schneerson and co-workers [1,2] for the immunization of small children, the main target group of bacterial meningitis. The physical characterization of these immunogens has been difficult, since their surface net charge is high and since the particles have a relatively large size which is in the range of intact viruses. Moreover, the size distribution of vaccine particles varies continuously over a wide range (polydisperse distribution) due to the randomizing steps in their method of preparation. When such samples are subjected to one-dimensional agarose electrophoresis, they exhibit an uninterpretable smear rather than a pattern of distinct zones (Fig. 1). However, when a second dimension is added to the separation (apparatus shown in Fig. 2), the results become interpretable: Distribution patterns are obtained which are characteristic for each vaccine. The patterns are digitized by scanning and then...
Electrophoresis, 1991
Polystyrene sulfate and carboxylate particles (19-189 nm radius) were subjected to electrophoresi... more Polystyrene sulfate and carboxylate particles (19-189 nm radius) were subjected to electrophoresis in glutaraldehyde crosslinked polyvinyl alcohol of molecular weight 25.000 and 650.000 Da at various concentrations. The degree of crosslinking is severely limited by the mechanical properties of the gels that deteriorate beyond a glutaraldehyde concentration which decreases with increasing polyvinyl alcohol chain length. The effective fiber radius of the short-chain and long-chain polymer fiber was 45 +/- 25 and 131 +/- 47 nm, respectively. Thus, these media do not significantly exceed the apparent fiber thickness of agarose, are more difficult to prepare--but are well-defined synthetic products rather than natural ones, and have the advantage of carrying no net charge and can therefore be expected to exhibit no electroendosmosis.
Electrophoresis, 1987
A convex "Ferguson plot" of polystyrene particles in electrophoresis on 0.25 to 2.0 % polyacrylam... more A convex "Ferguson plot" of polystyrene particles in electrophoresis on 0.25 to 2.0 % polyacrylamide (30 % Bis-crosslinked)
Electrophoresis, 1987
The hypothesis was tested that polyacrylamide gel which is presumably of constant fiber structure... more The hypothesis was tested that polyacrylamide gel which is presumably of constant fiber structure within a practical range of gel concentrations would yield a linear Ferguson plot in the gel electrophoresis of particles in the size range of 10-100 nm. Polystyrene particles ranging from 22 to 60 nm in radius were subjected to gel electrophoresis on 30 % N,N'-methylenebisacrylamide-crosslinked polyacrylamide (2.0 to 3.2 %gel concentration) containing 50 mM 3-[(3-cholamidopropyl)-dimethy1 ammoniol-1-propane sulfonate (CHAPS). Visualization ofthe zones required transparent gels which were formed by polymerization both at 50 "C and in the presence of 6 M urea. Ferguson plots llog(mobi1ity) vs. gel concentration] were progressively curved with increasing particle size from 22.4 to 59.4 nm radius. As in agarose gel electrophoresis, this curvature comprises one or several sigmoidal curve elements, presumably indicative of particle compression [ 1, 21. However, by contrast with agarose gel electrophoresis, the curves can be aligned along a linear, rather than a convex axis, and may therefore be designated as "overall-linear" in essential agreement with the hypothesis underlying this study. However, contrary to expectation, the polyacrylamide gel electrophoresis of particles in the size range of interest did not provide a practical method since the gel concentration range comprising Ferguson plots of the polystyrene particles in polyacrylamide is excessively narrow and the concentration range needed for extrapolation of the Ferguson plot to obtain free mobility values is excessively wide.
Electrophoresis, 1992
We describe a modification of transverse pore gradient gel electrophoresis in which pore size is ... more We describe a modification of transverse pore gradient gel electrophoresis in which pore size is regulated by crosslinker proportion (%C) rather than by total monomer concentration (%T). We electrophoresed plasma lipoprotein [a] transversely across linear N,N'-methylenebisacrylamide gradients and measured mobility as a function of %C. This method allows for the simultaneous assessment of pore sizes generated over a wide range of crosslinker proportions.
Electrophoresis, 1991
Previous methods interpret zonal or polydisperse gel patterns of two-dimensional Serwer-type gels... more Previous methods interpret zonal or polydisperse gel patterns of two-dimensional Serwer-type gels in terms of size and free mobility (surface net charge density). These two parameters have been determined for each component without quantitatively measuring the abundance of the components. The present study advances these previous methods by determining the relative concentration of each component by computer evaluation of densitometrically analyzed gel patterns. Suitable procedures and their underlying algorithms are presented. The mathematical routines are implemented in a user-friendly software package, called GelFit and designed for a Macintosh personal computer. The program input consists of digitized images of gel staining patterns exemplified by those obtained from electrophoresis of native subcellular-sized particles. The data are processed through the following steps: (i) Noise reduction and calibration. (ii) Geometrical transformation of the pattern onto a rectangular size/free mobility coordinate system using rationales of the extended Ogston model. (iii) Analysis of the transformed image to determine density maxima, density profiles along iso-free-mobility or iso-size lines, curve fitting of one-dimensional profiles or two-dimensional surfaces using Gaussian functions and curve stripping of surfaces to determine the possible number of particle populations.
Electrophoresis, 1989
It should benotedthat theconvexplotoflog(mobility)vs. %T(Ferguson plot) shown in Fig. 1 is approx... more It should benotedthat theconvexplotoflog(mobility)vs. %T(Ferguson plot) shown in Fig. 1 is approximately equivalent to the sigmoidal plot of mobility vs. %T shown in Fig. 2, bottom panel. 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1989 0 173-0835/89/0404-0254 %OZ.S0/0 Electrophoresis 1989,10, 254-259 Sieving of ions across moving boundaries
Electrophoresis, 1987
Three plant viruses: turnip crinkle (TCV), hibiscus chlorotic ringspot (HCRSV) and pelargonium fl... more Three plant viruses: turnip crinkle (TCV), hibiscus chlorotic ringspot (HCRSV) and pelargonium flowerbreak (PFBV), and polystyrene size standards with radii of 22.4-59.4 nm can be stacked within trailing and leading ion net mobilities of 0.059 to 0.273 (relative to Na+). Stacking was carried out at pH 6.50,0.03 M ionic strength, 50 mM 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate, at a gel concentration of 0.4 %, in agarose gel electrophoresis conducted at 1.2 mA/cm2 of gel. Unstacking occurs under the same conditions at gel concentrations ranging from 0.5 to 1.1 % agarose, while it can be brought about between 0.1 and 0.7 % agarose when the pH is raised to 7.27, corresponding to a front moving boundary with a trailing ion net mobility of 0.216 (relative to Na+). Ferguson plots of viruses and polystyrene particles in the discontinuous buffer system are curvilinear and comparable to those obtained in a continuous buffer at pH 6.50 of the same composition and operative pH as that of the resolving phase of the discontinuous buffer. Particle radii and net charge values can be obtained from the non-linear Ferguson plot in the discontinuous buffer system by previously reported methods of computer simulation, but this Ferguson plot presents a more limited data base than that in the continuous buffer since it excludes gel concentrations which yield relative mobility (Rf) values of 1 .O. Since computer simulation provides the range of gel concentrations in which both thefiberradiusandlength [ 11, aswellasthesizeoftheparticle [2],remainconstantfor a particular preparation of agarose, a simplified alternative method of evaluating particle sizes exists. Within that specific gel concentration range, the linear segment of the Ferguson plot can be used to compute particle sizes by an operationally convenient, albeit approximative, method, using the same PAGE-PACK programs of D. Rodbard which are commonly used in the size determination of macromolecules by polyacrylamide gel electrophoresis. The two methods of particle size determination, based on either the entire non-linear Ferguson plot or on its linear segment in the appropriate gel concentration range, yield similar results (average deviation 12 %). The radii of three plant viruses are dependent to different degrees on the presence of Ca++ in the electrophoretic system. Values obtained in the presence of Ca++ are comparable to those found by electron microscopy.
Journal of Plant Physiology, 1985
Changes in the abscisic acid (ABA) content of epidermis and mesophyll of isolated Commelina commu... more Changes in the abscisic acid (ABA) content of epidermis and mesophyll of isolated Commelina communis L. leaves were followed and compared to changes in diffusion resistance during a water stress treatment. Diffusion resistance increased within 15 min before a rise in the ABA content of the epidermis could be determined. By application of (14)C-labelled ABA to isolated leaves via the transpiration stream it was found that the minimal amount of ABA to induce stomatal closure was in the range of 0.4 fmol per stomatal complex. Isolated epidermis was treated with tritiated ABA and subjected to microautoradiography. The stomatal complexes showed an accumulation of radioactive material. This accumulation was observable in living as well as in non-living, heat- or cold-treated epidermis. The results are discussed in relation to the hypothesis that ABA regulates stomatal closure in water-stressed leaves.
Springer eBooks, 1980
It is well known that abscisic acid (ABA) was discovered in investigations on bud dormancy and ab... more It is well known that abscisic acid (ABA) was discovered in investigations on bud dormancy and abscission. Numerous attempts have been undertaken to establish a regulatory role of ABA in both of these processes. However, so far we have only little evidence that ABA functions as a dormancy hormone or as a regulator of abscission (1).
Planta, 1974
When pea seedlings lose about 5% of their water content the abscisic acid ((+)-ABA) level of the ... more When pea seedlings lose about 5% of their water content the abscisic acid ((+)-ABA) level of the shoots increases ca. 20 times and the level of bound ABA, in all probability ABA-glucose, ca.7-10 times. After watering both ABA and bound ABA contents decrease within 24-48 h to the level in the control plants.After application of (±)-[2-(14)C] ABA to wilted pea shoots at the time of watering radioactive substances appear in the water-soluble, ether-insoluble fraction of ethanolic extracts and increase with time whereas radioactivity in the acidic ether fraction decreases. The neutral ether fraction remains free of radioactivity. Three radioactive zones, A, B, and C, are seen on chromatograms of the water-soluble fraction. A increases considerably within the entire experimental time, whereas B increases in the first 4-8 h after application and subsequently decreases. The third substance, C, which releases free ABA after hydrolytic treatment, does not change during the experiment. Chromatograms of the acidic ether fraction yield ABA and a substance staying at the origin, possibly phaseic acid and/or dihydrophaseic acid. Only the activity of ABA decreases during the experiment.
Progress in Botany / Fortschritte der Botanik, 1982
PubMed, 1995
Significantly more information can be obtained if sample mobilities are measured at several gel c... more Significantly more information can be obtained if sample mobilities are measured at several gel concentrations (%T) and evaluated on the basis of a mathematical-physical model. This allows one to exploit differences in particle size, charge and shape, and results in the following advantages: (i) Charge and size isomers of proteins can be detected. It is possible to separate components of similar size, but different surface net charge density. (ii) Samples yielding patterns with no discernible peaks can be evaluated to produce size and charge distribution profiles, as shown for protein-conjugated meningitis vaccines. Particle distributions are calculated from 2-D Serwer-type gels. (iii) Different DNA conformations are recognized and reasonable size estimates are available for anomalously migrating DNA species (e.g., bent kinetoplast DNA) or DNA complexes (nucleosome core particles).
Electrophoresis, 1995
The extended Ogston model has frequently been applied to characterize particles in biological sam... more The extended Ogston model has frequently been applied to characterize particles in biological samples according to size and free mobility (surface net charge density). The analysis rests on the computer-assisted evaluation of the semi-logarithmic plot of mobility, µ, vs. gel concen- tration, T [g/lOO mL] (Ferguson plot). The model originates from the work of Chrambach and Rodbard and is based on experimental observations of Morris and mathematical rationales of Ogston. Recently, this model was challenged in a short communication by Slater and Guo.This letter is a preliminary response to that article stating that Slater and Guo’s objections appear not sufficiently substantiated as explained in the following.
ZAMM - Z. angew. Math. Mech., 1996
Gel electrophoresis is a frequently used analytical method in molecular biology and medicine for ... more Gel electrophoresis is a frequently used analytical method in molecular biology and medicine for the separation and characterization of macromolecules (proteins and nucleic acids) and subcellular-sized particles (e.g. viruses and small cell organelles). Significantly more information can be obtained if electrophoretic mobilities of samples are measured at several gel concentrations and evaluated on the basis of a mathematical-physical model. The rationales of the model and three computer-assisted applications are briefly described.
Electrophoresis, Mar 1, 1995
The extended Ogston model has frequently been applied to characterize particles in biological sam... more The extended Ogston model has frequently been applied to characterize particles in biological samples according to size and free mobility (surface net charge density). The analysis rests on the computer-assisted evaluation of the semi-logarithmic plot of mobility, µ, vs. gel concen- tration, T [g/lOO mL] (Ferguson plot). The model originates from the work of Chrambach and Rodbard and is based on experimental observations of Morris and mathematical rationales of Ogston. Recently, this model was challenged in a short communication by Slater and Guo.This letter is a preliminary response to that article stating that Slater and Guo’s objections appear not sufficiently substantiated as explained in the following.
Electrophoresis, Mar 1, 1995
Protein-conjugated meningitis vaccines have been developed by John Robbins, Rachel Schneerson and... more Protein-conjugated meningitis vaccines have been developed by John Robbins, Rachel Schneerson and co-workers [1,2] for the immunization of small children, the main target group of bacterial meningitis. The physical characterization of these immunogens has been difficult, since their surface net charge is high and since the particles have a relatively large size which is in the range of intact viruses. Moreover, the size distribution of vaccine particles varies continuously over a wide range (polydisperse distribution) due to the randomizing steps in their method of preparation. When such samples are subjected to one-dimensional agarose electrophoresis, they exhibit an uninterpretable smear rather than a pattern of distinct zones (Fig. 1). However, when a second dimension is added to the separation (apparatus shown in Fig. 2), the results become interpretable: Distribution patterns are obtained which are characteristic for each vaccine. The patterns are digitized by scanning and then...
Electrophoresis, 1991
Polystyrene sulfate and carboxylate particles (19-189 nm radius) were subjected to electrophoresi... more Polystyrene sulfate and carboxylate particles (19-189 nm radius) were subjected to electrophoresis in glutaraldehyde crosslinked polyvinyl alcohol of molecular weight 25.000 and 650.000 Da at various concentrations. The degree of crosslinking is severely limited by the mechanical properties of the gels that deteriorate beyond a glutaraldehyde concentration which decreases with increasing polyvinyl alcohol chain length. The effective fiber radius of the short-chain and long-chain polymer fiber was 45 +/- 25 and 131 +/- 47 nm, respectively. Thus, these media do not significantly exceed the apparent fiber thickness of agarose, are more difficult to prepare--but are well-defined synthetic products rather than natural ones, and have the advantage of carrying no net charge and can therefore be expected to exhibit no electroendosmosis.
Electrophoresis, 1987
A convex "Ferguson plot" of polystyrene particles in electrophoresis on 0.25 to 2.0 % polyacrylam... more A convex "Ferguson plot" of polystyrene particles in electrophoresis on 0.25 to 2.0 % polyacrylamide (30 % Bis-crosslinked)
Electrophoresis, 1987
The hypothesis was tested that polyacrylamide gel which is presumably of constant fiber structure... more The hypothesis was tested that polyacrylamide gel which is presumably of constant fiber structure within a practical range of gel concentrations would yield a linear Ferguson plot in the gel electrophoresis of particles in the size range of 10-100 nm. Polystyrene particles ranging from 22 to 60 nm in radius were subjected to gel electrophoresis on 30 % N,N'-methylenebisacrylamide-crosslinked polyacrylamide (2.0 to 3.2 %gel concentration) containing 50 mM 3-[(3-cholamidopropyl)-dimethy1 ammoniol-1-propane sulfonate (CHAPS). Visualization ofthe zones required transparent gels which were formed by polymerization both at 50 "C and in the presence of 6 M urea. Ferguson plots llog(mobi1ity) vs. gel concentration] were progressively curved with increasing particle size from 22.4 to 59.4 nm radius. As in agarose gel electrophoresis, this curvature comprises one or several sigmoidal curve elements, presumably indicative of particle compression [ 1, 21. However, by contrast with agarose gel electrophoresis, the curves can be aligned along a linear, rather than a convex axis, and may therefore be designated as "overall-linear" in essential agreement with the hypothesis underlying this study. However, contrary to expectation, the polyacrylamide gel electrophoresis of particles in the size range of interest did not provide a practical method since the gel concentration range comprising Ferguson plots of the polystyrene particles in polyacrylamide is excessively narrow and the concentration range needed for extrapolation of the Ferguson plot to obtain free mobility values is excessively wide.
Electrophoresis, 1992
We describe a modification of transverse pore gradient gel electrophoresis in which pore size is ... more We describe a modification of transverse pore gradient gel electrophoresis in which pore size is regulated by crosslinker proportion (%C) rather than by total monomer concentration (%T). We electrophoresed plasma lipoprotein [a] transversely across linear N,N'-methylenebisacrylamide gradients and measured mobility as a function of %C. This method allows for the simultaneous assessment of pore sizes generated over a wide range of crosslinker proportions.
Electrophoresis, 1991
Previous methods interpret zonal or polydisperse gel patterns of two-dimensional Serwer-type gels... more Previous methods interpret zonal or polydisperse gel patterns of two-dimensional Serwer-type gels in terms of size and free mobility (surface net charge density). These two parameters have been determined for each component without quantitatively measuring the abundance of the components. The present study advances these previous methods by determining the relative concentration of each component by computer evaluation of densitometrically analyzed gel patterns. Suitable procedures and their underlying algorithms are presented. The mathematical routines are implemented in a user-friendly software package, called GelFit and designed for a Macintosh personal computer. The program input consists of digitized images of gel staining patterns exemplified by those obtained from electrophoresis of native subcellular-sized particles. The data are processed through the following steps: (i) Noise reduction and calibration. (ii) Geometrical transformation of the pattern onto a rectangular size/free mobility coordinate system using rationales of the extended Ogston model. (iii) Analysis of the transformed image to determine density maxima, density profiles along iso-free-mobility or iso-size lines, curve fitting of one-dimensional profiles or two-dimensional surfaces using Gaussian functions and curve stripping of surfaces to determine the possible number of particle populations.
Electrophoresis, 1989
It should benotedthat theconvexplotoflog(mobility)vs. %T(Ferguson plot) shown in Fig. 1 is approx... more It should benotedthat theconvexplotoflog(mobility)vs. %T(Ferguson plot) shown in Fig. 1 is approximately equivalent to the sigmoidal plot of mobility vs. %T shown in Fig. 2, bottom panel. 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1989 0 173-0835/89/0404-0254 %OZ.S0/0 Electrophoresis 1989,10, 254-259 Sieving of ions across moving boundaries
Electrophoresis, 1987
Three plant viruses: turnip crinkle (TCV), hibiscus chlorotic ringspot (HCRSV) and pelargonium fl... more Three plant viruses: turnip crinkle (TCV), hibiscus chlorotic ringspot (HCRSV) and pelargonium flowerbreak (PFBV), and polystyrene size standards with radii of 22.4-59.4 nm can be stacked within trailing and leading ion net mobilities of 0.059 to 0.273 (relative to Na+). Stacking was carried out at pH 6.50,0.03 M ionic strength, 50 mM 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate, at a gel concentration of 0.4 %, in agarose gel electrophoresis conducted at 1.2 mA/cm2 of gel. Unstacking occurs under the same conditions at gel concentrations ranging from 0.5 to 1.1 % agarose, while it can be brought about between 0.1 and 0.7 % agarose when the pH is raised to 7.27, corresponding to a front moving boundary with a trailing ion net mobility of 0.216 (relative to Na+). Ferguson plots of viruses and polystyrene particles in the discontinuous buffer system are curvilinear and comparable to those obtained in a continuous buffer at pH 6.50 of the same composition and operative pH as that of the resolving phase of the discontinuous buffer. Particle radii and net charge values can be obtained from the non-linear Ferguson plot in the discontinuous buffer system by previously reported methods of computer simulation, but this Ferguson plot presents a more limited data base than that in the continuous buffer since it excludes gel concentrations which yield relative mobility (Rf) values of 1 .O. Since computer simulation provides the range of gel concentrations in which both thefiberradiusandlength [ 11, aswellasthesizeoftheparticle [2],remainconstantfor a particular preparation of agarose, a simplified alternative method of evaluating particle sizes exists. Within that specific gel concentration range, the linear segment of the Ferguson plot can be used to compute particle sizes by an operationally convenient, albeit approximative, method, using the same PAGE-PACK programs of D. Rodbard which are commonly used in the size determination of macromolecules by polyacrylamide gel electrophoresis. The two methods of particle size determination, based on either the entire non-linear Ferguson plot or on its linear segment in the appropriate gel concentration range, yield similar results (average deviation 12 %). The radii of three plant viruses are dependent to different degrees on the presence of Ca++ in the electrophoretic system. Values obtained in the presence of Ca++ are comparable to those found by electron microscopy.