Lan Wang, David Hukin, Jeremy Pritchard, Colin Thomas (2006) Comparison of plant cell turgor pressure measurement by pressure probe and micromanipulation, Biotechnology Letters, 28 (15): 1147-1150
Pritchard J, Griffiths B and Hunt EJ (2006) Can the plant mediated impacts on aphids of elevated CO2 and drought be predicted? Global Change Biology In press.
C. Doering–Saad , H.J. Newbury, C.E. Couldridge, J.S. Bale and J. Pritchard(2006) A phloem-enriched cDNA library from Ricinus: insights into phloem function Journal of Experimental Botany 55 3183-3193.
Emma J Hunt, J Pritchard, MJ Bennett, X Zhu, DA Barrett, T Allen, Bale JS and HJ Newbury (2006) The Arabidopsis thaliana/Myzus persicae model system demonstrates that a single gene can influence the interaction between a plant and a sucking insect pest. Molecular Ecology. In press.
Douglas AE, Price DRG, Minto LB, Jones E, Pescod KV, Francois CLMJ, Pritchard J, Boonham N (2006) Sweet problems: insect traits defining the limits to dietary sugar utilisation by the pea aphid, Acyrthosiphon pisum Journal of Experimental Biology 209 (8): 1395-1403.Pritchard J 2006 Preface to phloem-insect interaction Journal of Experimental Botany 57 (4): 728-728
Hall D, Evans AR, Newbury HJ, Pritchard J (2006) Functional analysis of CHX21: a putative sodium transporter in Arabidopsis Journal of Experimental Botany 57 (5): 1201-1210
A.J. Karley, D.A. Ashford, L.M. Minto, J. Pritchard and A.E. Douglas (2005) The significance of gut sucrase activity for osmoregulation in the pea aphid, Acyrthosiphon pisum Journal of Insect Physiology, 51: 1313-1319
Xunlin Zhu, P. Nicholas Shaw, Jeremy Pritchard, John Newbury, Emma J. Hunt, David A. Barrett (2005) Amino acid analysis by micellar electrokinetic chromatography with laser-induced fluorescence detection: Application to nanolitre-volume biological samples from Arabidopsis thaliana and Myzus persicae. Electrophoresis 26 911-919
Pritchard J, Ford-Lloyd B and Newbury HJl (2005) Roots as an Integrated Part of the Translocation Pathway In 'Vascular Transport in Plants' Eds: N.M. Holbrook and M. Zwieniecki, Elsevier/AP co-imprint, Oxford
Hampton CR, Bowen HC, Broadley MR, Hammond JP, Mead A, Payne KA, Pritchard J, White PJ (2004) Cesium toxicity in Arabidopsis. Plant Physiology 136 (3): 3824-3837
Jeremy Pritchard , A. Deri Tomos , John F. Farrar, Peter E. H. Minchin , Nick Gould , Matthew J. Paul , Elspeth A. MacRae , Richard A. Ferrieri , Dennis W. Gray and Michael R. Thorpe (2004). Turgor, solute import and growth in maize roots treated with galactose Functional Plant Biology, 31 1095 – 1103.
Alan Barnes, Jeffery Bale, Chrystala Constantinidou, Peter Ashton, Anthony Jones, and Jeremy Pritchard (2004) Determining protein identity from sieve element sap in Ricinus communis L. by quadrupole time of flight (Q-TOF) mass spectrometry. J. Exp. Bot. 55: 1473-1481
Gould N, Thorpe MR, Minchin PEH, Pritchard J, White PJ (2004) Solute is imported to elongating root cells of barley as a pressure driven flow of solution. Functional Plant Biology. 31: 391-397
Hale, B.K., Bale, J.S., Pritchard, J., Masters, G.J. and Brown, V.K. (2003) Effects of host plant drought stress on the performance of the bird cherry-oat aphid, Rhopalosiphum padi (L.): a mechanistic analysis. Ecological Entomology 28, 666-677.
Hale, B.K., Bale, J.S., Pritchard, J., Masters, G.J. and Brown, V.K. (2003) Effects of host plant drought stress on the performance of the bird cherry-oat aphid, Rhopalosiphum padi (L.): a mechanistic analysis. Ecological Entomology 28, 666-677.
Hukin D, Doering-Saad C, Thomas CR and Pritchard J (2002) Sensitivity of cell hydraulic conductivity to mercury is coincident with symplastic isolation and expression of plasmalemma aquaporin genes in growing maize roots. Planta 215: 1047-1056
Doering-Saad C, H.J. Newbury, J.S. Bale and J. Pritchard. (2002) Use of aphid stylectomy and RT-PCR for the detection of transporter mRNAs in sieve elements. J Exp Botany: 53: 631-637
Ponder KL, Watson R, Malone, M and Pritchard J (2002) Mineral content of excreta from the spittle bug Philaenus spumaris closely matches that of xylem sap New Phytologist 152 (2) 237-242
Watson R, Pritchard J, Malone M (2001) Direct measurement of sodium and potassium in the transpiration stream of salt-excluding and non-excluding varieties of wheat J EXP BOT 52 (362): 1873-1881
Ponder KL, Pritchard J, Harrington R, et al. (2001) Feeding behaviour of the aphid Rhopalosiphum padi (Hemiptera : Aphididae) on nitrogen and water-stressed barley (Hordeum vulgare) seedlings B ENTOMOL RES 91 (2): 125-130
Pritchard J (2000) Turgor pressure. Encyclopedia of Life Sciences, Macmillan
Pritchard J, Winch SK and Gould N (2000) Phloem Water Relations And Root Growth. Aust Journal of Plant Physiology 27 539-548
1) PRITCHARD_J, TOMOS_AD, JONES_RGW CONTROL OF WHEAT ROOT ELONGATION GROWTH .1. EFFECTS OF IONS ON GROWTH-RATE, WALL RHEOLOGY AND CELL WATER RELATIONS JOURNAL OF EXPERIMENTAL BOTANY, 1987, Vol.38, No.191, pp.948- 959
2) PRITCHARD_J, JONES_RGW, TOMOS_AD CONTROL OF WHEAT ROOT-GROWTH - THE EFFECTS OF EXCISION ON GROWTH, WALL RHEOLOGY AND ROOT ANATOMY PLANTA, 1988, Vol.176, No.3, pp.399-405
3) TOMOS_AD, MALONE_M, PRITCHARD_J THE BIOPHYSICS OF DIFFERENTIAL GROWTH ENVIRONMENTAL AND EXPERIMENTAL BOTANY, 1989, Vol.29, No.1, pp.7-23
4) PRITCHARD_J, WILLIAMS_G, JONES_RGW, TOMOS_AD RADIAL TURGOR PRESSURE PROFILES IN GROWING AND MATURE ZONES OF WHEAT ROOTS - A MODIFICATION OF THE PRESSURE PROBE JOURNAL OF EXPERIMENTAL BOTANY, 1989, Vol.40, No.214, pp.567- 571
5) PRITCHARD_J, BARLOW_PW, ADAM_JS, TOMOS_AD BIOPHYSICS OF THE INHIBITION OF THE GROWTH OF MAIZE ROOTS BY LOWERED TEMPERATURE PLANT PHYSIOLOGY, 1990, Vol.93, No.1, pp.222-230
6) PRITCHARD_J, JONES_RGW, TOMOS_AD MEASUREMENT OF YIELD THRESHOLD AND CELL-WALL EXTENSIBILITY OF INTACT WHEAT ROOTS UNDER DIFFERENT IONIC, OSMOTIC AND TEMPERATURE TREATMENTS JOURNAL OF EXPERIMENTAL BOTANY, 1990, Vol.41, No.227, pp.669- 675
7) SAAB_IN, SHARP_RE, PRITCHARD_J, VOETBERG_GS INCREASED ENDOGENOUS ABSCISIC-ACID MAINTAINS PRIMARY ROOT- GROWTH AND INHIBITS SHOOT GROWTH OF MAIZE SEEDLINGS AT LOW WATER POTENTIALS PLANT PHYSIOLOGY, 1990, Vol.93, No.4, pp.1329-1336
8) PRITCHARD_J, JONES_RGW, TOMOS_AD TURGOR, GROWTH AND RHEOLOGICAL GRADIENTS OF WHEAT ROOTS FOLLOWING OSMOTIC-STRESS JOURNAL OF EXPERIMENTAL BOTANY, 1991, Vol.42, No.241, pp.1043- 1049
Abstract
The growth rate of hydroponically grown wheat roots was reduced by mannitol solutions of various osmotic pressures. For example, following 24 h exposure to 0.96 MPa mannitol root elongation was reduced from 1.2 mm h-1 to 0.1 mm h-1. Mature cell length was reduced from 290-mu-m in unstressed roots to 100-mu-m in 0.96 MPa mannitol. This indicates a reduction in cell production rate from about 4 per h in the unstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4.5 mm in unstressed roots but became shorter as growth ceased in the proximal regions at higher levels of osmotic stress. The turgor pressure along the apical 5.0 mm of unstressed roots was between 0.5 and 0.6 MPa but declined to 0.41 MPa over the next 5.0 mm. Following 24 h in 0.48 (200 mol m-3) or 0.72 MPa (300 mol m-3 ) mannitol, turgor along the apical 5.0 mm was indistinguishable from that of unstressed roots but turgor declined more steeply in the region 5-10 mm from the tip. At the highest level of stress (0.96 MPa or 400 mol m-3 mannitol) turgor declined steeply within the apical 2.0 mm. Following 24 h of osmotic stress a comparison of the growth and turgor profiles indicated that the cell walls in the proximal region of the growing zone had become harder, i.e. the yield threshold had increased and/or wall extensibility had decreased. In short-term experiments the growth rate of the whole root was reduced from 1.18 mm h-1 to 0.4 mm h-1 immediately following immersion in 0.48 MPa mannitol but then recovered to 0.9 mm h-1 after 3-4 h. The same treatment reduced turgor at both 2.0 mm and 7.0 mm from the tip of the root. Turgor then recovered faster (within 3 h) and more completely at 2.0 mm than at 7.0 mm.
9) SAAB_IN, SHARP_RE, PRITCHARD_J EFFECT OF INHIBITION OF ABSCISIC-ACID ACCUMULATION ON THE SPATIAL-DISTRIBUTION OF ELONGATION IN THE PRIMARY ROOT AND MESOCOTYL OF MAIZE AT LOW WATER POTENTIALS PLANT PHYSIOLOGY, 1992, Vol.99, No.1, pp.26-33 IS: 0032-0889
Abstract
Previous work showed that accumulation of endogenous abscisic acid (ABA) acts both to maintain primary root growth and inhibit shoot growth in maize seedlings at low water potentials (psi(w)) (IN Saab, RE Sharp, J Pritchard, GS Voetberg [1990] Plant Physiol 93: 1329-1336). In this study, we have characterized the growth responses of the primary root and mesocotyl of maize (Zea mays L. cv FR27 x FRMo17) to manipulation of ABA levels at low psi(w) with a high degree of spatial resolution to provide the basis for studies of the mechanism(s) of ABA action. In seedlings growing at low psi(w) and treated with fluridone to inhibit carotenoid (and ABA) biosynthesis, ABA levels were decreased in all locations of the root and mesocotyl growing zones compared with untreated seedlings growing at the same psi(w). In the root, low psi(w) (-1.6 megapascals) caused a shortening of the growing zone, as reported previously. The fluridone treatment was associated with severe inhibition of root elongation rate, which resulted from further shortening of the growing zone. In the mesocotyl, low psi(w) (-0.3 megapascal) also resulted in a shortened growing zone. In contrast with the primary root, however, fluridone treatment prevented most of the inhibition of elongation and the shortening of the growing zone. Final cell length measurements indicated that the responses of both root and mesocotyl elongation to ABA manipulation at low psi(w). involve large effects on cell expansion. Measurements of the relative changes in root and shoot water contents and dry weights after transplanting to a psi(w) of -0.3 megapascal showed that the maintenance of shoot elongation in fluridone- treated seedlings was not attributable to increased water or seed-reserve availability resulting from inhibition of root growth. The results suggest a developmental gradient in tissue responsiveness to endogenous ABA in both the root and mesocotyl growing zones. In the root, the capacity for ABA to protect cell expansion at low psi(w) appears to decrease with increasing distance from the apex. In the mesocotyl, in contrast, the accumulation of ABA at low psi(w) appears to become increasingly inhibitory to expansion as cells are displaced away from the meristematic region.
10) PRITCHARD_J, HETHERINGTON_PR, FRY_SC, TOMOS_AD XYLOGLUCAN ENDOTRANSGLYCOSYLASE ACTIVITY, MICROFIBRIL ORIENTATION AND THE PROFILES OF CELL-WALL PROPERTIES ALONG GROWING REGIONS OF MAIZE ROOTS JOURNAL OF EXPERIMENTAL BOTANY, 1993, Vol.44, No.265, pp.1281- 1289 IS: 0022-0957
Abstract
A series of physical and chemical analyses were made on the expanding zone of maize seedling roots grown in hydroponics. Comparison of longitudinal profiles of local relative elemental growth rate and turgor pressure indicated that cell walls become looser in the apical 5 mm and then tighten 5- 1 0 mm from the root tip. Immersion of roots in 200 mol m-3 mannitol (an osmotic stress of 0.48 MPa) rapidly and evenly reduced turgor pressure along the whole growing region. Growth was reduced to a greater extent in the region 5-1 0 mm from the root tip than in the apical region. This indicated rapid wall- loosening in the root tip, but not in the more basal regions. Following 24 h immersion in 400 mol m-3 mannitol (an osmotic stress of 0.96 MPa) turgor had recovered to pre-stressed values. Under this stress treatment, growth was reduced in the region 4- 1 0 mm from the root tip, despite the recovery of turgor, indicating a tightening of the wall. In the root apex, local relative elemental growth rate was unchanged in comparison to control tissue, showing that wall properties here were similar to the control values. Cellulose microfibrils on the inner face of cortical cell walls became increasingly more parallel to the root axis along the growth profile of both unstressed and stressed roots. Orientation did not correlate with the wall loosening in the apical region of unstressed roots, or with the tightening in the region 5-10 mm from the root tip following 24 h of osmotic stress. Longitudinal profiles of the possible wall-loosening enzyme xyloglucan endotransglycosylase (XET) had good correspondence with an increase in wall loosening during development. In the zone of wall tightening following osmotic stress, XET activity was decreased per unit dry weight (compared with the unstressed control), but not per unit fresh weight.
11) RYGOL_J, PRITCHARD_J, ZHU_JJ, TOMOS_AD, ZIMMERMANN_U TRANSPIRATION INDUCES RADIAL TURGOR PRESSURE-GRADIENTS IN WHEAT AND MAIZE ROOTS PLANT PHYSIOLOGY, 1993, Vol.103, No.2, pp.493-500 IS: 0032-0889
Abstract
Previous studies have shown both the presence and the absence of radial turgor and osmotic pressure gradients across the cortex of roots. In this work, gradients were sought in the roots of wheat (Triticum aestivum) and maize (Zea mays) under conditions in which transpiration flux across the root was varied. This was done by altering the relative humidity above the plant, by excising the root, or by using plants in which the leaves were too young to transpire. Roots of different ages (4-65 d) were studied and radial profiles at different distances from the tip (5-30 mm) were measured. In both species, gradients of turgor and osmotic pressure (increasing inward) were found under transpiring conditions but not when transpiration was inhibited. The presence of radial turgor and osmotic pressure gradients, and the behavior of the gradient when transpiration is interrupted, indicate that active membrane transport or radial solvent drag may play an important role in the distribution of solutes across the root cortex in transpiring plants. Contrary to the conventional view, the flow of water and solutes across the symplastic pathway through the plasmodesmata cannot be inwardly directed under transpiring conditions.
12) PARDOSSI_A, PRITCHARD_J, TOMOS_AD LEAF ILLUMINATION AND ROOT COOLING INHIBIT BEAN LEAF EXPANSION BY DECREASING TURGOR PRESSURE JOURNAL OF EXPERIMENTAL BOTANY, 1994, Vol.45, No.273, pp.415- 422 IS: 0022-0957
Abstract
Phaseolus vulgaris plants with expanding primary leaves were subjected to dark-light or light-dark transition at a root temperature of 25 degrees C, or to root cooling to 10 degrees C. Illumination or darkening caused rapid changes in water flux through the plants and in epidermal turgor pressure when analysed by pressure probe. However, these were not concurrent with variations in bulk leaf water potential and turgor pressure as determined by the pressure chamber method. In addition, the turgor pressure of epidermis measured with the pressure probe was invariably 0.05 to 0.15 MPa lower than that measured in bulk tissue with the pressure chamber. Cooling roots to 10 degrees C induced water stress and wilting. Both techniques indicated a decrease of turgor pressure, but a 20-30 min lag was observed with the pressure chamber. Due to stomatal closure and decreased transpiration, root-cooled plants regained cell turgor after 5-7 h of cooling, but bulk tissue and epidermal turgor (as well as leaf growth rate) remained significantly lower than control levels. These findings indicate that changes in turgor pressure as the result of hydraulic signalling are sufficient to explain the rapid changes in growth rate following illumination or cooling reported in earlier work (Sattin et al., 1990). They also indicate that data obtained by use of the pressure chamber must be treated with caution.
13) PRITCHARD_J THE CONTROL OF CELL EXPANSION IN ROOTS NEW PHYTOLOGIST, 1994, Vol.127, No.1, pp.3-26 IS: 0028-646X DT: Review
Abstract
The expansion of roots is considered at the level of the single cell. The water relations of cell expansion are discussed. Water entry, solute import and cell wall properties are considered as possible regulatory points. It is argued that root cell expansion can be understood in terms of cell turgor pressure and the physical properties of the cell wall, provided solute supply is not limiting. Various measurements of cell wall properties in roots are presented and the assumptions underlying their measurements are presented. It is concluded that cell wall properties must be measured over short time periods to prevent alterations in wall properties during the experiment. The radial location of the load-bearing layers is discussed and it is concluded that, unlike aerial tissue, growth is limited by the properties of the inner layer of the root cortex. Evidence is presented to show that cell wall properties can change both during development and following turgor perturbation. In general, however, turgor itself is tightly regulated, particularly towards the root tip. A number of environmental situations are presented in which root growth is altered. The mechanism of the alteration is discussed at the single cell level. These 'stresses' include osmotic stress, low temperature and soil compaction. In many cases the alteration of root growth is consistent with changes in the cell wall properties of the growing cells. Severe stress, resulting in near cessation of root cell extension, can result in a change (usually an increase) in turgor pressure. The change in turgor pressure of the cells in the growing zone is smaller than that which would be expected from a continuation of an unstressed solute import rate. This exemplifies both the change in cell wall properties and the tight turgor homeostasis of root tips. The biochemical processes which underlie the modulation of cell wall properties are presented as they are currently understood in roots. Measurements of the chemical composition of the wall have not revealed any useful differences which can explain the developmental or stress-induced changes in cell wall properties. Recent work on cell wall enzymes and proteins may provide information about control of cross-linkages within the wall. In the last section the relative importance of apoplastic and symplastic solute transport to the expanding cells is considered. At present the consensus appears to favour the symplastic route, but the apoplastic pathway may also operate, possibly as a scavenging mechanism for leaked ions. The regulation of turgor pressure by linking solute import with wall loosening is discussed.
14) TOMOS_D, PRITCHARD_J BIOPHYSICAL AND BIOCHEMICAL CONTROL OF CELL EXPANSION IN ROOTS AND LEAVES JOURNAL OF EXPERIMENTAL BOTANY, 1994, Vol.45, No.280, pp.1721- 1731 IS: 0022-0957
Abstract
The endogenous regulation of the extension of cells and tissues appears to be dominated by cell wall mechanics. By simultaneously measuring growth rate at near-single cell resolution and single cell turgor pressure we have begun to chart the behaviour of an expanding cell as it passes from the meristem to the mature region of the roots of maize, wheat, barley, tomato, and Pinus pinaster. A key feature is that turgor pressure is unchanged throughout the development of the cell. Two phases can be distinguished within the expanding zone. (i) An acceleration phase in which the cell walls loosen. The cells of this phase can rapidly alter their wall mechanics following water stress and have the most powerful capacity for osmotic adjustment. This phase is associated with a peak in the activity of the potential cell-wall-loosening enzyme XET. (ii) A decelerating phase in which the walls stiffen. This phase can be initiated prematurely by a number of external factors such as NaCl, high osmotic pressure, galactose and, possibly, soil impedance. The corresponding behaviour of examples of leaf (Lolium, wheat and barley) and stem (Sinapis) growth are discussed. Finally the presence of, and roles for, high concentrations of solutes in the walls of expanding cells are discussed. In this context motor cells that are responsible for reversible movement (e.g. those of Phaseolus pulvini) are compared and contrasted with those undergoing irreversible growth. In the pulvini, movement is due to changes in turgor pressure brought about by changes in the apoplast osmotic pressure.
15) TRIBOULOT_MB, PRITCHARD_J, TOMOS_D STIMULATION AND INHIBITION OF PINE ROOT-GROWTH BY OSMOTIC- STRESS NEW PHYTOLOGIST, 1995, Vol.130, No.2, pp.169-175 IS: 0028-646X
Abstract
The effect of osmotic stress on the regulation of extension of roots of pine seedlings (Pinus pinaster Ait.) was studied. Extension rate (r) was measured as increase in root length, and as local growth rate (LGR) along the growing region. Turgor pressure (P) was measured over the same profile using the cell pressure probe. Correlation of LGR and P allowed changes in cell wall mechanical properties to be followed. In unstressed plants, differences in LGR along the root apex were owing to variations in the mechanical properties of the cell walls since P remained constant at 0.5 MPa along the first 10 mm of the root tip. Contrary to expectation, a moderate water stress of 0.15 MPa stimulated root growth despite a small reduction in P to 0.4 MPa. The walls of the expanding cells became looser, allowing enhanced growth in spite of reduced turgor. Examination of LGR showed that these changes occurred uniformly over the whole elongation zone. The advantage to the plant of this is discussed. Higher stresses (0.45 and 0.66 MPa) decreased cell turgor to a greater degree (less than or equal to 0.3 MPa) and decreased growth rate. At the highest stress (0.66 MPa), P was maximal in cells that were still elongating, resulting in a longitudinal gradient in turgor. In both treatments LGR remained unchanged at the apex of the growing zone. Wall loosening appeared to have occurred in this region. Pine root extension is therefore modulated by changes in cell wall properties, with cell wall loosening resulting in increased growth at moderate stress. It appears that growth under higher stresses is limited by inability to maintain turgor.
16) JOHNSON_JM, PRITCHARD_J, GORHAM_J, TOMOS_AD GROWTH, WATER RELATIONS AND SOLUTE ACCUMULATION IN OSMOTICALLY STRESSED SEEDLINGS OF THE TROPICAL TREE COLOPHOSPERMUM MOPANE TREE PHYSIOLOGY, 1996, Vol.16, No.8, pp.713-718 IS: 0829-318X
Abstract
Root and hypocotyl elongation, water status and solute accumulation were studied in osmotically stressed seedlings of the tropical tree, Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Leonard, which grows in hot arid areas of southern and central Africa. Seeds were imbibed for 24 h and then subjected to a polyethylene-glycol-generated osmotic stress of -0.03 (control), -0.2, -0.8, -1.6 or -2.0 MPa for 60 h. Seedlings subjected to moderate water stress (-0.2 MPa) had higher root growth rates (2.41 +/- 0.24 mm h(-1)), greater final root lengths (111 +/- 3.8 mm) and longer cells immediately behind the root elongation zone than control seedlings (1.70 +/- 0.15 mm h(-1) and 93 +/- 3.9 mm, respectively). Root lengths of seedlings in the -0.8 and -1.6 MPa treatments were similar to those of control seedlings, whereas the -2.0 Mpa seedlings had significantly shorter roots. Both root and hypocotyl tissues exhibited considerable osmotic adjustment to the external water potential treatments. Seedlings in the -0.03, -0.2, and -0.8 MPa treatments had similar cell turgor pressures (0.69 +/- 0.10, 0.68 +/- 0.07 and 0.57 +/- 0.04 MPa, respectively), whereas the -2.0 MPa treatment lowered cell turgor pressure to 0.17 +/- 0.04 MPa. Root vacuolar osmotic pressures were generally similar to sap osmotic pressures, indicating that the increased root elongation observed in moderately water-stressed seedlings was not caused by increased turgor pressure difference. Neutral-fraction solute concentrations, including the osmoticum pinitol, increased approximately two-fold in root sap in response to a low external water potential. In hypocotyl sap of seedlings in the -2.0 MPa treatment, pinitol more than doubled, sucrose increased from about 2 to 75 mol m(-3) but glucose and fructose remained unchanged and, as a result, total sugars increased only slightly. The benefits of rapid early root elongation and osmoticum accumulation under conditions of water stress are discussed in relation to seedling establishment.
17) PRITCHARD_J APHID STYLECTOMY REVEALS AN OSMOTIC STEP BETWEEN SIEVE TUBE AND CORTICAL-CELLS IN BARLEY ROOTS JOURNAL OF EXPERIMENTAL BOTANY, 1996, Vol.47, No.303, pp.1519- 1524 IS: 0022-0957
Abstract
The aim of the present study was to quantify osmotic pressures directly in the translocation pathway, from leaf to growing root tip, in order to understand the forces driving solutes from a source to a sink. Solutes move through the translocation pathway down an osmotically derived turgor gradient, Accordingly aphid stylectomy and single cell sampling techniques have been combined to examine the osmotic pressure of root phloem and growing root cells. Sieve tube sap was obtained from shoots and, for the first time, roots of barley seedlings using aphid stylectomy, Vacuolar sap was also obtained from a variety of cells in leaf and root tissues using single cell sampling methods. Osmotic pressure of sieve tube sap from roots and shoots was measured at high temporal resolution (within min) and over long periods of time (up to 24 h). Osmotic pressure did not change significantly in the minutes immediately following excision, suggesting that confidence can be placed in the assumption that stylet exudate is representative of sieve tube sap in vivo. There were no differences in the osmotic pressure of sieve tube sap from shoots (1.24 +/- 0.26 MPa, n = 10) or roots (1.42 +/- 0.15 MPa, n = 13). However, osmotic pressure of sap from root cortical cells (0.71 +/- 0.09, n = 12) was about 0.7 MPa lower than that of the sieve elements from roots, this difference may be maintained by consumption of incoming solutes at the root tip. Results are discussed in the context of pressure driven flow in the phloem and symplastic contact between root tip cells and sieve tube. It is hoped that the approach described here will provide important insights into the nature of the relationship between root cell extension and assimilate supply through the phloem.
18) Pritchard_J, Fricke_W, Tomos_D Turgor-regulation during extension growth and osmotic stress of maize roots. An example of single-cell mapping PLANT AND SOIL, 1996, Vol.187, No.1, pp.11-21 IS: 0032-079X
Abstract
The growing cells of hydroponic maize roots expand at constant turgor pressure (0.48 MPa) both when grown in low- (0.5 mol m(- 3) CaCl2) or full-nutrient (Hoagland's) solution and also when seedlings are stressed osmotically (0.96 MPa mannitol). Cell osmotic pressure decreases by 0.1-0.2 MPa during expansion. Despite this, total solute influx largely matches the continuously-varying volume expansion-rate of each cell. K+ in the non-osmotically stressed roots is a significant exception- its concentration dropping by 50% regardless of the presence or absence of K+ in the nutrient medium. This corresponds to the drop in osmotic pressure. Nitrate appears to replace Cl- in the Hoagland-grown cells. Analogous insensitivity of solute gradients to external solutes is observed in the radial distribution of water and solutes in the cortex 12 mm from the tip. Uniform turgor and osmotic pressures are accompanied by opposite gradients of K+ and Cl-, outwards, and hexoses and amino acids, inwards, for plants grown in either 0.5 mol m(-3) CaCl2 or Hoagland's solution (with negligible Cl-). K+ and Cl- levels within both gradients were slightly higher when the ions were available in the medium. The gradients themselves are independent of the direction of solute supply. In CaCl2 solution all other nutrients must come from the stele, in Hoagland's solution inorganic solutes are available in the medium. 24 h after osmotic stress, turgor pressure is recovered at all points in each gradient by osmotic adjustment using organic solutes. Remarkably, K+ and Cl- levels hardly change, despite their ready availability. Hexoses are responsible for some 50% of the adjustment with mannitol for a further 30%. Some 20% of the final osmotic pressure remains to be accounted for. Proline and sucrose are not significantly involved. Under all conditions a standing water potential step of 0.2 MPa between the rhizodermis and its hydroponic medium was found. We est that this is due to solute leakage.
19) Triboulot_MB, Pritchard_J, Levy_G Effects of potassium deficiency on cell water relations and elongation of tap and lateral roots of maritime pine seedlings NEW PHYTOLOGIST, 1997, Vol.135, No.2, pp.183-190 IS: 0028-646X
Abstract
The effects of potassium deficiency (KD) and all-macronutrient deficiency (MD) on elongation of tap and lateral roots were studied on maritime pine seedlings (Pinus pinaster Ait.) in hydroponic culture. Tap root elongation was unaffected by either of the two deficiencies. By marked contrast, lateral root elongation was strongly reduced. The analyses of cell turgor pressure and relative elemental growth rate (REGR) profile in the growing zone allowed us to determine the effects of the nutrient stresses on cell-wall properties. For both deficiency treatments, elongation rate, REGR profile (measured only for control and KD) and turgor pressure in the fastest growing cells were unaffected in the tap root, suggesting that KD and MD did not modify cell-wall properties in the growing zone. In lateral roots, KD shortened the growing zone and significantly reduced REGR. However, turgor pressure remained unaffected in this region. The absence of turgor pressure change suggests that KD reduced elongation of lateral roots by tightening cell walls. In mature cells of the two types of roots, turgor and osmotic pressures tended to be reduced by the nutrient deficiencies, indicating that these parameters were better maintained in the growing cells. Cell turgor and osmotic pressures of control plants were 0.1 MPa lower at 30 mm (mature cells) than at 2-4 mm (expanding cells) from the meristem. Moreover, these parameters were 0.1 MPa lower in expanding cells of lateral roots than in those of tap the root. Turgor and osmotic pressures were not homogeneous throughout the root system and were affected differently by the nutrient deficiencies depending on the location in the root system.
20) Bengough_AG, Croser_C, Pritchard_J A biophysical analysis of root growth under mechanical stress PLANT AND SOIL, 1997, Vol.189, No.1, pp.155-164 IS: 0032-079X
Abstract
The factors controlling root growth in hard soils are reviewed alongside summarised results from our recent studies. The turgor in cells in the elongation zone of roots pushes the apex forward, resisted by the external pressure of the soil and the tension in the cell walls. The external pressure of the soil consists of the pressure required to deform the soil, plus a component of frictional resistance between the root and soil. This frictional component is probably small due to the continuous sloughing of root cap cells forming a low-friction lining surrounding the root. Mechanically impeded roots are not only thicker, but are differently shaped, continuing to increase in diameter for a greater distance behind the root tip than in unimpeded roots. The osmotic potential decreases in mechanically impeded roots, possibly due to accumulation of solutes as a result of the slower root extension rate. This more negative osmotic potential is not always translated into increased turgor pressure, and the reasons for this require further investigation. The persistent effect of mechanical impedance on root growth is associated with both a stiffening of cell walls in the axial direction, and with a slowing of the rate of cell production.
21) R.J. Watson, J.Pritchard and M. Malone"Biological syringes The use of Philaenus spumarius to analyse xylem transport. SEB poster abstract J. Exp Bot. [P8.3], Canterbury 1997.
One mechanism for salt tolerance involves exclusion of Na from the xylem. In this study, xylem-feeding P.spumarius spittlebugs were used to extract sap from the xylem of intact transpiring plants.
Salt-tolerant (cv Ilam) and salt-sensitive (cv Tabigha) strains of barley were compared after treatment with 100mM NaCl. The excreta from feeding P.spumarius was collected and analysed for [Na] and [K] by flame photometry. Bulk tissue [Na] was also determined in leaves.
Sodium accumulated to different amounts in leaves: the tolerant variety contained 186+10 mM while the sensitive variety contained 233+15 mM (P<0.05).
In both varieties, the Na content of the insect excreta (which reflects xylem sap) increased after salt treatment: the tolerant variety contained 3.0+0.4 mM compared with 0.4+0.1 mM for the control (P<0.0001); the salt-sensitive variety contained 2.0+0.2 mM compared with 0.4+0.1 mM for the control (P<0.0001).
However, no significant difference was observed between the Na content of insect excreta between the two plant varieties after salt treatment, despite the differential accumulation of Na in the leaf.
P.spumarius insects can be used to sample xylem fluid. When salt stressed, sodium ion concentration of the xylem sap increased in both plant varieties. The basis of the differential accumulation of salt is not reflected in large changes in xylem salt concentration. More work is to be carried out to elucidate this further.
22) S.K. Winch and J. Pritchard, Root extension and apoplastic pH: the effects of drought SEB poster abstract J. Exp Bot. [P8.06], Canterbury 1997.
Root growth is affected by drought. These changes can be mediated by alterations in cell wall properties. The acid growth hypothesis indicates that cell wall pH and wall properties are correlated.A negative relationship was observed between long-term (>24h) osmotic stress and maize root elongation rate. Unstressed roots grew at 2.6 ± 0.1 mm h-1. 200 mM mannitol (0.46 MPa) caused a slight reduction in mean growth rate (2.2 ± 0.1 mm h-1) whereas 400 mM mannitol (0.96 MPa) reduced the rate to (1.1 ± 0.1 mm h-1).pH microelectrodes were constructed and used to measure apoplastic pH. A negative correlation between mannitol stress and the rate of apoplastic acidification was recorded. In unstressed roots the mean rate of apoplastic acidification in the growing zone was 0.06 pH units min-1, which was significantly higher (p < 0.001) than that of the mature (non-growing) region (0.04 pH units min-1). An osmotic stress of 0.46 MPa caused a decrease in the rate of acidification in both growing and non-growing zones (0.04 and 0.01 pH units min-1 respectively). 400 mM mannitol (0.96 MPa) elicited a further reduction in acidification in the growing region (0.02 pH units min-1). Growth rate of roots showed a negative correlation with changes in cell wall pH. The short-term effects of osmotic stress are currently under investigation.Bengough G, Croser C Pritchard J (1997) A biophysical analysis of root growth under mechanical stress. Plant and Soil 155-164
23 Pritchard_J (1998) Control of root growth: Cell walls and turgor In ‘ Variation in growth rate and productiivity of higher plants’ eds H. Lambers, H Poorter and MMI van Vuuren 1998, pp 1-9, Backhuys Publishers, Leiden, The Netherlands
24 Winch S, Pritchard J (1999) Acid-induced wall loosening is confined to the accelerating region of the root growing zone J EXP BOT 501481-1487
25 Malone M, Watson R and Pritchard J (1999) The spittle bug Philaenus spumaris feeds from mature xylem at the full hydraulic tension of the transpiration stream. New Phytologist 143 261-271.
26 Croser C, Bengough. A.G., and Pritchard. J. (2000) The effect of mechanical impedance on root growth in pea (Pisum sativum L.). 1. Rates of cell flux and mitosis. New Phytologist (In Press)
27 Croser C., Bengough. A.G., and Pritchard. J. (2000). The effect of mechanical impedance on root growth in pea (Pisum sativum L.). 2. Cell expansion and wall rheology during expansion (In Press)