Response to oxygen deficiency in primary maize roots. I. Development of oxygen deficiency in the stele reduces radial solute transport to the xylem

1998 ◽  
Vol 25 (6) ◽  
pp. 745 ◽  
Author(s):  
J. Gibbs ◽  
D.W. Turner ◽  
W. Armstrong ◽  
M.J. Darwent ◽  
H. Greenway
Keyword(s):  
Solute Transport ◽  
Oxygen Deficiency ◽  
Pressure Probe ◽  
Root Pressure ◽  
Primary Roots ◽  
Root Pressure Probe ◽  
O2 Supply ◽  
Dependent Transport ◽  
Energy Dependent ◽  
Oxygen Concentrations

A root pressure probe and transport of 36Cl- from the medium to the xylem were used to test whether development of oxygen deficiency in the stele, but not the cortex, reduces radial solute transport in excised primary roots of maize. Oxygen micro-electrodes demonstrated that a core of anoxia developed within the stele of roots exposed to 0.05 mol m-3 O2 at 25°C, and that oxygen concentrations in the pericycle were near or below the Km for O2 uptake by cells, while oxygen concentrations in the endodermis, cortex and epidermis were sufficient to fully support oxidative phosphorylation. Decreasing the external O2 concentration from 0.27 mol m-3 (aerated) to 0.05 mol m-3 decreased root pressure by about 45% to a new steady state over 4–6 h. Uptake of 36Cl- by roots grown without Cl- demonstrated that the decrease in root pressure at low O2 concentrations was almost fully accounted for by a decrease in the rate of net radial energy-dependent ion transport into the xylem. Even so, some energy-dependent transport continued at low O2 supply. The data suggest that energy-dependent solute transport into the xylem is one of the first processes adversely affected when O2 supply to roots is low, and provide further evidence against the classical theory of radial solute transport (Crafts-Broyer hypothesis).

Energy dependent transport length scales in strongly diffusive carbon nanotubes

2006 ◽  
Vol 18 (19) ◽  
pp. 4581-4587 ◽  
Author(s):  
B Lassagne ◽  
B Raquet ◽  
J M Broto ◽  
J González
Keyword(s):  
Carbon Nanotubes ◽  
Length Scales ◽  
Transport Length ◽  
Dependent Transport ◽  
Energy Dependent

Mucilage exudation facilitates root water uptake in dry soils

2014 ◽  
Vol 41 (11) ◽  
pp. 1129 ◽  
Author(s):  
Mutez A. Ahmed ◽  
Eva Kroener ◽  
Maire Holz ◽  
Mohsen Zarebanadkouki ◽  
Andrea Carminati
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Root Surface ◽  
Pressure Probe ◽  
Root Pressure ◽  
Plant Trait ◽  
Suction Cup ◽  
Relaxation Curves

As plant roots take up water and the soil dries, water depletion is expected to occur in the rhizosphere. However, recent experiments showed that the rhizosphere was wetter than the bulk soil during root water uptake. We hypothesise that the increased water content in the rhizosphere was caused by mucilage exuded by roots. It is probably that the higher water content in the rhizosphere results in higher hydraulic conductivity of the root–soil interface. In this case, mucilage exudation would favour the uptake of water in dry soils. To test this hypothesis, we covered a suction cup, referred to as an artificial root, with mucilage. We placed it in soil with a water content of 0.03 cm3 cm–3, and used the root pressure probe technique to measure the hydraulic conductivity of the root–soil continuum. The results were compared with measurements with roots not covered with mucilage. The root pressure relaxation curves were fitted with a model of root water uptake including rhizosphere dynamics. The results demonstrated that when mucilage is added to the root surface, it keeps the soil near the roots wet and hydraulically well conductive, facilitating the water flow from dry soils towards the root surface. Mucilage exudation seems to be an optimal plant trait that favours the capture of water when water is scarce.

Turgor Pressure in Mechanically Impeded Lupin Roots

1990 ◽  
Vol 17 (1) ◽  
pp. 49 ◽  
Author(s):  
BJ Atwell ◽  
JC Newsome
Keyword(s):  
Volume Expansion ◽  
Root Elongation ◽  
Sandy Loam ◽  
Turgor Pressure ◽  
Mechanical Impedance ◽  
Pressure Probe ◽  
Soil P ◽  
Primary Roots ◽  
Root Apices ◽  
Probe Measurements

Seedlings of lupin (Lupinus angustifolius cv. 75A-258) were grown in cores of sandy loam which was compacted to bulk densities of 1.6 and 1.8 Mg m-3 . There was a substantial decrease in root elongation rate at the higher bulk density. After 4-7 d, roots were rinsed free of soil and clamped loosely in a Perspex block for measurement of turgor pressure (P) using a pressure probe. Measurements were made at 3-4 positions on each root, each estimation taking 2 min. Turgor pressures in the terminal 15 mm of the axes ranged between 0.213 and 0.530 at 1.6 Mg m-3 and 0.210 and 0.570 MPa at 1.8 Mg m-3; mean P values were 0.365 and 0.351 MPa in roots growing at 1.6 and 1.8 Mg m-3, respectively. These measurements were made on roots removed from the soil; P could have been greater in roots still growing in compact soil. Anatomical studies showed that the distal boundary of the zone of cell expansion was 2-4 mm nearer the apex in roots growing at 1.8 than at 1.6 Mg m-3. Using this information, we showed that the mean P of expanding tissue was the same in roots of the two treatments. The apparent rise in P near the apex of roots at 1.8 Mg m-3 was not statistically significant. Primary roots growing against high mechanical impedance had a 34% lower rate of elongation and a 22% greater diameter, resulting in nearly identical rates of volume expansion (35.1 and 34.9 mm3 d-1 at 1.6 and 1.8 Mg m-3 respectively). Furthermore, the rate of O2 uptake was the same in 10 mm root apices from both treatments so that there was no evidence that the carbohydrate requirement for respiration was enhanced by high soil strength. Moreover, while mechanical impedance decreased root elongation, it did not significantly affect our estimate of P. We believe that P in lupin roots changes in response to mechanical impedance only when volume expansion or utilization of solutes are affected.

scholarly journals Fluoroquinolone Transport by Human Monocytes: Characterization and Comparison to Other Cells of Myeloid Lineage

2000 ◽  
Vol 44 (10) ◽  
pp. 2609-2614 ◽  
Author(s):  
Steven J. Bounds ◽  
Robin Nakkula ◽  
John D. Walters
Keyword(s):  
Inhibitory Effect ◽  
Human Monocytes ◽  
Monocytic Differentiation ◽  
Granulocytic Differentiation ◽  
Temperature Dependent ◽  
Myeloid Lineage ◽  
Transport Pathways ◽  
Dependent Transport ◽  
Energy Dependent ◽  
Human Polymorphonuclear Leukocytes

ABSTRACT Human monocytes transport and accumulate ciprofloxacin and other fluoroquinolones. Although little is known about the mechanisms of transport, we expected monocytes to be similar to other cells of myeloid lineage. In the present study, monocyte fluoroquinolone transport was characterized and compared to the corresponding transport pathways of human polymorphonuclear leukocytes (PMNs) and HL-60 cells. Ciprofloxacin transport by monocytes was saturable, temperature dependent, sodium independent, and relatively insensitive to pH. Quiescent monocytes transported ciprofloxacin with aKm of 171 μg/ml and aV max of 32.7 ng/min/106 cells. Adenine competitively inhibited ciprofloxacin transport by quiescent monocytes (Ki = 3.8 mM), but nucleosides had no significant inhibitory effect. In all of these respects, transport by monocytes was similar to that observed for quiescent PMNs and immature HL-60 cells. Unlike PMNs, however, monocytes and immature HL-60 cells did not exhibit dramatically enhanced ciprofloxacin transport when activated by phorbol myristate acetate (PMA). Consistent with this finding, HL-60 cells committed to granulocytic differentiation exhibited a significant component of PMA-inducible ciprofloxacin transport activity, while HL-60 cells committed to monocytic differentiation did not. In PMNs, the PMA-inducible component of transport appeared to be mobilized from a granule compartment, since its activity could be modulated by agents that enhance or inhibit stimulated degranulation. Thus, quiescent monocytes, PMNs, and HL-60 cells take up ciprofloxacin via similar energy-dependent transport mechanisms. Unlike granulocytes, monocytes do not express a second, higher-affinity pathway for ciprofloxacin accumulation when they are activated by PMA.

On the Energy-Dependent Transport Equation

1963 ◽  
Vol 15 (4) ◽  
pp. 476-477 ◽  
Author(s):  
G. C. Summerfield ◽  
P. F. Zweifel
Keyword(s):  
Transport Equation ◽  
Dependent Transport ◽  
Energy Dependent
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