Transport of the Auxin 2,4-Dichlorophenoxyacetic Acid Through Absiccion Zones, Pulvini, and Petioles of Phaseolus vulgaris

Measurements were made of the transport of 2,4-dichlorophenoxyacetic acid-¹⁴C (2,4-D) through segments cut from the region of the distal abscission zone in young and old primary leaves of Phaseolus vulgaris L. When old leaves were used basipetal transport of 2,4-D in segments including pulvinar tissue, abscission zone, and petiolar tissue was much less than in wholly petiolar segments. In both young and old plants, segments consisting entirely of pulvinar tissue transported 2,4-D basipetally at a velocity about half that in petiolar tissue. At both ages the flux of 2,4-D through pulvinar tissue was less than that through petiolar tissue. In segments from old leaves the flux through pulvinar tissue was much less than in young plants; the flux through petiolar tissue changed little with age. There was no change with age in the velocity of basipetal transport. The distribution of ¹⁴C along segments including the abscission zone showed no marked discontinuity. It was concluded that the pulvinus limited the basipetal movement of 2,4-D through segments from old leaves which included both pulvinar and petiolar tissue, but there was no evidence that the abscission zone itself was a barrier to auxin transport.     

Auxin Transport in Tendril Segments of Passiflora caerulea

The movement of auxin through tendril segments of Passiflora caerulca L. has been investigated using IAA-2-¹⁴C. It has been shown that (1) flux of IAA through the segments is strongly polarized basipetally: (2) the amount of ¹⁴C recovered in the basal receiver blocks increases linearly within a transport period of 6 h; (3) velocity of basipetal transport is 14.5 mm h^?1; (4) at least 70% of the radioactivity in the receiver blocks is confined to the IAA molecule: approximately 55% of ¹⁴C from methanolic extracts of the segments is IAA: (5) at low temperatures (2–4°C) the basipetal transport is abolished; (6) white light promotes basipetal transport, and this effect is abolished in a CO₂-free atmosphere; (7) no difference could be detected in ¹⁴C content between dorsal and ventral halves of tendril segments nor among individual dorsal and ventral receiver blocks.     

Polar transport related to mobilization of plant constituents

Indole-3-acetic acid (IAA), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), sucrose, and mannitol, were tested for polar transport through 5-mm hypocotyl segments of bean (Phaseolus vulgaris var. Pinto) seedlings. All 4 compounds were transported in a polar direction. Autoradiographs of segments through which ¹⁴C-labeled compounds were transported indicated areas of ¹⁴C concentration near the morphological base of segments. There was a direct correlation of IAA transport with the ability to initiate roots as well as with the degree of ¹⁴C accumulation in the morphological base of segments. Unlabeled IAA in lanolin applied to segments appeared to reduce transport of IAA-¹⁴C through those segments when measured by the accumulation of ¹⁴C in a receiver-block of agar, caused an increase in ¹⁴C accumulation in the region to which the unlabeled IAA was applied, and also caused a decrease in accumulation of ¹⁴C at the morphological base of upright segments. Histological studies showed that IAA accelerated cell division and the formation of root primordia particularly at the basal ends, and that these responses sometimes occurred at the expense of cell proliferation at the apical ends of segments. The data presented support the hypothesis that polar movement of IAA, and other endogenous and exogenous substances, in isolated stem segments was controlled by mobilization and utilization of plant constituents at the growth centers.     

The effect of cycloheximide on IAA-stimulated transport of 14C-ABA and 14C-sucrose in long pea epicotyl segments

The effect of cycloheximide (CH) on the indol-3yl-acetic acid (IAA)-stimulated transport of ¹⁴C-labelled abscisic acid (ABA) and ¹⁴C-labelled sucrose was studied in 110 mm long pea epicotyl segments. IAA application resulted in elongation growth of the segments. This effect was decreased by CH treatment which also reduced [¹⁴C] ABA and [¹⁴C] sucrose accumulation in the growing apical part of the segments. A reduction in [¹⁴C] IAA uptake and in protein synthesis in this part of the segments was also observed. The simultaneous inhibition of protein synthesis and reduction of [¹⁴C] ABA and [¹⁴C] sucrose transport suggests that IAA can stimulate the transport of ABA and sucrose through a protein synthesis-based elongation growth.     

Transport of 14C-lableled indoleacetic acid in Vicia root segments

IAA transport in Vicia root segments was investigated for comparisonwith that in intact roots. Lanolin paste (1-mm-wide ring) oragar blocks (3?3?1.5mm), both containing IAA-2-¹⁴C were appliedto the surface or a cut end of the root segments, respectively;transported ¹⁴C was collected in receiver agar blocks placedon the cut end of the segments. When lanolin paste was appliedto 5-mm segments, basipetal transport of IAA predominated overacropetal transport. When agar blocks were applied to 1- and2-mm segments, the same was true; in longer segments (3 and5 mm long), however, basipetal movement occurred predominantlyat first but was surpassed by acropetal movement after 2–3hr. Among the segments tested (regions 2–4, 4–6and 8–10 mm from the tip), the most apical one showedthe distinctest predominancy of basipetal movement. The velocitiesof the acropetal and basipetal movement of the ¹⁴C were estimatedat 3–3.8 and 8–12 mm/hr, respectively. Autoradiographicstudy and the experiment in which wire was inserted longitudinallythrough the central part of the segments showed that basipetalmovement occurred mainly through the outer part of the rootsand acropetal movement mainly through the central cylinder.The present results were compatible with those obtained previouslywith intact roots. Some properties of polar movement, such asits specificity, inhibition by TIBA, and dependency on terneprature are described. (Received March 22, 1978; )     

Transport Gradient of Indoleacetic Acid in Pine Seedlings

Movement of indoleacetic acid (IAA-1-¹⁴C) through 5-min segments from stems and roots of Pinus taeda L., P. jeffreyi Gtrev. and Balf., and P. ponderosa Laws, seedlings was measured. All three species showed the same general pattern of IAA-1-¹⁴C transport. Predominantly downward movement occurred at all points along the stem and root; least IAA-1-¹⁴C transport occurred in segments obtained near the shoot apex; and most occurred in segments obtained near or just below the cotyledons. This pattern of transport gradient is different from that reported in other plants. These results could be interpreted in either of two ways: (1) that transport limitations may control movement of the growth-regulator, or (2) that the transport gradient may be an indication of endogenous growth-regulator levels.     

Electroosmotic Phenomena in Plant Tissues

The effect of a direct electric current on electrolyte transport through plant tissues was studied by applying it to 10-mm segments of the mesocotyls of etiolated maize seedlings, similar segments of one-year linden shoots with the normal conducting system and without vascular bundles, and isolated elements of the xylem and cell wall segments. At current densities of 9–38 A/mm² (10–20 V), electrolyte solutions in plant tissues always moved toward the cathode. The results suggest that electroosmosis is one of the factors responsible for changes in solution transport through the conductive plant tissues that occur under the effect of electric current.     

A model for membrane transport through alpha-helical protein pores

In this communication we explore possible mechanisms by which hydrogen-bonded, knobs-into-holes packed side chains from adjoining α-helical segments could function in proton transport through membranes and mechanisms by which proton transport could be coupled to active transport of other substances.     

Possible explanation of IAA-stimulated transport of14C-ABA in long pea (Pisum sativum L.) epicotyl segments

Effects of 2,3,5-triiodobenzoic acid (TIBA) and age of etiolated pea epicotyl segments on the indol-3-ylacetic acid (IAA) stimulated transport of¹⁴C-abscisic acid (ABA) was studied. In spite of a slight decrease of IAA transport after the application of TIBA, the IAA stimulation of¹⁴C-ABA transport did not change. In segments excised from epicotyls of different age,³H-IAA transport was identical and the induction of prolongation growth by IAA in segments from the upper part of the epicotyl was observed. The IAA ap{ie226-01}ation to the growing segments was connected with intensive attraction of¹⁴C-ABA to the site {ie226-02}AA application, while the application of IAA to the older segments was growth ineffective ana no stimulation of¹⁴C-ABA transport by IAA was observed.     

Suitable experimental design for determination of auxin polar transport in space using a spacecraft.

It is necessary to establish a suitable experimental design for the determination of auxin (indole-3-acetic acid: IAA) polar transport in space using a spacecraft in concerning with the role of gravity. Problems in space experiments are as follows: I) Selection of suitable plant species; II) Preservation of integrity of plant segments for activities of auxin polar transport; III) Stop of auxin polar transport of the segments after the transport experiment in space. Segments of etiolated pea epicotyls and etiolated maize coleoptiles showed relatively high activities of auxin polar transport among dicotyledonous and monocotyledonous plants tested, respectively. The activities decreased dramatically when the segments were pre-stored at 25 degrees C only for 1 day. On the other hand, the storage at low temperature (5 degrees C) in the presence of antioxidants or chelating agents, especially EGTA, maintained relatively high activities of auxin polar transport in pea epicotyl segments. Low temperature (5 degrees C) substantially inhibited the activity of auxin polar transport. Based on the results in this study, a suitable experimental design for the space experiment of auxin polar transport using a spacecraft is also proposed.     

Convective flow dominates aerosol delivery to the lung segments

Most previous computational studies on aerosol transport in models of the central airways of the human lung have focused on deposition, rather than transport of particles through these airways to the subtended lung regions. Using a model of the bronchial tree extending from the trachea to the segmental bronchi (J Appl Physiol 98: 970-980, 2005), we predicted aerosol delivery to the lung segments. Transport of 0.5- to 10-μm-diameter particles was computed at various gravity levels (0-1.6 G) during steady inspiration (100-500 ml/s). For each condition, the normalized aerosol distribution among the lung segments was compared with the normalized flow distribution by calculating the ratio (R(i)) of the number of particles exiting each segmental bronchus i to the flow. When R(i) = 1, particle transport was directly proportional to segmental flow. Flow and particle characteristics were represented by the Stokes number (Stk) in the trachea. For Stk < 0.01, R(i) values were close to 1 and were unaffected by gravity. For Stk > 0.01, R(i) varied greatly among the different outlets (R(i) = 0.30-1.93 in normal gravity for 10-μm particles at 500 ml/s) and was affected by gravity and inertia. These data suggest that, for Stk < 0.01, ventilation defines the delivery of aerosol to lung segments and that the use of aerosol tracers is a valid technique to visualize ventilation in different parts of the lung. At higher Stokes numbers, inertia, but not gravitational sedimentation, is the second major factor affecting the transport of large particles in the lung.     

The movement of 2,4-dichlorophenoxy acetic acid in root segments of Pisum sativum L.

Summary An acropetal polarisation of the movement of 2,4-dichlorophenoxy acetic acid (2,4-D) through subapical segments of Pisum seedling primary roots has been monitored throughout a 60 h transport period in darkness at 25° C using [1-¹⁴C]2,4-D and [2-¹⁴C]2,4-D. Uptake of 2,4-D does not proceed at a constant rate; periods in which the amount of ¹⁴C in the root segments and receiver blocks increases rapidly are followed by periods in which the amount of radioactivity remains relatively constant or declines slightly. These oscillations do not appear to be related to the time of day at which the experiments are begun or ended. Immobilisation and degradation of 2,4-D during transport in the segments seems to be low. Replacement of [1-¹⁴C]2,4-D donor blocks after 25 h by blocks containing unlabelled 2,4-D results in continued transport of the compound into receiver blocks, with only small amounts of ¹⁴C remaining in the root tissues. Radioactivity is also exported from the segments into the blocks used to replace the donor blocks, with larger amounts being exported into the blocks applied to the apical ends than into those applied to the basal ends of the segments. This radioactivity may be taken-up again by the segments but more ¹⁴C is exported into these blocks towards the end of the experiments. The possibility of regular oscillations in uptake and movement of 2,4-D in Pisum root segments is discussed.     

Influenza A Virus Assembly Intermediates Fuse in the Cytoplasm

Reassortment of influenza viral RNA (vRNA) segments in co-infected cells can lead to the emergence of viruses with pandemic potential. Replication of influenza vRNA occurs in the nucleus of infected cells, while progeny virions bud from the plasma membrane. However, the intracellular mechanics of vRNA assembly into progeny virions is not well understood. Here we used recent advances in microscopy to explore vRNA assembly and transport during a productive infection. We visualized four distinct vRNA segments within a single cell using fluorescent in situ hybridization (FISH) and observed that foci containing more than one vRNA segment were found at the external nuclear periphery, suggesting that vRNA segments are not exported to the cytoplasm individually. Although many cytoplasmic foci contain multiple vRNA segments, not all vRNA species are present in every focus, indicating that assembly of all eight vRNA segments does not occur prior to export from the nucleus. To extend the observations made in fixed cells, we used a virus that encodes GFP fused to the viral polymerase acidic (PA) protein (WSN PA-GFP) to explore the dynamics of vRNA assembly in live cells during a productive infection. Since WSN PA-GFP colocalizes with viral nucleoprotein and influenza vRNA segments, we used it as a surrogate for visualizing vRNA transport in 3D and at high speed by inverted selective-plane illumination microscopy. We observed cytoplasmic PA-GFP foci colocalizing and traveling together en route to the plasma membrane. Our data strongly support a model in which vRNA segments are exported from the nucleus as complexes that assemble en route to the plasma membrane through dynamic colocalization events in the cytoplasm.     

Gastric mucosal cell homeostatic physiome. Critical role of ER-initiated membranes restitution in the fidelity of cell function renewal.

Homeostatic cell physiology is preserved through the fidelity of the cell membranes restitution. The task is accomplished through the assembly of the precisely duplicated segments of the cell membranes, and transport to the site of their function. Here we examined the mechanism that initiates and directs the restitution of the intra- and extracellular membranes of gastric mucosal cell. The homeostatic restitution of gastrointestinal epithelial cell membrane components was investigated by studying the lipidomic processes in endoplasmic reticulum (ER) and Golgi. The biomembrane lipid synthesis during the formation of transport vesicles in the systems containing isolated organelle and the cell-specific cytosol (Cyt) from rat gastric mucosal epithelial cells was assessed. The results revealed that lipids of ER transport vesicle and the transmembrane and intravesicular cargo are delivered en bloc to the point of destination. En bloc delivery of proteins, incorporated into predetermined in ER lipid environment, ensures fidelity of the membrane modification in Golgi and the restitution of the lipid and protein elements that are consistent with the organelle and the cell function. The mechanism that maintains apical membrane restitution is mediated through the synthesis of membrane segments containing ceramide (Cer). The Cer-containing membranes and protein cargo are further specialized in Golgi. The portion of the vesicles destined for apical membrane renewal contains glycosphingolipids and phosphatidylinositol 3-phosphate. The vesicles containing phosphatidylinositol 4-phosphate are directed to endosomes. Our findings revealed that the preservation of the physiological equilibrium in cell structure and function is attributed to (1) a complete membrane segment synthesis in ER, (2) its transport in the form of ER-transport vesicle to Golgi, (3) the membrane components-defined maturation of lipids and proteins in Golgi, and (4) en bloc transfer of the new segment of the membrane to the cell apical membrane or intracellular organelle.     

The CorA Mg(2+) transport protein of Salmonella typhimurium. Mutagenesis of conserved residues in the second membrane domain

Salmonella typhimurium CorA is the archetypal member of the largest family of Mg(2+) transporters of the Bacteria and Archaea. It contains three transmembrane segments. There are no conserved charged residues within these segments indicating electrostatic interactions are not used in Mg(2+) transport through CorA. Previous mutagenesis studies of CorA revealed a single face of the third transmembrane segment that is important for Mg(2+) transport. In this study, we mutated hydroxyl-bearing and other conserved residues in the second transmembrane segment to identify residues involved in transport. Residues Ser(260), Thr(270), and Ser(274) appear to be important for transport and are oriented such that they would also line a face of an alpha-helix. In addition, the sequence (276)YGMNF(280), found in virtually all CorA homologues, is critical for CorA function because even conservative mutations are not tolerated at these residues. Finally, mutations of residues in the second transmembrane segment, unlike those in the third transmembrane segment, revealed cooperative behavior for the influx of Mg(2+). We conclude that the second transmembrane segment forms a major part of the Mg(2+) pore with the third transmembrane segment of CorA.     

Decarboxylation and transport of auxin in segments of sunflower and cabbage roots

Summary The movement of ¹⁴C from indole-3-acetic acid (IAA) ¹⁴C has been examined in 5 mm root segments of dark-grown seedlings of Helianthus annuus and Brassica oleracea. Contaminants from distilled water, phosphate buffer and the razor-blade cutter increase the decarboxylation of IAA-¹⁴C, and cutting of root segments results in an activation of IAA-destroying enzymes at the cut surfaces. When these sources of errors were eliminated the following was shown: a) Both in sunflower and cabbage there is a slight acropetal flux of ¹⁴C through the root segments into the agar receiver blocks. The amount of ¹⁴C found in the receiver blocks increases with the lenght of the transport period. b) When the root segments, after the transport period, are cut in two equal parts and these assayed separately, the amounts of ¹⁴C in the two parts indicate a greater acropetal than basipetal transport. c) The total radioactivity of the receiver blocks is in part due to IAA-¹⁴C and in part to ¹⁴CO₂, the latter being a result of enzymatic destruction of auxin. d) Addition of ferulic acid, an inhibitor of IAA oxidases, to the receiver blocks markedly inhibits the decarboxylation of IAA-¹⁴C and thus increases the amount transported. This effect is more pronounced after a 20 hr than after a 6 hr transport period.     

Fully efficient chromosome dimer resolution in Escherichia coli cells lacking the integral membrane domain of FtsK

In bacteria, septum formation frequently initiates before the last steps of chromosome segregation. This is notably the case when chromosome dimers are formed by homologous recombination. Chromosome segregation then requires the activity of a double‐stranded DNA transporter anchored at the septum by an integral membrane domain, FtsK. It was proposed that the transmembrane segments of proteins of the FtsK family form pores across lipid bilayers for the transport of DNA. Here, we show that truncated Escherichia coli FtsK proteins lacking all of the FtsK transmembrane segments allow for the efficient resolution of chromosome dimers if they are connected to a septal targeting peptide through a sufficiently long linker. These results indicate that FtsK does not need to transport DNA through a pore formed by its integral membrane domain. We propose therefore that FtsK transports DNA before membrane fusion, at a time when there is still an opening in the constricted septum.     

Transport and metabolism of h-gibberellin a(1) in dioecious cucumber seedlings

The transport of ³H-GA₁ through hypocotyl segments of cucumber (Cucumis sativus L.) was found to be nonpolar. The transport of ³H-GA₁ was increased by pretreatment with relatively high concentrations of either IAA or Ethephon (2-chloroethylphosphonic acid). Hypocotyl segments from plants of a gynoecious genotype transported more ³H-GA₁ than those of an androecious. The metabolism of ³H-GA₁ in hypocotyl segments was neither related to the sex genotype of the cucumber plant nor influenced by pretreatment with Ethephon. The primary metabolite of GA₁ was suggested to be GA₈. Two other suspected metabolites were not identified. Differences in the endogenous GA of gynoecious and androecious plants could not be accounted for by transport differences.     

Role of calcium in the polar secretion of indoleacetic Acid

The rate of auxin transport in sunflower hypocotyls (Helianthus annuus L. cv `Russian mammoth') or corn coleoptiles (Zea mays L. cv `WF9 × 38') was less in seedlings grown in Ca-deficient medium than in controls. The rate of IAA transport depended on the concentration of Ca in the root medium up to 1 millimolar. Further increases in auxin transport were observed when the isolated segments were incubated in medium containing up to 30 millimolar Ca. We suggest that the rate of auxin transport in plant tissue is dependent on the pool of ionic Ca in the extracellular space.

Segments from Ca-deficient seedlings exhibited a high specific requirement for Ca²⁺ in auxin transport. Magnesium, strontium, and several other divalent cations tested for their ability to replace Ca²⁺ in restoring auxin transport showed no effect; partial replacement by lanthanum was observed.

Auxin transport, or auxin flux through the segment, which is the result of IAA secretion by individual cells, was reduced in the low Ca²⁺ segments due both to lowered velocity and to reduced capacity of transport. The requirement for Ca²⁺ in the secretion of auxin is believed to be equivalent to the phenomenon observed in animal cell secretion, where the influx of Ca²⁺ serves as a link between an external stimulus and the secretion response.

     

The molecular and cellular physiology of basolateral organic anion transport in mammalian renal tubules

Basolateral transport of organic anions (OAs) into mammalian renal proximal tubule cells is a tertiary active transport process. The final step in this process involves movement of OA into the cells against its electrochemical gradient in exchange for alpha-ketoglutarate (alphaKG) moving down its electrochemical gradient. Two homologous transport proteins (OAT1 and OAT3) that function as basolateral OA/alphaKG exchangers have been cloned and sequenced. We are in the process of determining the functional distribution and regulation of OAT1 and OAT3 in renal tubules. We are using rabbit OAT1 (rbOAT1) and OAT3 (rbOAT3) expressed in heterologous cell systems to determine substrate specificity and putative regulatory steps and isolated rabbit proximal renal tubule segments to determine functional distribution and physiological regulation of these transporters within their native epithelium. Rabbit OAT1 and OAT3 differ distinctly in substrate specificity. For example, rbOAT1 has a high affinity for the classical renal OA transport substrate, p-aminohippurate (PAH), whereas rbOAT3 has no affinity for PAH. In contrast, rbOAT3 has a high affinity for estrone sulfate (ES), whereas rbOAT1 has only a very slight affinity for ES. Both rbOAT1 and rbOAT3 appear to have about the same affinity for fluorescein (FL). These differences and similarities in substrate affinities make it possible to functionally map transporters along the renal tubules. Initial data indicate that OAT1 predominates in S2 segments of the rabbit proximal tubules, but studies of other segments are just beginning. Transport of a given substrate in any tubule segment depends on both the affinity of each transporter which can accept that substrate as well as the level of expression of each of those processes in that particular tubule segment. Basolateral PAH transport (presumably OAT1 activity) appears to be down-regulated by activation of protein kinase C (PKC) and up-regulated via mitogen-activated protein kinase (MAPK) through phospholipase A(2) (PLA(2)), prostaglandin E(2) (PGE(2)), cyclic AMP, and protein kinase A (PKA) activation.