Late Maturation of Large Metaxylem Vessels in Soybean Roots: Significance for Water and Nutrient Supply to the Shoot

The large, late metaxylem (LMX) in the roots of soybean beginsdevelopment in the centre of the stele after lignification ofthe early metaxylem poles. Subsequent maturation of the firstappearing LMX elements is gradual. They were never mature inthe 8-d-old seedlings examined. In 10 to 15-d-old plants thefirst LMX matured to open vessels at a mean of 17 cm proximalto the root tip. Additional LMX vessels developed in more proximalregions of the roots and these also matured gradually. Based on calculations from relative vessel diameters, the potentialflow of xylem sap in a single central LMX vessel is 50 timesthat in the total of all the early metaxylem (EMX) vessels ofa typical primary root of soybean. There was a marked dependence of relative leaf area on the lengthof primary root with open LMX vessels. This may result fromthe predicted increased water and nutrient flow to the shoot,facilitated by the opening of the large vessels. It is suggestedthat, as in maize, the living LMX elements may function in ionaccumulation. Dicotyledonous roots, soybean, Glycine max, xylem vessels, xylem maturation, water conduction     

Pathways and processes of water and nutrient movement in roots

Recent work in our laboratory provides evidence for a revised view of the functioning of roots of maize, and probably of all the grasses. The development of coherent soil sheaths on the distal 30-cm of these roots, and the loss of the sheaths further back, led us to investigate the differences in surface structure, anatomy, carbon exudation and microflora of the sheathed and bare zones. The significant differences are summarized. But the fact which underlies all these differences is the maturation of the late metaxylem (LMX). In the sheathed zones the LMX elements are still alive and non-conducting; only the early metaxylem (EMX) and protoxylem are open. In the bare zones they are open vessels. This leads directly to the dryness of bare zones and the wetness of sheathed zones, and indirectly to the other differences noted. Branch root junctions are shown to be structures of great significance. Besides connecting the branches to the axile systems, they serve also to connect the EMX and LMX vessels, and contain a tracheid barrier which prevents air embolisms entering the main vessels. These discoveries force us to revise the traditional view of water uptake by the root hair zone, and to suggest that much water must also enter bare roots, possibly via the laterals. There is some published evidence for this. The living LMX elements of the sheathed zone accumulate large concentrations of potassium which must joint the transpiration water at the transition to the bare zone. Calculations suggest that this may be only a tenth of the requirement of a mature plant, and that the balance may enter the bare zones with the transpiration water.     

Accumulation of high levels of potassium in the developing xylem elements in roots of soybean and some other dicotyledons

Summary Potassium concentrations have been determined by cryo-analytical scanning microscopy in vacuoles of cells of the roots of soybean and six other dicotyledons. Developing vessel elements accumulate the highest concentration of potassium in any cell type in these roots, and those of the secondary xylem have more (median 190 mM normalized to 120%) than those of either the early (median 100 mM, normalized 80%) or late metaxylem (median 110 mM, normalized 100%). Potassium concentration in these developing vessels always exceeds those of their adjacent parenchyma (60–80%), which in turn are higher than those in cells of the cortex (30–40%), including the endodermis. Potassium concentration in the vessels increases during their development until cell death and maturation when it drops dramatically (normalized 4–12%). Developing vessel elements are clearly major sites of potassium accumulation in roots and need to be considered in any models of ion uptake, accumulation, circulation, or exudation.Abbreviations EDX energy dispersive X-ray microanalysis - EMX early metaxylem - K elemental potassium - LMX late metaxylem - CSEM cryo-scanning electron microscopy - SX secondary xylem Dedicated to the memory of Professor John G. Torrey     

Effects of Temperature on the Development of Metaxylem in Primary Wheat Roots and Its Hydraulic Consequence

The effects of different temperatures on the development ofmetaxylem were studied in the primary seminal root of winterwheat (Triticum aestivum L.) seedlings. Xylem development wasstudied microscopically at different distances behind the rootapex after safranin staining to reveal lignification. Diameter of the central late metaxylem (LMX) and its proportionto the stele cross-sectional area increased in the acropetaldirection. Diameter of the LMX and stele decreased with an increasein growing temperature. Numbers of early metaxylem (EMX) wereseven, seven and six at 10, 20 and 30 C, respectively. EMXwas lignified much more rapidly than the LMX along the seminalroot axes. Lignification of xylem elements commenced furthertowards the root apex at the higher temperatures. The LMX vesselsof the roots grown at the higher temperature had thicker secondarywalls. The relative conductivity of seminal roots, calculated fromPoiseuille's equation, decreased as growing temperature increased.In a drought-prone environment where wheat plants rely heavilyon stored soil water, a lowered axial conductivity in the rootswould be advantageous. The plants would tend to conserve waterduring vegetative growth for use during the critical periodsof flowering and grain-filling. Breeders selecting wheat plants for altered LMX diameters shouldcontrol temperatures during primary root development, sectionthe roots at the same distance from the tip and be aware thatcross walls may exist in the LMX for up to 30 cm from the tip. Wheat, Triticum aestivum L., roots, xylem development, hydraulic conductivity, temperature     

Are radial changes in vascular anatomy mechanically induced or an ageing process? Evidence from observations on buttressed tree root systems

To investigate the effect of changes in mechanical loading conditions on radial anatomical patterns, we here compare the trunk with the roots in two locations of three species of buttressed trees. The proximal part of the buttress roots is highly mechanically loaded throughout juvenile growth whereas the distal part of the buttresses is though to be mechanically unimportant at formation but become progressively more mechanically loaded during growth. We measured the frequency and diameter of the vessels and the vessel area fraction, and from this calculated the specific conductivity of tissue samples of the core-, intermediate- and outer wood. As in previous studies there was an increase in vessel size, vessel area fraction and specific conductivity from the pith to the bark in the trunk. In the proximal part of the buttress roots, however, there was no increase in vessel size and conductivity from core wood and out in agreement with the high mechanical loading found here throughout growth. There was instead a decrease in vessel size, vessel area fraction and specific conductivity from core- to outer wood in the distal part of the buttress roots in accordance with the increase in mechanical loading. Hence, it appears that the radial anatomical patterns are not a passive function of cambial ageing but may be modified in response to local mechanical loading.     

Changes in axial hydraulic conductivity along elongating leaf blades in relation to xylem maturation in tall fescue

Xylem maturation in elongating leaf blades of tall fescue ( Festuca arundinacea ) was studied using staining and microcasting. Three distinctive regions were identified in the blade: (1) a basal region, in which elongation was occurring and protoxylem (PX) vessels were functioning throughout; (2) a maturation region, in which elongation had stopped and narrow (NMX) and large (LMX) metaxylem vessels were beginning to function; (3) a distal, mature region in which most of the longitudinal water movements occurred in the LMX. The axial hydraulic conductivity ( K _h) was measured in leaf sections from all these regions and compared with the theoretical axial hydraulic conductivity ( K _t) computed from the diameter of individual inner vessels. K _t was proportional to K _h throughout the leaf, but K _t was about three times K _h. The changes in K _h and K _t along the leaf reflected the different stages of xylem maturation. In the basal 60 mm region, K _h was about 0.30±0.07 mmol s⁻¹ mm MPa⁻¹. Beyond that region, K _h rapidly increased with metaxylem element maturation to a maximum value of 5.0±0.3 mmol s⁻¹ mm MPa⁻¹, 105 mm from the leaf base. It then decreased to 3.5±0.2 mmol s⁻¹ mm MPa⁻¹ near the leaf tip. The basal expanding region was observed to restrict longitudinal water movement. There was a close relationship between the water deposition rate in the elongation zone and the sum of the perimeters of PX vessels. The implications of this longitudinal vasculature on the partitioning of water between growth and transpiration is discussed.     

Hydraulic propagation of pressure along immature and mature xylem vessels of roots of Zea mays measured by pressure-probe techniques

Turgor pressure was measured in cortical cells and in xylem elements of excised roots and roots of intact plants of Zea mays L. by means of a cell pressure probe. Turgor of living and hence not fully differentiated late metaxylem (range 0.6–0.8 MPa) was consistently higher than turgor of cortical cells (range 0.4–0.6 MPa) at positions between 40 and 180 mm behind the root tip. Closer to the tip, no turgor difference between the cortex and the stele was measured. The turgor difference indicated that late-metaxylem elements may function as nutrient-storage compartments within the stele. Excised roots were attached to the root pressure probe to precisely manipulate the xylem water potential. Root excision did not affect turgor of cortical cells for at least 8 h. Using the cell pressure probe, the propagation of a hydrostatic pressure change effected by the root pressure probe was recorded in mature and immature xylem elements at various positions along the root. Within seconds, the pressure change propagated along both early and late metaxylems. The half-times of the kinetics, however, were about five times smaller for the early metaxylem, indicating they are likely the major pathway of longitudinal water flow. The hydraulic signal dissipated from the source of the pressure application (cut end of the root) to the tip of the root, presumably because of radial water movement along the root axis. The results demonstrate that the water status of the growth zone and other positions apical to 20 mm is mainly uncoupled from changes of the xylem water potential in the rest of the plant.Abbreviations and Symbols CPP cell pressure probe - EMX early metaxylem - LMX Late metaxylem - P_c cell turgor - P_r root pressure - RPP root pressure probe - t_1/2,c half-time of water exchange across a single cell - t_1/2 half-time of water exchange across multiple cells We thank Antony Matista for his expert assistance in the construction and modification of instruments. The work was supported by grant DCB8802033 from the National Science Foundation and grant 91-37100-6671 from USDA, and by the award of a Feodor Lynen-Fellowship from the Alexander von Humboldt-Foundation (Germany) to J.F.     

Persistent xylem cross-walls reduce the axial hydraulic conductivity in the apical 20 cm of barley seminal root axes: implications for the driving force for water movement

Abstract. Xylem vessels in the apical 25 cm of barley seminal axes were examined by scanning electron microscopy of fractured freeze dried or critical point dried specimens. In the apical 11 cm, there were three cross walls cm⁻¹ root in the central xylem vessel. The frequency then declined with distance but did not become less than 1.0 cm⁻¹ root until the 22–25-cm zone.
Suction was applied to the proximal end of segments of seminal axes whose surfaces had been sealed with wax to prevent radial entry of water. Perfusion of the xylem with solutions of Tinopal CBS-X revealed the conductive xylem vessels by fluorescent staining of their walls. In the apical 20 cm of the axis, only a variable number of smaller xylem vessels conduct water. Beyond this zone, the much larger central vessel becomes functional.
The flow of water (Jv) in the apical zone was very much less for a given presure (△P) than in the proximal zone > 25 cm from the tip, and could be predicted by the Poiseuille equation provided the correct number of functional vessels are known. This information, together with earlier results on water uptake along the root length are used to predict the attenuation of the hydrostatic driving force for water uptake along the root length.
Estimates of K⁺ concentrations in stelar parenchyma and xylem vessels were made by electron microproble X-ray analysis. These results show that [K⁺] in the xylem vessels may be two to three times greater in the zone 1–2 cm from the root tip than in the basal zone. Such a gradient of solute potential may, to some extent, offset the decreasing influence of the leaf water potential in apical zones where xylem is not fully conductive.     

Vessel development and the importance of lateral flow in water transport within developing bundles of current-year shoots of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.)

In the developing xylem bundles of young stems, the presence of immature living vessel elements can strongly restrict or even block axial hydraulic conductance, especially in newly matured vessels. Lateral connections between vessels may provide an alternative pathway for water movement to bypass these closed, living elements. Using the grapevine as a model system, the present study aimed to demonstrate the effects of living vessel elements on water movement patterns, and the importance of lateral flow for effective water conductivity in the developing bundles. Living vessel elements were detected using dye staining and the pattern of vessel development and maturation was then monitored. The importance of lateral flow was confirmed using several approaches: (1) capacity for lateral flow, (2) effect of increasing the distance of water transport, and (3) effect of ion concentrations. Living vessel elements were found along the developing bundles, they occupied a significant proportion of the distal and peripheral parts of the flow path, forming a substantial barrier to apoplastic water flow. Water in the developing xylem bundles could move easily from vessel to vessel and between secondary and primary xylem. Furthermore, data from increasing the transport length and altering the ion concentrations supported the critical contribution of the lateral flow to the total hydraulic conductance within the developing bundles. The hydraulic architecture of the developing xylem bundles is described. The results are discussed in terms of reliability and efficiency of water transport during shoot growth and development.     

Xylem of rattans: vessel dimensions in climbing palms

We examined 11 species in four genera of rattans (Calamus, Daemonorops, Korthalsia, Plectocomia) growing in their native rainforest habitat in Singapore. Using aqueous safranin dye, we found that >95% of all vascular bundles at the base of a mature stem were functioning to transport water. We determined the frequency of vessel lengths in the long stems of these climbing palms by infiltration with dilute latex paint. Separate length distributions were made for metaxylem and protoxylem vessels; in both, there were many short and a few long vessels. The longest protoxylem vessels ranged from 7.5 to 62 cm in length, but one stem had an exceptional protoxylem vessel measuring 3.0 m. Maximum metaxylem vessel diameters were positively correlated to maximum vessel lengths in these species. The longest metaxylem vessel was found in K. rigida and was 3.96 m in length and was constructed from ～1200 vessel elements (cells). The widest vessel in that same stem was 532 μm in diameter. Long, wide vessels decrease resistance and increase water transport efficiency. In addition, we suggest that wide metaxylem vessels may have an important function in water storage.     

Development of water conducting capacity in the root systems of young plants of corn and some other c4 grasses

Development of the primary and early nodal roots was studied in Zea mays L., Zea mexicana (Schrad.) Reeves & Mangelsd., Sorghum bicolor (L.) Moench., and Sorghum sudanese (Piper) Stapf. in relation to shoot development. In all the types studied all roots reached lengths of about 30 centimeters before the late metaxylem (LMX) was open, and young plants with total root lengths of around 100 centimeters had almost no open LMX. On average, corn seedlings with up to 36 square centimeters of leaf had no open LMX. The name “immature apices” is suggested for such long but not fully functional roots. In plants up to 50 days old a fairly constant proportion of less than half the total root length had open LMX. A pilot study of stomatal resistance on days of high evaporative demand suggested that young seedlings may show higher resistance than older plants in the afternoon. Estimates of longitudinal permeability of corn roots with only early metaxylem vessels open indicate very steep gradients of water potential would develop under such conditions.     

PROTOXYLEM MATURATION IN THE SEEDLING LEAF OF WHEAT

Protoxylem (PX) maturation was followed in vascular bundles of the first foliage leaf (L#1) of wheat seedlings, using clearings and sectioned materials to assess development changes. L#1 contained seven to 11 longitudinal bundles. The seven bundles with largest diameters contained PX vessels, but the number of bundles with PX varied with leaf length. Repeated vessel maturation maintained PX continuity as older vessels collapsed due to leaf extension. Thus, the number of PX vessels in each bundle was also a function of leaf length, and the PX content of a bundle was a function of the stage of leaf development and how soon during leaf development the bundle attained mature PX. Distance from the leaf tip to the start point for PX was greater for bundles later to mature. Thus, the pattern of distal start points in mature leaves reflected the progression of PX maturation from the midrib to bundles of lower rank. It is suggested that the involvement of more and more bundles in PX maturation as the leaf ages is a general occurrence in grass leaves, and that assessing how many bundles will have PX requires observations late in leaf development.     

The free thoracoumbilical flap for resurfacing large soft-tissue defects of the lower extremity

Both cadavers and living patients were studied regarding a method to resolve large skin defects with bone exposure in the leg, with long-distance thrombosis of the anterior tibial vessels or posterior tibial vessels resulting from traumatic lesions. Forty-six casting mold specimens of cadaveric legs were investigated. There were rich communication branches among the anterior tibial artery, posterior tibial artery, and fibular artery in the foot and ankle, which complemented each other well. Twenty-six patients with large skin defects with bone exposure in the proximal or middle segment of the leg were admitted to the authors' hospital. Among those patients, 19 demonstrated long-distance thrombosis of the anterior tibial vessels or posterior tibial vessels resulting from traumatic lesions. During treatment, a thoracoumbilical flap based on the inferior epigastric vessels was anastomosed to the distal stump of the anterior tibial vessels or the posterior tibial vessels, with reversed flow. All defects were successfully repaired, with good color and texture matches of the flaps. This method can be used for patients with normal anterior tibial vessels or posterior tibial vessels, normal distal stumps of the injured blood vessels, and good reversed flow. The method has the advantages of dissecting blood vessels in the recipient area during the débridement, not affecting the blood circulation of the injured leg, not sacrificing blood vessels of the opposite leg, and not fixing the patient in a forced posture. The muscles are less bulky in the distal one-third of the leg, and the blood vessels are shallow and can be dissected and anastomosed easily. When the flap is used for reconstruction in the proximal two-thirds of the leg, the blood vessel pedicle of the free flap is at a straight angle, without kinking.     

Actin filaments, stereocilia, and hair cells of the bird cochlea. III. The development and differentiation of hair cells and stereocilia

The cochleae of chick embryos of 8 days of incubation until hatching (21 days) were examined by scanning electron microscopy. Unlike what one would expect from the literature, the total number of hair cells per cochlea (10,405 +/- 529) is already determined and visible in a 10-day embryo and the growth of the cochlea is a result of the growth in size and surface area of the hair cells. We also find that the hair cells differentiate simultaneously throughout the cochlea and have followed the differentiation of individual hair cells throughout development. During development we find that the total number, hexagonal packing, and orientation of the stereocilia in each hair cell is determined early and accurately (9- to 10-day embryos). The stereocilia then begin to elongate in all the cells of the cochlea at approximately 0.5 micron/day. By Day 12 the tallest stereocilia in each cell are 1.5-1.8 micron long, the mature length for cells at the proximal end of the cochlea. At this point all stereocilia cease elongating, but those along the inferior edge gradually increase in width from 0.11 micron to maximally 0.19 micron in 17-day embryos. When the stereocilia on the inferior edge reach their mature width, widening ceases and the elongation of stereocilia in the distal hair cells begins again. When these stereocilia have attained their mature lengths, they stop growing. Thus elongation and widening of stereocilia are separated in time. During this period, 11 to 13 days, the shape of the tufts at the proximal end of the cochlea changes. This occurs because stereocilia in the front of each tuft are absorbed while others at the sides appear de novo. This rearrangement converts a circular bundle of stereocilia to a rectangular bundle.     

Development of biochemical specialization and organelle partitioning in the single-cell C4 system in leaves of Borszczowia aralocaspica (Chenopodiaceae)

The terrestrial plant Borszczowia aralocaspica (Chenopodiaceae) has recently been shown to contain the entire C(4) photosynthesis mechanism within individual, structurally and biochemically polarized chlorenchyma cells rather than in a dual cell system, as has been the paradigm for this type of carbon fixation (Nature 414: 543-546, 2001). Analysis of carbon isotope composition and (14)CO(2) fixation shows that photosynthesis and growth of B. aralocaspica occurs through carbon acquired by C(4) photosynthesis. The development of this unique single-cell C(4) system in chlorenchyma cells was studied by analysis of young (0.2-0.3 cm length), intermediate (ca. 0.5-0.6 cm length), and mature leaves (ca. 3 cm length). The length of chlorenchyma cells approximately doubles from young to intermediate and again from intermediate to the mature leaf stage. In young chlorenchyma cells, there is a single type of chloroplast; the chloroplasts are evenly distributed throughout the cytosol, and all contain starch and rubisco. During leaf development, the activities of phosphoenolpyruvate carboxylase (PEPC; which is cytosolic), rubisco, and pyruvate,Pi dikinase (PPDK) increase on a chlorophyll basis. As leaves mature, chloroplasts differentiate into two distinct structural and biochemical types that are spatially separated into the proximal and distal parts of the cell (the proximal end being closest to the center of the leaf). The early stages of this polarization are observed in intermediate leaves, and the polarization is fully developed in mature leaves. The chloroplasts in the distal ends of the cell have reduced grana and little starch, while those at the proximal ends have well-developed grana and abundant starch. In mature leaves, PPDK is expressed in chloroplasts at the distal end of the cells, while rubisco and adenosine diphosphate glucose (ADPG) pyrophosphorylase are selectively expressed in chloroplasts at the proximal end of the cell. Mitochondrial polarization also occurs during development as nicotinamide-adenine dinucleotide phosphate-malic enzyme (NAD-ME) and the photorespiratory enzyme glycine decarboxylase are expressed in mature but not young leaves and are localized in mitochondria at the proximal end of the cells. The data show that single-cell C(4) develops from a single pool of identical organelles that develop differential biochemical functions and spatial partitioning in the cell during maturation.     

Dosimetric penumbra effects in catheter-based intravascular brachytherapy using a centered photon or beta line source

Purpose: In catheter-based intravascular brachytherapy, either photon or beta emitters are often used in a linear arrangement so that blood vessels of 10-30 mm lengths can be treated. With a line source, the dose gradient in the radial direction and longitudinal direction depend on the type of radionuclides used in the treatment. The purpose of this study was to investigate the dose fall-off at the edges of a linear source in a blood vessel for different types of photon and beta emitters.Materials/Methods: Dose distributions were calculated on cylindrical blood vessels of various radii. Radioactive sources of 192Ir, 125I, 103Pd, 188Re, 32P, and 90Y/Sr were studied. All the sources were assumed to be in the form of a line. The dose rate at a point in space produced by a radioactive source was computed by integrating the point dose rate kernel of the corresponding radionuclide over the radioactive line. The point dose rate kernel was computed with Monte Carlo simulation of radiation transport. The edge effects were characterized with three newly defined quantities: longitudinal dose uniformity (LDU), effective coverage length (ECL), and margin length (ML). LDU was defined as the ratio of dose at a distance along the long axis of the vessel to the dose at center. ECL was defined as the length over which the LDU was greater than 0.95. ML was defined as half of the length difference between source length L and ECL, which is essentially the length segment at each edge that is covered by the source physical length but is being underdosed.Results: All beta emitters provided more uniform dose distributions and covered a larger portion of blood vessels longitudinally than photon emitters. Typical MLs were 2-3 mm for beta emitters and 4-6 mm for gamma emitters. As the radial depth of the point of interest increased, both the LDU and ECL decreased and ML increased. The ML increased from 2 to 3 mm for beta emitters and from 4 to 6 mm for photon emitters when the radial depth of the point of interest increased from 1.5 to 2.5 mm (typical proximal and distal media points for a 3-mm diameter lumen). The ML increased with increasing source length for all radionuclides. For beta emitters the ML increased initially from 1.5 mm to more than 2.5 mm as source length increased from 5 to 10 mm. When the source length was longer than 15 mm, the ML remains nearly constant, about 3 mm. For photon emitters, ML increased continuously from 1.5 mm to more than 6.0 mm, as source length increased from 5 to 50 mm.Conclusions: A formalism to quantify the dose uniformity along the length of a blood vessel undergoing catheter-based intravascular brachytherapy has been developed. This formalism was used to study the edge effects at the ends of several beta and photon sources. The results indicated that for a centered source the ML at each end due to penumbra effects was about 2 to 3 mm for beta emitters; about 4-6 mm for photon emitters. The ML increases as the radial depth of point of interest in the vessel increases. The ML increases also with increasing source length, especially for photon sources.     

Na-K]ATPase activity in proximal and distal tubules of the rat kidney: modification and application of a quantitative cytochemical technique

A modified cytochemical assay for [Na-K]ATPase in cryostat sections of kidney was further characterized and used to quantify activity in seven functionally distinct sites along the rat nephron. The activity of [Na-K]ATPase was defined as the difference in ATPase activity in specifically identified tubules contained in serial sections incubated with and without ouabain. Preincubation of sections with ouabain was required for maximal inhibition of [Na-K]ATPase activity in several distal sites. The concentration of ouabain necessary for maximal inhibition of activity was 3.0 mM and half-maximal inhibition was obtained in all regions with 30-100 microM ouabain. In distal sites, [Na-K]ATPase formed a higher proportion of total ATPase activity (60-80 per cent) than in proximal sites (20-40 per cent). Enzyme activity was quantified using two different methods. The first measured activity over the basal region of tubules and gave an index of the concentration of [Na-K]ATPase over the basal lateral infoldings of cells composing the tubule. The second read activity over the entire cross section of tubules and provided an estimate of [Na-K]ATPase per length of tubule. The highest activities over the basal basal region were obtained from tubules of the distal nephron including the inner (MALin) and outer (MALout) medullary ascending limb, distal convoluted tubule (DCT) and connecting segment (CS). Lower activities were obtained in proximal convoluted (PCT) tubules, proximal straight (PS) tubules and the papillary collecting duct (PD). Distal convoluted tubules contained the highest activity per length of tubule. Other sites contained lower levels of activity in the following order: MALin greater than MALout greater than PCT greater than PD greater than PS. The modifications introduced increase the sensitivity and precision of this assay and permit the application of this technique to studies of [Na-K]ATPase activity in the major functional regions of the rat nephron.     

An ultrastructural study of acid phosphatase localization in Phaseolus vulgaris xylem by the use of an azo-dye method.

The localization of acid phosphatase during xylem development has been examined in the bean, Phaseolus vulgaris. The azo dye, the final reaction product, is initially prominent in the dictyosomes, vesicles apparently participating in secondary wall formation, and in the middle lamella of the young vessel element. Final reaction particles are also present in mitochondria, chloroplasts, and certain vacuoles and are sparsely scattered in the cytoplasm. At a later stage of vessel differentiation, the azo dye is concentrated in the disintegrating cytoplasm and along the fibrils of the partially hydrolysed primary wall and middle lamella. In the mature vessel element, the azo dye is still present along the disintegrated primary wall at the side of the vessel and covers the secondary wall. In the parenchyma cell adjacent to the vessel element, acid phosphatase localization is found in the dictyosomes, endoplasmic reticulum, mitochondria, small vacuoles, and the middle lamella. The controls from all stages of vessel element development were free of azo dye particles. The concentration of acid phosphatase along the secondary walls of the mature vessels and in the middle lamella between other cells indicates that this enzyme has other functions besides autolysis of the cytoplasm and primary cell wall. Acid phosphatase may participate in the formation of the secondary wall and may also have a role in the secretion and transport of sugars.     

Effect of moderate salinity on patterns of potassium, sodium and chloride accumulation in cells near the root tip of barley: Role of differentiating metaxylem vessels

X-Ray microanalysis of fully hydrated, bulk-frozen samples was used to measure concentrations of potassium, sodium and chloride in various cell types along seminal roots of barley ( Hordeum vulgare L. cv. California Mariout) seedlings (1 to 150 mm from the tip). In the cytoplasm of all meristematic cells 1 mm from the root tip, the average concentrations of potassium and chloride were ca 200 and 15 m M , respectively. The potassium level was also high in the vacuoles of incipient xylem elements and did not drop to significantly lower values until 10 mm from the tip in protoxylem, 50 mm in early metaxylem and 150 mm in late metaxylem (LMX). Light microscopy observations (Nomarski optics) of hand-cut sections showed the presence of cytoplasmic strands and also the presence of intact cross walls in LMX up to a distance of 100 mm. Both quantitative analysis of ion contents and structural observations suggested that LMX elements act as a large transitional sink of accumulated ions and therefore may not function as a main pathway of transport until perforation of the end wall takes place 100–150 mm from the root tip. Treatment with 50 m M NaCl resulted in higher concentrations of sodium and chloride in LMX elements than in the surrounding cells, suggesting that living xylem elements, which develop a large central vacuole at an early stage of root differentiation, may assist in alleviating salinity stress in the meristematic region of barley root tips. Further, it is proposed that reabsorption of sodium and chloride from the LMX, especially before the disappearance of the cross walls, may provide a means of salinity tolerance.     

Basal body replication in green algae--when and where does it start?

Basal body duplication in the green alga Spermatozopsis similis was reinvestigated using GT335, an antibody binding to polyglutamylated tubulins, and antibodies directed to p210, a component of the flagellar transition region which represents the distal border of the basal body. p210 was also detected in small spots at the base of each basal body which increased in size prior to mitosis. The presence of p210 on one of the microtubular flagellar roots suggested a transport of basal body material along these tracks. Immunogold electron microscopy confirmed the presence of p210 in the probasal bodies. Further, small probasal bodies are apparently connected to the mature basal bodies by centrin fibers as observed after artificially induced basal body separation in Xenopus egg extract. While basal bodies grew, most of the p210 remained at the tip of elongating basal bodies, but two or four additional spots were observed in distinct patterns near the base of the basal bodies. In cytokinesis, basal body pairs separated and p210 was observed in a strong signal at the tip and a weaker one in the vicinity of the proximal end of each basal body. We interpret the data as indicating that a new p210-containing structure forms near the proximal end of the basal bodies during basal body elongation, representing the precursor of the next generation of basal bodies. Thus, basal bodies appear to seed the succeeding generation already during their own development, a mechanism which could ensure the correct number and position of basal bodies.