A non-invasive measurement of phloem and xylem water flow in castor bean seedlings by nuclear magnetic resonance microimaging

A flow-sensitive nuclear magnetic resonance (NMR) microimaging technique was applied to measure directly the in-vivo water flow in 6-d-old castor bean seedlings. The achieved in-plane resolution of the technique allowed discrimination between xylem and phloem water flow. Both the xylem- and the phloem-average flow velocities in the intact seedling could be quantified. Furthermore, the total conductive cross-sectional area of the xylem vessels and the phloem sieve elements could be determined using the non-invasive and non-destructive NMR microimaging technique. Hence, it was possible to calculate the in-vivo volume flow rates for both xylem and phloem water flow. Our non-destructive technique showed that previously used methods to measure phloem water flow affected the flow rate itself. In the intact seedlings we found values of 16.6 l·h^–1, two fold lower than those previously estimated from phloem exudation rates. Finally, our results demonstrate for the first time that water is internally circulated between phloem and xylem, and that water flow within the xylem is maintained by this internally circulated water, even in the absence of any significant transpiration or evaporation.Abbreviation NMR nuclear magnetic resonance     

Non invasive imaging of water flow in plants by NMR microscopy

Summary Water flow in the stems of the horsetailEquisetum hyemale, the flowering plantStachys sylvatica and the mossDendroligotrichum dendroides was observed non-invasively using NMR microscopy. A Pulsed Gradient Spin Echo sequence using a single phase encoding step was used. We demonstrate by this method that water flow inEquisetum occurs in the carinal canals and in the xylem vessels of the vascular tissue ofStachys and in the central water-onducting strand ofDendroligotrichum.Abbreviations CPU central processing unit - ID internal diameter - NMR nuclear magnetic resonance - RF radio frequency - TS transverse section     

Transferzellen im Xylem derValerianaceae

Stems, incl. rhizomes, and roots of 42 species ofValerianaceae were investigated in order to reveal the occurrence, structure and distribution of xylem transfer cells. Within nodes and internodes their frequency, distribution and gradients of development are similar to other families. — Within the secondary xylem of some species transfer cells can develop from cambial derivates, inValeriana tuberosa andPatrinia villosa even from pith cells. Within the turnip ofV. tuberosa transfer cells are very frequent and well developed. Here, after degradation of the cell-wall ingrowths they can be redifferentiated into storage cells which usually contain starch grains (Hüllenstärkekörner). In the transitional zone between stem and root of some predominantly herbaceous taxa transfer cells are often very frequent and form large protuberances before they degrade and lignify. SEM observations inValeriana decussata show that the cell-wall ingrowths are degradated at the beginning of lignification with the exception of brush-like protuberances remaining in the half-bordered pit-pairs. During the subsequent process of lignification the simple pits of a wall adjacent to a vessel can be transformed into corresponding pit-pairs. In this case the residues of the protuberances within the pit chamber can be transformed into incrustations similar to the vestures of bordered pits described byBailey (1933). Structural similarities between the brush-like protuberances in the half-bordered pits of theValeriana transfer cells and the ingrowths found inLauraceae (Castro 1982, 1985) are evident. Supposedly, all the cambial derivatives inValerianaceae can develop protuberances at least within their pits. Thus, it appears possible to interpret the vestures of the bordered pits as rudimentary protuberances, and to suggest that they have a specific function in the selective transport of solutes.

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Transferzellen im Xylem derValerianaceae

     

Xylem structure and water transport in a twiner,a scrambler,and a shrub of Lonicera (Caprifoliaceae)

Summary Wood structure and function was investigated in different growth forms of temperate honeysuckles (Lonicera spp.). All three species had many narrow vessels and relatively few wide ones, with the measured K _h (flow rate/pressure gradient) approximately 24–55% of the theoretical K _h predicted by Poiseuille's law. Only the twiner, Lonicera japonica, had some vessels greater than 50 m in diameter. The twiner also had the narrowest stem xylem diameters, suggesting the greater maximum vessel diameter hydraulically compensated for narrow stems. Conversely, the free-standing shrub, L. maackii, had the greatest annual increments of xylem but the least percent conductive xylem implying that a great portion of the wood was involved with mechanical support. The scrambler, L, sempervirens had low maximum vessel diameter, high Huber values (= xylem area/leaf area), and low specific conductivities (= measured K _h/xylem area), much like the shrub. The greatest vessel frequency occurred in the scrambler (901 vessels · mm^-2), the highest thus far recorded in vines. The lowest Huber value and highest specific conductivity occurred in the twiner, suggesting little self-support but relatively efficient water conduction. LSC (= measured K _h/leaf area) and maximum vessel diameter of Lonicera vines were near the low end of the range for vines in general.     

Resistance to water flow in xylem of Picea abies (L.) Karst. trees grown under contrasting light conditions

Summary The relative hydraulic conductivity (k) of xylem and resistance (R) to water flow through trunk, primary roots and branches in Picea abies trees growing under contrasting light conditions were investigated. The xylem permeability to water was measured by forcing 10 mM water solution of KC1 through excised wood specimens. From the values of k, the sapwood transverse area and the length of conducting segments, R of the whole trunk, branches and roots was calculated. The relative conductivity of xylem in open-grown trees exceeded that of shade-grown trees by 1.4–3.1 times, while k was closely correlated with the hydraulically effective radius (R _e) of the largest tracheids (R ² was 0.85–0.94 for open- and 0.51–0.79 for shade-grown trees). Because of both a low k and a smaller sapwood area in shade-grown trees the resistance to water movement through their trunk, roots and branches was many times higher. The distribution of R between single segments of the water-conducting pathway differed considerably in trees from different sites. At high water status the largest share of the total resistance in open- as well as shade-grown trees resides in the apical part of the trunk. The contribution of the branches to total xylem resistance is supposed to increase with developing water deficit.     

Dynamic studies of phloem and xylein flow in fully differentiated plants by fast nuclear-magnetic-resonance microimaging

Summary A fast nuclear-magnetic-resonance imaging method was developed in order to measure simultaneously and quantitatively the water flow velocities in the xylem and the phloem of intact and transpiring plants. Due to technical improvements a temporal resolution of 7 min could be reached and flow measurements could be performed over a time course of 12–30 h. The novel method was applied to the hypocotyl of 35– to 40-day-old, leafy plants ofRicinus communis which were subjected to different light-dark regimes. The results showed that the xylem flow velocities and the xylem volume flow responded immediately to light on-off changes. Upon illumination the flow velocity and the volume flow increased as expected in respect to literature. In contrast, the phloem flow velocity did not change in response to the light-dark regimes. Interestingly, though, the volume flow in the phloem increased during darkness. These findings can be explained by assuming that the conducting area of the phloem becomes enlarged during the dark period due to opening of sieve pores.     

Hydraulic resistance to radial water flow in growing hypocotyl of soybean measured by a new pressure-perfusion technique

Hydraulic resistances to water flow have been determined in the cortex of hypocotyls of growing seedlings of soybean (Glycine max L. Merr. cv. Wayne). Data at the cell level (hydraulic conductivity, Lp; half-time of water exchange, T _1/2; elastic modulus, ; diffusivity for the cell-to-cell pathway, D _c) were obtained by the pressure probe, diffusivities for the tissue (D _t) by sorption experiments and the hydraulic conductivity of the entire cortex (Lp_r) by a new pressure-perfusion technique. For cortical cells in the elongating and mature regions of the hypocotyls T _1/2=0.4–15.1 s, Lp=0.2·10^-5–10.0·10^-5 cm s^-1 bar^-1 and D _c=0.1·10^-6–5.5·10^-6 cm² s^-1. Sorption kinetics yielded a tissue diffusivity D _t=0.2·10^-6–0.8·10^-6 cm² s^-1. The sorption kinetics include both cell-wall and cell-to-cell pathways for water transport. By comparing D _c and D _t, it was concluded that during swelling or shrinking of the tissue and during growth a substantial amount of water moves from cell to cell. The pressure-perfusion technique imposed hydrostatic gradients across the cortex either by manipulating the hydrostatic pressure in the xylem of hypocotyl segments or by forcing water from outside into the xylem. In segments with intact cuticle, the hydraulic conductance of the radial path (Lp_r) was a function of the rate of water flow and also of flow direction. In segments without cuticle, Lp_r was large (Lp_r=2·10^-5–20·10^-5 cm s^-1 bar^-1) and exceeded the corticla cell Lp. The results of the pressure-perfusion experiments are not compatible with a cell-to-cell transport and can only the explained by a preferred apoplasmic water movement. A tentative explanation for the differences found in the different types of experiments is that during hydrostatic perfusion the apoplasmic path dominates because of the high hydraulic conductivity of the cell wall or a preferred water movement by film flow in the intercellular space system. For shrinking and swelling experiments and during growth, the films are small and the cell-to-cell path dominates. This could lead to larger gradients in water potential in the tissue than expected from Lp_r. It is suggested that the reason for the preference of the cell-to-cell path during swelling and growth is that the solute contribution to the driving force in the apoplast is small, and tensions normally present in the wall prevent sufficiently thick water films from forming. The solute contribution is not very effective because the reflection coefficient of the cell-wall material should be very small for small solutes. The results demonstrate that in plant tissues the relative magnitude of cell-wall versus cell-to-cell transport could dependent on the physical nature of the driving forces (hydrostatic, osmotic) involved.Abbreviations and symbols D _c diffusivity of the cell-to-cell pathway - D _t diffusivity of the tissue - radial flow rate per cm² of segment surface - Lp hydraulic conductivity of plasma-membrane - Lp_r radial hydraulic conductance of the cortex - T _1/2 half-time of water exchange between cell and surroundings - volumetric elastic modulus     

Xylem changes in the correlative inhibition of lateral bud growth in flax (Linum usitatissimum L.)

Xylem or tracheary changes at the base of the cotyledonary buds of flax seedlings (Linum usitatissimum L.), released from inhibition by decapitation of the main apex were studied. The differentiation of xylem strands and/or tracheary elements was correlated with the growth in length of the lateral buds, especially 48–72 hr after the removal of the main apex. The xylem strands, connected to the hypocotylary stele or not, and the tracheary elements increased with age within and outside the strands of both non-decapitated and decapitated seedlings. In the latter, the differentiation of these structures, however, occurred much earlier and in greater abundance in the same regions. The early growth in length of lateral buds, 1 or 2 hr after decapitation, was correlated with the early development of tracheary perforations in the xylem strands. The xylary strands with perforated elements are known to be more efficient than those without them. Therefore, it is suggested that the inhibition of lateral-bud growth was due, in fact, to a lack of appropriate tracheary perforations in the bud xylem strands that were connected with the hypocotylary stele of flax seedlings.     

Xylem and Phloem Derived Polyamines during Flowering in Two Diverse Rose Species

Polyamine contents in xylem (root) and phloem (leaf) exudates in two diverse species of rose, viz. Rosa damascena Mill and Rosa bourboniana Desport, were analyzed before, during, and after flowering in the main flowering season, that is, April–May. Only free putrescine (Put) was detected in the xylem and phloem exudates at these time points, and it was high during the peak flowering period. In phloem, Put content was significantly higher in R. bourboniana than in R. damascena at all three stages; whereas in the xylem exudate it was relatively higher in R. damascena at the peak flowering period. A spray of α-difluoromethylornithine (DFMO), an irreversible inhibitor of the putrescine biosynthetic inhibitor ornithine decarboxylase (ODC), markedly decreased the flowering. This effect was reversed by application of Put alone or in combination with DFMO. The significance of this finding is discussed in light of polyamine translocation during flowering. *IHBT Communication: 0354     

Relationships between sap flow and water potential in woody or perennial plants on islands of the Great Barrier Reef

Abstract. This paper describes studies on trees of Pisonia grandis , bushes of Argusia argentea , and the perennial herb Melanthera biflora , growing on One Tree Island, a coral cay of the Great Barrier Reef with 'soil' of coarse coral rubble. Water potential (Ψ_b, measured on small shoots with a pressure chamber), sap flow, stomatal conductance, vapour pressure deficit and photon flux density were monitored over day/night cycles. Sap flow and Ψ_b responded to changes in light and humidity. From these experiments good linear correlations were found between sap flow in a shoot and Ψ_b of similar adjacent shoots. The linearity suggests that the resistance to sap flow is constant as Ψ_b varies. The correlation, however, does not indicate a causal relationship between Ψ_b of an individual shoot on the plant and its sap flow. Ψ_b was only slightly different in shaded shoots from those in sunshine, although sap flow would be expected to differ between them. Enclosing shoots and so reducing their transpiration and sap flow to very low rates resulted in only small changes in Ψ_b of the enclosed shoots; Tb of such enclosed shoots should closely approximate that of the xylem at the point of shoot attachment. From these results it is suggested that the resistance to water flow in shoot and leaf xylem is small compared to the resistance further down the plant, in the root or at the root/soil interface. Shoot xylem water potential would be similar for all parts of the plant, and in such plants the water potential of shoots in the shade would be determined by the overall water use of the plant.     

鼎湖山锥栗木质部形成及其对气候的响应

为了解鼎湖山锥栗(Castaneahenryi)木质部的年内生长动态及其对气候因子的响应,利用微树芯采样技术对锥栗木质部进行连续监测,采用广义可加模型拟合生长过程,并利用混合效应模型分析木质部形成与气候因子的关系。结果表明,鼎湖山锥栗木质部在2015年几乎保持全年生长,呈现显著的季节性差异。在doy200 (200 days of year)之前木质部快速生长(生长季前期),doy300之后(生长季后期)生长速率出现下降趋势。生长季前期的木质部生长速率与温度、光合有效辐射存在显著正相关关系,生长季后期木质部生长速率与气候因子之间的相关关系并不显著。这说明中国南亚热带阔叶树种锥栗木质部形成及其调节机制具有季节性差异,反映了木质部形成对环境的适应性。     

Xylem ingestion by winged aphids

When aphids and their host plant are incorporated in a DC electrical circuit, phloem and xylem ingestion register as separate waveforms of the electrical penetration graph (EPG) signal. Aphids are primarily phloem feeders; xylem ingestion is seldom reported but can be induced experimentally by fasting the insects in desiccating conditions. In experiments with the black bean aphid, Aphis fabae Scop., young winged (alate) and unwinged (apterous) virginoparous adults were collected from their natal host plants (broad bean, Vicia faba L.) and allowed 3-h continuous EPG-recorded access to V. faba seedlings. Several aphids (47% of both morphs) showed ingestion from phloem sieve elements. Alate aphids also showed frequent xylem ingestion (60% of individuals), but no apterous aphids exhibited this activity. The EPG technique involves attachment of a fine gold wire electrode to each insect, a process that may affect normal behaviour at the plant surface. However, when the technique was modified to monitor the stylet activities of freely-settled aphids, high levels of xylem ingestion by alates were also recorded. The results suggest that the developmental physiology of winged aphids somehow predisposes them to xylem ingestion, possibly as a result of dehydration during the teneral period. Alate aphids may reduce their weight by fasting before take-off, giving aerodynamic benefits, but making rehydration, via xylem uptake, a priority following plant contact.     

Assessment of overall metabolism inAmoeba proteus measured by a microcalorimetric method

Summary We have carried out calorimetric determinations of the overall metabolism ofAmoeba proteus. There was no significant difference in metabolic activity between cells that were starved 3, 4, and 5 days. After 7 and 10 days a significantly lower metabolism was found (p < 0.05).The mean value of heat production rate (thermal power) for the cells after 3 days starvation was found to be 0.84 ± 0.14 nW/cell. Optimal number of cells in the ampoule (1,500–4,800) was accompanied by a steady-state power-time curve. With higher cell concentrations (> 5,000) the power-time curve showed an initial peak. The fall in heat production after about 1 hour varied between 30–60%. The decrease in power value was much larger than expected from cell mortality during the calorimetric experiment.Increasing number of cells (range 1,500–10,000) in the calorimetric ampoule caused a decrease of heat production rate per cell. The correlation coefficient was r=–0.85(p < 0.001). The coefficient of variation of the method was found to be 4.8 %. It seems that the use of microcalorimetric technique can be valuable in recording metabolic events in protozoes.     

Hydrogen sulfide consumption measured at low steady state concentrations using a sulfidostat

Although >10 microM hydrogen sulfide typically is toxic to eukaryotic cells, <1 microM sulfide is rapidly consumed and oxidized. To measure sulfide consumption in such low concentrations, we built a "Sulfidostat." The apparatus uses a sulfide-specific electrode to measure the concentration of free sulfide. The electrode is connected to a computer that controls a syringe pump. The pump injects Na(2)S solution into the sample chamber to maintain a constant concentration. Since the response of the electrode to low sulfide concentrations at neutral pH had not been previously validated, that was measured. Then using the Sulfidostat, the rate of sulfide consumption is the rate at which it is pumped into the sample to maintain a constant concentration. The protozoan Tetrahymena pyriformis was used to demonstrate the apparatus; maximum sulfide consumption occurred near 0.5 microM sulfide at a rate of 250 nmol (g protein)(-1) s(-1). That is higher than the rate calculated from the disappearance of sulfide following a bolus addition, a difference that can be explained by the slow response of the electrode and by reversible binding of sulfide by the cells. The Sulfidostat can measure sulfide consumption at concentrations lower than previously have been possible.     

Utilisation of a tropical bay as a nursery area by sharks of the families Carcharhinidae and Sphyrnidae

Synopsis At least eight species of sharks of the families Carcharhinidae and Sphyrnidae use Cleveland Bay in northern Australia as a communal nursery area.Carcharhinus dussumieri, C. fitzroyensis, C. limbatus andC. tilstoni use the bay as a seasonal primary nursery, with juveniles occurring in it for only a few months each year immediately after birth. Alternatively,Carcharhinus sorrah, Rhizoprionodon acutus andR. taylori use the bay as a year-round primary and secondary nursery, with juveniles remaining in it up to the size at maturity. AdultR. taylori also persist in the bay, a behavioural pattern possibly explained by their small maximum size. While present immediately after birth the type of utilisation pattern displayed bySphyrna lewini could not be clarified in this study. Although diets of these species in the bay are similar, there is probably little direct competition for food due to the highly productive habitats in the bay supporting an abundance of food resources. The highest numbers of juveniles occur when prey species are the most abundant, and when temporal separation of some seasonally-occurring species of sharks in effect.     

Pollen flow of cultivated rice measured under experimental conditions

The pollen flow pattern of a cultivated rice variety, Minghui-63, was studied at horizontal and vertical levels under experimental conditions. Data obtained from pollen traps for six designed populations (as pollen sources) at different intervals showed that the dispersal of rice pollen decreased with the increase of distance from pollen sources and that the rice pollen flow was significantly influenced by weather conditions, particularly by wind direction and speed. For a mean wind speed of 2.52 m/s in a downwind direction, the observed distance of rice pollen dispersal was 38.4 m, indicating that rice pollen grains normally disperse at a relatively small range. However, the maximum distance of rice pollen flow could be up to 110 m, using regression analysis of pollen flow and wind speed, when the wind speed reached 10 m/s in this study. The frequency of pollen flow was positively correlated with pollen source size within a given range, suggesting that pollen flow will occur effectively at a considerable rate in rice fields with sufficiently large pollen sources. In addition, many more pollen grains were detected at the height of 1.0–1.5 m than at 2.0 m, indicating that rice pollen mainly disperses at relatively low heights. Results from this study are useful both for minimizing transgene escape from transgenic rice and in situ conservation of wild relatives of rice, as well as for hybrid seed production, where an effective isolation buffer zone needs to be established.     

Diurnal changes in the radius of a subalpine Norway spruce stem: their relation to the sap flow and their use to estimate transpiration

Diurnal changes in the stem radius of a subalpine mature Norway spruce were measured simultaneously with the flow of sap in xylem. Matric potentials in the soil were > -35 kPa. The kinetics of the flow were closely related to the changes in the radius of the stem resulting from depletion of its extensible tissues. The radius of the stem oscillated daily and, fairly independently of this, fluctuated over several days. The daily shrinkage (_d) was correlated with the daily flow through its base (Q_d). When the crown transpired little and was nearly saturated during rainy days, ASd tended to increase relative to Q_d. Using a linear relation, the estimates of flow by _d deviated less than ± 10% from the values measured by heat balance, provided that the periods of calibration in their ratio of dry to rainy days were comparable to those estimated. If the two periods differed in this respect, the estimates of flow deviated up to 42%. A quadratic relation yielded estimates that depended less on weather. It reduced maximal deviations to ±22%. Since _d additionally may represent the time pattern of the daily transpiration better than Q_d, analysing changes in the radius of stems may supplement or partly replace measurements of sap flow in stems.     

A survey of root pressures in vines of a tropical lowland forest

Pre-dawn xylem pressures were measured with bubble manometers attached near the stem bases of 32 species of vines on Barro Colorado Island, Panama, to determine if pressures were sufficient to allow for possible refilling of embolized vessels. Of 29 dicotyledonous species 26 exhibited only negative xylem pressures, even pre-dawn during the wet season. In contrast, three members of the Dilleniaceae exhibited positive pre-dawn xylem pressures, with a maximum of 64 kPa in Doliocarpusmajor. A pressure of 64 kPa is sufficient to push water to a height of 6.4 m against gravity, but the specimens reached heights of 18 m. Thus, in all 29 dicotyledons examined, the xylem pressures were not sufficient to refill embolized vessels in the upper stems. In contrast, two of the smaller, non-dicotyledonous vines, the climbing fern Lygodiumvenustrum and the viny bamboo Rhipidocladumracemiflorum, had xylem pressures sufficient to push water to the apex of the plants. Therefore, a root pressure mechanism to reverse embolisms in stem xylem could apply to some but not to most of the climbing plants that were studied. Received: 18 March 1996 / Accepted: 24 October 1996     

Postpollination drop production in hybrid larch is not related to the diurnal pattern of xylem water potential

The hourly production of postpollination drops in the ovules of three hybrid larch trees (Larix x. marschlinsii Coaz) was examined and compared with the measured diurnal pattern of xylem water potential of the same trees under non-stressed conditions during two reproductive seasons. There was no consistent relationship between xylem water potential and ovular drop production in hybrid larch. Individual trees that showed a diurnal drop production in one year did not follow a similar pattern the other year. One tree produced drops in over half of its ovules hourly, regardless of the measured xylem water potential. Variation in number of drops produced per ovule and drop mass was observed between the three trees both years, and between years for two of the trees. This variation was not in response to xylem water potential or environmental conditions. Here we report the first simultaneous measurements of branch water status and the production of ovular secretions for any conifer. We conclude that the postpollination drop production of hybrid larch is not regulated by a tree's overall water status, but is under the control of localized structures such as the cone or the ovule.