In Situ Measurement of Epidermal Cell Turgor, Leaf Water Potential, and Gas Exchange in Tradescantia virginiana L

A combined system has been developed in which epidermal cell turgor, leaf water potential, and gas exchange were determined for transpiring leaves of Tradescantia virginiana L. Uniform and stable values of turgor were observed in epidermal cells (stomatal complex cells were not studied) under stable environmental conditions for both upper and lower epidermises. The changes in epidermal cell turgor that were associated with changes in leaf transpiration were larger than the changes in leaf water potential, indicating the presence of transpirationally induced within-leaf water potential gradients. Estimates of 3 to 5 millimoles per square meter per second per megapascal were obtained for the value of within-leaf hydraulic conductivity. Step changes in atmospheric humidity caused rapid changes in epidermal cell turgor with little or no initial change in stomatal conductance, indicating little direct relation between stomatal humidity response and epidermal water status. The significance of within-leaf water potential gradients to measurements of plant water potential and to current hypotheses regarding stomatal response to humidity is discussed.     

Focus on Water: Polarity of Water Transport across Epidermal Cell Membranes in Tradescantia virginiana

Using the automated cell pressure probe, small and highly reproducible hydrostatic pressure clamp (PC) and pressure relaxation (PR) tests (typically, applied step change in pressure = 0.02 MPa and overall change in volume = 30 pL, respectively) were applied to individual Tradescantia virginiana epidermal cells to determine both exosmotic and endosmotic hydraulic conductivity (L_pOUT and L_pIN, respectively). Within-cell reproducibility of measured hydraulic parameters depended on the method used, with the PR method giving a lower average coefficient of variation (15.2%, 5.8%, and 19.0% for half-time, cell volume [V_o], and hydraulic conductivity [L_p], respectively) than the PC method (25.4%, 22.0%, and 24.2%, respectively). V_o as determined from PC and PR tests was 1.1 to 2.7 nL and in the range of optically estimated V_o values of 1.5 to 4.9 nL. For the same cell, V_o and L_p estimates were significantly lower (about 15% and 30%, respectively) when determined by PC compared with PR. Both methods, however, showed significantly higher L_pOUT than L_pIN (L_pOUT/L_pIN ≅ 1.20). Because these results were obtained using small and reversible hydrostatically driven flows in the same cell, the 20% outward biased polarity of water transport is most likely not due to artifacts associated with unstirred layers or to direct effects of externally applied osmotica on the membrane, as has been suggested in previous studies. The rapid reversibility of applied flow direction, particularly for the PR method, and the lack of a clear increase in L_pOUT/L_pIN over a wide range of L_p values suggest that the observed polarity is an intrinsic biophysical property of the intact membrane/protein complex.The conductivity of membranes to water (hydraulic conductivity [L_p]) is an important property of the cells of all organisms, and whether plant cell membranes exhibit a polarity in this property has been debated for a number of decades (Dainty and Hope, 1959; Steudle, 1993). Most early evidence for polarity was based on transcellular osmotic experiments using giant algal cells in the Characeae, in which the relative areas of cell membrane exposed to conditions of osmotic inflow (endosmosis) or outflow (exosmosis) could be varied and, hence, L_p for both directions determined (Tazawa and Shimmen, 2001). Interpretation of these experiments is complicated by unstirred layer (USL) effects (Dainty, 1963), but even after accounting for these, it was concluded that inflow L_p (L_pIN) was higher than outflow L_p (L_pOUT) in these cells, with L_pOUT/L_pIN of about 0.65 (Dainty, 1963). When using osmotic driving forces in algal cells, L_pOUT/L_pIN values of between 0.5 and 0.91 have been reported in many studies (Steudle and Zimmermann, 1974; Steudle and Tyerman, 1983; Tazawa et al., 1996), and the same direction of polarity was also reported using osmotic driving forces in whole roots of maize (Zea mays; Steudle et al., 1987). When applying hydrostatic driving forces in algal cells using the pressure probe (Steudle, 1993), which is less influenced by USL effects (Steudle et al., 1980), L_pOUT/L_pIN has been closer to 1 (0.83–1; Steudle and Zimmermann, 1974; Steudle and Tyerman, 1983). However, in higher plant cells, an analysis of the data presented by Steudle et al. (1980, 1982) and Tomos et al. (1981) indicates the opposite polarity, with L_pOUT/L_pIN averaging from 1.2 to 1.4. Moore and Cosgrove (1991) used two contrasting hydrostatic methods to measure L_p in sugarcane (Saccharum spp.) stem cells: (1) the most commonly used pressure relaxation (PR) method, in which cell turgor pressure (P_cell) changes during the measurement, and (2) the more technically demanding pressure clamp (PC) method, in which P_cell is maintained constant. Consistent with other studies in higher plant cells, Moore and Cosgrove (1991) reported average L_pOUT/L_pIN from 1.15 (PC) to 1.65 (PR). Using the PR method in epidermal cells of barley (Hordeum vulgare), Fricke (2000) reported only a modest L_pOUT/L_pIN (based on reported half-time [T_1/2]) of 1.08. In view of the contribution of proteins (e.g. aquaporins) to overall membrane L_p, Tyerman et al. (2002) suggested that polarity may result either from asymmetry in the pores themselves or from an active regulation of the conductive state of the pores in response to the experimental conditions that cause inflow or outflow. Either of these mechanisms may explain the wide range of values reported in the literature for L_pOUT/L_pIN. Cosgrove and Steudle (1981) reported that a substantial (6-fold) and rapid (within 20 s) reduction in L_p could occur in the same cell, and in hindsight, this presumably reflected the influence of aquaporins. Cosgrove and Steudle (1981) did not consider the lower L_p as indicative of the L_p in situ, and Wan et al. (2004) reported that a reduction in L_p was associated with perturbations to P_cell on the order of 0.1 MPa. Hence, if measured membrane L_p itself can exhibit substantial changes over relatively short periods of time in the same cell, then further study of systematic differences between L_pOUT and L_pIN will require a robust hydrostatic methodology (PC or PR) that can reversibly and reproducibly apply small perturbations in pressure (P) to individual cells over short periods of time.For the PR method, a T_1/2 of water exchange is measured by fitting an exponential curve to the observed decay in P_cell over time following a step change in volume, and membrane L_p can be calculated if cell surface area (A), cell volume (V_o), and volumetric elastic modulus (ε) are known (Steudle, 1993). In practice, A and V_o are typically calculated from optical measurements of individual cell dimensions or estimates using average values, and ε is calculated based on V_o and an empirical change in pressure (dP) to change in volume (dV) relation for each cell (Steudle, 1993; Tomos and Leigh, 1999). In the PC method, first developed by Wendler and Zimmermann (1982), V_o (and, given reasonable assumptions about cell geometry, A) is estimated without the need for optical measurements, and L_p can be measured without the need to determine dP/dV or ε. However, this method is technically more demanding because it requires precise P control as well as a continuous record of the volume flow of water across the cell membrane (as measured by changes in the position of the cell solution/oil meniscus within the glass capillary over time) and has rarely been used (Wendler and Zimmermann, 1982, 1985; Cosgrove et al., 1987; Moore and Cosgrove, 1991; Zhang and Tyerman, 1991; Murphy and Smith, 1998). Since volume (V) is continuously changing over time, this approach may also be influenced by the hydraulic conductance of the capillary tip (K_h) used to make the measurements as well as surface tension effects due to the progressive changes in capillary diameter with meniscus position, and these influences have not been quantitatively addressed.Automation of the pressure probe operation, particularly automatic tracking of the meniscus location in the glass microcapillary tip, would address many of the above-mentioned issues, and to date, several attempts have been made to monitor the meniscus location using electrical resistance (Hüsken et al., 1978) or hardware-based image analysis (Cosgrove and Durachko, 1986; Murphy and Smith, 1998). Recently, Wong et al. (2009) redesigned the automated cell pressure probe (ACPP), originally proposed by Cosgrove and Durachko (1986), using a software-based meniscus detection system and a precise pressure control system. In the new ACPP system, both the position of the meniscus and oil pressure (P_oil) are recorded frequently (typically at 10 Hz), and P_oil is controlled with a resolution of ±0.002 MPa. We have combined the ACPP with a new technique to reproducibly fabricate microcapillary tips of known hydraulic properties (Wada et al., 2011) in order to correct for K_h and surface tension effects in both PC and PR estimates of the water relations parameters of Tradescantia virginiana epidermal cells and have determined the relation of L_pOUT to L_pIN in these cells.     

Pressure and Solute Potentials in Stomatal Cells of Tradescantia virginiana

The postulated mechanical advantage of subsidiary cells overguard cells has been estimated using leaves of Tradescantiavirginiana. The turgor pressures of subsidiary cells were adjusted to bezero or maximal by plasmolytic treatments, and the resultingstomatal apertures were measured. The ‘mechanical advantage’was calculated from two mathematical models which define itas an ‘antagonism ratio’. The discussion deals withmethods of preparing the tissue, the validity of the plasmolytictreatments, and the function of the antagonism ratio in relationto the Spannungsphase     

Hydrogen Peroxide-Dependent Oxidation of Flavonoids and Hydroxycinnamic Acid Derivatives in Epidermal and Guard Cells of Tradescantia virginiana L.

Luteolin, kaempferol, quercetin, caffeic acid and ferulic acidwere identified in acid-hydrolyzed epidermal strips of Tradescantiavirginiana using HPLC and spectrophotometry. The amount of flavonoidswas much smaller than that of cinnamic acid derivatives. Morethan 80% of the flavonoids were found in methanol extracts ofepidermal strips. Caffeic acid was found in both methanol extractsand the residues in nearly equal amounts, while more than 80%of the ferulic acid was found in the residues after methanolextraction. These data suggest that most of the ferulic acidand part of the caffeic acid bind to macromolecules as estersin the cell wall and that flavonoids are localized mainly inthe cytoplasm. The localization of esters of hydroxycinnamicacids in cell walls was ascertained by fluorometric analysis.These phenolic compounds were oxidized by H₂O₂ (0.025–1mM) in epidermal and guard cells and the oxidation was inhibitedby KCN and NaN₃: luteolin glycosides were less sensitive toH₂O₂ than quercetin and kaempferol glycosides in flavonoids.Ferulic acid esters were more sensitive to H₂O₂ than caffeicacid esters in hydroxycinnamic acid derivatives. On the basisof these data, the physiological significance of the oxidationof phenolic compounds by H₂O₂ is discussed. (Received October 9, 1987; Accepted February 3, 1988)     

Correlations Between the Unbound Water Content of Guard Cells and Stomatal Aperture in Tradescantia virginiana L.

When the apertures of stomata in an epidermal strip changedthere was found to be a simultaneous change in the unbound watercontent of the tissue. This occurred even when only the guardcells were living. It was concluded that the change in unboundwater occurred in the guard cells, and possibly the guard cellwalls.     

紫鸭跖草花粉母细胞减数分裂细胞核和染色体含有F—肌动蛋白

肌动蛋白间接免疫荧光标记实验观察到紫鸭跖草花粉母细胞减数分裂前期Ⅰ细胞核,中期┘染色体,二分体和四分体均发现较明亮的黄绿色荧光,说明其中含有肌动蛋白。经ＴＲＩＴ－Ｃ鬼等环肽荧光标记后,减数分裂前Ⅰ细胞核,二分枝及中期Ⅰ染色体均发现较明亮的红色荧光;ＣＤ处理后细胞核和染色体的荧光明显减弱或没有荧光,说明其中存在Ｆ－肌动蛋白。     

Water Pathways in Leaves of Hedera helix L. and Tradescantia virginiana L.

Hydraulic conductances of leaf tissues of Hedera helix and Tradescantiavirginiana leaves were measured. It was found that water couldflow most easily through the veins, but that the cell wallsof at least the ventral epidermis were more efficient at resupplyingwater lost from the epidermal tissue than was the mesophyllat rehydrating itself. Vein and bundle-sheath extensions, whichare characteristic of mesomorphic leaves (e.g. T. virginiana),seem to be important in maintaining a close hydraulic connectionbetween the epidermis and the vascular tissue. In leaves notcontaining vein and bundle-sheath extensions, typically xeromorphicleaves (e.g. H. helix), there is not such a close connectionbetween the epidermis and vascular tissue. This was shown inexperiments involving the sudden application of a reduced pressurepotential to either the epidermis or the other tissues of leaves,and the measurement of transient stomatal opening.     

Cell Potentials and Turgor Pressures in Epidermal Cells of Tradescantia and Commelina

Cell membrane potentials have been measured both in epidermalstrips and intact leaf sections of Tradescantia virginiana andCommelina communis, and in epidermal cells over green and overalbino mesophyll cells of T. albiflora var. albovittata. Membranepotentials (_cell) in strips were considerably lower than thosein intact sections and were insensitive to light and to theabsence or presence of calcium. Their response to external cationlevels was indifferent to ionic species. However, in intactleaf sections incubated with calcium present, membrane potentialsresponded to K⁺ levels but not to Na⁺. were more negative thancells in epidermal strips, and responded to changes in illumination. Long-term recordings of _cell and vacuolar K⁺ levels in T. virginianaduring stomatal closure suggest that the fluctuations of _cellwere unrelated to K⁺ movement (which we could not detect) andthus probably to stomatal movement as well. Turgor pressures measured in epidermal cells of intact leafsections of T. virginiana were found to be of the same magnitudeas those previously reported for epidermal strips. It is concludedthat epidermal cells maintain their solute contents during strippingwithout the involvement of an electrophysiological transportsystem. With the possible exception of lateral subsidiary cells,there was no evidence suggesting that ordinary epidermal cellsare capable of osmotic adjustment even when additional KCI wassupplied in the osmoticum. Absolute turgor levels in intactleaf sections kept at constant external KCI were unrelated tosteady state _cell.     

Evidence for a CO2 Inhibited Proton Extrusion Pump in the Stomatal Cells of Tradescantia virginiana

The effect of CO₂ on the electrical potential difference (p.d.)of the cells of the stomatal complex of Tradescantia virginianahas been investigated. Enhanced levels of CO₂ affected all thecells equally by depolarizing the p.d. On removal of the CO₂there was an immediate hyperpolarization, the degree of whichwas linearly related to the length of time the CO₂ was given.Changes in the pH of the cytoplasm and the vacuolar sap wereobserved during and after treatment with CO₂. The metabolicinhibitor 2,4-DNP eliminated the effect of CO₂ on the p.d. Theseresults wuld be explained by postulating an electrogenic protonpump in the plasmalemma which is inhibited by CO₂. Key words: CO₂, Proton pump, Stomata     

pH Gradients in the Stomatal Complex of Tradescantia virginiana

pH of the vacuolar sap, cytoplasm, and apoplast of the cellsof the stomatal complex of Tradescantia virginiana was measuredusing micro-electrodes. Marked differences in vacuolar and apoplasticpH were observed between leaves with open and closed stomata.Cytoplasmic pH appeared to be uniform in all the cells and didnot change with stomatal aperture. The information obtainedenabled proton motive force across the plasmalemma and tonoplastof the guard cells to be calculated. The results are discussedin relation to the accumulation of potassium by the guard cellon stomatal opening. Key words: Stomata, pH gradients, Proton pumps     

The Hydraulic Pathways in Nicotiana glauca (Grah.) and Tradescantia virginiana (L.) Leaves, and Water Potentials in Leaf Epidermes

The hydraulic conductances of leaves of a species which exhibitsstomatal responses to humidity (Nicotiana glauca) are significantlylower than the conductances in a species which does not exhibitsuch responses (Tradescantia virginiana). This difference couldat least partly account for their difference in stomatal responseto humidity. In both species, the hydraulic conductance betweenthe leaf bulk and its epidermis is much lower than the conductancein any other part of the pathway. The apparently conflictingresults, reported in recent literature, on the hydraulic conductancesand water pathways in leaves are reinterpreted, and shown tobe due to misinterpretation of results. The recently publishedcriticisms of a technique used to measure hydraulic conductivityare commented on and refuted. An examination of the factors that influence the water potentialat the sites of evaporation from the inner walls of the epidermisnear stomatal pores showed that the water potential at thesesites is lower than the bulk epidermal water potential. Thewater potential at these sites changes in a complex way as stomatalaperture changes. As it is reduced the ratio of: ‘waterpotential at sites of evaporation on the inner walls of theepidermis near stomatal pores/bulk leaf water potential‘increases. The positive feedback effect of this phenomenon,which tends to keep stomatal water potential constant as thestomata close and therefore enhances closure, and two other‘passive’ positive feedback effects on the waterpotential at sites of evaporation near stomata that have beenreported in the literature are briefly discussed. Nicotiana glauca (Grah.), Tradescantia virginiana (L.), sub-stomatal cavities, peristomatal evaporation, stomata, humidity response, leaf hydraulic conductance, water potential     

An Electrophysiological Study of the Stomatal Complex of Tradescantia virginiana

Measurements of electrical potential difference (PD) and potassiumactivity were carried out on the intact leaf of Tradescantiavirginiana. PD gradients across the stomatal complex were observedwith both open and closed stomata. The guard cell PD appearedto be linearly related to stomatal aperture. With the stomataopen a gradient of potassium activity across the stomatal complexwas observed which became reversed on stomatal closure. Calculationof the driving forces on potassium suggested that it was distributedpassively between the vacuoles of the cells of the stomatalcomplex. The electrophysiological data obtained from this investigationenabled potassium activity in the apoplast to be calculated.The results showed that on stomatal closure there was a massiveincrease in the potassium activity in the guard cell wall. Key words: Stomata, Ionic gradients, Electrical potentials     

Leaf Epidermal Cells： A Trap for Lipophilic Xenobiotics

Plant surfaces are covered by a layer of cuticle, which functions as a natural barrier to protect plants from mechanical damage, desiccation, and microbial invasion. Results presented in this report show that the epicuticular wax and the cuticle of plant leaves also play an important role in resisting xenobiotic invasion. Although the epicuticular wax is impermeable to hydrophilic xenobiotics, the cuticle not only restricts the penetration of hydrophilic compounds into leaf cells, but also traps lipophilic ones. The role of the epidermal cells of plant leaves in resisting xenobiotic invasion has been neglected until now. The present study shows, for the first time, that the epidermal cells may reduce or retard the transport of lipophilic xenobiotics into the internal tissues through vacuolar sequestration. Although the guard cells appear to be an easy point of entry for xenobiotics, only a very small proportion of xenobiotics present on the leaf surface actually moves into leaf tissues via the guard cells .     

Direct turgor pressure measurements in individual leaf cells of Tradescantia virginiana

The water relations of leaves of Tradescantia virginiana were studied using the miniaturized pressure probe (Hüsken, E. Steudle, Zimmermann, 1978 Plant Physiol. 61, 158–163). Under well-watered conditions cell turgor pressures, P _o, ranged from 2 to 8 bar in epidermal cells. In subsidiary cells P _o was about 1.5 to 4.5 bar and in mesophyll cells about 2 to 3.5 bar. From the turgor pressure, relaxation induced in individual cells by changing the turgor pressure directly by means of the pressure probe, the half-time of water exchange was measured to be between 3 and 100 s for the epidermal, subsidiary, and mesophyll cells. The volumetric elastic modulus, , of individual cells was determined by changing the cell volume by a defined amount and simultaneously measuring the corresponding change in cell turgor pressure. The values for the elastic modulus for epidermal, subsidiary, and mesophyll cells are in the range of 40 to 240 bar, 30 to 200 bar, and 6 to 14 bar, respectively. Using these values, the hydraulic conductivity, L _p, for the epidermal, subsidiary, and mesophyll cells is calculated from the turgor pressure relaxation process (on the basis of the thermodynamics of irreversible processes) to be between 1 and 55·10^-7 cm s^-1 bar^-1. The data for the volumetric elastic modulus of epidermal and subsidiary cells indicate that the corresponding elastic modulus for the guard cells should be considerably lower due to the large volume changes of these cells during opening or closing. Recalculation of experimental data obtained by K. Raschke (1979, Encycl. Plant Physiol. N.S., vol. 7, pp 383–441) on epidermal strips of Vicia faba indicates that the elastic modulus of guard cells of V. faba is in the order of 40–80 bar for closed stomata. However, with increasing stomatal opening, i.e., increasing guard cell volume, decreases. Therefore, in our opinion Raschke's results would indicate a relationship between guard cell volume and which would be inverse to that for plant cells known in the literature. assumes values between 20–40 bar when the guard cell colume is soubled.     

Stomatal response characteristics of Tradescantia virginiana grown at high relative air humidity

Plants produced at high relative air humidity (RH) show poor control of water loss after transferring to low RH, a phenomenon which is thought to be due to their stomatal behaviour. The stomatal anatomy and responses of moderate (55%) and high (90%) RH grown Tradescantia virginiana plants to treatments that normally induce stomatal closure, i.e. desiccation, abscisic acid (ABA) application and exposure to darkness were studied using attached or detached young, fully expanded leaves. Compared with plants grown at moderate RH the transpiration rate, stomatal conductance and aperture of high RH grown plants measured at the same condition (40% RH) were, respectively, 112, 139 and 132% in light and 141, 188 and 370% in darkness. Besides the differences in stomatal size (guard cell length was 56.7 and 73.3 µm for moderate and high RH grown plants, respectively), there was a clear difference in stomatal behaviour. The stomata responded to desiccation, ABA and darkness in both moderate and high RH grown plants, but the high variability of stomatal closure in high RH grown plants was striking. Some stomata developed at high RH closed in response to darkness or to a decrease in relative water content to the same extent as did stomata from moderate RH grown plants, whereas others closed only partly or did not close at all. Evidently, some as yet unidentified physiological or anatomical changes during development disrupt the normal functioning of some stomata in leaves grown at high RH. The failure of some stomata to close fully in response to ABA suggests that ABA deficiency was not responsible for the lack of stomatal closure in response to desiccation.     

Role of Osmotic Potential Gradients during Water Stress and Leaf Senescence in Fragaria virginiana

The physiological basis underlying differences in sensitivity of different aged leaves to water stress was investigated in Fragaria virginiana Duchesne. Differential susceptibility of only older leaves to water stress in the field during summer months appeared related to gradients in leaf osmotic potential within the plant and by an age dependency in the ability of leaves to adjust osmotically when challenged by periodic water deficits. Under greenhouse conditions, older leaves senesced invariably during an imposed water stress while control leaves of comparable age and stressed younger leaves remained green. Osmotic potentials of intermediate aged and younger leaves became approximately 1 to 2 bars lower after a single cycle of imposed stress and up to 10 bars lower after two cycles of stress. Pronounced gradients in leaf osmotic potential within individual whole plants were observed following two cycles of water stress that were significantly different from control values. Osmotic adjustment was dependent on leaf age with the greatest capacity for adjustment in the intermediate aged leaves. Loss of osmotic adjustment was rapid upon rewatering with a half-life of 4 days. An irreversible component of adjustment was observed, amounting to about 10% (or 2 bars) of the maximally adjusted state. This irreversible component could be accounted for in part by significant changes in cell size and other anatomical alterations in the leaf that affect cellular osmotic volume, and, hence, cellular water relations.     

Growth Rate and Water Relations of Citrus Leaf Flushes

Growth rates of seasonal leaf flushes of ‘Valencia’orange [Citrus sinensis (L.) Osbeck] were measured and waterrelations characteristics of young (new) and over-wintered (old)citrus leaves were compared. New flush leaves had lower specificleaf weights and lower midday leaf water potentials than comparablyexposed old leaves. Spring and summer flush new leaves had higherosmotic potentials than old leaves. These differences becamenon-significant as the new leaves matured. During summer conditions,water-stressed new leaves reached zero turgor and stomatal conductancealso began to decrease in them at higher leaf water potentialsthan in old leaves. Old leaves were capable of maintaining openstomata at lower leaf water potentials. Opened flowers and newflush leaves lost more water, on a dry weight basis, than flowerbuds, fruit or mature leaves. The results illustrate differencesin leaf water potential and stomatal conductance which can beattributed to the maintenance of leaf turgor by decreases inleaf osmotic potentials as leaves mature. These changes in citrusleaf water relations are especially important since water stressresulting from high water loss rates of new tissues could reduceflowering and fruit set. Citrus sinensis (L.) Osbeck, orange, Citrus paradisi Macf., grapefruit, growth rate, leaf water relations, osmotic potential, water potential, stomatal conductance     

A Theoretical Model of Jigsaw-Puzzle Pattern Formation by Plant Leaf Epidermal Cells

Plant leaf epidermal cells exhibit a jigsaw puzzle–like pattern that is generated by interdigitation of the cell wall during leaf development. The contribution of two ROP GTPases, ROP2 and ROP6, to the cytoskeletal dynamics that regulate epidermal cell wall interdigitation has already been examined; however, how interactions between these molecules result in pattern formation remains to be elucidated. Here, we propose a simple interface equation model that incorporates both the cell wall remodeling activity of ROP GTPases and the diffusible signaling molecules by which they are regulated. This model successfully reproduces pattern formation observed in vivo, and explains the counterintuitive experimental results of decreased cellulose production and increased thickness. Our model also reproduces the dynamics of three-way cell wall junctions. Therefore, this model provides a possible mechanism for cell wall interdigitation formation in vivo.     

Water Movement into and through Tradescantia virginiana (L.) Leaves: I. UPTAKE DURING CONDITIONS OF DYNAMIC EQUILIBRIUM

Water uptake into the ventral epidermis and the other tissuesof excised T. virginiana leaves was measured separately andsimultaneously when the uptake rates were steady. It was foundthat uptake into the ventral epidermis was proportionately greater,compared with uptake into the remainder of a leaf, than wouldbe expected from the ratio of conductances of the two pathways.This result led to the conclusion that not only is the epidermisa pathway for water transport in the transpiration stream butthat it is an important site of evaporation for stomatal transpiration.