SECONDARY PULVINUS OF ROBINIA PSEUDOACACIA (LEGUMINOSAE): STRUCTURAL AND ULTRASTRUCTURAL FEATURES

The structure of the secondary pulvinus of Robinia pseudoacacia has been examined together with ultrastructural features of motor cells both in open and closed pulvini, to identify ultrastructural changes associated with leaflet movement. Pulvini have a central vascular core bordered by thick-walled collenchyma cells, which in turn are surrounded by several layers of cortical parenchyma cells. Cortical motor cells exhibit ultrastructural features similar to those reported in homologous cells of other pulvini. The vacuolar compartment contains two kinds of vacuoles: nontannin vacuoles, which change both in number and size during leaflet movement, and tannin vacuoles, which may act as an ion reservoir. No differences in wall thickness were found between flexor and extensor motor cells. Thick walls of collenchyma cells show numerous pits with plasmodesmata through which the phloem parenchyma cells and the inner cortical motor cells are connected. Tannin vacuoles and calcium oxalate crystals are common inclusions of phloem parenchyma cells. The tissue arrangement and the occurrence of pits with plasmodesmata in the central cylinder cells provide evidence of symplastic continuity through the central cylinder between the extensor and flexor regions of the motor organs. The greater amplitude of Robinia leaflet movements may be related to the extension of motor regions, the scarcity of lignification in the central vascular core, and the thin flexor walls.     

Rhythmic and Blue Light-Induced Turgor Movements and Electrical Potential in the Laminar Pulvinus of Phaseolus vulgaris L.

The well-known circadian movement in Phaseolus leaves is usuallysuperimposed with small and somewhat irregular rhythmic changesof pulvinar movement. This study examines the relationship betweenthese small pulvinar movements and the membrane potential ofthe motor cell as well as the effect of light on them. Bluelight affected both the movements and potential while red andgreen lights of the same photon flux had little effect. Also,the difference in the membrane potential between the extensorand flexor cells was found to be closely related to the rhythmicturgor movement of the pulvinus. Changes in the potential differencealways preceded the movement. Sequential changes of the potentialdifference and turgor pressure in the motor cells, includingthe light-induced ones, are discussed in relation to the leafmovement. (Received August 8, 1985; Accepted November 11, 1985)     

Elemental analysis of freeze-dried thin sections of Samanea motor organs: barriers to ion diffusion through the apoplast

Leaflet movements in the legume Samanea saman are dependent upon massive redistribution of potassium (K), chloride (Cl), and other solutes between opposing (extensor and flexor) halves of the motor organ (pulvinus). Solutes are known to diffuse through the apoplast during redistribution. To test the possibility that solute diffusion might be restricted by apoplastic barriers, we analyzed elements in the apoplast in freeze-dried cryosections of pulvini using scanning electron microscopy/x-ray microanalysis. Large discontinuities in apoplastic K and Cl at the extensor-flexor interface provide evidence for a barrier to solute diffusion. The barrier extends from the epidermis on upper and lower sides of the pulvinus to cambial cells in the central vascular core. It is completed by hydrophobic regions between phloem and cambium, and between xylem rays and surrounding vascular tissue, as deduced by discontinuities in apoplastic solutes and by staining of fresh sections with lipid-soluble Sudan dyes. Thus, symplastic pathways are necessary for ion redistribution in the Samanea pulvinus during leaflet movement. In pulvini from leaflets in the closed state, all cells on the flexor side of the barrier have high internal as well as external K and Cl, whereas cells on the extensor side have barely detectable internal or external K or Cl. Approximately 60% of these ions are known to migrate to the extensor during opening; all return to the flexor during subsequent closure. We propose that solutes lost from shrinking cells in the outer cortex diffuse through the apoplast to plasmodesmata-rich cells of the inner cortex, collenchyma, and phloem; and that solutes cross the barrier by moving through plasmodesmata.     

Potassium Flux and Leaf Movement in Samanea saman : I. Rhythmic Movement

Samanea leaflets usually open in white light and fold together when darkened, but also open and dose with a circadian rhythm during prolonged darkness. Leaflet movement results from differential changes in the turgor and shape of motor cells on opposite sides of the pulvinus; extensor cells expand during opening and shrink during closure, while flexor cells shrink during opening and expand during closure but change shape more than size. Potassium in both open and closed pulvini is about 0.4 N. Flame photometric and electron microprobe analyses reveal that rhythmic and light-regulated postassium flux is the basis for pulvinar turgor movements. Rhythmic potassium flux during darkness in motor cells in the extensor region involves alternating predominance of inwardly directed ion pumps and leakage outward through diffusion channels, each lasting ca 12 h. White light affects the system by activating outwardly directed K⁺ pumps in motor cells in the flexor region.     

Comparative Effects of lndole-3-acetic acid, Abscisic acid, Gibberellic acid and 6-Benzylaminopurine on the Dark- and Light-induced Pulvinar Movements in Cassia fasciculata Michx

Effects of plant hormones were examined on the dark- and light-inducedmovements of Cassia fasciculata. Indole-3-acetic acid (IAA),gibberellic acid (GA₃) and 6-benzylaminopurine (6-BAP) inhibitedthe scotonastic movement whereas abscisic acid (ABA) enhancedit. After brief treatments (5 to 30 min), the ABA effect wasinhibitory rather than promotional. Hormonal treatment in theacidic range gave the best physiological response for ABA, butthe greatest efficiency of IAA, GA₃ and 6-BAP was obtained withpH values close to neutrality. Three to 5 h were needed beforeexpression of the physiological effect triggered by GA₃ and6-BAP, while 5 min treatments were sufficient for IAA and ABA.Light-induced movements were largely enhanced by IAA and slightlyby GA₃ but inhibited by 6-BAP and ABA. The results are discussedin relation to the ionic changes in the pulvinar motor cells,regulating leaflet movements. Key words: Abscisic acid, auxins, cytokinins, gibberellic acid, pulvinar movements     

H fluxes in excised samanea motor tissue : I. Promotion by light

Previous investigators revealed that white light-promoted leaflet opening in Samanea saman (Jacq) Merrill depends upon K⁺ uptake by extensor cells and efflux from flexor cells of the pulvinus, while dark-promoted closure depends upon K⁺ fluxes in the opposite directions. We now monitored H⁺ fluxes during pulvinar movement to test a model proposing coupled H⁺/K⁺ fluxes. H⁺ fluxes were monitored by measuring changes in the pH of a weakly buffered solution (initial pH = 5.5) bathing excised strips of extensor or flexor tissue. White light at hour 3 of the usual dark period promoted pulvinar opening, H⁺ efflux from extensor cells and uptake by flexor cells, while darkness at hours 2 to 4 of the usual light period promoted pulvinar closure, H⁺ uptake by extensor cells and efflux from flexor cells. The following conditions altered H⁺ fluxes during dark-promoted closure. (a) Light reversed the directions of the fluxes in both extensor and flexor cells. (b) Anoxia increased the rate of H⁺ uptake by extensor cells and promoted H⁺ uptake (rather than efflux) by flexor cells, consistent with an outwardly directed H⁺ pump. KCN showed similar effects initially, but they were transient. (c) Increase in external pH from 5.5 to 6.7 promoted H⁺ efflux (rather than uptake) by extensor cells and increased the rate of H⁺ efflux from flexor cells, presumably by decreasing the rate of inward diffusion. (d) Change in external K⁺ did not alter H⁺ fluxes by extensor cells, but removal of external K⁺ decreased the rate of H⁺ efflux from flexor cells by 70%. These observations support a model for coupled H⁺/K⁺ fluxes in pulvinar cells during light-and dark-promoted leaflet movements.     

Auxin- and abscisic acid-dependent osmoregulation in protoplasts of Phaseolus vulgaris pulvini.

Protoplasts isolated from the laminar pulvinus of Phaseolus vulgaris and bathed in a medium containing KCl as the major salt were found to swell in response to IAA and to shrink in response to ABA. The protoplasts of flexor cells and those of extensor cells responded similarly. The results indicate that the cellular content of osmotic solutes is enhanced by IAA and reduced by ABA. The IAA-induced swelling was abolished when either the K(+) or the Cl(-) of the bathing medium was replaced by an impermeant ion or when the medium was adjusted to neutral pH (instead of pH 6). The response was inhibited by vanadate. It is concluded that the swelling is caused by enhanced influxes of K(+) and Cl(-), which probably occur through K(+) channels and Cl(-)/H(+) symporters, respectively. The ABA-induced shrinking was inhibited by 5-nitro-2-(3-phenylpropylamino)-benzoic acid, an anion-channel inhibitor, suggesting that it is caused by Cl(-) efflux through anion channels and charge-balancing K(+) efflux through outward-rectifying K(+) channels. It appears that the two plant hormones act on pulvinar motor cells to regulate their turgor pressure, as they do in stomatal guard cells. The findings are discussed in relation to the pulvinar movements induced by environmental stimuli.     

Potassium Channels in Motor Cells of Samanea saman: A Patch-Clamp Study

Leaflet movements in Samanea saman are driven by the shrinking and swelling of cells in opposing (extensor and flexor) regions of the motor organ (pulvinus). Changes in cell volume, in turn, depend upon large changes in motor cell content of K⁺, Cl⁻ and other ions. We performed patch-clamp experiments on extensor and flexor protoplasts, to determine whether their plasma membranes contain channels capable of carrying the large K⁺ currents that flow during leaflet movement. Recordings in the “whole-cell” mode reveal depolarization-activated K⁺ currents in extensor and flexor cells that increase slowly (t_½ = ca. 2 seconds) and remain active for minutes. Recordings from excised patches reveal a single channel conductance of ca. 20 picosiemens in both cell types. The magnitude of the K⁺ currents is adequate to account quantitatively for K⁺ loss, previously measured in vivo during cell shrinkage. The K⁺ channel blockers tetraethylammonium (5 millimolar) or quinine (1 millimolar) blocked channel opening and decreased light- and dark-promoted movements of excised leaflets. These results provide evidence for the role of potassium channels in leaflet movement.     

Relationships between structure and motility ofAlbizzia motor organs: Changes in ultrastructure of cortical cells during dark-induced closure

Summary Paired leaflets ofAlbizzia julibrissin spread apart (open) in the daytime and fold together (close) at night. We examined the structure of cells in open and closedAlbizzia motor organs (pulvini) to identify reversible changes in structure associated with motility. Pulvini were fixed in glutaraldehyde and stained using conventional methods. The pulvinus has a central vascular cylinder bordered by thick-walled collenchyma cells, in turn surrounded by an endodermis and many layers of cortical parenchyma. Cortical cells in the extensor undergo large changes in shape during leaflet closure linked with: formation of wall infoldings, development of a large periplasmic space filled with fibrils and membranes, development of lobes on the nucleus, evagination of the nuclear outer envelope membrane, break-up of the large central vacuole to form many small vacuoles, and linking of the plasmalemma to inner regions of the cytoplasm by microfilaments. Cortical cells in the flexor, by contrast, remain relatively stable during leaflet movement. Microtubules are present near the plasmalemma in both extensor and flexor cells; in the extensor, spherical coated vesicles are located near the microtubules. The possible function of these structures in regulating intracellular shuttling processes is discussed.     

Effects of Anoxia and Red Light on Changes Induced by Blue Light in the Membrane Potential of Pulvinar Motor Cells and Leaf Movement in Phaseolus vulgaris L.

In the dark, the membranes of the pulvinar motor cells of Phaseolusvulgaris L. were rapidly depolarized under anoxic conditionsand repolarized with re-aeration. This change in potential mayhave been due to suppression by anoxia of a respiration-dependent,electrogenic ion pump in the motor cells. When the pulvinuswas irradiated with blue light (BL) in the depolarized stateunder anoxic conditions, no marked depolarization occurred.Furthermore, a short pulse of BL did not induce transient depolarization.On continuous irradiation with red light (RL), the motor cellunder anoxic conditions showed slow recovery of the depolarizedmembrane potential. When a pulse of BL was superimposed on theRL after the recovery, transient depolarization occurred again. The leaf showed a small downward movement under anoxic conditionsbut recovered with re-aeration. Upward movement of the leafcaused by continuous application of BL to flexor cells changedto a downward movement under anoxic conditions, and re-aerationled to a return to upward movement. Unidirectional irradiationby BL of the flexor side did not cause upward movement of theleaf under anoxic conditions. However, unidirectional irradiationof RL to the flexor side caused downward movement of the leafunder anoxic conditions, which could be changed to upward movementby superimposition of irradiation with BL. The experimentalresults clearly show that BL acts mainly to inhibit (depolarize)an electrogenic component of the membrane potential in pulvinarmotor cells which is dependent on a supply of energy from respirationor photophsphorylation. (Received November 1, 1989; Accepted April 12, 1990)     

Blue light activates potassium-efflux channels in flexor cells from Samanea saman motor organs via two mechanisms

Light-induced leaflet movement of Samanea saman depends on the regulation of membrane transporters in motor cells. Blue light (BL) stimulates leaflet opening by inducing K(+) release from the flexor motor cells. To elucidate the mechanism of K(+)-efflux (K(D))-channel regulation by light, flexor motor cell protoplasts were patch-clamped in a cell-attached configuration during varying illumination. Depolarization elicited outward currents through single open K(D) channels. Changes in cell membrane potential (E(M)) were estimated by applying voltage ramps and tracking the change of the apparent reversal potential of K(D)-channel current. BL shifted E(M) in a positive direction (i.e. depolarized the cell) by about 10 mV. Subsequent red light pulse followed by darkness shifted E(M) oppositely (i.e. hyperpolarized the cell). The BL-induced shifts of E(M) were not observed in cells pretreated with a hydrogen-pump inhibitor, suggesting a contribution by hydrogen-pump to the shift. BL also increased K(D)-channel activity in a voltage-independent manner as reflected in the increase of the mean net steady-state patch conductance at a depolarization of 40 mV relative to the apparent reversal potential (G(@40)). G(@40) increased by approximately 12 pS without a change of the single-channel conductance, possibly by increasing the probability of channel opening. Subsequent red-light and darkness reversed the change in G(@40). Thus, K(+) efflux, a determining factor for the cell-volume decrease of flexor cells, is regulated by BL in a dual manner via membrane potential and by an independent signaling pathway.     

Circadian rhythm leaf movement of Phaseolus vulgaris and the role of calcium ions

Legume plants, due to their distinctive botanical characteristics, such as leaf movements, physiological characteristics, such as nitrogen fixation, and their abilities to endure environmental stresses, have important roles in sustainable pastures development. Leaf movement of legume plants is turgor regulated and osmotically active fluxes of ions between extensor and flexor of pulvinus cause this movement. To determine the role of calcium ions in circadian leaf movements of Phaseolus vulgaris L., a radiotracer technique experiment using ⁴⁵Ca ions were employed. Measurements were taken during circadian leaf movements, and samples were taken from different parts of the leaflet. The ⁴⁵Ca β-particle activity reduced from leaflet base pulvinus to leaf tip. The pulvinus had the highest activity, while the leaf tip had the lowest. By increase of the ratio of ⁴⁵Ca β-particle activity within flexor to extensor (Fl/Ex) the midrib-petiole angle, as an indicator of leaf movement, increased linearly during circadian leaf movement (r = 0.86). The ⁴⁵Ca β-particle activity of Flex/Ext ratio reduced linearly (r = −0.88) toward midnight. In conclusion, it was found that calcium ions accumulation is opposite to the fluxes of osmatically active ions and water movement. Calcium ions accumulate at less negative water potential side of the pulivnus.Key words: pulvinus, extensor, flexor, leaf movement, rhythm, circadian, calcium, Phaseolus vulgaris, radioactive     

X-ray microanalysis of ion distribution within root cortical cells of the halophyte Suaeda maritima (L.) Dum.

The ion content of compartments within cortical cells of mature roots of the halophyte Suaeda maritima grown at 200 mol·m^-3 NaCl has been studied by X-ray microanalysis of freeze-substituted thin sections. Sodium and Cl were found in the vacuoles at about four-times the concentration in the cytoplasm or cell walls, whereas K was more concentrated in the cell walls and cytoplasm than in vacuoles. The vacuolar Na concentration was 12- to 13-times higher than that of K. The Na concentration of cell walls of cortical cells was about 95 mol·m^-3 of analysed volume. The cytoplasmic K concentration within the mature cortical cells was estimated to be 55 mol·m^-3 of analysed volume.     

Role of pulvinar chloroplasts in light-driven leaf movements of the trifoliate leaf of bean (Phaseolus vulgaris L.)

Laminar pulvini of bean (Phaseolus vulgaris L.) contain numerouschloroplasts in cells of their motor tissue. The quantitativerelationships of the chloroplast pigments, chlorophyll a andb, ß-carotene, lutein, neoxanthin as well as the xanthophyllcycle carotenoids (violaxanthin, antheraxanthin and zeaxanthin)were similar to those of mesophyll chloroplasts from leafletlaminae. Exposure of pulvinules to light caused deepoxidationof violaxanthin to zeaxanthin, showing that the xanthophyllcycle is functioning. Chlorophyll fluorescence analysis of pulvinulesconfirmed that their chloroplasts are capable of both photosyntheticelectron transport and non-photochemical fluorescence quenching,showing that they build up a considerable transthylakoid protongradient in the light. Application of DCMU to excised pulvinulesand laminar discs, as well as to pulvinules of intact, attachedterminal leaflets blocked electron transport and fluorescencequenching. Application of the uncoupler CCCP to intact pulvinulesalso prevented non-photochemical fluorescence quenching. Therate of movement of the low-light-adapted terminal leaflet inresponse to exposure of its pulvinule to overhead red light(500 µmol m^–2 s^–1) was reduced when the pulvinulewas pretreated with DCMU. The pulvinar response to overheadblue light (50 µmol ^–2 s^–1), which is morepronounced than to red light, was not affected by similar pretreatmentwith DCMU. Pretreatment with CCCP caused a short lag in theresponse to red light, but did not affect its subsequent rate.The results suggest that the pulvinar response to red, but notto blue light, requires non-cyclic electron transport and theresulting generation of ATP Key words: Leaf movements, light, non-cyclic electron transport, Phaseolus, pulvinar chloroplasts     

Oscillations of the Membrane Potential of Pulvinar Motor Cells In Situ in Relation to Leaflet Movements of Desmodium motorium

The ultradian rhythmic movement of the lateral leaflets of Desmodiummotorium is accompanied by rhythmic changes of the extra- andintracellular electrical potentials in the pulvinus, which aremeasured in situ in the pulvinus against the bathing solutionof the petiole. Extra- and intracellular potentials oscillatewith 180'b0 phase difference to each other, as shown by simultaneousmeasurements of both types of potentials in the abaxial partof the pulvinus. Light-induced changes of these potentials movein opposite directions. The in situ membrane potential of themotor cells of the pulvinus was calculated from the differencebetween the extra- and intracellular potentials. It was foundto oscillate between –136 and –36 mV, in phase withthe intracellular and inverse to the extracellular potential.The phase relationship between the leaflet movement rhythm andthe in situ membrane potential rhythm was as follows: downwardmovement is preceded and accompanied by a strong depolarization,upward movement by hyperpolarization. Our results suggest that membrane depolarization in pulvinarmotor cells of Desmodium motorium drives and controls potassiumefflux and hyperpolarization potassium influx via potassiumchannels. Key words: Desmodium pulvinus, leaf movement, pulvinar motor cells, electrical potential     

Microautoradiographic localisation of [3H]sucrose and [3H]mannitol in Robinia pseudoacacia pulvinar tissues during phytochrome-mediated nyctinastic closure

Summary. We have analysed the incorporation of [³H]sucrose and [³H]mannitol in pulvinar motor cells of Robinia pseudoacacia L. during phytochrome-mediated nyctinastic closure. Pairs of leaflets, excised 2 h after the beginning of the photoperiod, were fed with 50 mM [³H]sucrose or [³H]mannitol, irradiated with red (15 min) or far-red (5 min) light and placed in the dark for 2–3 h. Label uptake was measured in whole pulvini by liquid scintillation counting. The distribution of labelling in pulvinar sections was assessed by both light and electron microautoradiography. [³H]Sucrose uptake was twice that of [³H]mannitol incorporation in both red- and far-red-irradiated pulvini. In the autoradiographs, [³H]sucrose and [³H]mannitol labelling was localised in the area from the vascular bundle to the epidermis, mainly in vacuoles, cytoplasm, and cell walls. Extensor and flexor protoplasts displayed a different distribution of [³H]sucrose after red and far-red irradiation. Far-red light drastically reduced the [³H]sucrose incorporation in extensor protoplasts and caused a slight increase in internal flexor protoplasts. After red light treatment, no differences in [³H]sucrose labelling were found between extensor and flexor protoplasts. Our results indicate a phytochrome control of sucrose distribution in cortical motor cells and seem to rule out the possibility of sucrose acting as an osmoticum. Correspondence and reprints: Unidad de Fisiología Vegetal, Facultad de Biología, Universidad de Barcelona, Avenida Diagonal 645, 08028 Barcelona, Spain.     

STRUCTURAL SPECIALIZATION OF THE SITE OF RESPONSE TO VECTORIAL PHOTO-EXCITATION IN THE SOLAR-TRACKING LEAF OF LAVATERA CRETICA

Structural features of the pulvinus of the solar-tracking leaf of Lavatera cretica L. that are involved in its capacity for omnidirectional and fully reversible bending in response to vectorial excitation of the lamina were studied by light- and scanning electron microscopy. Pulvini that had bent in the plane at right angles to the midvein were bisected along that plane and the symmetrical tissues of the expanded and contracted flanks were compared. The pulvinus contains a central vascular core and exhibits a transversely furrowed exterior. These specialized features enable the fully mature tissue of this region of the petiole to bend reversibly. The epidermis, chlorenchyma, peripheral collenchyma, and cortical parenchyma in the pulvinus form concentric, radially symmetric sheaths around the vascular core and exhibit structural features in their cell walls that would allow considerable changes in cell volume and consequently enable the omnidirectional bending of this pulvinus. Thickened wall portions of the pulvinar epidermis and peripheral collenchyma exhibit a highly specialized architecture, consisting of alternating thick and thin strips, that enhances their flexibility, while maintaining mechanical support. Cell walls of the chlorenchyma and the cortical parenchyma are thin and capable of reversible infolding. Those of the cortical parenchyma also exhibit numerous prominent transverse pit fields, indicative of anisotropic orientation of their microfibrillar lattice transverse to the pulvinar axis. This orientation is compatible with elastic deformation of the cortical parenchyma cells along the pulvinar axis. Filament-like cytoplasmic strands were observed along the walls of pulvinar motor cells, predominantly transverse to the pulvinar axis, but their function (if any) in volume changes of these cells is unknown.     

Subcellular localization of mineral deposits in the roots of wheat (Triticum aestivum L.)

Summary Mineral distribution in the roots of wheat (Triticum aestivum L. cv. Wheaton) was investigated using X-ray microanalysis of bulk frozen hydrated roots in SEM and of freeze substituted sections in TEM. Results obtained using the two methods agreed reasonably well. A total often elements were detected: Na, Mg, Si, P, S, Cl, K, Ca, Mn, and Fe. Of these Si, P, Ca, and Mn were incorporated into biomineralized structures. Silica was deposited in the endodermal walls in the older parts of the root. Silicon was also detected in the large central metaxylem lumina in the basal zone of the root, and in the smaller peripheral metaxylem and the immediately contiguous pericycle and outer parenchyma cells bridging the small metaxylem vessels to the endodermal layer. In the basal zone of the root some of the inner cortical cells contained intracellular electron opaque deposits. These were associated with the cell walls, had non-opaque inclusions and microanalysis revealed that they consisted of calcium, phosphorus and manganese.Abbreviations A apical zone of root - M midzone of root - B basal zone of root - SEM scanning electron microscope - TEM transmission electron microscope     

The Locations and Amounts of Endogenous lons and Elements in the Cap and Elongating Zone of Horizontally Oriented Roots of Zea mays L: An Electron-probe EDS Study

We used quantitative electron-probe energy-dispersive x-raymicroanalysis to localize endogenous Na, Cl, K, P, S, Mg andCa in cryofixed and freeze-dried cryosections of the cap (i.e.the putative site of graviperception) and elongating zone (i.e.site of gravicurvature) of horizontally oriented roots of Zeamays. Ca, Na, Cl, K and Mg accumulate along the lower side ofcaps of horizontally oriented roots. The most dramatic asymmetriesof these ions occur in the apoplast, especially the mucilage.We could not detect any significant differences in the concentrationsof these ions in the central cytoplasm of columella cells alongthe upper and lower sides of caps of horizontally-oriented roots.However, the increased amounts of Na, Cl, K and Mg in the longitudinalwalls of columella cells along the lower side of the cap suggestthat these ions may move down through the columella tissue ofhorizontally-oriented roots. Ca also accumulates (largely inthe mucilage) along the lower side of the elongating zone ofhorizontally-oriented roots, while Na, P, Cl and K tend to accumulatealong the upper side of the elongating zone. Of these ions,only K increases in concentration in the cytoplasm and longitudinalwalls of cortical cells in the upper vs lower sides of the elongatingzone. These results indicate that (1) gravity-induced asymmetriesof ions differ significantly in the cap and elongating zoneof graviresponding roots, (2) Ca accumulates along the lowerside of the cap and elongating zone of graviresponding roots,(3) increased growth of the upper side of the elongating zoneof horizontally-oriented roots correlates positively with increasedamounts of K in the cytoplasm and longitudinal walls of corticalcells, and (4) the apoplast (especially the mucilage) may bean important component of the pathway via which ions move ingraviresponding rots of Zea mays. These results are discussedrelative to mechanisms for graviperception and gravicurvatureof roots. Corn, gravitropism (root), ions, x-ray microanalysis, Zea mays     

Phytochrome and Circadian Clocks in Samanea: Rhythmic Redistribution of Potassium and Chloride within the Pulvinus during Long Dark Periods

Previous investigations with the electron microprobe reveal that the movements of Samanea leaflets are correlated with massive redistribution of K within the pulvinus. Evidence is now presented that Cl moves with K, whether plants are in white light or darkness, whether or not the amplitude of free running oscillations has damped, and whether or not the rhythm has been rephased by phytochrome photoconversion. The mid-extensor to mid-flexor ratio of K + Cl is correlated with leaflet angle under all conditions. Total Cl in both inner cortex and motor region is approximately 0.6 as high as K. The stoichiometry between Cl and the migratory fraction of K is close to, but not precisely 1:1 in all regions of the pulvinus, suggesting that other ions or systems may also be involved in the balancing of electrical charges.