Nickel in higher plants: further evidence for an essential role

Soybeans (Glycine max [L.] Merr.) grown in Ni-deficient nutrient solutions accumulated toxic urea concentrations which resulted in necrosis of their leaflet tips, a characteristic of Ni deficiency. Estimates of the Ni requirement of a plant were made by using seeds produced with different initial Ni contents. When compared to soybeans grown from seeds containing 2.5 nanograms Ni, plants grown from seeds containing 13 nanograms Ni had a significantly reduced incidence of leaflet tip necrosis. Plants grown from seeds containing 160 nanograms Ni produced leaves with almost no leaflet tip necrosis symptoms. Neither Al, Cd, Sn, nor V were able to substitute for Ni.

In other experiments, a small excess of EDTA was included in the nutrient solution in addition to that needed to chelate micronutrient metals. Under these conditions, nodulated nitrogen-fixing soybeans had a high incidence of leaflet tip necrosis, even when 1 micromolar NiEDTA was supplied. However, in nutrient solutions containing inorganic sources of N, 1 micromolar NiEDTA almost completely prevented leaflet tip necrosis, although no significant increase in leaf urease activity was observed. Cowpeas (Vigna unguiculata [L.] Walp) grown in Ni-deficient nutrient solutions containing NO₃ and NH₄ also developed leaflet tip necrosis, which was analogous to that produced in soybeans, and 1 micromolar NiEDTA additions prevented these symptoms.

These findings further support our contention that Ni is an essential element for higher plants.

     

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     

AXIAL ROTATION OF ERYTHRINA HERBACEA LEAFLETS

The leaflets of Erythrina herbacea, a leguminous plant native to subtropical North America, undergo daily movements. During the night, leaflets are oriented with their tips pointing downwards and show no rotation around the midrib of each leaflet. In the morning, leaflets rise, passing through a horizontal orientation and, somewhat before noon, reach a maximum average midrib elevation of approximately sixty degrees above the horizontal plane. Simultaneously, each leaflet rotates about the midrib by an average angle of forty to fifty degrees. These leaflet movements result in an initial increase in the relative leaflet surface area presented to the sun during the morning, a decrease in interception of direct solar radiation around noon, followed by a second maximum in light interception in early afternoon.     

The enigmatic fast leaflet rotation in Desmodium motorium: Butterfly mimicry for defense?

I propose that the enigmatic leaflet movements in elliptical circles every few minutes of the Indian telegraph (semaphore) plant Desmodium motorium ( = D. gyrans = Hedysarum gyrans = Codariocalyx motorius), which has intrigued scientists for centuries, is a new type of butterfly or general winged arthropod mimicry by this plant. Such leaflet movement may deceive a passing butterfly searching for an un-occupied site suitable to deposit its eggs, that the plant is already occupied. It may also attract insectivorous birds, reptiles or arthropods to the plant because it looks as if it is harboring a potential prey and while they patrol there, they can find insects or other invertebrates that indeed attack the plant. The possibility that diurnal mammalian herbivores may also be deterred by these movements should not be dismissed.     

Rhythmic potassium flux in albizzia: effect of aminophylline, cations, and inhibitors of respiration and protein synthesis

Rhythmic leaflet movement in Albizzia is controlled by rhythmic K⁺ flux in pulvinal motor cells. The angle assumed by darkened leaflets during the open phase of the rhythm can be altered by various compounds and changes in temperature; such treatments are ineffective during the closed phase. In all cases, effects on leaflet angle are correlated with and probably a consequence of K⁺ flux in pulvinal motor cells. Incubation at low temperature (6C) or on sodium azide (1.0 mm) reduces K⁺ in the ventral motor region and increases K⁺ in the dorsal motor region, thereby decreasing leaflet angle. Incubation on cycloheximide (0.1 mm) or sodium acetate (0.05 m) inhibits protein synthesis; if the incubation period immediately precedes the opening phase, these compounds prevent both K⁺ flux into the ventral motor cells and leaflet opening. Magnesium nitrate (0.05 m), supplied after leaflets have started to open, promotes K⁺ secretion from the dorsal motor cells and increases the angle of opening.     

Effects of Respiration Inhibitors and Uncouplers on Dark- and Light-Induced Leaflet Movements of Cassia fasciculata

Respiration inhibitors, in particular KCN and NaN₃, inhibited slightly the dark-induced (scotonasty) as well as the light-induced (photonasty) leaflet movements of Cassia fasciculata: they act only at concentrations higher than 1 millimolar and 0.1 millimolar, respectively. Amytal induced a stronger inhibitory effect on scotonasty. Salicylhydroxamic acid, which inhibits the cyanide-insensitive respiration pathway, was also poorly effective when applied alone. KCN and salicylhydroxamic acid applied together increased the inhibition. Uncouplers of oxidative phosphorylation were very effective: 2,4-dinitrophenol and carbonylcyanide-m-chlorophenylhydrazone inhibited the scotonastic movements at concentrations higher than 10 μm and 1 μm, respectively. Although uncouplers reduced the photonastic movements at higher concentrations, they promoted leaflet opening at other concentrations in an unexpected way.     

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.     

Breakdown in membrane asymmetry regulation leads to monocyte recognition of P. falciparum-infected red blood cells

The human malaria parasite Plasmodium falciparum relies on lipids to survive; this makes its lipid metabolism an attractive drug target. The lipid phosphatidylserine (PS) is usually confined to the inner leaflet of the red blood cell membrane (RBC) bilayer; however, some studies suggest that infection with the intracellular parasite results in the presence of this lipid in the RBC membrane outer leaflet, where it could act as a recognition signal to phagocytes. Here, we used fluorescent lipid analogues and probes to investigate the enzymatic reactions responsible for maintaining asymmetry between membrane leaflets, and found that in parasitised RBCs the maintenance of membrane asymmetry was partly disrupted, and PS was increased in the outer leaflet. We examined the underlying causes for the differences between uninfected and infected RBCs using fluorescent dyes and probes, and found that calcium levels increased in the infected RBC cytoplasm, whereas membrane cholesterol was depleted from the erythrocyte plasma membrane. We explored the resulting effect of PS exposure on enhanced phagocytosis by monocytes, and show that infected RBCs must expend energy to limit phagocyte recognition, and provide experimental evidence that PS exposure contributes to phagocytic recognition of P. falciparum-infected RBCs. Together, these findings underscore the pivotal role for PS exposure on the surface of Plasmodium falciparum-infected erythrocytes for in vivo interactions with the host immune system, and provide a rationale for targeted antimalarial drug design.     

Phototropic leaf movements and photosynthetic performance in an amphibious fern, Marsilea quadrifolia

Diurnal phototropism has not been reported in ferns. In this study we found that the four leaflets of the amphibious fern Marsilea quadrifolia are capable of adjusting their leaflet angle and leaflet azimuth in response to changes in the position of the sun’s direct beam, exhibiting more diaphototropic movements (orienting the plane of the lamina perpendicular to incident light) in the morning and late afternoon, and more paraphototropic movements (orienting the plane of the lamina parallel to incident light) at noon. In addition, by cutting off the leaflet lamina and covering portions of leaflets with black tape, the junction between the leaflet and petiole was found to be responsible for light reception. Among the light spectrum investigated, blue light was the most effective at inducing diaphototropism. The role of diurnal phototropism in enhancing carbon return and ameliorating photoinhibition was also evaluated. It was concluded that diurnal phototropic leaf movement represents one of the plastic responses enabling this amphibious fern to grow under terrestrial conditions.     

Changes in Morphometry and Elemental Composition of Robinia pseudoacacia Pulvinar Motor Cells During Leaflet Movements

Changes in shape and size of Robinia pulvinar cortical cellsin relation to leaflet movements have been investigated usingan image processing system applied to drawings of transverseand longitudinal pulvinar sections. Both the size and shapeof cell sections underwent change during movement. The dorsal-leftside region of the cortex has been characterized as the extensorregion which increases turgor during opening. Morphometric changesoccur throughout the cortical motor cells except in the threeor four inner layers. K, Cl, S, and Ca distribution in cellwalls and protoplasts of inner and outer motor cells have beenmeasured with X-ray microanalysis. The distribution patternof K and Cl shows that these ions are mainly responsible forturgor changes. K and Cl were simultaneously depleted in apoplastand protoplast, which suggests that cell walls do not possessa high enough ionic reservoir during Robinia leaflet movements.Ca was always higher in flexor cell walls than in extensor regionsof closed pulvini. This fact could be related to a lower abilityto extend of flexor cells which underwent fewer morphomerticchangrs during movement.     

Effects of Salicylic and Acetylsalicylic Acids on the Scotonastic and Photonastic Leaflet Movements of Cassia fasciculata

Salicylic and acetylsalicylic acids applied on excised leaves of Cassia fasciculata modify the dark-induced (scotonastic) and light-induced (photonastic) leaflet movements. They inhibit the scotonastic movements in a dose-dependent manner from 1 × 10⁻⁴ to 1 × 10⁻³ molar and they promote the photonastic movements at an optimum concentration of 5 × 10⁻⁴ molar. These results suggest that these phenolic compounds do not act specifically on the K⁺ uptake, which was shown to be inhibited by their action on other materials.     

Substrate Selectivity of Lysophospholipid Transporter LplT Involved in Membrane Phospholipid Remodeling in Escherichia coli

Lysophospholipid transporter (LplT) was previously found to be primarily involved in 2-acyl lysophosphatidylethanolamine (lyso-PE) recycling in Gram-negative bacteria. This work identifies the potent role of LplT in maintaining membrane stability and integrity in the Escherichia coli envelope. Here we demonstrate the involvement of LplT in the recycling of three major bacterial phospholipids using a combination of an in vitro lysophospholipid binding assay using purified protein and transport assays with E. coli spheroplasts. Our results show that lyso-PE and lysophosphatidylglycerol, but not lysophosphatidylcholine, are taken up by LplT for reacylation by acyltransferase/acyl-acyl carrier protein synthetase on the inner leaflet of the membrane. We also found a novel cardiolipin hydrolysis reaction by phospholipase A₂ to form diacylated cardiolipin progressing to the completely deacylated headgroup. These two distinct cardiolipin derivatives were both translocated with comparable efficiency to generate triacylated cardiolipin by acyltransferase/acyl-acyl carrier protein synthetase, demonstrating the first evidence of cardiolipin remodeling in bacteria. These findings support that a fatty acid chain is not required for LplT transport. We found that LplT cannot transport lysophosphatidic acid, and its substrate binding was not inhibited by either orthophosphate or glycerol 3-phosphate, indicating that either a glycerol or ethanolamine headgroup is the chemical determinant for substrate recognition. Diacyl forms of PE, phosphatidylglycerol, or the tetra-acylated form of cardiolipin could not serve as a competitive inhibitor in vitro. Based on an evolutionary structural model, we propose a “sideways sliding” mechanism to explain how a conserved membrane-embedded α-helical interface excludes diacylphospholipids from the LplT binding site to facilitate efficient flipping of lysophospholipid across the cell membrane.     

Population variation of leaflet sleep movements in Oxalis grandis (Oxalidaceae)

To identify intraspecific variation in the expression of circadian leaflet movements, we observed changes in leaflet elevation angle in a controlled environment and in the field. Two morphologically and ecologically distinct populations of Oxalis grandis were compared: a typical mesic forest ecotype and an atypical, densely hirsute ecotype found on partially exposed shale outcroppings. Significant genotypic variation was detected within both populations. The controlled environment experiment revealed significant differences in the intrinsic rhythm between the two populations, primarily at the beginning and end of the photophase. We observed leaflet ascent and descent prior to lights-on and lights-off, respectively, processes we define as anticipatory. Hirsute ecotype plants showed a greater anticipation of lights-on, whereas the mesic ecotype plants showed a greater anticipation of lights-off. In the field, significant differences in leaflet elevation between the populations occurred in early morning and late afternoon, but not immediately preceding dusk. Contrary to the controlled environment experiment, mesic ecotype plants showed greater anticipation of dawn; plants from both populations showed similar anticipation of dusk. Plants of the hirsute ecotype exhibited higher sensitivity to sudden fluctuations in light level. We hypothesize that differences in light sensitivity partially explain the differences in the leaflet angle patterns between the field and controlled environments.     

Studies on electron-transport reactions of photosynthesis in plastome mutants of oenothera

Fluorescence characteristics and light-induced absorbance changes of 5 plastome mutants of Oenothera, all having a defect in photosynthesis, were investigated to localize the site of the block in their photosynthetic mechanism and to relate mutational changes in the plastome to specific biochemical events in photosynthesis. In 4 of the mutants examined photosystem 2 was largely, or completely, nonfunctional. Excitation of system 2 did not cause reduction of oxidized cytochrome f in these mutants. The system-2 dependent absorbance change at 518 mμ seen in normal leaves was absent in the mutants. Moreover, the mutants had a high initial fluorescence in the presence and in the absence of 3- (3,4-dichlorophenyl)-1,1-dimethylurea, which did not change during illumination, indicating that the reaction centers of system 2 were affected by the mutations. Photosystem 1 functioned normally.

A fifth mutant had an impaired photosystem 1. Even high intensity far-red light did not lead to an accumulation of oxidized cytochrome f as was seen in normal plants. Photosystem 2 was functioning, as evidenced by the fast reduction of the primary system-2 oxidant, and by the characteristics of the 518-mμ absorbance change.

Because 1 of the 2 photosystems is functional in all mutants, and because they all have the enzymes of the photosynthetic carbon cycle, it appears that the effect of the mutation is specific. The results suggest that the plastome controls reactions within the electron-transport chain of photosynthesis.

     

Chasing and pursuit in the dolichopodid fly Poecilobothrus nobilitatus

1. Male Poecilobothrus nobilitatus show two distinct kinds of pursuit. Females are “shadowed” at a distance of a few cm, using both rotational and lateral movements. Other males are chased, in a pursuit that involves only rotation and fast forward flight. The rotational component of pursuit appears to have the same control system in both types of tracking, and it is best described as a continuous translation of the error angle between the direction of the target and the pursuing fly's body axis into the pursuing fly's angular velocity. The constant of proportionality is 30–40°·s^?1 per degree, and the delay in the system is about 15 ms. Pursuit on the ground is 2–3 times slower than in flight, although the delay seems to be similar.
2. Attempts were made to see whether the aerial pursuits could be modelled effectively by a saccadic or discontinuous control system, as suggested for Musca pursuit (Wagner 1986). It was found that the velocity profiles of the chases could be fitted by an overlapping series of plausible saccade-like events, However, the correlation between visual information (error angle and error angular velocity) available just before each fictive saccade correlated poorly with saccade peak velocity. It is thus concluded that Poedlobothrus pursuit is basically continuous in nature, but it is argued that the two types of mechanism are hard to distinguish in natural behaviour.

     

Rhythmic Leaflet Movement in Albizzia julibrissin: Effect of Electrolytes and Temperature Alteration

The rhythmic movement of darkened Albizzia leaflets is accompanied by K⁺ flux in pulvinule motor cells whose turgor changes control opening and closing. The azide-sensitive open phase is promoted by an increase in temperature from 16 to 33C (Q₁₀ = 3), implying active transport of K⁺ ions during this period. The azide-insensitive closed phase is less temperature-sensitive and has a Q₁₀ less than 1, implying diffusion or some other physical process as the predominant pathway of K⁺ flux at this time. Thus rhythmic leaflet movement is probably due to oscillation in active K⁺ transport or membrane permeability or both. External electrolytes (0. 1 n) alter leaflet angle during the open, but not the closed, phase of the rhythm. All chlorides except NH₄⁺ promote opening, with divalent more effective than monovalent ions. Some anions promote and others inhibit opening; activity is not correlated with charge. It is likely that electrolytes alter leaflet movement by altering K⁺ flux, accomplishing this by interacting with key macromolecules in motor cell membranes.     

Tryptophan 2,3-dioxygenase in the development of the stick insect,Carausius morosus Br

Summary A detailed kinematical analysis of oscillating fly wings using high speed cine films in three-table projection and model reconstructions show a variety of quick changes in beating and rotating movements. There are especially quick changes in the geometrical angle of attack during the upper and lower reversal phases and quick twisting movements and bending oscillations during some of the beating phases. A dozen possibilities for instationary aerodynamic effects are discussed, including quick oscillations in angle of attack, quick turning movements in the reversal points, circulation possibly induced by a quick supination during the beginning of upstroke (fast supination effect), oblique attack by the fluid, circulation possibly induced by a forced oscillation of the trailing edge during the beginning of downstroke (swinging edge effect), tangential transport of the boundary layer by undulatory movements, rolling movements during the turning phases, high-frequency small oscillations of the wing surface, and a quick oscillation during late upstroke. Weis-Fogh's clap and fling mechanism and flip mechanism could not be detected in Calliphorid flies.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft     

Histochemical Approach to Properties of Vicia faba Guard Cell Phosphoenolpyruvate Carboxylase

Properties of phosphoenolpyruvate carboxylase in guard cells dissected from frozen-dried Vicia faba L. leaflets were studied using quantitative histochemical techniques. Control experiments with palisade cells and whole leaflet extract proved that the single cell approach was valid. Most characteristics of enzyme activity in guard cells were identical to those in the leaflet extract. The activities were highly dependent on temperature, with maximum activity at 25 to 35 C. Half-maximum activity (with 1 millimolar phosphoenolpyruvate [PEP]) was observed at 0.1 millimolar Mg²⁺. Two-hundred millimolar NaCl inhibited the reaction by 50%. With frozen-dried leaflet extract, the apparent K_m(PEP) was 0.15 millimolar at pH 7.7; with guard cells, the values were 1.49, 0.5 to 0.8, and 0.24 millimolar in three successive experiments. Additional experiments showed that apparent K_m(PEP) of guard cell activity from plants within a single growth lot was reproducible and did not change during stomatal opening. Mixed extract experiments proved that soluble compounds were not responsible for the difference observed between leaflet and guard cell activities. The differences in apparent K_m(PEP) of guard cell activity could not be unambiguously interpreted. The physiological implications of the properties of this enzyme in guard cells are discussed.     

Effect of Growth Regulators on CO(2) Assimilation in Leaves, and its Correlation with the Bud Break Response in Photosynthesis

Experiments have been done to confirm the previously reported effect of indoleacetic acid (IAA) on the rate of CO₂ assimilation in bean leaves. It was shown that spraying the leaves of a variety of plants caused an increase in the rate of CO₂ assimilation from 30% to 100% during the half-hour to 1 hour period following spraying. The only plant tested which did not show such an effect was corn.

The breaking of dormancy of axial buds in the bean plant was correlated with an increase in the rate of CO₂ assimilation in adjacent leaves for a brief period of time. It has been shown that IAA solution sprayed on 1 leaflet of a leaf can cause an increase in the rate of CO₂ assimilation in the other leaflets, and that IAA applied to the cut stem of a leaflet or a developing bud can be transported to adjacent leaves and cause an increase in the CO₂ assimilation rate. The reaction caused by IAA is very similar to that caused by the breaking of dormancy of a bud. This indicates that the bud break response in CO₂ assimilation in leaves is caused by auxin synthesized in a bud as it begins to grow, and exported into adjacent leaves.