Search Results - (Author, Cooperation:S. M. Assmann)

2014-05-17

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Arabidopsis/genetics/*metabolism ; Arabidopsis Proteins/genetics/*metabolism ; Cell Membrane/*metabolism ; Membrane Proteins/genetics/*metabolism ; *Protein Interaction Maps ; Signal Transduction ; Two-Hybrid System Techniques

2013-11-26

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Arabidopsis/*genetics ; Base Sequence ; Codon, Initiator/genetics ; Computational Biology ; Genome, Plant/*genetics ; Molecular Sequence Data ; *Nucleic Acid Conformation ; Phylogeny ; Polyadenylation/genetics ; Protein Biosynthesis/genetics ; RNA Splice Sites/genetics ; RNA, Messenger/chemistry/genetics/metabolism ; RNA, Plant/analysis/*chemistry/genetics/*metabolism ; RNA, Ribosomal, 18S/chemistry/genetics/metabolism ; *Regulatory Sequences, Ribonucleic Acid/genetics ; Sequence Analysis, RNA ; Stress, Physiological/genetics ; Structure-Activity Relationship

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Numerous studies conducted on both whole plants and isolated epidermes have documented stomatal sensitivity to CO2. In general, CO2 concentrations below ambient stimulate stomatal opening, or an inhibition of stomatal closure, while CO2 concentrations above ambient have the opposite effect. The rise in atmospheric CO2 concentrations which has occurred since the industrial revolution, and which is predicted to continue, will therefore alter rates of transpirational water loss and CO2 uptake in terrestrial plants. An understanding of the cellular basis for guard cell CO2 sensing could allow us to better predict, and perhaps ultimately to manipulate, such vegetation responses to climate change. However, the mechanisms by which guard cells sense and respond to the CO2 signal remain unknown. It has been hypothesized that cytosolic pH and malate levels, cytosolic Ca2+ levels, chloroplastic zeaxanthin levels, or plasma-membrane anion channel regulation by apoplastic malate are involved in guard cell perception and response to CO2. In this review, these hypotheses are discussed, and the evidence for guard cell acclimation to prevailing CO2 concentrations is also considered.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract. An Ohm's law analogy is frequently employed to calculate parameters of leaf gas exchange. For example, resistance to water vapour loss is calculated as the quotient of vapour pressure difference (VPD) and vapour loss by transpiration. In the present research, this electrical analogy was extended. Steady-state transpiration as a function of VPD, assayed in leaflets of Vicia faba using gas exchange techniques, was compared with steady-state K+ current magnitude as a function of voltage in isolated guard cell protoplasts of Vicia faba, assayed using the patch clamping technique in the whole cell configuration. An electrophysiological model originally developed to explain the kinetics of current changes following step changes in voltage across a cell membrane was used to fit the kinetics of transpiration changes following step changes in VPD applied to leaflets of Vicia faba. Following step increases in VPD, transpiration exhibited an initial increase, reflecting the increased driving force for water loss and, for large step increases in VPD, a transient decrease in stomatal resistance. Transpiration subsequently declined, reflecting stomatal closure. By analogy to electrophysiological responses, it is hypothesized that the humidity parameter that is sensed by guard cells is VPD. Two models based on epidermal water relations were also applied to transpiration kinetics. In the first model, the transient increase in transpiration following a step increase in VPD was attributed partially to an increase in the Physical driving force (VPD) and partially to a transient decrease in stomatal resistance resulting from reduced epidermal backpressure. In the second model, the transient decrease in stomatal resistance was attributed to a direct response of the guard cells to VPD. Both models based on water relations gave good fits of the data, emphasizing the need for further study regarding the metabolic nature of the guard cell response to humidity.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract. The effect of atmospheric humidity on the kinetics of stomatal responses was quantified in gas exchange experiments using sugarcane (Saccharum spp. hybrid) and soybean (Glycine max). Pulses of blue light were used to elicit pulses of stomatal conductance that were mediated by the specific blue light response of guard cells. Kinetic parameters of the conductance response were more closely related to leaf-air vapour pressure difference (VPD) than to relative humidity or transpiration. Increasing VPD significantly accelerated stomatal opening in both sugarcane and soybean, despite an approximately five-fold faster response in sugarcane. In contrast, the kinetics of stomatal recovery (closure) following the pulse were similar in the two species. Acceleration of opening by high VPD was observed even under conditions where soybean exhibited a feedforward response of decreasing transpiration (E) with increasing evaporative demand (VPD). This result suggests that epidermal, rather than bulk leaf, water status mediates the VPD effect on stomatal kinetics. The data are consistent with the hypothesis that increased cpidermal water loss at high VPD decreases the backpressure exerted by neighbouring cells on guard cells. allowing more rapid stomatal opening per unit of guard cell metabolic response to blue light.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract Environmental stresses can decrease photosynthesis by a direct effect on photosynthetic capacity of the mesophyll or by a CO2 limitation resulting from stomatal closure. In the present study, a ‘path-dependent method’ (Jones, 1985) for the partitioning of a stress-related decline in assimilation rate between non-stomatal and stomatal factors was evaluated, using light quality as a ‘stress’. Kinetic data on assimilation rate and conductance of Phragmipedium longifolium following a change in light quality from 95 μmol m−2s−1 white light to 95 μmol m−2s−1 red light failed to generate a smooth response curve for conductance. Partitioning of limitations on assimilation by a path-dependent method that utilizes the actual trajectories of conductance and assimilation was therefore not feasible. A simplified path-dependent method (Jones, 1985) which assumes that either mesophyll cells or guard cells respond first to a stress was applied to steady-state measurements of assimilation and conductance under red and white illumination. Either 5% or 23% of the observed reduction in assimilation rate under white light was attributable to stomatal factors, depending on whether the ‘stomatal first’ or the ‘mesophyll first’ path was assumed. In the absence of additional information indicating the appropriate choice of path, arbitrary choice may therefore lead to widely divergent estimates, and potentially erroneous conclusions. An alternative approach to the evaluation of the importance to carbon assimilation of stomatal and non-stomatal factors is suggested.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract. The significance of blue light-stimulated stomatal conductance for carbon assimilation (A), stomatal conductance (g), intercellular CO2 (Ci), stomatal limitation of A (L), transpiration (E) and water use efficiency (W = A/E), was determined in a C4 and a C3 species. W and L were evaluated for steady-state gas exchange with constant, saturating red light (As, gs, Es), and for the integrated gas exchange above the steady state baseline induced by a single, brief pulse of blue light (Ap, gp, Ep). Sugarcane (Saccharum spp. hybrid), a C4 grass, and soybean (Glycine max) a C3 dicot, were compared. Sugarcane exhibited typical C4 behaviour, with A saturing at Ci of ca. 200 μmol mol−1, compared to 〉500 μmol mol−1 in soybean. Steady-state W was also considerably higher in sugarcane. The extent of stomatal opening in response to a blue light pulse, from baseline (gs) to the maximum value of conductance during the opening response (gm), was similar in the two species. More rapid opening and closing of stomata in sugarcane resulted in a smaller integrated magnitude of the conductance response (gp) than in soybean. At the peak of the blue light response, both species exhibited similar levels of L. During the response to the pulse of blue light, A and Ci increased and L decreased to a greater extent in sugarcane than in soybean. As a result, the gas exchange attributed to the stomatal response to blue light exhibited a higher ratio of Ap to Ep (Wp) in sugarcane than in soybean. This Wp was lower in both species than was the Ws associated with the steady state gas exchange. The two species did not differ in the rate of induction of photosynthetic utilization of elevated Ci. The greater stimulation of A in sugarcane was attributed to its C4 attributes of greater carboxylation efficiency (slope of the A versus Ci relationship), lower gs and prevailing Ci,s, and greater Ls under steady-state red illumination. Despite saturation of A at low levels of Ci in C4 species, the gas exchange attributed to the stomatal response to blue light decreased L and contributed considerably to carbon acquisition, while maintaining the high level of W associated with C4 metabolism.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Figure 1 shows a typical change in hydraulic conductivity, commonly referred to as 'stomatal conductance' of a leaf of Vicia f aba L. (cv. long pod) following application of a transient blue light stimulus under a constant background illumination with high fluence rates of red light. As with ...

Electronic Resource

1432-2048

Guard cell ; Patch clamp ; Potassium channel (kinetics) ; Stomate ; Vicia ; Zea

Springer Online Journal Archives 1860-2000

Biology

Abstract We describe and compare inward and outward whole-cell K+ currents across the plasma membrane surrounding guard-cell protoplasts from the dicotyledon, Vicia faba, and the graminaceous monocotyledon, Zea mays. Macrosopic whole-cell current is considered in terms of microscopic single-channel activity, which involves discrete steps between conducting (open) and nonconducting (closed) states of the channel protein. Kinetic equations are used to model the number of open and closed states for channels conducting K+ influx (K(in)) and K+ efflux (K(out)) in the two species, and to calculate the rate at which open-closed transitions occur. The opening and closure of K(in) channels in both Vicia and Zea follow single-exponential timecourses, indicating that K(in)-channel proteins in each species simply fluctuate between one open and one closed state. In both species, opening of K(in) channels is voltage-independent, but closure of K(in) channels is faster at more positive membrane potentials. In response to identical voltage stimuli, K(in) channels in Zea open and close approximately three times as fast as in Vicia. In contrast to K(in), K(out) channels in Zea open and close more slowly than in Vicia. The closure of K(out) channels follows a single-exponential timecourse in each species, indicating one open state. The kinetics of K(out)-channel opening are more complicated and indicate the presence of at least two (Vicia) or three (Zea) closed states.

Electronic Resource

1432-2048

Guard cell ; Patch clamp ; Plasma membrane ; Potassium channels ; Zea (K+ currents)

Springer Online Journal Archives 1860-2000

Biology

Abstract Knowledge of ion fluxes in the dumbell-shaped guard cells of grass species has been limited by the difficulty of obtaining isolated epidermes or guard-cell protoplasts for use in radioactive-tracer or electrophysiological studies. We describe here a method for isolating guard-cell protoplasts from Zea mays L. Whole-cell patch clamp has been used to measure K+-channel current across the plasma membrane surrounding these protoplasts. Two populations of K+-permeable channels have been identified. Hyperpolarization of the membrane to potentials (Vm) more negative than -100 mV results in inward K+ current through one population of channels. Inward current activation is faster than in the dicotyledon, Vicia faba L. (mean activation half-time 26 ms (Z. mays) versus 123 ms (V. faba) at Vm=-180 mV). Steady-state current density is less than in V. faba (-22 μA · cm−2 (Z. mays) versus -40 μA · cm−2 (V. faba) at Vm=- 180 mV in 12 mM external K+). Depolarization of the membrane to potentials more positive than -20 mV results in outward K+ current through a second population of channels; these channels activate and (upon repolarization of the membrane) deactivate more slowly than in V. faba (mean activation half-time 375 ms (Z. mays) versus 187 ms (V. faba) at Vm=+ 80 mV) but result in a similar steady-state current density (23.8 μA · cm−2 (Z. mays) versus 28.7 μA · cm−2 (V. faba) at Vm= + 80 mV with 105 mM internal K+). Omission of K+ eliminates the current. The K+ current is sensitive to both internal and external Ca2+ concentration: increasing internal Ca2+ from 2 nM to 0.2 μM or increasing external Ca2+ from 1 mM to 8.5 mM reduces the magnitude of both inward and outward current.

Electronic Resource

1432-1939

Blue light ; Gas exchange ; Guard cell ; Phytochrome ; Red/far ; red ratio

Springer Online Journal Archives 1860-2000

Biology

Summary The effects on plant growth and stomatal physiology of alterations in light quantity and quality during development were investigated in the C3 monocot, Commelina communis. Reduction in light intensity resulted in decreased branching and stem elongation, with effects more severe under “neutral shade” (R:FR≥1.0) than under “leaf shade” (R:FR≤0.4) conditions. Shade treatments had no effect on the leaf area or stomatal density of newly expanded leaves. Gas exchange measurements on leaves that had expanded under the different treatments indicated that a reduction in light intensity decreased the magnitude and slowed the kinetics of stomatal responses to pulses of blue light, particularly in plants from the neutral shade treatment. These results indicate that the specific stomatal response to blue light is plastic, and is modulated by the light environment prevailing during leaf development.

Electronic Resource

1432-2013

Key words Laser ; Patch clamp ; Guard cell ; Stomata ; Cell wall ; Microsurgery ; Vicia faba ; Commelina communis

Springer Online Journal Archives 1860-2000

Medicine

Abstract  Laser microsurgery can be used to perform both cell biological manipulations, such as targeted cell ablation, and molecular genetic manipulations, such as genetic transformation and chromosome dissection. In this report, we describe a laser microsurgical method that can be used either to ablate single cells or to ablate a small area (1–3 μm diameter) of the extracellular matrix. In plants and microorganisms, the extracellular matrix consists of the cell wall. While conventional patch clamping of these cells, as well as of many animal cells, requires enzymatic digestion of the extracellular matrix, we illustrate that laser microsurgery of a portion of the wall enables patch clamp access to the plasma membrane of higher plant cells remaining situated in their tissue environment. What follows is a detailed description of the construction and use of an economical laser microsurgery system, including procedures for single cell and targeted cell wall ablation. This methodology will be of interest to scientists wishing to perform cellular or subcellular ablation with a high degree of accuracy, or wishing to study how the extracellular matrix affects ion channel function.

Electronic Resource

1432-1424

K+ channel ; Ca2+ channel ; selectivity ; permeation ; plant ; Vicia faba

Springer Online Journal Archives 1860-2000

Biology

Chemistry and Pharmacology

Summary The whole-cell patch-clamp method has been used to measure Ca2+ influx through otherwise K+-selective channels in the plasma membrane surrounding protoplasts from guard cells of Vicia faba. These channels are activated by membrane hyperpolarization. The resulting K+ influx contributes to the increase in guard cell turgor which causes stomatal opening during the regulation of leaf-air gas exchange. We find that after opening the K+ channels by hyperpolarization, depolarization of the membrane results in tail current at voltages where there is no electrochemical force to drive K+ inward through the channels. Tail current remains when the reversal potential for permeant ions other than Ca2+ is more negative than or equal to the K+ equilibrium potential (−47 mV), indicating that the current is due to Ca2+ influx through the K+ channels prior to their closure. Decreasing internal [Ca2+] (Ca i ) from 200 to 2 nm or increasing the external [Ca2+] (Ca o ) from 1 to 10 mm increases the amplitude of tail current and shifts the observed reversal potential to more positive values. Such increases in the electrochemical force driving Ca2+ influx also decrease the amplitude of time-activated current, indicating that Ca2+ permeation is slower than K+ permeation, and so causes a partial block. Increasing Ca o also (i) causes a positive shift in the voltage dependence of current, presumably by decreasing the membrane surface potential, and (ii) results in a U-shaped current-voltage relationship with peak inward current ca. −160 mV, indicating that the Ca2− block is voltage dependent and suggesting that the cation binding site is within the electric field of the membrane. K+ channels in Zea mays guard cells also appear to have a Ca i -, and Ca o -dependent ability to mediate Ca2+ influx. We suggest that the inwardly rectiying K+ channels are part of a regulatory mechanism for Ca i . Changes in Ca o and (associated) changes in Ca i regulate a variety of intracellular processes and ion fluxes, including the K+ and anion fluxes associated with stomatal aperture change.

Electronic Resource