How is the extensibility of growing plant cell walls regulated? In the past, most studies have focused on the role of the cellulose/xyloglucan network and the enigmatic wall-loosening agents ...expansins. Here we review first how in the closest relatives of the land plants, the Charophycean algae, cell wall synthesis is coupled to cell wall extensibility by a chemical Ca(2+)-exchange mechanism between Ca(2+)-pectate complexes. We next discuss evidence for the existence in terrestrial plants of a similar "primitive" Ca(2+)-pectate-based growth control mechanism in parallel to the more recent, land plant-specific, expansin-dependent process.
Specimens consisting of two tandem internodal cells were prepared using Chara corallina in order to analyze the electrical response upon wounding. When one cell (victim cell) was killed by severing, ...another cell (receptor cell) generated a sharp spike followed by a long-lasting depolarization at the nodal end. It has been reported that K+ released from the victim cell is involved in generation of the long-lasting depolarization (Shimmen 2006). In the present study, the trigger to induce the sharp spike was studied. When the turgor pressure of the victim cell was decreased by adding 1 M methanol to the external medium, a sharp spike similar to that induced by wounding was generated at the nodal end of the receptor cell. It is suggested that the sudden disappearance of the turgor pressure of the victim cell due to severing is a trigger to induce the sharp spike of the receptor cell.
Primary physicochemical steps in microwounding of plants were investigated using electrochemical nano- and microprobes, with a focus on the role of oxygen in the wounding responses of individual ...plant cells. Electrochemical measurements of cell oxygen content were made with carbon-filled quartz micropipettes with platinum-coated tips (oxygen nanosensors). These novel platinum nanoelectrodes are useful for understanding cell oxygen metabolism and can be employed to study the redox biochemistry and biology of cells, tissues and organisms. We show here that microinjury of Chara corallina internodal cells with the tip of a glass micropipette is associated with a drastic decrease in oxygen concentration at the vicinity of the stimulation site. This decrease is reversible and lasts for up to 40 minutes. Membrane stretching, calcium influx, and cytoskeleton rearrangements were found to be essential for the localized oxygen depletion induced by cell wall microwounding. Inhibition of electron transport in chloroplasts or mitochondria did not affect the magnitude or timing of the observed response. In contrast, the inhibition of NADPH oxidase activity caused a significant reduction in the amplitude of the decrease in oxygen concentration. We suggest that the observed creation of localized anoxic conditions in response to cell wall puncture might be mediated by NADPH oxidase.
Expansive growth of plant cell is conditioned by the cell wall ability to extend irreversibly. This process is possible if (i) a tensile stress is developed in the cell wall due to the coupling ...effect between turgor pressure and the modulation of its mechanical properties through enzymatic and physicochemical reactions and if (ii) new cell wall elements can be synthesized and assembled to the existing wall. In other words, expansive growth is the result of coupling effects between mechanical, thermal and chemical energy. To have a better understanding of this process, models must describe the interplay between physical or mechanical variable with biological events. In this paper we propose a general unified and theoretical framework to model growth in function of energy forms and their coupling. This framework is based on irreversible thermodynamics. It is then applied to model growth of the internodal cell of Chara corallina modulated by changes in pressure and temperature. The results describe accurately cell growth in term of length increment but also in term of cell pectate biosynthesis and incorporation to the expanding wall. Moreover, the classical growth model based on Lockhart's equation such as the one proposed by Ortega, appears as a particular and restrictive case of the more general growth equation developed in this paper.
Hydrolyzable tannin (3,6-bis-O-digalloyl-1,2,4-tri-O-galloyl-β-d-glucose) has a dual effect on the cell membrane: (1) it binds to a plasmalemmal protein of the Chara corallina cell ...(C50 = 2.7 ± 0.3 μM) and (2) it forms ionic channels in the lipid membrane. Based on these facts, a molecular model for the interaction of tannins with the cell membrane is proposed. The model suggests that the molecules of hydrolyzable tannin bind electrostatically to the outer groups of the membrane protein responsible for the Ca2+-dependent chloride current and blocks it. Some tannin molecules penetrate into the hydrophobic region of the membrane, and when a particular concentration is reached, they form ion-conducting structures selective toward Cl−.
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•The findings led to new insights into interaction of flavonoids with cell membranes.•Tannin selectively blocks Ca-activated chloride channels.•Tannin interacts with membrane protein and forms selective pores in the membrane.
This study deals with effects of membrane excitation on photosynthesis and cell protection against excessive light, manifested in non-photochemical quenching (NPQ). In
Chara corallina cells, NPQ and ...pericellular pH displayed coordinated spatial patterns along the length of the cell. The NPQ values were lower in H
+-extruding cell regions (external pH ∼
6.5) than in high pH regions (pH ∼
9.5). Generation of an action potential by applying a pulse of electric current caused NPQ to increase within 30–60 s. This effect, manifested as a long-lived drop of maximum chlorophyll fluorescence (
F
m′), occurred at lower photosynthetic flux densities (PFD) in the alkaline as compared to acidic cell regions. The light response curve of NPQ shifted, after generation of an action potential, towards lower PFD. The release of NPQ by nigericin and the rapid reversal of action potential-triggered NPQ in darkness indicate its relation to thylakoid ΔpH. Generation of an action potential shortly after darkening converted the chloroplasts into a latent state with the
F
m identical to that of unexcited cells. This state transformed to the quenched state after turning on weak light that was insufficient for NPQ prior to membrane excitation of the cells. The ionophore, A23187, shifted NPQ plots similarly to the action potential effect, consistent with a likely role of a rise in the cytosolic Ca
2+ level in the action potential-induced quenching. The results suggest that a rapid electric signal, across the plasma membrane, might exert long-lived effects on photosynthesis and chlorophyll fluorescence through ion flux-mediated pathways.
The hydraulic resistance (the reciprocal of the hydraulic conductivity
L
p)
L
p
−1
was measured in cells of
Chara corallina
by the method of transcellular osmosis. Treatment of cells with 100 mM KCl ...decreased
L
p
−1
significantly. Subsequent treatment of the cells with 70 mM CaCl
2
recovered the decreased
L
p
−1
to the original value. To know whether K
+
or Ca
2+
/Mg
2+
acts on the cell wall and/or the membrane, the hydraulic resistances of the cell wall (
L
p
w
−1
) and that of the membrane (
L
p
m
−1
) were determined in one and the same cell. For this, a pair of cells (twin cells) were made from an internodal cell, one used for measurement of
L
p
−1
and the other used for the measurement of
L
p
w
−1
. From
L
p
−1
and
L
p
w
−1
,
L
p
m
−1
was calculated. Both
L
p
−1
and
L
p
w
−1
were decreased by K
+
, while
L
p
m
−1
was not affected by K
+
. The same result was obtained with 5 mM EGTA.
L
p
w
−1
was decreased more than it was by KCl but
L
p
m
−1
remained constant after EGTA treatment. The recovery of the K
+
-decreased
L
p
−1
with Ca
2+
can be explained exclusively by the recovery of
L
p
w
−1
with Ca
2+
. The Ca
2+
recovery of
L
p
w
−1
was observed in the intact cell wall but not in the cell wall tube isolated from an internodal cell. The different response to Ca
2+
between the intact cell wall and the isolated cell wall was discussed in relation to the tension in the cell wall which may be an important factor for the ionic regulation of hydraulic conductivity.
Enzyme-less chemistry appears to control the growth rate of the green alga Chara corallina. The chemistry occurs in the wall where a calcium pectate cycle determines both the rate of wall enlargement ...and the rate of pectate deposition into the wall. The process is the first to indicate that a wall polymer can control how a plant cell enlarges after exocytosis releases the polymer to the wall. This raises the question of whether other species use a similar mechanism. Chara is one of the closest relatives of the progenitors of terrestrial plants and during the course of evolution, new wall features evolved while pectate remained one of the most conserved components. In addition, charophytes contain auxin which affects Chara in ways resembling its action in terrestrial plants. Therefore, this review considers whether more recently acquired wall features require different mechanisms to explain cell expansion.
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