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Cytorrhysis is the permanent and irreparable damage to the cell wall after the complete collapse of a plant cell due to the loss of internal positive pressure (hydraulic
turgor pressure Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibriu ...
). Positive pressure within a plant cell is required to maintain the upright structure of the
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering me ...
.
Desiccation Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...
(relative water content of less than or equal to 10%) resulting in cellular collapse occurs when the ability of the plant cell to regulate turgor pressure is compromised by environmental stress. Water continues to diffuse out of the cell after the point of zero turgor pressure, where internal cellular pressure is equal to the external atmospheric pressure, has been reached, generating negative pressure within the cell. That negative pressure pulls the center of the cell inward until the cell wall can no longer withstand the strain. The inward pressure causes the majority of the collapse to occur in the central region of the cell, pushing the organelles within the remaining cytoplasm against the cell walls. Unlike in
plasmolysis Plasmolysis is the process in which cells lose water in a hypertonic solution. The reverse process, deplasmolysis or cytolysis, can occur if the cell is in a hypotonic solution resulting in a lower external osmotic pressure and a net flow of wat ...
(a phenomenon that does not occur in nature), the
plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (the ...
maintains its connections with the cell wall both during and after cellular collapse. Cytorrhysis of plant cells can be induced in laboratory settings if they are placed in a
hypertonic solution In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane- ...
where the size of the solutes in the solution inhibit flow through the pores in the cell wall matrix.
Polyethylene glycol Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...
is an example of a solute with a high molecular weight that is used to induce cytorrhysis under experimental conditions. Environmental stressors which can lead to occurrences of cytorrhysis in a natural setting include intense drought, freezing temperatures, and pathogens such as the rice blast fungus (''Magnaporthe grisea'').


Mechanisms of avoidance

Desiccation tolerance refers to the ability of a cell to successfully rehydrate without irreparable damage to the cell wall following severe dehydration. Avoiding cellular damage due to metabolic, mechanical, and
oxidative Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
stresses associated with desiccation are obstacles that must be overcome in order to maintain desiccation tolerance. Many of the mechanisms utilized for drought tolerance are also utilized for desiccation tolerance, however the terms desiccation tolerance and drought tolerance should not be interchanged as the possession of one does not necessarily correlate with possession of the other. High desiccation tolerance is a trait typically observed in
bryophytes The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited in si ...
, which includes the hornwort, liverwort and moss plant groups but it has also been observed in angiosperms to a lesser extent. Collectively these plants are known as
resurrection plants A resurrection plant is any poikilohydric plant that can survive extreme dehydration, even over months or years. Examples include: * '' Anastatica hierochuntica'', also known as the Rose of Jericho, a plant species native to deserts of North Afric ...
.Proctor, Michael C. F. C, Roberto G. Ligrone, and Jeffrey G. Duckett. "Desiccation Tolerance in the Moss Polytrichum Formosum: Physiological and Fine-structural Changes during Desiccation and Recovery."Annals of Botany 99.1 (2007): 75-93. Web.


Resurrection plants

Many resurrection plants use constitutive and inducible mechanisms to deal with drought and then later desiccation stress. Protective proteins such as cyclophilins, dehydrins, and LEA proteins are maintained at levels within a desiccation resistant species typically only seen during drought stress for desiccation sensitive species, providing a greater protective buffer as inducible mechanisms are activated. Some species also continuously produce
anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical com ...
s and other polyphenols. An increase in the hormone ABA is typically associated with activation of inducible metabolic pathways. Production of sugars (predominantly sucrose), aldehyde dehydrogenases, heat shock factors, and other LEA proteins are upregulated after activation to further stabilize cellular structures and function. Composition of the cell wall structure is altered to increase flexibility so folding can take place without irreparably damaging the structure of the cell wall. Sugars are utilized as water substitutes by maintaining hydrogen bonds within the cell membrane. Photosynthesis is shut down to limit production of reactive oxygen species and then eventually all metabolic are drastically reduced, the cell effectively becoming dormant until rehydration.


References

{{Reflist Plant physiology