Cytorrhysis

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Schematic of typical plant cell Plant cell structure-en.svg
Schematic of typical plant cell

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). [1] Positive pressure within a plant cell is required to maintain the upright structure of the cell wall. [1] Desiccation (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. [2] That negative pressure pulls the center of the cell inward until the cell wall can no longer withstand the strain. [1] 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. [1] Unlike in plasmolysis (a phenomenon that does not occur in nature), the plasma membrane maintains its connections with the cell wall both during and after cellular collapse. [1]

Contents

Cytorrhysis of plant cells can be induced in laboratory settings if they are placed in a hypertonic solution where the size of the solutes in the solution inhibit flow through the pores in the cell wall matrix. [1] [3] Polyethylene glycol is an example of a solute with a high molecular weight that is used to induce cytorrhysis under experimental conditions. [3] 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). [3] [4] [5]

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. [6] Avoiding cellular damage due to metabolic, mechanical, and oxidative stresses associated with desiccation are obstacles that must be overcome in order to maintain desiccation tolerance. [6] [7] 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. [7] High desiccation tolerance is a trait typically observed in bryophytes, which includes the hornwort, liverwort and moss plant groups but it has also been observed in angiosperms to a lesser extent. [7] Collectively these plants are known as resurrection plants. [8]

Resurrection plants

Many resurrection plants use constitutive and inducible mechanisms to deal with drought and then later desiccation stress. [7] 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. [6] [7] Some species also continuously produce anthocyanins and other polyphenols. [7] An increase in the hormone ABA is typically associated with activation of inducible metabolic pathways. [7] 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. [6] [7] 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. [7] Sugars are utilized as water substitutes by maintaining hydrogen bonds within the cell membrane. [8] 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. [7]

Related Research Articles

Abiotic stress is the negative impact of non-living factors on the living organisms in a specific environment. The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way.

<span class="mw-page-title-main">Plasmolysis</span> Process in which cells lose water in a hypertonic solution

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 water into the cell. Through observation of plasmolysis and deplasmolysis, it is possible to determine the tonicity of the cell's environment as well as the rate solute molecules cross the cellular membrane.

<span class="mw-page-title-main">Reactive oxygen species</span> Highly reactive molecules formed from diatomic oxygen (O₂)

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<i>Pleopeltis polypodioides</i> Species of fern

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<span class="mw-page-title-main">Cryptobiosis</span> Metabolic state of life

Cryptobiosis or anabiosis is a metabolic state in extremophilic organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop, preventing reproduction, development, and repair. When environmental conditions return to being hospitable, the organism will return to its metabolic state of life as it was prior to cryptobiosis.

Moisture stress is a form of abiotic stress that occurs when the moisture of plant tissues is reduced to suboptimal levels. Water stress occurs in response to atmospheric and soil water availability when the transpiration rate exceeds the rate of water uptake by the roots and cells lose turgor pressure. Moisture stress is described by two main metrics, water potential and water content.

Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall.

<span class="mw-page-title-main">Guard cell</span> Paired cells that control the stomatal aperture

Guard cells are specialized plant cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatal pore. The stomatal pores are largest when water is freely available and the guard cells become turgid, and closed when water availability is critically low and the guard cells become flaccid. Photosynthesis depends on the diffusion of carbon dioxide (CO2) from the air through the stomata into the mesophyll tissues. Oxygen (O2), produced as a byproduct of photosynthesis, exits the plant via the stomata. When the stomata are open, water is lost by evaporation and must be replaced via the transpiration stream, with water taken up by the roots. Plants must balance the amount of CO2 absorbed from the air with the water loss through the stomatal pores, and this is achieved by both active and passive control of guard cell turgor pressure and stomatal pore size.

<span class="mw-page-title-main">Osmotic shock</span> Shock caused by a sudden change in the solute concentration around a cell

Osmotic shock or osmotic stress is physiologic dysfunction caused by a sudden change in the solute concentration around a cell, which causes a rapid change in the movement of water across its cell membrane. Under hypertonic conditions - conditions of high concentrations of either salts, substrates or any solute in the supernatant - water is drawn out of the cells through osmosis. This also inhibits the transport of substrates and cofactors into the cell thus “shocking” the cell. Alternatively, under hypotonic conditions - when concentrations of solutes are low - water enters the cell in large amounts, causing it to swell and either burst or undergo apoptosis.

In botany, drought tolerance is the ability by which a plant maintains its biomass production during arid or drought conditions. Some plants are naturally adapted to dry conditions, surviving with protection mechanisms such as desiccation tolerance, detoxification, or repair of xylem embolism. Other plants, specifically crops like corn, wheat, and rice, have become increasingly tolerant to drought with new varieties created via genetic engineering. From an evolutionary perspective, the type of mycorrhizal associations formed in the roots of plants can determine how fast plants can adapt to drought.

Poikilohydry is the lack of ability to maintain and/or regulate water content to achieve homeostasis of cells and tissue connected with quick equilibration of cell/tissue water content to that of the environment. The term is derived from Ancient Greek ποικίλος.

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<span class="mw-page-title-main">Osmosis</span> Chemical process

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Osmoprotectants or compatible solutes are small organic molecules with neutral charge and low toxicity at high concentrations that act as osmolytes and help organisms survive extreme osmotic stress. Osmoprotectants can be placed in three chemical classes: betaines and associated molecules, sugars and polyols, and amino acids. These molecules accumulate in cells and balance the osmotic difference between the cell's surroundings and the cytosol. In plants, their accumulation can increase survival during stresses such as drought. In extreme cases, such as in bdelloid rotifers, tardigrades, brine shrimp, and nematodes, these molecules can allow cells to survive being completely dried out and let them enter a state of suspended animation called cryptobiosis.

Dehydrin (DHN) is a multi-family of proteins present in plants that is produced in response to cold and drought stress. DHNs are hydrophilic, reliably thermostable, and disordered. They are stress proteins with a high number of charged amino acids that belong to the Group II Late Embryogenesis Abundant (LEA) family. DHNs are primarily found in the cytoplasm and nucleus but more recently, they have been found in other organelles, like mitochondria and chloroplasts.

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Trebouxia gelatinosa is a common symbiotic species of green alga in the family Trebouxiaceae. Formally described as new to science in 1975, it is usually found in association with different species of lichen-forming fungi.

References

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  5. de Jong, Joke C.; McCormack, Barbara J.; Smirnoff, Nicholas; Talbot, Nicholas J. (1997). "Glycerol generates turgor in rice blast". Nature. 389 (6648): 244. Bibcode:1997Natur.389..244D. doi: 10.1038/38418 . S2CID   205026525.
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  7. 1 2 3 4 5 6 7 8 9 10 Gechev, Tsanko S.; Dinakar, Challabathula; Benina, Maria; Toneva, Valentina; Bartels, Dorothea (2012-07-26). "Molecular mechanisms of desiccation tolerance in resurrection plants". Cellular and Molecular Life Sciences. 69 (19): 3175–3186. doi:10.1007/s00018-012-1088-0. PMID   22833170. S2CID   15168972.
  8. 1 2 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.