Hyperhydricity (previously known as vitrification) is a physiological

malformation A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...

that results in excessive hydration, low

lignification Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity an ...

, impaired stomatal function and reduced

mechanical strength The field of strength of materials, also called mechanics of materials, typically refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the re ...

of tissue culture-generated plants. The consequence is poor regeneration of such plants without intensive greenhouse acclimation for outdoor growth. Additionally, it may also lead to leaf-tip and bud necrosis in some cases, which often leads to loss of apical dominance in the shoots. In general, the main symptom of hyperhydricity is translucent characteristics signified by a shortage of chlorophyll and high water content. Specifically, the presence of a thin or absent

cuticular A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

layer, reduced number of palisade cells, irregular stomata, less developed cell wall and large intracellular spaces in the

mesophyll cell A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...

layer have been described as some of the anatomic changes associated with hyperhydricity.

Causes

The main causes of hyperhydricity in plant

tissue culture Tissue culture is the growth of tissues or cells in an artificial medium separate from the parent organism. This technique is also called micropropagation. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, su ...

are those factors triggering

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

es such as high salt concentration, high

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...

, low light intensity, gas accumulation in the atmosphere of the jar, length of time intervals between subcultures; number of subcultures, concentration and type of

gelling agent A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still dif ...

, the type of explants used, the concentrations of microelement and hormonal imbalances. Hyperhydricity is commonly apparent in liquid culture-grown plants or when there is low concentration of gelling agent. High ammonium concentration also contributes to hyperhydricity.

Control

Hyperhydricity can be monitored by modifying the atmosphere of the culture vessels. Adjusting the relative humidity in the vessel is one of the most important parameters to be controlled. Use of gas-permeable membranes may help in this regard as this allows increased exchange of

water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous p ...

and other gases such as ethylene with the surrounding environment. Using higher concentration of a gelling agent, on top of the use of a higher-strength gelling agent may reduce the risk from hyperhydricity. Hyperhydricity can also be controlled by bottom cooling, which allows water to condense on the medium, the use of cytokinin-meta-topolin (6-(3-Hydroxybenzylamino)purine), the combination of lower

cytokinin Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and le ...

and

ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...

in the medium, use of nitrate or

glutamine Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral ...

as the sole

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

source and decreasing the ratio of NH4+:NO3- in the medium. In studies on calcium deficiency in tissue cultures of ''Lavandula angustifolia'', it was shown that an increase in calcium in the medium reduced hyperhydricity.

Notes and references

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External links

* http://users.ugent.be/~pdebergh/tro/tro3_d01.htm Cell culture Biotechnology Cell biology Plant physiology

Causes

Control

See also

Notes and references

External links