Hyperhydricity
Encyclopedia
Hyperhydricity is a physiological
malformation that results in excessive hydration
, low lignification, impaired stomatal function and reduced mechanical strength 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 lack of a cuticular layer, reduced number of palisade cells, irregular stomata, less developed cell wall
and large intracellular spaces in the mesophyll cell layer have been described as some of the anatomic changes associated with hyperhydricity.
are those factors triggering oxidative stress
es such as high salt concentration, high relative humidity
, low light intensity
, gas accumulation in the atmosphere of the jar, length of time intervals between subculture
s; number of subcultures, concentration and type of gelling agent, the type of explants utilized, 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.
and other gasses 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), combination of lower cytokinin
content and ammonium nitrate in the media, use of nitrate
or glutamine
as the sole nitrogen
source and decreasing the ratio of NH4 +:NO3 − in the medium.
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
malformation that results in excessive hydration
Tissue hydration
Tissue hydration is the process of absorbing and retaining water in biological tissues.-Plants:Land plants maintain adequate tissue hydration by means of an outer waterproof layer. In soft or green tissues, this is usually a waxy cuticle over the outer epidermis...
, low lignification, impaired stomatal function and reduced mechanical strength of tissue culture-generated plants. The consequence is poor regeneration of such plants without intensive greenhouse
Greenhouse
A greenhouse is a building in which plants are grown. These structures range in size from small sheds to very large buildings...
acclimation for outdoor growth. Additionally, it may also lead to leaf-tip and bud necrosis
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
in some cases, which often leads to loss of apical dominance
Apical dominance
In plant physiology, apical dominance is the phenomenon whereby the main central stem of the plant is dominant over other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets....
in the shoots. In general, the main symptom of hyperhydricity is translucent characteristics signified by a shortage of chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
and high water content. Specifically, the presence of a thin or lack of a cuticular layer, reduced number of palisade cells, irregular stomata, less developed cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
and large intracellular spaces in the mesophyll cell layer have been described as some of the anatomic changes associated with hyperhydricity.
Causes
The main causes of hyperhydricity in plant tissue cultureTissue culture
Tissue culture is the growth of tissues or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar...
are those factors triggering oxidative stress
Oxidative stress
Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...
es such as high salt concentration, high relative humidity
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
, low light intensity
Light intensity
Several measures of light are commonly known as intensity. These are obtained by dividing either a power or a luminous flux by a solid angle, a planar area, or a combination of the two...
, gas accumulation in the atmosphere of the jar, length of time intervals between subculture
Subculture
In sociology, anthropology and cultural studies, a subculture is a group of people with a culture which differentiates them from the larger culture to which they belong.- Definition :...
s; number of subcultures, concentration and type of gelling agent, the type of explants utilized, 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
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
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 vaporWater vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
and other gasses 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), combination of lower cytokinin
Cytokinin
Cytokinins are a class of plant growth substances 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 leaf senescence...
content and ammonium nitrate in the media, use of nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
or glutamine
Glutamine
Glutamine is one of the 20 amino acids encoded by the standard genetic code. It is not recognized as an essential amino acid but may become conditionally essential in certain situations, including intensive athletic training or certain gastrointestinal disorders...
as the sole nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
source and decreasing the ratio of NH4 +:NO3 − in the medium.
See Also
- Callus (cell biology)Callus (cell biology)Plant callus is a mass of undifferentiated cells derived from plant tissue for use in biological research and biotechnology. In plant biology, callus cells are those cells that cover a plant wound. To induce callus formation, plant tissues are surface sterilized and then plated onto in vitro...
- Chimera (plant)Chimera (plant)Chimeras in botany are usually single organisms composed of two genetically different types of tissue. They occur in plants, on the same general basis as with animal chimeras...
- Somatic EmbryogenesisSomatic EmbryogenesisSomatic embryos are mainly produced in vitro and for laboratory purposes, using either solid or liquid nutrient media which contain plant growth regulators . The main PGRs used are auxins but can contain cytokinin in a smaller amount. Somatic embryogenesis is a process where a plant or embryo is...
- Embryo rescueEmbryo RescueEmbryo Rescue is one of the earliest and successful forms of in-vitro culture techniques that is used to assist in the development of plant embryos that might not survive to become viable plants. Embryo rescue plays an important role in modern plant breeding, allowing the development of many...