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Hyperhydricity
Hyperhydricity (previously known as vitrification) 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.〔Kei-ichiro U, Susan C and Kalidas S (1998). Reduced hyperhydricity and enhanced growth of tissue culture-generated raspberry (Rubus sp.) clonal lines by Pseudomonas sp. isolated from oregano. Process Biochemistry 33(4): 441-445.〕 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.〔Cassells A and Curry R (2001). Oxidative stress and physiological, epigenetic and genetic variability in plant tissue culture: implications for micropropagators and genetic engineers. Plant Cell Tissue And Organ Culture. 64(2-3):145-157〕 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.〔Franck T, Kevers C, Gaspar T, Dommes J, Deby C, Greimers R, Serteyn D and Deby-Dupont G (2004). Hyperhydricity of Prunus avium shoots cultured on gelrite: a controlled stress response. Plant Physiology and Biochemistry, 42: 519-527〕
==Causes==
The main causes of hyperhydricity in plant tissue culture are those factors triggering oxidative stresses such as high salt concentration, high relative humidity, 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, the type of explants utilized, the concentrations of microelement and hormonal imbalances.〔2〕 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.〔Franck T, Kevers C, Gaspar T, Dommes J, Deby C, Greimers R, Serteyn D and Deby-Dupont G (2004). Hyperhydricity of Prunus avium shoots cultured on gelrite: a controlled stress response. Plant Physiology and Biochemistry, 42: 519-527〕
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