Biochemical and Physiological Aspects of Hyperhydricity in Liquid Culture System

Large-scale liquid cultures and automation have proven the potential to resolve manual handling of in vitro cultures at various stages and decreases production cost. However, hyperhydricity is a major problem during in vitro culture of many crops in liquid culture systems. The environment inside culture vessel normally used in plant micropropagation is characterized by high humidity, limited gaseous exchange between the internal atmosphere of the culture vessel and its surrounding environment, and the accumulation of ethylene, conditions that may induce physiological disorders. Hyperhydricity is a disorder of tissue-cultured plants where leaves become translucent and stems swollen, distorted and brittle. Although numerous hypotheses have been put forward to explain hyperhydricity but there is still a lack of knowledge about the nature of signals responsible for hyperhydricity and the metabolic processes which are affected by its development. The concept of stress in relation to hyperhydricity is not completely established. Therefore, it remains difficult to assume that hyperhydric tissues are stressed. Previous studies argued that abnormal morphology observed in hyperhydricity could be attributed to changes occurring at cellular level due to the modifications of membrane composition or DNA content. In order to understand stress and morphological responses in hyperhydric tissues, in the present article, we are reviewing different biochemical and physiological mechanisms of hyperhydricity in several plant species.