Hyperosmotic versus Hypoosmotic Stress in Plants

The balance of water between the cell and its environment is crucial to all organisms, but especially for root plant cells that are exposed to extrinsic condition directly. High salt concentration in soil leads to loose of water from the plant cell (hyper-osmotic stress). Sufficient supply with water causes that the plant cell is turgid (i.e. increases its volume, the cell membrane experiences turgor pressure from the cell interior against the resistance of the cell wall), which is healthy state for most plants. However, upon repeated flooding (e.g. in a tropical rain-forest climate), the plants may experience a prolonged hypo-osmotic stress. Whereas the hyper-osmotic stress is one of the most studied abiotic stress factor, hypo-osmotic is at the edge of scientists´ interest, still considered as “physiological conditions”. However, both types of osmotic stress are characterized by involvement of stress sensing, oxidative burst, and signal transduction. In this study, sensors of osmotic stress (mechano-sensitive ion channels), osmolytes, and processes followed hypo- and hyper-osmotic stress are emphasized, although hypo-osmotic stress in comparison to hyper- have to be largely studied.