Water relations in plants and its role in plant metabolism

Plant Water Relations

• Water is known as the liquid gold or elixir of life and a major constituent of all living cells.
  
• Water content in cell ranges from 70 to 90 per cent.
  
• Water is dynamic in plant. It forms the major constituent of living things (cells) and all the vital processes of the life are carried out in it.
  
• In living tissue, water is the medium for many biochemical reactions and extraction processes.
  
• Inorganic nutrients, photosynthates and hormones are transported in aqueous solution.
  
• Movement of water form soil solution to root, stem and then to atmosphere, this continuous movement from soil to atmosphere is called as soil-plant-atmosphere water continuum [SPAC].
  
• Evaporation of water can control the temperature of leaf on canopy. Soil nutrients are available to plant roots only when dissolved in water.

Functions of water in plant system

• Water is the main constituent of protoplasm comprising up to 90-95 per cent of its total weight. In the absence of water, protoplasm becomes inactive.
• Organic constituents of plants such as carbohydrates, proteins, nucleic acids, enzymes etc. lose their physical and chemical properties in the absence of water.
• Water participates directly in many metabolic processes. Inter-conversion of carbohydrates and organic acids depend upon hydrolysis and condensation reactions.
• Water increases the rate of respiration. Seeds respire fast in the presence of water.
• Water is the source of hydrogen atom for the reduction of CO2 in the reaction of photosynthesis.
• Water acts as a solvent and acts as a carrier for many substance. It forms the medium in which several reactions take place.
• Water present in the vacuoles helps in maintaining the turgidity of the cells which is a must for proper activities of life and to maintain the form and structure.
• Water helps in translocation of solutes.
• In tropical plants, water plays a very important role of thermal regulation against high temperature.
• The elongation phase of cell growth depends on absorption of water.