In this article we will discus about the strategies for stress-tolerant plant.
Several microorganisms have been used as a model system to characterize stress induced genes. It is because they are equipped with wide array of stress relieving genes. Recently, attention has been focused towards higher plants in search of stress tolerance genes and successful attempt to introduce these genes into stress sensitive plants.
Generally, when plants or microorganisms are continuously exposed to environmental stress, their stress relieving genes that are transcribed might encode enzymes involved in regulating particular metabolic pathways or proteins with specific functions. Response to abiotic stresses enables the organisms to adapt to an unfavourable condition singly by altering the metabolic flow.
Water Deficit Conditions:
Drought is one of the most severe environmental stresses affecting almost all plant functions. A severe water deficient condition arises in drought stressed plants. Both drought and freezing temperature creates water deficiency in plants. It is a situation in which the demands exceed the supply of water. Water deficit in plants is due to scanty rainfall condition called drought.
Extended or prolonged drought conditions reduce the amount of water available to plant growth. Water deficit condition can also occur in environment due to high level of salt concentration in the soil making the plant inefficient to extract water. Freezing temperature withdraws water from the cell and forms an ice crystal between the cells.
Water can be described thermodynamically, in terms of its freeze energy content or chemical potential. Water potential is another term used by plant physiologists. Atleast two pressure potentials have been identified in plants. One is water potential (Ψw) and other is osmotic potential (Ψp). Another term turgor potential is the difference between these two pressure potentials.
Water potential:
Ψw = ΨS + Ψp + Ψg + Ψm
During rainy season, plants are generally in well watered condition and its water potential is maximum when compared to osmotic potential which is always negative to water potential. During drought conditions, water potential recedes first in the environment, followed by steep decrease in the soil.
Consequently, water demand exceeds water supply, water potential also steeply drops inside the cell and finally turgor pressure will collapse. At this stage water potential equals osmotic pressure. Most of the stressed plants exhibit this initial phenomenon.
Ψw = ΨS + Ψs
Since metabolic changes occurring in stressed plants are not correlated with changes in plant water potential, another parameter known as relative water content (RWC) is employed to assess water status of plant. When the amount of water uptake by roots matches water loss by leaves, the RWC of leaves active in transpiration process exhibit the ranges from 80 to 90%.
If this critical value (RWC) drops in the organs, tissue death takes place immediately. Therefore, when water potential of a plant drops, the RWC also declines. Certain plants however, maintain higher RWC despite their Ψw by maintaining osmotic adjustment.