Plants affected by salt stress are unable to take water from soil, due to an osmotic imbalance between soil and plant.

Salinity imposes two stresses on the cell: one is the loss of turgor due to the hypertonicity of the extracellular medium, and the other is a direct effect of toxic ions on metabolism. Therefore plants have developed several defence mechanisms. The Na/H+ antiporter is heavily involved and is powered by the action of the H+-ATPase which is highly expressed in leafs and roots during salt stress.

Location and timing of ABA biosynthesis

• Released during desiccation of the vegetative tissues and when roots encounter soil compaction.
• Synthesized in green fruit and seeds at the beginning of the wintering period
• Mobile within the leaf and can be rapidly translocated from the roots to the leaves by the transpiration stream in the xylem.
• Produced in response to environmental stress, such as heat stress, water stress, salt stress.
• Synthesized in all plant parts, e.g. roots, flowers, leaves and stems

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