Control of Plant Water Use by ABA Induction of Senescence and Dormancy: An Overlooked Lesson from Evolution.

Drought stress is a condition that in specific climate contexts results in insufficient water availability and often limits plant productivity through perturbing development and reducing plant growth and survival. Plants use senescence of old leaves and dormancy of buds and seeds to survive extreme environmental conditions. The plant hormone ABA accumulates after drought stress, and increases plant survival by inducing quick responses such as stomatal closure, and long-term responses such as extended growth inhibition, osmotic regulation, accumulation of cuticular wax, senescence, abscission and dormancy. Here we focus on how the long-term ABA responses contribute to plant survival during severe drought stress. Leaf senescence and abscission of older leaves reduce total plant transpirational water loss and increase the transfer of nutrients to meristems and to some storage tissues. Osmotic regulation favors water consumption in sink tissues, and accumulation of cuticular wax helps to seal the plant surface and limits non-stomatal water loss.