Plants optimize the morphology, physiology and metabolism of their organs and cells in
order to maximize productivity under the drought conditions. The reactions of the plants to
water stress differs significantly at various organizational levels depending upon intensity
and duration of stress as well as plant species and its stage of development. Stress resistance
in plant is divided into two categories, including stress tolerance and stress avoidance.
Drought avoidance is the ability of plant to maintain high tissue water potential under
drought conditions, while drought tolerance is a plant’s stability to maintain its normal
functions even at low tissue water potentials. Drought avoidance is usually achieved
through morphological changes in the plant, such as reduced stomatal conductance,
decreased leaf area, development of extensive root systems and increased root/shoot ratios.
On the other hand, drought tolerance is achieved by cell and tissue specific physiological,
biochemical, and molecular mechanisms, which include specific gene expression and
accumulation of specific proteins. The dehydration process of drought-tolerant plants is
characterized by fundamental changes in water relation, biochemical and physiological
process, membrane structure, and ultrastructure of sub cellular organelles. Some plants are
able to cope with arid environments by mechanisms that mitigate drought stress, such as
stomatal closure, partial senescence of tissues, reduction of leaf growth, development of water storage organs, and increased root length and density, in order to use water more
efficiently. Water flux through the plant can be reduced or water uptake can be increased by
several physiological adaptations. Many lichens, bryophytes, and a few ferns can survive in
a dried state. Resistant dried structures like seeds and pollen grains are frequently present in
most plant species. Among vascular plants, a small group of angiosperms known as
poikilohydric or resurrection plants, such as Craterostigma plantagineum can tolerate extreme
dehydration at the whole plant level. This suggests that the genetic properties required for
drought tolerance are present in flowering plant.
Plants optimize the morphology, physiology and metabolism of their organs and cells inorder to maximize productivity under the drought conditions. The reactions of the plants towater stress differs significantly at various organizational levels depending upon intensityand duration of stress as well as plant species and its stage of development. Stress resistancein plant is divided into two categories, including stress tolerance and stress avoidance.Drought avoidance is the ability of plant to maintain high tissue water potential underdrought conditions, while drought tolerance is a plant’s stability to maintain its normalfunctions even at low tissue water potentials. Drought avoidance is usually achievedthrough morphological changes in the plant, such as reduced stomatal conductance,decreased leaf area, development of extensive root systems and increased root/shoot ratios.On the other hand, drought tolerance is achieved by cell and tissue specific physiological,biochemical, and molecular mechanisms, which include specific gene expression andaccumulation of specific proteins. The dehydration process of drought-tolerant plants ischaracterized by fundamental changes in water relation, biochemical and physiologicalprocess, membrane structure, and ultrastructure of sub cellular organelles. Some plants areable to cope with arid environments by mechanisms that mitigate drought stress, such asstomatal closure, partial senescence of tissues, reduction of leaf growth, development of water storage organs, and increased root length and density, in order to use water moreefficiently. Water flux through the plant can be reduced or water uptake can be increased byseveral physiological adaptations. Many lichens, bryophytes, and a few ferns can survive ina dried state. Resistant dried structures like seeds and pollen grains are frequently present inmost plant species. Among vascular plants, a small group of angiosperms known aspoikilohydric or resurrection plants, such as Craterostigma plantagineum can tolerate extremedehydration at the whole plant level. This suggests that the genetic properties required fordrought tolerance are present in flowering plant.
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