Plants phenomena affecting plant growth and development

Plants experience water stress either when the water supply to their roots becomes
limiting or when the transpiration rate becomes intense. Water stress is primarily caused by the
water deficit, i.e. drought. Drought stress tolerance is seen in almost all plants but its extent
varies from species to species and even within species. Water deficit and salt stresses are global
issues to ensure survival of agricultural crops and sustainable food production (Jaleel et al.,
2007). Conventional plant breeding attempts have changed over to use physiological selection
criteria since they are time consuming and rely on present genetic variability (Zhu, 2002).
Tolerance to abiotic stresses is very complex, due to the intricate of interactions between stress
factors and various molecular, biochemical and physiological phenomena affecting plant growth
and development (Razmjoo et al., 2008).
Drought stress is considered to be a moderate loss of water, which leads to stomatal
closure and limitations of gas exchange. Desiccation is much more extensive loss of water,
which can potentially lead to gross disruption of metabolism and cell structure and eventually to
the cessation of enzyme catalyzed reactions (Smirnoff, 1993; Jaleel et al., 2007). Drought stress
is characterized by reduction of water content, diminished leaf water potential, turgor loss,
closure of stomata decrease in cell enlargement and growth.
Water stress inhibits cell enlargement more than cell division. It reduces plant growth by
affecting various physiological and biochemical processes, such as photosynthesis, respiration,
translocation, ion uptake, carbohydrates, nutrient metabolism and growth promoters (Jaleel et al.,
2008; Farooq et al., 2008). In plants, a better understanding of the morpho-anatomical and
physiological basis of changes in water stress resistance could be used to select or create new
varieties of crops to obtain a better productivity under water stress conditions. The reactions of
plants to water stress differ significantly at various organizational levels depending upon
intensity and duration of stress as well as plant species and developmental stage (Chaves et al.,
2002; Jaleel et al., 2008). The drought stress factors negatively affect growth and productivity,
and plants have evolved different mechanisms to respond to such challenges. At the molecular
level this involves induction of stress-responsive and stress-tolerance genes (Matsui et al., 2008),
often mediated by the phytohormone abscisic acid (ABA). ABA is referred to as the plant stress
hormone because, in addition to its role in development, it plays a key role in responses to
abiotic stress factors by regulating stomatal closure to optimize transpiration, and by triggering
the activation of many stress-related genes (Cutler et al., 2010; Lindemose et al., 2013).