De novo synthesis of ABA occurs in root tissue, induced by variation in root water potential, soil oxygen content, and degree of soil compaction, and also responding to changes in nutritional conditions in the rhizosphere. For example limitation of P cause low ABA accumulation in leaves and K+ limitation may lead to an increased biosynthesis of ABA in the roots. The changes in ABA concentration in a range of plant tissues (i.e. roots, axes, and leaves) and fluids (i.e. xylem and phloem) may vary with situations such as a moderate salt stress increase ABA transport .

De novo synthesis of ABA occurs in root tissue, induced by variation in root water potential, soil oxygen content, and degree of soil compaction, and also responding to changes in nutritional conditions in the rhizosphere. For example limitation of P cause low ABA accumulation in leaves and K+ limitation may lead to an increased biosynthesis of ABA in the roots. The changes in ABA concentration in a range of plant tissues (i.e. roots, axes, and leaves) and fluids (i.e. xylem and phloem) may vary with situations such as a moderate salt stress increase ABA transport .

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Adaptation to water stress results from an alteration in gene expression by up-regulation of the major ABA- and/or stress-responsive genes, like RD (response to dehydration), COR (cold responsive), LEA (late embryogenesis abundant)/dehydrin-like, and aquaporin genes .Their products activate chaperones to protect cellular proteins from degradation, activate proteinases to remove damaged proteins, and aquaporins are likely to control the water status of plant cells . In plants, drought protection is mainly triggered by ABA, the key phytohormone involved in response to abiotic stress . Genes encoding enzymes involved in ABA biosynthesis are up-regulated in response to drought. This results in a rapid, feed-forward accumulation of ABA and induction of adaptive mechanisms.Since it is stress related hormone,any change wrt climate or biotic stress leads to a proprtional change in endogeneous ABA levels.

Great! Thank you Kulvir.