Initiation and regulation of water deficit-induced abscisic acid accumulation in maize leaves and roots: cellular volume and water relations

Water deficit-induced ABA accumulation in relation to cellular water relati ons was investigated in maize root and leaf tissues, While polyethylene gly col (PEG) treatment led to a significant increase of ABA content in both ro ot and leaf tissues, ethylene glycol (EG), a permeable monomer of PEG, had no effect on ABA accumulation at similar or much lower osmotic potentials. A rapid and massive accumulation of ABA in leaf tissues occurred at a speci fic threshold of PEG 6000 concentration, about 20% (w/v), and closely coinc ided with the start of the tissue weight loss and the obvious decrease of c ellular osmotic potential. Pretreatment with EG lowered the cell sap osmoti c potential and also lowered the capability of both root and leaf tissues t o accumulate ABA in response to further air-drying or PEG treatment. When s amples were dehydrated and incubated under pressure, a method to maintain h igh water potential and pressure potential during dehydration, ABA accumula tion was similar to those dehydrated and incubated under atmospheric pressu re. Such results suggest that both the absolute water potential and pressur e potential per se had no direct effects on the dehydration-induced ABA acc umulation. The results have provided evidence that the initiation of ABA ac cumulation is related to the weight loss of tissues or changes in cellular volume rather than the cell water relation parameters, and the capability o f ABA accumulation can be regulated by cellular osmotic potential.