Poster: Hormones

Abs # 597: ABA deficiency causes high levels of reactive oxygen species in the growth zone of maize roots under water deficits.

Presenter:	Sharp, Robert E.
Authors	Cho, In-Jeong  (A)   Sivaguru, Mayandi  (B)   Sharp, Robert E. (A)
Affiliations:	(A): Dept. Agronomy, Univ. Missouri-Columbia (B): Molecular Cytology Core Facility, Univ. Missouri-Columbia

Previous work showed that accumulation of abscisic acid (ABA) is required for root growth maintenance under water stress. These results were obtained by using mutants and inhibitors to restrict ABA synthesis in maize seedlings. Root elongation of ABA-deficient seedlings under water stress was inhibited compared with the wild type, and this effect was prevented when ABA levels in the root growth zone were restored by exogenous application. Reactive oxygen species (ROS) are produced in greater amounts in stressed tissues. We are investigating the hypothesis that ABA accumulation functions to prevent excess ROS levels during water stress. Levels of ROS in the root apical region (encompassing the growth zone) were studied with the fluorescent dye Carboxy-H₂DCFDA, and imaged using confocal microscopy. The effect of ABA deficiency under water stress was studied using the vp14 mutant, in which ABA levels are deficient in water-stressed but not well-watered roots. Under well-watered conditions, ROS levels were low in roots of both wild-type and vp14 seedlings. Under water deficits, ROS levels were slightly greater in wild-type roots and increased dramatically in vp14. The increased ROS levels in vp14 were prevented when ABA was restored to the wild-type level. Interestingly, the effects of water deficits and ABA-deficiency on ROS levels were specific to the zone of cell elongation. The relation of the increase in ROS to the inhibition of elongation in ABA-deficient roots is under investigation.