Poster: Oxidative stress

Abs # 93: ABA deficiency causes high levels of reactive oxygen species in the growth zone of maize roots under water deficits: increase in ROS precedes breach in plasma membrane integrity

Presenter:	Cho, In-Jeong , ic751@mizzou.edu
Authors	Cho, In-Jeong  (A)   Sivaguru, Mayandi  (B)   Sharp, Robert  (A)
Affiliations:	(A): Dept. of Agronomy, Univ. Missouri-Columbia (B): Molecular Cytology Core Facility, Univ. Missouri-Columbia

Abscisic acid (ABA) is required for root growth maintenance under water deficits in maize seedlings. Using an ABA-deficient mutant vp14, here we demonstrate that ABA functions in maintaining plasma membrane integrity by preventing excess levels of reactive oxygen species (ROS) during water deficits. Levels of ROS in the root apical region (encompassing the growth zone) were studied with the fluorescent dye Carboxy-H₂DCFDA, and using confocal microscopy. Under well-watered conditions, ROS levels were low in the root apical region 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 by exogenous ABA application. Increase in ROS levels under stress conditions is known to alter several cellular functions including the plasma membrane integrity. Imaging with propidium iodide (PI), which labels cell nuclei only when plasma membrane properties are compromised, indicated loss of plasma membrane integrity in the growth zone of the ABA-deficient roots. This effect was also prevented by restoring ABA to the wild-type level. To reveal the sequence of increase in ROS and breach in plasma membrane integrity we simultaneously analyzed ROS levels and PI staining in individual cells during time course experiments. These results indicate that increase in ROS levels preceded and caused the loss of plasma membrane integrity in the growth zone of vp14 roots under water deficits. The relation of these events to the inhibition of root elongation caused by ABA-deficiency under water deficits is currently under investigation.