The role of PLDα1 in ABA inhibition of main root elongation in Arabidopsis was studied . When the seedlings were treated with ABA, elongation of main root of wild- type (WT) was inhibited more obviously than that of pldα1. In main
root protoplasts, the activity of both PLDα1 and NADPH oxidase increased under ABA treatment, and the NADPH oxidase activity increased much more in WT than in pldα1. When 10μmol L- 1 PA was added into the growth medium, the NADPH oxidase activity increased in pldα1 protoplasts. The concentration of ROS in Arabidopsis root protoplasts increased more quickly in WT than in pldα1 after ABA addition. When H2O2 was added into the culture medium, main root elongation was inhibited in both genotypes. All these results suggested that, PA produced by PLDα1 acted as a regulator in ABAmediated
root elongation in Arabidopsis via NADPH oxidase-produced ROS. In addition, root hair of pldα1 was shorter than that of WT. On the tip of root hair, pldα1 had lower concentration of ROS and Ca2+ than WT .