1. ¹College of life sciences, Northwest Sci-Tech University of Agriculture and Forestry, Yangling 712100, China.
2. ²Department of Biology, Henan University, Kaifeng 475001, China.
3. ³National Laboratory of Soil Erosion and Dryland Farming, the Institute of Soil and Water Conservation, Chinese Academy of Sciences, Yangling 712100, China.

Correspondence: Zhang XIAO, E-mail: xzhangcn@china.com Tel: 0378 -2874021, 2865799

Received 10 January 2001; Revised 25 June 2001; Accepted 4 July 2001.

Abstract

A number of studies show that environmental stress conditions increase abscisic acid (ABA) and hydrogen peroxide (H₂O₂) levels in plant cells. Despite this central role of ABA in altering stomatal aperture by regulating guard cell ion transport, little is known concerning the relationship between ABA and H₂O₂ in signal transduction leading to stomatal movement. Epidermal strip bioassay illustrated that ABA-inhibited stomatal opening and ABA-induced stomatal closure were abolished partly by externally added catalase (CAT) or diphenylene iodonium (DPI), which are a H₂O₂ scavenger and a NADPH oxidase inhibitor respectively. In contrast, internally added CAT or DPI nearly completely or partly reversed ABA-induced closure in half-stoma. Consistent with these results, whole-cell patch-clamp analysis showed that intracellular application of CAT or DPI partly abolished ABA-inhibited inward K⁺ current across the plasma membrane of guard cells. H₂O₂ mimicked ABA to inhibit inward K⁺ current, an effect which was reversed by the addition of ascorbic acid (Vc) in patch clamping micropipettes. These results suggested that H₂O₂ mediated ABA-induced stomatal movement by targeting inward K⁺ channels at plasma membrane.