Abstract
Cytokinins (CKs) play crucial roles not only for plant growth but also for osmotic stress signaling. Many recent data showed that CKs are signals traveling from roots to shoots, and ABA:CK ratios in xylem sap are important for stress signaling. However, the role of endogenous CKs in osmotic stress response is still unclear. In plants, the key enzymes involved in CK-metabolism are adenosine phosphate-isopentenyltransferases (AtIPTs) and cytokinin oxidases (AtCKXs). To unravel the relationship between CK metabolism and osmotic stress response, we performed functional analyses of CK-deficient plants, atipt mutants and AtCKX-overexpressors, in osmotic stress response. The atipt mutants and AtCKX-OX plants with decreased CK contents showed increased salt tolerance, suggesting that endogenous CKs act as negative regulators in salt stress response. Different molecular and genetic approaches have been used to elucidate the mechanism of CK-dependent osmotic stress response. From these data, we will discuss the crosstalk between CK, ABA and osmotic stress signaling.
