Abstract: Subcellular localization of AtNCED3 , AtAAO3 and AtSDR1 proteins, and dynamic changes of ABA levels in root and leaf were investigated in the present study . Results showed that the guard cells were not the main site of ABA biosynthesis, and SDR might play an important role in ABA precursor processing and transportation . The transcription level of ABA synthase gene in roots was significantly higher than that in leaves under dehydration condition , while the ABA concentration in leaf tissues were 10 times higher than root . Detection of ABA concentration in both detached leaves and attached leaves suggested that ABA accumulation in leaves was mainly derived from root-sourced ABA, it was confirmed that ABA synthesis in roots was affected by the supply of precursor carotenoids with the fluridone treatment and shading experiments. These data revealed that ABA levels in leaves were regulated by root-sourced ABA transportation and leaf-sourced carotenoids supply. Our present results showed that vascular system might be involved in the coordination and integration of this complex regulatory mechanism for ABA signal accumulation. The conclusion provided relevant information for exploring molecular mechanism of stress signal transduction, manipulating endogenous ABA levels, and enhancing plants resistance
against environmental stresses .

Key words: ABA synthase gene