Molecular And Physiological Mechanism Of Root Growth Regulated By ABA Signal In Cadmium-and Cadmium With Zinc-Treated Rice

ABA, auxin and MAPK are important signal molecules in plants. The molecular and physiological mechanism of rice root system growth regulated by ABA signal was investigated using rice (Oryza sativa L No.11) treated with cadmium and cadmium and zinc interactions.1. Physiological mechanism of root system growth regulated by ABA signal in cadmium and cadmium with zinc treated rice.The changes of root growth and physiology was analysed in rice treated with Cd, Zn, ABA, ABA inhibitor, Cd+ABA, Cd+ABA inhibitor, Cd+Zn, Cd+Zn+ABA and Cd+Zn+ABA inhibitor. ABA inhibitor suppressed rice root system growth whatever under Cd or Cd plus Zn conditions. The rice root system growth was inhibited more by Cd than the treatments without Cd. Zn can reduce the inhibition of Cd on rice root system growth. Treatments with ABA resulted in more accumulation of H2O2than treatments with ABA inhibitor either under Cd or under Cd plus Zn conditions. Similar changes of cell integrity and H2O2accumulation and location were obseverd in each treatment. Detection with ICP or Cd specific probe showed that Zn reduced the accumulation of Cd in rice root. The accumulation and distribution of auxin was tested using the DR5-GUS transgenic rice and the results showed that ABA inhibitor enhanced the accumulation of auxin but ABA reduced the accumulation of auxin in rice roots either with or without Cd or Cd plus Zn. Analysis at RNA and protein showed that the regulation of Cd alone on auxin are related to activate transcription and protein stability, and the changes of auxin induced by Cd with ABA were related to the protein stability and transport controlling. ABA inhibitor alone regulated auxin by activating transcription, and Cd+ABA inhibitor regulated auxin was related to protein de novo synthesis and transport controlling.2. Molecular mechanism of root system growth regulated by ABA signal in cadmium and cadmium with zinc treated rice.The expression of auxin gene (OsARFs, OsIAAs, OsPINs, OsPID, OsYUCCAs), cell-cycle gene (OsCycs, OsCDKs et al.), ABA gene (OsABA8oxs, OsNCEDs) and OsMAPK gene families was analysed by RT-PCR after treatment with above compounds for9day and13day. In the9-day-treated rice roots, there were75genes regulated by ABA (including ABA and ABA inhibitor). In Cd+ABA (including Cd+ABA and Cd+ABA inhibitor) treatments, the expressions of65genes were up/down-regulted. In Cd+Zn+ABA (including Cd+Zn+ABA and Cd+Zn+ABA inhibitor) treatments, the expressions of80genes were changed. In the13-day-treated rice roots, there were82genes were regulated by ABA (including ABA and ABA inhibitor). In Cd+ABA (including Cd+ABA and Cd+ABA inhibitor) treatments, the expressions of69genes were up/down-regulted. In Cd+Zn+ABA (including Cd+Zn+ABA and Cd+Zn+ABA inhibitor) treatments, the expressions of87genes were changed.Conclusion:ABA signal taked part in the regulation of rice root growth more or less under non-stress, Cd or Cd with Zn conditions. This role of ABA on root growth was performed via the modified auxin and MAPK signals as well as the veried expression of cell cycle genes. Different changes of expression of auxin, cell cycle and MARK genes induced by ABA were found in non-stress, Cd or Cd with Zn treated rice roots. The results implied that differential signaling pathways were existence and crosstalk between ABA, auxin and MAPK signal occurred during signal transduction under these conditions. The results also showed that the expression level of the genes regulated by ABA was related to the root development period. It suggested that the regulation of root growth by ABA signal was not only related to environmental conditions but also to the growth and development of root systems.