A Crucial Role for Cytokinins in Pea ABRl7-mediated Enhanced Germination and Early Seedling Growth of Arabidopsis thaliana under Saline and Low-temperature Stresses

摘要

The role of cytokinins (CKs) in mediating the previously observed ABR17-mediated enhancement of germination of Arabidopsis thaliana under salinity and low-temperature stresses has been evaluated. We determined the endogenous concentrations of CK in the three transgenic and wild-type seedlings, which indicated that the transgenic seedlings had higher endogenous concentrations of CK. Furthermore, the relative levels of expression of ABR17 cDNA and the primary CK response gene, ARR5, were evaluated in the transgenic and wild-type seedlings by quantitative real-time polymerase chain reaction (RT-PCR). Our results indicated that two of the three independently derived transgenic plants possessed higher levels of ABR17 transcripts, which correlated well with increased ARR5 expression, further supporting a possible role for CK in mediating the observed phenomenon. In addition, the exogenous application of various CKs on the germination of wild-type A. thaliana under these abiotic stress conditions enhancedits germination. Finally, the ribonuclease (RNase) activity of the pea ABR17 protein was also demonstrated after expression of its cDNA in Escherichia coli, purification of the recombinant protein, and in vitro RNase assays. Our findings are discussed within the context of ABR17-mediated enhancement of endogenous CK concentrations, the involvement of CKs in germination under abiotic stress, as well as the role of the RNase activity of ABR17 protein in mediating the observed effects.