Water Channels And Potassium Channels Are Co-regulated In Rice And Involved In Seed Germination

Water channel proteins and potassium channel proteins are likely critical for a plant tomaintain proper cytosolic osmolarity in response to drought or other stresses. However,evidence linking water channel and potassium channel functions in plants remains to bedemonstrated. In our study we examined K~+ channel/transporters and water channels in rice(Oryza sativa L. spp indica cv. Guangluai 4) to reveal a potential functional correlation. ThemRNA expression levels of plasma membrane intrinsic proteins (PIPs) and K~+channel/transporters responded similarly to K+ starvation or water deprivation. Transcriptionof the PIP-and K~+ channel-encoding genes was induced by K~+ starvation, and could bedown-regulated by polyethylene glycol (PEG)-mediated water deficit. Consistent with theinduced PIP expression, root hydraulic conductivity (Lp) also increased during K~+ starvation.Furthermore, the K~+ uptake capacity, but not the K+ content, was likely influenced by K~+starvation. The K~+ channel inhibitor, Cesium chloride (CsCl) treatment decreased K~+ contentin the rice seedlings, and reduced root Lp as did the water channel inhibitor, mercuric chloride(HgCl2). These results are compatible with the conclusion that PIP and K~+channel/transporters are functionally co-regulated in rice osmoregulation.Previous studies have demonstrated the possible role of several aquaporins in seedgermination. But the investigation of the role of more aquaporins, especially with aquaporinfamily in this process, still remains required. In our research work, the developmentalregulation of plasma membrane intrinsic protein (PIP) expression was described by analyzingits expression throughout germination and post-germination processes in rice embryos. Theexpression patterns of the PIPs suggest these aquaporins play different roles in seedgermination and in seedling growth. Partial silencing of the water channel genes, OsPIP1;1and OsPIP1;3, reduced seed germination while over-expression OsPIP1;3 promoted seedgermination under water stress conditions. Moreover, spatial expression analysis indicatedthat OsPIP1;3 expressed predominantly in embryo during seed germination. Our data alsorevealed that the NO donors, sodium nitroprusside (SNP) and S-nitrosoglutathione (GSNO),promoted seed germination;furthermore, the NO scavenger,2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), inhibitedgermination and reduced the stimulatory effects of SNP and GSNO on germination of rice.Exogenous NO stimulated the transcription of OsPIP1;1, OsPIP1;2, OsPIP1;3 and OsPIP2;8in germinating seeds. These results suggest that water channels play an important role in seedgermination, acting, at least partly, in response to the NO signaling pathway.