Co-regulation of water channels and potassium channels in rice

Aquaporins and potassium channel proteins are probably critical for a plant to maintain proper cytosolic osmolarity in response to drought or other stresses. However, evidence linking water channel and potassium channel functions in plants remains to be demonstrated. The present study examined K⁺ channel/transporters and water channels in rice (Oryza sativa L. spp. indica cv. Guangluai 4) to reveal a potential functional correlation. The mRNA expression levels of plasma membrane intrinsic proteins (PIPs) and K⁺ channel/transporters responded similarly to K⁺ starvation or water deprivation. Transcription of the PIP- and K⁺ channel-encoding genes was induced by K⁺ starvation and could be downregulated by polyethylene glycol (PEG)-mediated water deficit. Consistent with the induced PIP expression, root hydraulic conductivity (Lp) also increased during K⁺ starvation. Furthermore, the K⁺ uptake capacity, but not the K⁺ content, was probably influenced by K⁺ starvation. Caesium chloride treatment decreased K⁺ content in the rice seedlings and reduced root Lp as did mercuric chloride. These results are compatible with the conclusion that PIP and K⁺ channel/transporters are functionally co-regulated in rice osmoregulation.