The Expression of Tobacco (Nicotiana tabacum) NtPIP2; 1 Aquaporin in Xenopus Oocytes and Study of its sensitivity to Mercury

Movement of water across cellular membranes is facilitated by the presence of water channels named aquaporins (AQPs). Mercurial compounds are potent blockers of plant and animal aquaporins. However some aquaporin isoforms such as NtAQP1 in tobacco are mercury-insensitive. The aim of this research was to determine the sensitivity of tobacco NtPIP2;1 to mercury. In this experimental study, after invitro transcription of NtPIP2;1 and cRNA synthesis, cRNA was injected to Xenopus oocytes by microinjection. Two days after incubation, oocytes were subjected to 1 mM mercury chloride for 10 min. Then, oocyte volume swelling assay in hypotonic medium was conducted and the membrane osmotic water permeability coefficient (Pf) was determined. Pf for control and mercury chloride-treated oocytes expressing NtPIP2;1 was respectively calculated 0.99×10-2 and 0.98×10-2 cm s-1, which was not significant (P>0.05). Comparing the amino acid sequence of NtPIP2;1 with NtAQP1, a mercury-insensitive aquaporin, revealed the similar to NtAQP1 replacement of cys with Thr in 233 position near the aquaporin pore in NtPIP2;1. NtPIP2;1 encodes a mercury-insensitive aquaporin in tobacco which could be due to cysteine replacement with threonin near the aquaporin pore.