The Physiological Roles Of ZmPIPs In Young Maize Responses To Short Term Water Stress And Rewater

Plant water transport and its regulation is a basic and very important process, and aquaporins seem essential for the regulation of plant water status. There have been many plant aquaporins which were found in various plants, and these channel portions may give people a new way to understand the molecular mechanism of that process. But the roles of aquaporins in plant water relations under changeable water conditions are known little. Our objective was to investigate transcriptional regulation of aquaporins in different root tissues under water stress and the later rewatering. Maize seeds (line: 478) were chosen and grown in a humid atmosphere with 1/2 Hoagland solution. After 7-8d, 10%PEG was used to form water stress and 48 h later plants were rewatered. Parameters about water status were measured every two hours after treatments, meantime, root and leaf samples were harvested and the relative amounts of mRNA encoding four Zea mays plasma membrane AQPs(ZmPIPs) were determined in these samples by Q-RT-PCR. The results showed that:1. In well water condition, transcription of four ZmPIPs is exactly regulated and clearly shows a diurnal rhythm both in root and leaf mature zones and elongation zones. Furthermore, in root and leaf mature zones, transcription of ZmPIPs was up regulated after dawn and came to their maximums at 10:00 or 12:00, and this may be related to the diurnal rhythm of plants water status parameters. But in cell elongation zones of roots and leaves, it was down regulated when lighted and up regulated before evening. Under water stress condition, water status parameters went down firstly and then went up in diurnal rhythms which showed that after lighting some stoma closed and then opened, and many ZmPIPs were up regulated in leaves which enhanced the water uptake ability of leaves and might contribute to open stoma.2. After water stress by 10%PEG, stoma in leaves were closed and then opened several hours later; so Pn, Gs and Ci went down at first and then recovered. But compared with controls, Tr did not change very mach in water stress treatments. The transcription of ZmPIP2;5 was down regulated in roots significantly, but others didn't change so much compared with their controls. Except ZmPIP2;2, other ZmPIPs were up regulated significantly in leaf mature zones, but in leaf elongation zones, ZmPIP2 members were down regulated and ZmPIP1 members were regulated up and down. This may suggest that when plants get short term water stress they may enhance the water uptake ability of leaf mature zones, which might contribute to open stoma and maintain water potential and transpiration of leaves.3. When plants were rewatered, there were more leaf stoma which were closed compared to stressed controls, and Ls went up with Gs and Tr going down. Four hours later, these parameters went up and excelled stressed controls significantly or very significantly, and more important, these parameters reached well watered treatments nearly. During rewater treatments, transcription of ZmPIPs was greatly up regulated in root elongation zones, meanwhile, ZmPIP1;1 and ZmPIP2;2 were also up regulated while ZmPIP1;2 and ZmPIP2;5 were down regulated in root mature zones. But in leaves, only ZmPIP2;2 was up regulated slightly, other ZmPIPs were all down regulated significantly. This may suggest that plants would enhance the water uptake ability of young roots and inhibit water dissipation of leaves when facing rewater treatments, then which can help stressed plants release from water deficit, and several hours later the stressed plants recovered to well water conditions finally.4. Under changeable water conditions, plants can regulate the transcription of ZmPIPs differently according to different tissues structures and functions, and so as the diurnal rhythm of transcription after adapting to new water condition. ZmPIP1 and ZmPIP2 subfamilies members showed similar regulation ways of transcription both in diurnal rhythm and responses to short term water stress and rewater. This may suggest that when face to changeable sounding water conditions plants can up or down regulate transcription of ZmPIPs according to different tissues structures and functions, to get a compromise with the new water condition.