title: Transpiration from shoots triggers diurnal changes in root aquaporin expression.
abstract: Root hydraulic conductivity (Lp(r)) and aquaporin amounts change diurnally. Previously, these changes were considered to be spontaneously driven by a circadian rhythm. Here, we evaluated the new hypothesis that diurnal changes could be triggered and enhanced by transpirational demand from shoots. When rice plants were grown under a 12h light/12h dark regime, Lp(r) was low in the dark and high in the light period. Root aquaporin mRNA levels also changed diurnally, but the amplitudes differed among aquaporin isoforms. Aquaporins, such as OsPIP2;1, showed moderate changes, whereas root-specific aquaporins, such as OsPIP2;5, showed temporal and dramatic induction around 2h after light initiation. When darkness was extended for 12h after the usual dark period, no such induction was observed. Furthermore, plants under 100% relative humidity (RH) showed no induction even in the presence of light. These results suggest that transpirational demand triggers a dramatic increase in gene expressions such as OsPIP2;5. Immunocytochemistry showed that OsPIP2;5 accumulated on the proximal end of the endodermis and of the cell surface around xylem. The strong induction by transpirational demand and the polar localization suggest that OsPIP2;5 contributes to fine adjustment of radial water transport in roots to sustain high Lp(r) during the day.
authors.affiliation: Climate Change Research Team, National Agricultural Research Center for Tohoku Region, Morioka, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Sakurai-Ishikawa
authors.forename: Mari
authors.initials: M
authors.lastname: Murai-Hatano
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Hayashi
authors.forename: Arifa
authors.initials: A
authors.lastname: Ahamed
authors.forename: Keiko
authors.initials: K
authors.lastname: Fukushi
authors.forename: Tadashi
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Yoshichika
authors.initials: Y
authors.lastname: Kitagawa
mesh_terms: D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D012275:Oryza / Q000235:genetics / Q000502:physiology*; D009997:Osmotic Pressure; D017440:Photoperiod; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000502:physiology*; D018526:Plant Transpiration; D012333:RNA, Messenger / Q000378:metabolism; D018749:RNA, Plant / Q000378:metabolism; D013696:Temperature; D014867:Water / Q000378:metabolism; D052584:Xylem / Q000378:metabolism
chemical_list: D020346:Aquaporins; D008565:Membrane Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D014867:Water