Abstract
Root aquaporin amounts change diurnally. So far, such diurnal change was considered to be basically driven by circadian cycle entrained by the day/night cycle. Here, we evaluated the new hypothesis that root aquaporin induction by light could be triggered by transpirational demand from shoots rather than light itself. When rice plants were grown under 12-h light/12-h dark regime, root aquaporin mRNA levels showed diurnal pattern, but the amplitudes were different among aquaporin members. OsPIP2;1 and OsPIP2;2 showed moderate diurnal changes. They reached a maximum at 2 hour after light on and a minimum at several hours after light off. Other root specific aquaporins such as OsPIP2;4 and OsPIP2;5 basically showed similar diurnal patterns, but showed temporal and dramatic peak at 1 to 4 hours after light on. Such strong induction was not observed when dark treatment was further extended after 12-h of dark period. Furthermore, plants under over-humid condition did not show such induction even in the presence of light. These results suggest that light-induced transpiration from shoots triggers the temporal and dramatic induction observed in OsPIP2;4 and OsPIP2;5.
