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Transpiration from shoots triggers diurnal changes in root aquaporin expression

2011; Wiley; Volume: 34; Issue: 7 Linguagem: Inglês

10.1111/j.1365-3040.2011.02313.x

1365-3040

JUNKO SAKURAI‐ISHIKAWA, Mari Murai‐Hatano, Hidehiro Hayashi, Arifa Ahamed, K. Fukushi, Tadashi Matsumoto, Yoshichika Kitagawa,

Plant Stress Responses and Tolerance

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 12 h light/12 h 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 2 h after light initiation. When darkness was extended for 12 h 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.