Plasma membrane aquaporins in the motor cells of Samanea saman: diurnal and circadian regulation.
Leaf-moving organs, remarkable for the rhythmic volume changes of their motor cells, served as a model system in which to study the regulation of membrane water fluxes. Two plasma membrane intrinsic protein homolog genes, SsAQP1 and SsAQP2, were cloned from these organs and characterized as aquaporins in Xenopus laevis oocytes. Osmotic water permeability (P(f)) was 10 times higher in SsAQP2-expressing oocytes than in SsAQP1-expressing oocytes. SsAQP1 was found to be glycerol permeable, and SsAQP2 was inhibited by 0.5 mM HgCl(2) and by 1 mM phloretin. The aquaporin mRNA levels differed in their spatial distribution in the leaf and were regulated diurnally in phase with leaflet movements. Additionally, SsAQP2 transcription was under circadian control. The P(f) of motor cell protoplasts was regulated diurnally as well: the morning and/or evening P(f) increases were inhibited by 50 microM HgCl(2), by 2 mM cycloheximide, and by 250 microM phloretin to the noon P(f) level. Our results link SsAQP2 to the physiological function of rhythmic cell volume changes.
Moshelion
Menachem
M
Department of Agricultural Botany, Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food, and Environmental Quality Sciences, the Hebrew University of Jerusalem, Rehovot 76100, Israel.
Becker
Dirk
D
Biela
Alexander
A
Uehlein
Norbert
N
Hedrich
Rainer
R
Otto
Beate
B
Levi
Hadas
H
Moran
Nava
N
Kaldenhoff
Ralf
R
D000595:Amino Acid Sequence; D000818:Animals; D020346:Aquaporins / Q000235:genetics* / Q000502:physiology; D001692:Biological Transport / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D007887:Fabaceae / Q000235:genetics* / Q000502:physiology; D005260:Female; D015870:Gene Expression; D008627:Mercuric Chloride / Q000494:pharmacology; D008969:Molecular Sequence Data; D009865:Oocytes; D010693:Phloretin / Q000494:pharmacology; D018515:Plant Leaves / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics* / Q000502:physiology; D018516:Pulvinus / Q000166:cytology / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014867:Water / Q000378:metabolism; D014982:Xenopus laevis
D020346:Aquaporins; D010940:Plant Proteins; D014867:Water; D008627:Mercuric Chloride; D003513:Cycloheximide; D010693:Phloretin; D004121:Dimethyl Sulfoxide