Osmoregulation of leaf motor cells

Abstract 

“Osmotic Motors” – the best-documented explanation for plant leaf movements – frequently reside in specialized motor leaf organs, pulvini. The movements result from dissimilar volume and turgor changes in two oppositely positioned parts of the pulvinus. This Osmotic Motor is powered by a plasma membrane proton ATPase, which drives KCl fluxes and, consequently, water, across the pulvinus into swelling cells and out of shrinking cells. Light signals and signals from the endogenous biological clock converge on the channels through which these fluxes occur. These channels and their regulatory pathways in the pulvinus are the topic of this review.

Abbreviations: ABA, abscissic acid, AMP-PNP, 5′-adenylyl-imidodiphosphate, BAPTA, 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid, BL, blue light, CRY, cryptochrome, DAG, diacylglycerol, H7, 1-(5-isoquinolinesulpho-nyl)-2-methylpiperazin, GLR, glutamate receptor channel, IP₃, inositol 1,4,5-trisphosphate, K_D(H) channels, depolarization (hyperpolarization)-dependent K channels, MscS, mechanosensitive channel small, NPPB, 5-nitro-2-(3-phenylpropylamino)benzoic acid, OA, okadaic acid, P_f, osmotic water permeability, PHOT, phototropin, PHYA(E), phytochrome A(or E), PIs, phosphatidylinositides, PKA, cAMP-dependent protein kinase, PLA₂, phospholipase A₂, PLCδ, phospholipase C-δ, Pr and Pfr, the red and the far-red absorbing forms of phytochrome, PRC, phase response curve, PtdCh, phosphatidylcholine, PtdInsPs, phosphatidyl-inositol phosphates, R, red light, SAC, stretch-activated channel, SV, slow vacuolar [channel], TEA, tetraethyl ammonium, TMB-8, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate, TPK, tandem-pore K [channel], TRP, transient receptor potential [channel]

Keywords: Pulvinus, Leaf movement, Stretch-activated channels, Potassium channels, Aquaporins, Biological clock