Abstract
In mesophyll cells of the aquatic monocot Vallisneria, red light induces rotational cytoplasmic streaming, which is regulated by the cytoplasmic concentration of Ca2+. Our previous investigations revealed that red light induces Ca2+ efflux across the plasma membrane (PM), and that both the red light-induced cytoplasmic streaming and the Ca2+ efflux are sensitive to vanadate, an inhibitor of P-type ATPases. In this study, pharmacological experiments suggested the involvement of PM H+-ATPase, one of the P-type ATPases, in the photoinduction of cytoplasmic streaming. We hypothesized that red light would activate PM H+-ATPase to generate a large H+ motive force (PMF) in a photosynthesis-dependent manner. We demonstrated that indeed, photosynthesis increased the PMF and induced phosphorylation of the penultimate residue, threonine, of PM H+-ATPase, which is a major activation mechanism of H+-ATPase. The results suggested that a large PMF generated by PM H+-ATPase energizes the Ca2+ efflux across the PM. As expected, we detected a putative Ca2+/H+ exchange activity in PM vesicles isolated from Vallisneria leaves.
Highlights
Intracellular movements are closely associated with a wide spectrum of plant cell activities, including cell division [1,2,3], cell growth [4,5], redistribution of cell organelles [6,7], organized trafficking of membrane vesicles [3,8], and so on
But not that of H+ in the plasma membrane (PM) vesicles isolated from Vallisneria leaves (Figure S1)
Based on the present results, we propose that PM H+ -ATPase plays crucial roles in the photoinduction of cytoplasmic streaming in mesophyll cells of Vallisneria
Summary
Intracellular movements are closely associated with a wide spectrum of plant cell activities, including cell division [1,2,3], cell growth [4,5], redistribution of cell organelles [6,7], organized trafficking of membrane vesicles [3,8], and so on. Actin filaments and microtubules are representative cytoskeletal components that support a variety of unique motile machineries. The actin cytoskeleton is known to play pivotal roles in the regulation of intracellular movements, especially in response to environmental fluctuation, through its tremendously flexible nature [9,10]. Ca2+ -sensitive regulatory mechanisms for the actomyosin-dependent generation of motive force have been extensively investigated, and a number of actin-linked and myosin-linked components responsible for the Ca2+ sensitivity have been identified [11,12]. It is well documented that Ca2+ fluxes across the plasma membrane (PM) and the sarcoplasmic reticulum membrane of those motile cells function to control the cytoplasmic concentration of Ca2+ and excitation-contraction coupling [13].
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