Shoot circumnutation and winding movements require gravisensing cells

Abstract

Circumnutation and winding in plants are universal growth movements that allow plants to survive despite their sessile nature. However, the detailed molecular mechanisms controlling these phenomena remain unclear. We previously found that a gravitropic mutant of Japanese morning glory (Pharbitis nil or Ipomoea nil), Shidare-asagao (weeping), is defective not only in circumnutation but also in the winding response. This phenotype is similar to that of the Arabidopsis SCARECROW (SCR) mutant. We therefore investigated whether morning glory SCR (PnSCR) is involved in the weeping phenotype. We found that one amino acid was inserted into the highly conserved VHIID motif in weeping-type PnSCR; this mutation caused abnormal endodermal differentiation. We introduced either the mutant or WT PnSCR into Arabidopsis scr mutants for complementation tests. PnSCR of the WT, but not of weeping, rescued the shoot gravitropism and circumnutation of scr. These results show that both the abnormal gravitropism and the circumnutation defect in weeping are attributable to a loss of PnSCR function. Thus, our data show that gravisensing endodermal cells are indispensable for shoot circumnutation and the winding response and that PnSCR is responsible for the abnormal phenotypes of weeping.Arabidopsis ͉ gravitropic mutant ͉ gravity sensing ͉ morning glory ͉ SCARECROW

Up, down, and all around: How plants sense and respond to environmental stimuli

“…Nevertheless, the spaceflight study seemed to be definitive COMMENTARY and provides strong evidence that periodic growth oscillations (i.e., circumnutations) persist in the absence of significant gravitational accelerations. Thus, these results are in conflict with the study reported by Kitazawa et al (6). How do we reconcile these two reports and two hypotheses about the relationship between gravitropism and circumnutation?…”

Circumnutation as a visible plant action and reaction

“…Gravitropic mutants (pgm1, scr2-1) of Arabidopsis thaliana and Pharbitis nil were defective in circumnutations so there was a link between circumnutation and gravitropism. [38][39][40] Investigations of auxin-resistant axr2-1 mutant of Arabidopsis supported the notion that auxin participates in circumnutation. 39 In Oryza sativa coleoptiles, phy A mutants that cannot express phyA were investigated to clarify the involvement of phytochromes in red light induced circumnutation inhibition.…”

“…44 The endodermal cells (statocytes with amyloplasts functioning as statoliths) also play an important role in circumnutations, as revealed by scr mutants of Arabidopsis and Pharbitis nil. 38,39 Plasmodesmata, by which cells create a continuous system (symplast) facilitating intercellular communication, are equally important. Brown' circumnutation model 33 Circumnutation related to Ca 2+ -dependent protein kinases; it may also stimulate the activity of cytoskeleton elements.…”

“…7,12,13 Recent investigations of Arabidopsis thaliana and Pharbitis nil mutants scr i pgm (having defective differentiation of endodermal cells) reveal that gravitropic response is an essential component in plant shoot circumnutation. [38][39][40] Circumnutations as the Result of Actions of Endo-and Exogenous Factors. A combined model.…”

Auxin Polar Transport and Automorphosis in Plants

“…Thus at least it seems reasonable to assume the existence of an internal oscillator mechanism that is affected by gravitational stimuli (Johnsson, 1997). Recently it has been reported that a gravitropic mutant of Japanese morning glory (Pharbitis nil or Ipomoea nil), Shidare-asagao (weeping), is also defective in circumnutation, and that both defect of circumnutation and abnormal gravitropism are attributable to a loss of PnSCR (SCARECROW) function, suggesting that shoot circumnutation requires gravisensing endodermal cells (Kitazawa et al, 2005).…”