title: Changes in starch and inositol 1,4,5-trisphosphate levels and auxin transport are interrelated in graviresponding oat (Avena sativa) shoots.
abstract: This study was conducted to unravel a mechanism for the gravitropic curvature response in oat (Avena sativa) shoot pulvini. For this purpose, we examined the downward movement of starch-filled chloroplast gravisensors, differential changes in inositol 1,4,5-trisphosphate (IP(3)) levels, transport of indole-3-acetic acid (IAA) and gravitropic curvature. Upon gravistimulation, the ratio for IAA levels in lower halves versus those in upper halves (L/U) increased from 1.0 at 0 h and reached a maximum value of 1.45 at 8 h. When shoots were grown in the dark for 10 d, to deplete starch in the chloroplast, the gravity-induced L/U of IAA was reduced to 1.0. N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), both auxin transport inhibitors, significantly reduced the amount of gravitropic curvature and gravity-induced lateral IAA transport, but did not reduce the gravity-induced late change in the L/U ratio of IP(3) levels. U73122, a specific phospholipase C (PLC) inhibitor, decreased gravity-induced curvature. Because U73122 reduced the ratio of L/U of IAA imposed by gravistimulation, it is clear that IAA transport is correlated with changes in IP(3) levels upon gravistimulation. These results indicate that gravistimulation-induced differential lateral IAA transport may result from the onset of graviperception in the chloroplast gravisensors coupled with gravity-induced asymmetric changes in IP(3) levels in oat shoot pulvini.
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, Korea.
authors.forename: Hye Sup
authors.initials: HS
authors.lastname: Yun
authors.forename: Se-Hwan
authors.initials: SH
authors.lastname: Joo
authors.forename: Peter B
authors.initials: PB
authors.lastname: Kaufman
authors.forename: Tae-Wuk
authors.initials: TW
authors.lastname: Kim
authors.forename: Ara
authors.initials: A
authors.lastname: Kirakosyan
authors.forename: Sonia
authors.initials: S
authors.lastname: Philosoph-Hadas
authors.forename: Seong-Ki
authors.initials: SK
authors.lastname: Kim
authors.forename: Soo Chul
authors.initials: SC
authors.lastname: Chang
mesh_terms: D018554:Avena / Q000378:metabolism* / Q000502:physiology; D001483:Base Sequence; D001692:Biological Transport; D017931:DNA Primers; D018522:Gravitropism; D007210:Indoleacetic Acids / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D018520:Plant Shoots / Q000378:metabolism*; D015398:Signal Transduction; D013213:Starch / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D007210:Indoleacetic Acids; D015544:Inositol 1,4,5-Trisphosphate; D013213:Starch