Changes in starch and inositol 1,4,5-trisphosphate levels and auxin transport are interrelated in graviresponding oat (Avena sativa) shoots.
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.
Yun
Hye Sup
HS
Department of Life Science, Chung-Ang University, Seoul 156-756, Korea.
Joo
Se-Hwan
SH
Kaufman
Peter B
PB
Kim
Tae-Wuk
TW
Kirakosyan
Ara
A
Philosoph-Hadas
Sonia
S
Kim
Seong-Ki
SK
Chang
Soo Chul
SC
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*
D017931:DNA Primers; D007210:Indoleacetic Acids; D015544:Inositol 1,4,5-Trisphosphate; D013213:Starch