Ik. Perera et al., A role for inositol 1,4,5-trisphosphate in gravitropic signaling and the retention of cold-perceived gravistimulation of oat shoot pulvini, PLANT PHYSL, 125(3), 2001, pp. 1499-1507
Plants sense positional changes relative to the gravity vector. To date, th
e signaling processes by which the perception of a gravistimulus is linked
to the initiation of differential growth are poorly defined. We hare invest
igated the role of inositol 1,4,5-trisphosphate (InsP(3)) in the gravitropi
c response of oat (Avena sativa) shoot pulvini. Within 15 s of gravistimula
tion, InsP(3) levels increased 3-fold over vertical controls in upper and l
ower pulvinus halves and fluctuated in both pulvinus halves over the first
minutes. Between 10 and 30 min of gravistimulation, InsP(3) levels in the l
ower pulvinus half increased 5-fold over the upper. Changes in InsP(3) were
confined to the pulvinus and were not detected in internodal tissue, highl
ighting the importance of the pulvinus for both graviperception and respons
e. Inhibition of phospholipase C blocked the long-term increase in InsP(3),
and reduced gravitropic bending by 65%. Short-term changes in InsP(3) were
unimpaired by the inhibitor. Gravitropic bending of oat plants is inhibite
d at 4 degreesC; however, the plants retain the information of a positional
change and respond at room temperature. Both short- and long-term changes
in InsP(3) were present at 4 degreesC. We propose a role for InsP(3) in the
establishment of tissue polarity during the gravitropic response of oat pu
lvini. InsP(3) may be involved in the retention of cold-perceived gravistim
ulation by providing positional information in the pulvini prior to the red
istribution of auxin.