Iy. Perera et al., Transient and sustained increases in inositol 1,4,5-hisphosphate precede the differential growth response in gravistimulated maize pulvini, P NAS US, 96(10), 1999, pp. 5838-5843
Citations number
40
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
The internodal maize pulvinus responds to gravistimulation with differentia
l cell elongation on the lower side, As the site of both graviperception an
d response, the pulvinus is an ideal system to study how organisms sense ch
anges in orientation. We observed a transient 5-fold increase in inositol 1
,4,5-trisphosphate (IP3) within 10 s of gravistimulation in the lower half
of the pulvinus, indicating that the positional change was sensed immediate
ly. Over the first 30 min, rapid IP3 fluctuations were observed between the
upper and lower halves. Maize plants require a presentation time of betwee
n 2 and 4 h before the cells on the lower side of the pulvinus are committe
d to elongation. After 2 h of gravi-stimulation, the lower half consistentl
y had higher IP3, and IP3 levels on the lower side continued to increase up
to approximate to 5-fold over basal levels before visible growth, As bendi
ng became visible after 8-10 h, IP3 levels returned to basal values, Additi
onally, phosphatidylinositol 4-phosphate 5-kinase activity in the lower pul
vinus half increased transiently within 10 min of gravistimulation, suggest
ing that the increased IP3 production was accompanied by an up-regulation o
f phosphatidylinositol 1,5-bisphosphate biosynthesis. Neither IP3 levels no
r phosphatidylinositol 4-phosphate 5-kinase activity changed in pulvini hal
ves from vertical control plants. Our data indicate the involvement of IP3
and inositol phospholipids in both short- and long-term responses to gravis
timulation. As a diffusible second messenger, IP3 provides a mechanism to t
ransmit and amplify the signal from the perceiving to the responding cells
in the pulvinus, coordinating a synchronized growth response.