Phosphoinositides and phosphatidic acid regulate pollen tube growth and reorientation through modulation of [Ca2+]c and membrane secretion.
The maintenance of a calcium gradient and vesicle secretion in the apex of pollen tubes is essential for growth. It is shown here that phosphatidylinositol-4,5-bisphosphate (PIP2) and D-myo-inositol-1,4,5-trisphosphate (IP3), together with phosphatidic acid (PA), play a vital role in the regulation of these processes. Changes in the intracellular concentration of both PIP2 and IP3 (induced by photolysis of caged-probes), modified growth and caused reorientation of the growth axis. However, measurements of cytosolic free calcium ([Ca2+]c) and apical secretion revealed significant differences between the photo-release of PIP2 or IP3. When released in the first 50 mum of the pollen tube, PIP2 led to transient growth perturbation, [Ca2+]c increases, and inhibition of apical secretion. By contrast, a concentration of IP3 which caused a [Ca2+]c transient of similar magnitude, stimulated apical secretion and caused severe growth perturbation. Furthermore, the [Ca2+]c transient induced by IP3 was spatially different causing a pronounced elevation in the sub-apical region. These observations suggest different targets for the two phosphoinositides. One of the targets is suggested to be PA, a product of PIP2 hydrolysis via phospholipase C (PLC) or phospholipase D (PLD) activity. It was found that antagonists of PA accumulation (e.g. butan-1-ol) and inhibitors of PLC and PLD reversibly halted polarity. Reduction of PA levels caused the dissipation of the [Ca2+]c gradient and inhibited apical plasma membrane recycling. It was also found to cause abolition of the apical zonation. These data suggest that phosphoinositides and phospholipids regulate tip growth through a multiple pathway system involving regulation of [Ca2+]c levels, endo/exocytosis, and vesicular trafficking.
Monteiro
David
D
Universidade de Lisboa, Faculdade de Ciências de Lisboa, ICAT, 1749-016 Lisboa, Portugal.
Liu
Qunlu
Q
Lisboa
Saskia
S
Scherer
G E F
GE
Quader
Hartmut
H
Malhó
Rui
R
D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D019684:Magnoliopsida / Q000502:physiology*; D010712:Phosphatidic Acids / Q000502:physiology*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000502:physiology*; D011058:Pollen / Q000502:physiology*; D013997:Time Factors
D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium