PLANT PHYSIOLOGY , Vol 111, Issue 1 101-107, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Intracellular Localization of Phospholipase D in Leaves and Seedling Tissues of Castor Bean
L. Xu, A. Q. Paulsen, S. B. Ryu and X. Wang
Department of Biochemistry (L.X., S.B.R., X.W.) and Division of Biology (A.Q.P.), Kansas State University, Manhattan, Kansas 66506
The intracellular distribution of phospholipase D (PLD; EC 3.1.4.4) in
castor bean (Ricinus communis L.) tissues was investigated by subcellular
fractionation and by immuno-electron microscopy. Centrifugal fractionation
revealed that most PLD in young leaves was soluble, whereas in mature
leaves a majority of PLD was associated with microsomal membranes. Further
separation of microsomal membranes by a two-phase partitioning system
indicated that PLD was associated with both plasma and intracellular
membranes. Sucrose gradient separation of intracellular membranes showed
PLD present in the endoplasmic reticulum, a submicrosomal band, and in
soluble fractions but not in mitochondria and glyoxysomes of
postgermination endosperm. Immunocytochemical studies found high gold
labeling in vacuoles in young leaves, suggesting that the high level of
soluble PLD in young leaves is due to release of PLD from vacuoles during
tissue disruption. In addition to the labeling in vacuoles, gold particles
were also found in the cytoplasmic matrices and plasma membrane in leaves
and in 2-d postgermination seedlings. Collectively, these results show that
PLD in castor bean leaf and seedling tissues is localized in the vacuole
and is associated with the endoplasmic reticulum and plasma membrane and
that the relative distribution between the soluble and membrane
compartments changes during castor bean leaf development.