Ultrastructure of Paraquat-Treated Slash Pine (Pinus elliottii Engelm.)

The introduction of paraquat (l, 1‘-dimethyl-4,4‘-bipyridylium ion) into the transpiration stream of young slash pine (Pinus elliottii Engelm.) trees significantly enhances oleoresin biogenesis and results in localized resin soaking in treated portions of the bole. All affected cells of the xylem symplast, including those not directly associated with resin ducts, begin to synthesize excessive oleoresin and secrete or lose it initially through pits into the lumen of contiguous tracheids. Oleoresin is observed in plastids, mitochondrial envelopes, vacuoles, and ER cisternae in both control and treated trees. Cells near the site of paraquat treatment show extreme damage to membrane integrity, depletion of starch, and loss of cellular organization. The transport of oleoresin across cellular membranes does not appear to be achieved by transporting vesicles or by a mechanism involving exocytosis. Although oleoresin is observed in various cellular organelles, it is unclear if its synthesis occurs in association with these organelles or whether this compartmentation results from random contact and solubilization of this lipophilic material in the membranes of different organelles.