Ultrastructure of Paraquat-treated Pine Cells (Pinus elliottii Engelm.) in Suspension Culture

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Abstract
The ultrastructure of liquid suspension cultures of Pinus elliottii was studied, noting characteristics of dividing and senescent cells. The cultures were treated with 0.01, 0.1, 1.0, and 10.0 mg l−1 paraquat, an herbicide which stimulates oleoresin synthesis and resinosis in the xylem of treated pine trees. The ultrastructural effects of the toxin were studied at each paraquat concentration over a period of 24 days. Destructive effects of paraquat on vacuolar and organelle membranes and cytoplasm are observable in one day in cells supplied with 10.0 mg l−1. At 1.0 mg l−1 vacuolar membranes and cell organelles are present at seven days, but the cultures continually decline until at 14 days they are dead. At concentrations of 0.1 and 0.01 mg l−1 the effects of the toxin on fine structure cannot be separated from normal cell senescence. At low concentrations of paraquat the amyloplastids accumulate large amounts of starch. No accumulation of oleoresin was detected. The ultrastructural observations are correlated with physiological studies in suspension culture and in living trees.