Paraquat Induced Changes in Reserve'carbohydrates, Fatty Acids and Oleoresin Content of Young Slash Pines

The induction of a 15 to 20 fold increase in oleoresin content of resin soaked xylem in paraquat treated pine stems raises many intriguing questions of a physiological nature. Our knowledge of stem anatomy and physiology of oleoresin formation in pines appears to exclude the possibility that resin soaking results from long range transport of oleoresin via vertical resin ducts to resin soaked areas. First, the length of vertical resin ducts is relatively short averaging less than six inches long with occasional ducts extending up to three feet in slash pine (Pinus elliottii Englem.) (unpublished, Brown and Helseth, 1966). Secondly, there appears to be no significant reduction of oleoresirl content in xylem well above or below resin soaked areas, although there is a decreasing gradient of oleoresin away from these areas until normal levels are again reached along the stem. In addition, cytological observations on paraquat treated xylem indicates that membrane permeability of the secretory cells lining the resin ducts and associated vertical parenchyma cells is drastically altered. This allows outward leakage of oleoresin from these cells into adjacent tracheids by the path of least resistance, i.e., through the bordered pits. In untreated stems oleoresin secretion by the epithelial cells occurs preferentially into the duct, thereby maintaining pressures as high as 12 to 15 atmospheres within the normal undisturbed duct system. Hence, leaky ducts brought about by the effect of paraquat on membrane integrity and selectivity of parenchyma cells surrounding the ducts are not conducive to long range vertical movement or transport of oleoresin.