HYDROGEN-FLUORIDE EFFECTS ON PLASMA-MEMBRANE COMPOSITION AND ATPASE ACTIVITY IN NEEDLES OF WHITE-PINE (PINUS-STROBUS) SEEDLINGS PRETREATED WITH 12 H PHOTOPERIOD

Eastern white pine (Pinus strobus L.) seedlings were pretreated with 1 2 h photoperiod to induce dormancy. Dormant plants were fumigated with 0.5 ppb (0.4 mu g m(-3)) or 2.0 ppb (1.6 mu g m(-3)) hydrogen fluorid e (HF) for 2-28 days. Plasma membranes were isolated from needles of t reated and control seedlings to determine their chemical composition a nd ATPase activity. For all analyses, only those plants which did not show needle necrosis were selected. The amount of plasma membrane phos pholipid expressed on a plasma membrane protein basis was higher after 2 days in the 0.5 ppb HF treatment as compared to controls. After 2 d ays of 2.0 ppb HF treatment as well as after 8 and 28 days of both HF treatments phospholipid to protein ratios in fluoride treated seedling s were lower as compared to control levels. A decrease in sterol level s could be observed after 2 days in both HF treatments. A large increa se in the ratio of sterols to proteins was observed in plasma membrane s of eastern white pine seedlings treated with 0.5 ppb HF for 28 days. Increased sterol to phospholipid ratios were observed after 8 and 28 days in 0.5 ppb and after 2 and 8 days of 2.0 ppb HF treatment. A decr ease in ATPase activity was observed after 8 days with both fluoride t reatments. Drastic increase of ATPase activity was observed after 28 d ays of HF treated plants. Observed changes of sterol and phospholipid levels after only 2 days of fumigation suggest early fluoride effects on plasma membrane composition during plant dormancy.