Reduction in turgid water volume in jack pine, white spruce and black spruce in response to drought and paclobutrazol

Significant reductions in needle water content were observed in white spruc e (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill) B.S.P.), and jack pine (Pinus banksiana Lamb.) seedlings in response to a 10-day dr ought, although turgor was apparently maintained. When the seedlings were r e-watered after the drought, jack pine needles regained their original satu rated volume, whereas white spruce and black spruce needles did not. Signif icant drought-induced reductions in turgor-loss volume (i.e., tissue volume at the point of turgor loss) were observed in shoots of all three species, especially jack pine. Repeated exposure to 7 days of drought or treatment with the cytochrome P-450 inhibitor, paclobutrazol ((2RS,3RS)-1-(4-chloroph enyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol), reduced seedling he ight relative to that of untreated controls in all three species. The reduc tions in saturated and turgor-loss needle volumes in the paclobutrazol-trea ted seedlings were comparable with those of seedlings subjected to a 10-day drought. The treatment-induced reductions in shoot and needle water conten ts enabled seedlings to maintain turgor with tissue volumes close to, or be low, the turgor-loss volume of untreated seedlings. Paclobutrazol-treated s eedlings subsequently survived drought treatments that were lethal to untre ated seedlings.