CELL-WALL CHANGES IN WHITE SPRUCE (PICEA-GLAUCA) NEEDLES SUBJECTED TO REPEATED DROUGHT STRESS

White spruce [Picea glauca (Moench) Voss] seedlings were preconditioned by subjecting them to 3 cycles of a mild drought stress. After 1 week of stress relief their water status, soluble carbohydrate content and cell wall composition in newly formed needles were examined and compared with those in control seedlings. Both preconditioned and control seedlings were subsequently subjected to a severe drought stress and again analyzed. Preconditioning treatment both before and during subsequent stress exposure lowered osmotic potentials at full hydration, and after the loss of turgor, decreased lignin content and increased hemicellulose content of the cell walls. Severe drought had similar but more drastic effects on seedling water relations, sugar accumulation and cell wall hemicellulose content; it also decreased cell wall pectin levels. The decrease in pectin levels was accompanied by a loss of galactose and glucose from pectic substances. Little change in cellulose content was observed as a result of preconditioning and severe drought.