Effects of repeated stress on turgor pressure and cell elasticity changes in black spruce seedlings

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Abstract
One-year-old black spruce (Piceamariana (Mill.) B.S.P.) seedlings were preconditioned by exposing them to either one or two dehydration–rehydration cycles by using the osmoticum polyethylene glycol 3350. Preconditioned and unconditioned seedlings were then subjected to a more severe osmotic (water) stress by exposing them to a higher concentration of polyethylene glycol. Effects of repeated dehydration–rehydration cycles on cell-water relations were studied after 3, 7, and 13 days of stress relief using pressure–volume curve analysis. Repeated dehydration–rehydration cycles caused a cumulative increase in turgor potentials at full saturation. In these preconditioned plants there was also a progressive lowering of osmotic potentials and relative water contents at zero turgor, which increased over time with stress relief. The decline in osmotic potentials at zero turgor in osmotically stressed black spruce was associated with increased cell wall relaxation, followed by increased turgor potentials, in preconditioned but not in unconditioned seedlings. Saturated osmotic potentials were not altered by repeated, short-term conditioning stresses, suggesting that tissue elasticity was more important for turgor regulation than osmotic adjustment.

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