Response to an ozone gradient of growth and enzymes implicated in tolerance to oxidative stress in Acer saccharum (Marsh.) seedlings

Abstract

Two-year-old sugar maple (Acer saccharum Marsh.) seedlings were exposed in open top chambers to an extensive gradient of O3 (0 to 300 nL.L -1) during 85 days under two light environments (20% and 80% of full sun at noon on a sunny day). The growth of truncated seedlings (with one flush of leaves) and episodic seedlings (with two flushes) was decreased as O 3 increased, especially the growth of the second flush which developed under the oxidative treatment. Visible leaf injuries developed during the season under high O3 concentrations. Survivalist growth strategy of sugar maple, as seen by the root/shoot ratio, together with the enzymatic stimulations of glucose 6-phosphate dehydrogenase, phosphoenolpyruvate carboxylase and glutathione reductase allowed the seedlings to tolerate the O3 doses. However, at the end of the season, the cumulative oxidative stress in the second flush of the episodic seedlings exposed to concentrations over 150 nL.L-1O3 was too large and exceeded the capacity of seedlings for detoxification and repair. © INRA, EDP Sciences, 2006.