© 1998 Heron Publishing—Victoria, Canada
Ozone-induced changes in biosynthesis of Rubisco and associated compensation to stress in foliage of hybrid poplar
Bryan W. Brendley (1, 2) and Eva J. Pell (1)
1. Department of Plant Pathology and the Environmental Resources Research Institute, and Graduate Program in Plant Physiology,
The Pennsylvania State University, 211 Buckhout Laboratory, University Park, PA 16802, USA (ejp@psu.edu) / 2. Department of Biology, Gannon University, 109 University Square, Erie, PA 16541, USA / Received February 21, 1997
Summary
Experiments were conducted during the growing seasons of 1993–1995 to determine whether exposure to ozone (O3) affected the synthesis of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in hybrid poplar, Populus maximowizii A. Henry × trichocarpa Torr. & A. Gray, Clone 245. As the canopy aged, the concentration of Rubisco decreased at a more rapid rate in lower leaves
of hyrid poplar ramets subjected to chronic O3 exposure in open-top chambers than in comparable foliage of plants grown in charcoal-filtered air. There was no difference
in rate of synthesis of Rubisco between treatments, suggesting that loss of this protein in O3-treated leaves was caused by an accelerated rate of proteolysis. In foliage higher in the canopy, both concentration and
rate of synthesis of Rubisco were stimulated by O3 for a brief period when the leaves were young. Quantification of mRNA for the small (rbcS) and large (rbcL) transcripts of Rubisco did not reveal changes that were likely to reflect altered synthesis of Rubisco as a prime response
to O3. Analyses of Rubisco concentration and rate of Rubisco synthesis in foliage connected by vascular traces within the canopy
indicated that loss of Rubisco in older leaves was associated with an increase in this protein in younger leaves higher in
the canopy. These data support the notion that accelerated senescence may provide some compensatory benefit to the plant.
In 1995, the rate of synthesis of Rubisco was almost always higher in O3-treated foliage than in nontreated foliage, even when the concentration of Rubisco was adversely affected by the O3 treatment. Because accelerated foliar abscission in response to O3 was minimal in 1995 compared to other years, we speculate that, when abscission is delayed, Rubisco synthesis and concentration
become uncoupled.
Keywords:
mRNA, open-top chambers, Populus maximowizii, Populus trichocarpa, protein synthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase, senescence.
