PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Carbon assimilation in wild type and starchless mutant of Nicotiana as affected by CO₂ concentration.

Wang, Xianzhong¹, Griffin, Kevin², ¹ Indiana University-Purdue University Indianapolis, Indianapolis, Indiana² Lamont-Doherty Earth Observatory, Palisades, New York

ABSTRACT- Research based on the use of genetically manipulated plants can improve our understanding of the regulation of carbon metabolism. We examined the relationship between carbon assimilation physiology and carbohydrate contents in leaves of wild type and a starchless mutant (NS 458) of Nicotiana sylvestris (Speg et Comes) grown at ambient (365 mmol mol^-1) or elevated (730 mmol mol^-1) CO₂ concentration. Elevated CO₂ increased net photosynthesis (A) in wild type plants by 27%, but had no effect on A in starchless mutant plants. Leaf dark respiration (Rd) was not significantly affected by CO₂ level in wild type or mutant plants. There was a positive correlation between A and Rd in both wild type and mutant plants, regardless of CO₂ concentrations. However, the coefficient of determination (r²) was greater for elevated than for ambient CO₂ grown plants. Elevated CO₂ increased contents of soluble sugars and total non-structural carbon (TNC) of both wild type and mutants, but the magnitude of increase was much greater for mutants than for wild type plants. Total soluble sugar content (glucose, fructose and sucrose) and TNC more than doubled at elevated CO₂ for mutant plants, while their increases in response to CO₂ enrichment was 87% and 90%, respectively, for wild types. Although leaf Rd of the starchless mutant had a statistically positive correlation with glucose, total soluble sugar and TNC under elevated CO₂, the percentage of variation in leaf Rd attributable to carbohydrate content was low. Leaf Rd of wild type plants was uncorrelated with carbohydrate contents at ambient or elevated CO₂. Our study demonstrated that leaf Rd tends to increase with leaf A, especially at a higher CO₂ concentration, and that leaf carbohydrate content is not the most significant determinant of leaf Rd in N. sylvestris.

Key words: dark respiration, photosynthesis, carbohydrate, Nicotiana sylvestris