Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 2000
Publication Date: N/A
Interpretive Summary: The objective of this study was to test whether soil nitrogen levels, elevated CO2 and O3 affected proanthocyanidin (condensed tannin) content in cotton leaves. Proanthocyanidins are large molecules produced by some plants that are noted for their ability to bind protein. Proanthocyanidin levels are important because they can affect plant resistance to microbial pathogens and pests. Proanthocyanidins act as antibiotics and feeding deterrents. Microbial decomposition rates also can be slowed by increased proanthocyanidin levels. At 50 days after planting, proanthocyanidin concentration in leaves was increased 58% by nitrogen deficiency and about doubled by elevated CO2. Proanthocyanidin content was decreased 14% by O3. These results will be useful for predicting how changing environmental conditions and agronomic practices affect proanthocyanidin concentrations in cotton, which in turn could be used to better manage production.
Technical Abstract: The effects of N, elevated CO2 and O3 on C partitioning to secondary metabolites such as proanthocyanidins might be explained by the growth-differentiation balance hypothesis. This hypothesis relates the negative correlation between growth and cellular differentiation processes to environmental factors affecting source-sink interactions. To test this hypothesis, cotton (Gossypium hirsutum L.) was grown in pots with either optimum (0.8 g N dm-3) or deficient (0.4 and 0.2 g N dm-3) soil N and treated in open-top chambers with either ambient or elevated (+175 and +350 µmol mol-1) CO2 in combination with either charcoal-filtered air or nonfiltered air plus 1.5 times ambient O3. At 50 days after planting, proanthocyanidin concentration in canopy leaves was increased 58% by N deficiency and about doubled by elevated CO2 at each soil N level. Proanthocyanidin content was decreased 14% by O3. Root proanthocyanidin content was increased 15% by N deficiency and 11% by elevated CO2, but O3 had no significant effect. Foliar proanthocyanidin levels were highly correlated with C:N ratios. These results supported the growth-differentiation balance hypothesis and were consistent with treatment effects on source and sink limitations.