PARENT SESSION
Posters P3C C3 and Rubisco. Abstracts (617-630)

Rubisco inhibitors of Rhizophora mangle L. in the light. Hirotoki Takemasa^*,1, John Cheeseman^*,1, ¹ Department of Plant Biology, Urbana, IL, USA

ABSTRACT- Rhizophora mangle L., known commonly as red mangrove, is a coastline species that dominates many wetlands and islands of the neo-tropics including our research population in Twin Cays (Belize). They are exposed to and thrive on saline water and high incident light levels year-long and survive in what otherwise would be considered extreme conditions. Measurements taken on field and greenhouse plants indicate that A-Ci relationships appear horseshoe shaped, with internal CO₂ rising as assimilation and/or conductance falls, suggesting that Rubisco activity is downregulated during periods of low conductance. Comparing Rubisco activities in the light and dark, there is no evidence that R. mangle produces CA1P as a night-time regulator. There is a correlation between total Rubisco activity and incident light, while the ratio of total to initial activities (the carbamylation rate) changes little. There is up to 30% discrepancy between maximal activity, the activity taken after treatment of SO₄^2- ions that displace any inhibitors attached to Rubisco, and total activity. These results suggest the presence of a Rubisco inhibitor in the light.

KEY WORDS: gas exchange, Rubisco, regulation, Rhizophora