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

High Temperature Enhances Inhibitor Production but Reduces Fallover in Tobacco Rubisco. Stephen Schrader^*,1, Susanne von Caemmerer², Thomas Sharkey¹, T. John Andrews², ¹ Univ of Wisconsin - Madison, Madison, WI, USA² Australian National University, Canberra, ACT, Australia

ABSTRACT- The in vitro reaction velocity of ribulose-1,5-bisphosphate carboxylase / oxygenase (Rubisco) slowly declines over time (fallover) because of the enzymatic and non-enzymatic production of Rubisco inhibitors from its substrate ribulose-1,5-bisphosphate (RuBP). At 25C, fallover had a t_1/2 of 260 seconds, whereas at 45C, fallover was less severe with a t_1/2 of 1035 seconds. However, production of D-xylulose-1,5-bisphosphate (XuBP), 2-carboxytetritol-1,4-bisphosphate (CtBP), and D-glycero-2,3-diulose-1,5-bisphosphate (PdBP), inhibitors of rubisco, increased at 45C. This apparent dichotomy is explained by the Rubisco active site loosening at higher temperatures and releasing inhibitors more easily. Uncarbamylated, Mg2+ free rubisco incubated with RuBP released the inhibitor faster at 45C with a t_1/2 of 29 seconds compared to 25C with a t_1/2 of 375 seconds. This indicates that elevated temperatures do not restrict rubisco activity, but suggests the increased production of inhibitors may inhibit rubisco as temperatures decline.

KEY WORDS: Fallover, Rubisco, High Temperature, Heat Stress