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

Rubisco specificity factor tends to be larger in plant species from drier habitats and in species with persistent leaves. Jeroni Galmés^*,1, Alfred Keys², Josep Cifre¹, Rowan Mitchell², Martin Parry², Hipólito Medrano¹, Jaume Flexas¹, ¹ Laboratori de Fisiologia Vegetal, Palma, Balearic Islands, Spain² Crop Performance and Improvement, Harpenden, Hertfordshire, UK

ABSTRACT- The specificity factor of Rubisco is a measure of the relative capacities of the enzyme to catalyse carboxylation and oxygenation of ribulose 1,5-bisphosphate and hence to control the relative rates of photosynthetic carbon assimilation and photorespiration. Specificity factors of purified Rubisco from 24 species of C₃ plants found in various habitats in the Balearic Islands were measured at 25 ^oC. The results suggest that specifity factors are more dependent on environmental pressure than of phylogenetic factors. Irrespective of phylogenetic relationships, higher capacities for carboxylation were found in species characteristically growing in dryer environments and in species that are hemideciduous or evergreen. Effects of temperature on specificity factor of the purified enzyme from 14 species were consistent with the concept that larger specificity factors were associated with an increase in the activation energy for oxygenation compared to carboxylation of the 2,3-enediolate of RuBP to the respective transition state intermediates. The results are discussed in terms of selection pressures leading to the differences in specificity factors and the value of the observations for identifying useful genetic manipulation to change Rubisco polypeptide subunits.

KEY WORDS: Mediterranean, Rubisco Specificity Factor, Drought