PARENT SESSION

Symposium S6D Crop photosynthesis, agricultural biotechnology
Thursday September 2nd, 2004 10:20 AM-12:20 PM Room 510A
Chair: Vince DeLuca
Co-Chair: Maurice Ku

Can overexpression of SBPase and transketolase increase photosynthesis and growth? Stephane Lefebvre^*,1, Oksana Zahkleniuk¹, Julie Lloyd¹, Christine Raines¹, ¹ Department of biological Sciencies, University of Essex, Colchester, Essex, UK

ABSTRACT- The enzyme sedoheptulose-1,7-bisphosphatase (SBPase) functions in the regenerative phase of the Calvin cycle, producing sedoheptulose-7-phosphate, used for the synthesis of the Rubisco substrate, ribulose-1-5-bisphosphate. Previously it has been shown that small decreases in SBPase activity were accompanied with direct reductions in photosynthetic carbon assimilation capacity and reduction in growth rates. These data suggested that SBPase activity was close to limiting for photosynthetic carbon fixation. To investigate the consequences of increased SBPase activity, tobacco has been transformed with a construct containing an Arabidopsis thaliana SBPase cDNA, expression driven by the 35S CaMV promoter. The SBPase sense tobacco lines had between 20 to 60% higher SBPase activity than the wild type and when the plants were grown in high light conditions, photosynthetic capacity and growth were increased. Interestingly, in mature leaves only small increases in photosynthesis were observed but in younger leaves a 3-9% increase was evident. Destructive harvest at flowering revealed that the SBPase sense transgenic plants had a 20 to 30% increase in leaf area, and total above ground biomass, when compared to wild type plants. These results demonstrate that SBPase activity is an important determinant of photosynthetic capacity and growth, particularly during the early stage of plant development. It has also been shown that the enzyme transketolase has the potential to co-limit photosynthetic carbon assimilation. In order to test if photosynthetic capacity can be increased further we have produced transgenic tobacco plants expressing a transketolase sense construct and also, double transgenic tobacco plants, over-expressing both SBPase and transketolase.

KEY WORDS: Transketolase, SBPase, photosynthetic carbon assimilation, sense overexression