SUCROSE-PHOSPHATE SYNTHASE ACTIVITY AND YIELD ANALYSIS OF TOMATO PLANTS TRANSFORMED WITH MAIZE SUCROSE-PHOSPHATE SYNTHASE

Sucrose synthesis is a major element of the interactions between photo synthesis and plant growth and development. Tomato (Lycopersicon escul entum Mill. cv. UC82B) plants transformed with maize sucrose-phosphate synthase (SPS; EC 2.3.1.14) expressed from either a ribulose-1,5-bisp hosphate carboxylase-oxygenase (Rubisco) small subunit promoter (SSU) or the cauliflower mosaic virus 35S promoter (35S) were used to study effects of increased sucrose synthesis rates on plant growth. The plan ts were grown in growth chambers, field plots, and open-top chambers. The 35S plants had a 2 to 3-fold increase in young-leaf SPS activity, a 10 to 20-fold increase in young-root SPS activity and no increase in young-fruit SPS activity. The leaf SPS activity in;one of the 35S lin es fell to control levels by two months of age. The SSU plants had a 4 to 5-fold increase in leaf SPS activity and no significant increase i n root or young-fruit SPS activity. One 35S line, which maintained hig h leaf SPS activity throughout development, yielded 70-80% more than c ontrols at both normal and elevated CO2 in open-top chambers in the fi eld and 20-30% more than controls in two additional field trials. The other 35S line and the two SSU lines either yielded less or did not di ffer from controls under several growth conditions. Since only one of four transformed lines showed an increase in yield, we can not yet con clude that increased leaf SPS activity leads to increased yield. Howev er, increased leaf SPS activity appears to result in increased fruit s ugar content since all three lines with increased leaf SPS usually als o had increased fruit sugars.