Abstract
Sucrose-phosphate synthase (SPS) activity in source leaves of potato plants (Solanum tuberosum cv. May Queen) transformed with maize SPS gene under the control of a modified cauliflower mosaic virus (CaMV) 35S promoter was two to four times higher than the endogenous activity found in the control. A negative correlation (r=0.82) between SPS activity and the ratio of starch to sucrose was observed. There were no significant changes in starch synthesis enzyme (ADGPase and QE) activities in the leaves. Photosynthesis did not differ significantly between control and transgenic lines. Aboveground (leaves and stem) and belowground (tuber) dry matter in three transgenic lines harvested during tuber development increased up to 15% and 20%, respectively, indicating that increased capacity for sucrose synthesis in potato leaves may lead to favorable growth. Moreover, the activity of this enzyme in source leaves of two transgenic potatoes increased when reaction temperature was elevated from 15°C to 35°C, a response similar to that of SPS in maize. Since temperature is a limiting factor for growth of potato, the transgenic plants will be useful for future studies under higher temperature growth conditions.
