Reduction of the chloroplastic fructose-1,6-bisphosphatase in transgenic potato plants impairs photosynthesis and plant growth

Transgenic potato plants expressing reduced levels of the chloroplastic isoform of fructose-1,6-bisphosphatase (cp-FBPase) were created via the antisense RNA technique. Transformants with different levels of FBPase activity were selected and analysed with respect to photosynthesis, carbon metabolism, and growth. FBPase activity of less than 15% of wild-type levels led to reduced growth rates, probably due to the reduction of photosynthetic activity. A significant decrease in tuber yield is observed in plants with a FBPase activity below 15% of wild-type levels, whereas plants with 36% of wild-type enzyme activity still give normal tuber yields, even though they demonstrate a lowered photosynthetic capacity. Decreased photosynthesis also results in a reduction of total carbohydrate contents in leaves. Interestingly, increased carbohydrate partitioning towards soluble sugars is observed in plants displaying less than 15% of the wild-type FBPase activity. When excised leaf discs are placed on sucrose-containing media in darkness, discs derived from plants with a reduced FBPase activity accumulate higher amounts of starch. Possible implications are discussed.