ANTISENSE REPRESSION OF THE CHLOROPLAST TRIOSE PHOSPHATE TRANSLOCATORAFFECTS CARBON PARTITIONING IN TRANSGENIC POTATO PLANTS

The major chloroplast envelope membrane protein E29 is central for the communication between chloroplasts and cytosol. It has been identifie d as the triose phosphate translocator (TPT) exporting the primary pro ducts of the Calvin cycle (i.e., triose phosphates and 3-phosphoglycer ate) out of the chloroplast in a strict counter exchange for P(i). To study the in vivo role of the TPT, transgenic potato plants were const ructed that have a reduced expression of the TPT at both the RNA and p rotein level due to antisense inhibition. Chloroplasts isolated from t hese plants show a 20-30% reduction with respect to their ability to i mport P(i). The reduced TPT activity leads to a reduction of maximal p hotosynthesis by 40-60%, to a change in carbon partitioning into starc h at the expense of sucrose and amino acids, and to an increase of the leaf starch content by a factor of almost-equal-to 3. At early develo pmental stages the inhibited plants are retarded in growth compared to the wild type.