CONSTITUTIVE OR LIGHT-REGULATED EXPRESSION OF THE ROLC GENE IN TRANSGENIC POTATO PLANTS HAS DIFFERENT EFFECTS ON YIELD ATTRIBUTES AND TUBERCARBOHYDRATE-COMPOSITION

Tetraploid potato clones, transgenic for the rolC gene of Agrobacteriu m rhizogenes under control of the light-inducible ribulose bisphosphat e carboxylase small subunit promoter (rbcS-rolC), were compared, with respect to yield attributes and tuber carbohydrates, with transformed and untransformed controls and with 35S-rolC transgenic potato plants. In rbcS-rolC plants, the expression of the rolC gene was located main ly in leaves, while in 35S-rolC plants transcripts were detected as we ll in shoots and roots. Phenotypically, rbcS-rolC transgenic plants we re found to be slightly reduced in plant size with a few more tillers than control plants. Photosynthetic rate and chlorophyll content were significantly lower in all rolC transgenic plants irrespective of the type of construct used. Tuber yield was not significantly different be tween controls and rbcS-rolC transgenic plants, but was reduced in the 35S-rolC transformants. Sucrose level was unchanged in all rolC clone s investigated, whereas fructose content was significantly enhanced in 35S-rolC transformants, but not in the plants expressing the rolC gen e in aerial plant parts only. In both types of rolC transgenic plants, glucose content was lower than in controls, resulting in a significan t reduction of reducing sugar in tubers. The results suggest a hormona l influence on the carbohydrate composition of potato tubers.