Transgenic plants changed in carbon allocation pattern display a shift in diurnal growth pattern

Photosynthesis, partitioning of carbohydrates and growth have to be highly orchestrated to enable an efficient performance of plants. To study the diurnal relationships between carbon distribution and growth, we analysed transgenic potato plants with altered carbon allocation patterns. To modify carbohydrate supply of growing sinks, we used plants that accumulated starch as a consequence of inhibition in triose-phosphate export from chloroplasts and plants that were genetically inhibited in starch production. Carbon assimilation was analysed by gas exchange and single cell analysis of source leaves. Export was determined by microanalysis of phloem exudates and internodal growth rates were measured by displacement transducers. Gas exchange measurements showed similar assimilation rates in the wild-type and transgenic plants during the light period. Sugar analysis of phloem exudates and epidermal cells-revealed a severe shift of sucrose concentrations in the individual plant lines. Moreover, epidermal cells turned out to be a potential storage site for carbohydrates in potato. Finally, we could demonstrate that changing the diurnal rhythm of carbon allocation results in a change in the diurnal growth pattern.