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 diu rnal relationships between carbon distribution and growth, we analysed tran sgenic potato plants with altered carbon allocation patterns. To modify car bohydrate supply of growing sinks, we used plants that accumulated starch a s a consequence of inhibition in triose-phosphate export from chloroplasts and plants that were genetically inhibited in starch production. Carbon ass imilation was analysed by gas exchange and single cell analysis of source l eaves. Export was determined by microanalysis of phloem exudates and intern odal growth rates were measured by displacement transducers. Gas exchange m easurements showed similar assimilation rates in the wild-type and transgen ic plants during the light period. Sugar analysis of phloem exudates and ep idermal cells-revealed a severe shift of sucrose concentrations in the indi vidual plant lines. Moreover, epidermal cells turned out to be a potential storage site for carbohydrates in potato. Finally, we could demonstrate tha t changing the diurnal rhythm of carbon allocation results in a change in t he diurnal growth pattern.