| Abstract: | Dry weight increase, root respiration, photosynthesis, and shootdark respiration were measured prior to and during the developmentof the taproot of carrot (Daucus carota L., var. AmsterdamseBak) which stores sucrose and reducing sugars. Before storageof sugars in the taproot started, root respiration was highand up to 50% inhibited by salicyl hydroxamic acid (SHAM), indicatinga high activity of the alternative pathway. The onset of sugar storage in the taproot coincided with a sharpdecrease in alternative pathway activity. When sugars were storedin the taproot, the alternative pathway in the taproot was notoperative, although present. It was concluded that the alternative pathway only consumessugars that are not used for energy production in growth ormaintenance processes, for carbon skeletons, osmoregulationor storage, in accordance with the energy overflow model. Apositive quantitative relationship exists between the storageof sugars in the taproot and the efficiency of root respiration.After day 32 the amount of daily produced carbohydrates transportedto the root system increased and these sugars were stored inthe taproot. In this period less sugars were invested in structuralshoot growth. In the present investigation no positive influence from thedeveloping sink is found on photosynthetic rate or net assimilationrate. Both rates decrease with increasing age of the plants,although increasing amounts of sugars were stored in the taproot. |
