The Influence of Nitrogen Supply on the Use of Nitrate and Ribulose 1,5-bisphosphate Carboxylase/Oxygenase as Leaf Nitrogen Stores for Growth of Potato Tubers (Solanum tuberosum L.)

Millard, P. and Catt, J. W. 1988. The influence of nitrogensupply on the use of nitrate and ribulose 1,5-bisphosphate carboxylase/oxygenaseas leaf nitrogen stores for growth of potato tubers (Solanumtuberosum L.).—J. exp. Bot. 39: 1–11. The capacity of field-grown potato plants to store N in theirleaves for re-use during tuber growth was studied in two experiments.Increasing the N application from 0 g to 25 g N m^–2 providedplants with more N than they needed for growth and so allowedaccumulation of N in their leaves, principally as nitrate andprotein. Ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO)concentrations increased by approximately 120% in response toN application. During tuber growth there was an export of nitrate-Nfrom the leaves of N-replete plants and of RUBISCO-N from bothhigh and low N plants. RUBISCO-N was mobilized more rapidlyfrom leaves than N from other proteins and, together with nitrate,in one experiment accounted for over 90% of the N lost fromthe leaves irrespective of the N treatment. The potential contributionof mobilization of N stored in RUBISCO to the N content of tubersat final harvest was calculated as being between 11–15%,and appeared to be unaffected by the N supply to the plants. The distribution of N accumulating within the canopy, in responseto N application was studied. Nitrate accumulated predominantlyin the lowermost (shaded) leaves, while reduced N (includingRUBISCO) was found mainly in the younger leaves at the top ofthe canopy. This is discussed in relation to the growth of theplant and the supply of N. Key words: Solanum tuberosum, nitrogen, nitrate, ribulose, 1,5-bisphosphate carboxylase/oxygenase, storage