Millard, P. and Catt, J. W. 1988. 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.).—J. exp. Bot. 39: 1–11. The capacity of field-grown potato plants to store N in their leaves for re-use during tuber growth was studied in two experiments. Increasing the N application from 0 g to 25 g N m–2 provided plants with more N than they needed for growth and so allowed accumulation of N in their leaves, principally as nitrate and protein. Ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO) concentrations increased by approximately 120% in response to N application. During tuber growth there was an export of nitrate-N from the leaves of N-replete plants and of RUBISCO-N from both high and low N plants. RUBISCO-N was mobilized more rapidly from leaves than N from other proteins and, together with nitrate, in one experiment accounted for over 90% of the N lost from the leaves irrespective of the N treatment. The potential contribution of mobilization of N stored in RUBISCO to the N content of tubers at 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 response to N application was studied. Nitrate accumulated predominantly in the lowermost (shaded) leaves, while reduced N (including RUBISCO) was found mainly in the younger leaves at the top of the canopy. This is discussed in relation to the growth of the plant and the supply of N.
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Millard et al. (1988) studied this question.