No abstract

The distribution of nitrogen fractions in the organs of King Edward potato plants harvested at intervals during the growing season has been determined. A general picture of the nitrogen distribution is presented and certain problems suggested by the data are discussed.Each organ of the plant shows a uniformity in its nitrogenous composition during the whole season of active growth. The seed tubers are characterized by their high content of non‐protein nitrogen. This fraction yields the greater part of the nitrogen withdrawn from the seed tubers; the amide, amino and ‘other nitrogen’ fractions all being markedly depleted. The severely depleted tubers retain some 20% of their initial nitrogen content.The roots are rich in non‐protein nitrogen, in which nitrate nitrogen is an important fraction. The roots from ammonium sulphate‐treated plots had a higher total nitrogen content than those from untreated plots, due to accumulation of ammonia nitrogen.The ‘tops’ have a higher nitrogen content and a higher proportion of protein than the roots. There is an increase in protein content and a decrease in non‐protein nitrogen in passing from stems, to petioles, to leaf laminae. The depleted tubers and roots and stems have a uniform low‐protein content of the order 0.4‐0.6 mg. protein nitrogen per g. fresh weight.Asparagine and glutamine occur in approximately equal amounts in the seed tubers and roots. Glutamine is more completely withdrawn than asparagine from the tubers, and in the ‘tops’ it constantly exceeds asparagine in amount.A study of the concentration gradients, from leaves to petioles, to stems, to stem bases and new tubers, of the fractions of the non‐protein nitrogen focuses attention upon the ‘other nitrogen’ as containing the organic nitrogen most actively involved in translocation.The concentration and total content of the glycoside solanine in the different organs has been determined at each sampling.

Detached potato sprouts have been grown successfully in ammonium and nitrate culture solutions for 5 weeks. The pH and concentration of each solution were such that a similar rate of nitrogen absorption took place from both. The general appearance, increase in fresh and dry weight and the nitrogen distribution in the shoots and roots of sprouts removed at intervals for analysis have been compared. Sprouts, previously grown in nitrate or ammonium culture solutions, have been transferred and grown for 8 days on a minus-nitrogen culture solution, and the changes in appearance, growth rate and nitrogen distribution followed in a similar manner.The importance of aerating the culture solution, of frequent solution renewal and of an adequate supply of soluble iron for successful solution culture of potato sprouts is stressed.The ammonium sprouts developed more evenly and ultimately more rapidly than the nitrate sprouts.The nitrate sprouts were a lighter green, showed a tendency for the lower leaves to yellow and dry up and, when transferred to the minus-nitrogen solution, rapidly developed symptoms of nitrogen deficiency. Evidence is presented that, in young potato sprouts, the rate of nitrate reduction and assimilation are a serious limiting factor to the availability of nitrate nitrogen for protein synthesis.Ammonium assimilation takes place actively an-' mainly in the roots and stem bases. Nitrate assimilation takes place in both shoot and roots, but is more active in the shoot. Absorption of nitrate ions can take place even when a much higher concentration of nitrate ions is present in the root cells than in the external solution. The initial nitrate nitrogen present in the sprouts is not appreciably utilized during culture on ammonium solution.The ammonium shoots as cornpared with the nitrate shoots have a higher content of total nitrogen, protein nitrogen, non-protein organic nitrogen, amide and amino-acid nitrogen, but a lower content of inorganic nitrogen. The nitrate roots as compared with the ammonium roots have a higher content of total nitrogen, protein nitrogen and inorganic nitrogen, but a lower content of non-protein organic nitrogen, amide and other nitrogen.The higher protein content of the nitrate roots is associated with a higher percentage dry weight and a lower wntent of 'other' nitrogen. The significance of this relationship is discussed.During ammonium culture both asparaghe and glutamine accumulate, partidarly in the shoot.Evidence is presented that asparaghe is the amide primarily concerned in ammonia storage and also that it is formed during nitrate assimilation. Knowledge of the absorption and assimilation of ammonium and nitrate ions by plants is of fundamental importance for an understanding of fertilizer practice, and the present investigation, in which detached potato sprouts have been successfully flown in ammonium and nitrate culture solutions, forms part of a study of this problem. Johnston (1919Johnston ( , 1920 sprouted tubers in moist sawdust to develop sprouts suitable for growth in...