Respiration and Metabolism in Etiolated Wheat Seedlings as Influenced by Phosphorus Nutrition.

Phosphorus plays an important role in the process of respiration (12, 13, 29). It forms, in the presence of sugars, monoand di-hexosephosphoric acid esters (8, 27), which are then broken down in the respiratory process. Under certain conditions it may form with sucrose a sucrose phosphoric acid ester (19). It is also known that plants starved for phosphorus differ considerably in their chemical composition from those not thus starved. MACGILLIVRAY (15) has pointed out that tomato plants starved for phosphorus show a decrease in coagulable nitrogen, and an increase in total nitrogen. There is also a marked increase in percentage of sugar. KRAYBILL (10) also showed that when phosphate is limiting in tomato plants nitrates as well as carbohydrates accumulate. According to ECKERSON (5) the lack of phosphorus causes a breakdown of the reducase activity of the plant, which is then followed by an accumulation of nitrates, sugars, and starch, and results in an essentially nitrogen-starved plant. It is desirable then to know the relation between respiration and the chemical composition of plants deficient in phosphorus as compared with plants not deficient in phosphorus. In view of these facts and because phosphorus very often becomes limiting in agricultural soils the present investigation was undertaken. All of the chemical data cited above were obtained with green plants and after phosphorus starvation had become rather severe. It was the desire of the writer to determine some of the early symptoms of phosphorus starvation as shown by internal composition, as well as to measure the respiration during this period, and to relate any differences in composition to respiration, if possible. For these purposes large green plants are not suited; hence, etiolated seedlings with a considerable reserve of carbohydrates were used. Wheat was chosen as the most uniform plant at hand. Since LYON had obtained an increase in respiration owing to increased phosphate supply, the respiration behavior of wheat was reinvestigated, and, at the same time, the chemical changes caused by differences in phosphorus nutrition during early development were determined. It will be noted that the differences obtained in this work with different phosphorus treatments are small, as would be expected, since the seeds contain some phosphorus. The results, however, are in most cases consistent.