ANALYSIS OF THE PROCESS OF ANION UPTAKE OF INTACT MAIZE PLANTS

In all experiments sets of intact maize plants were used, high salt as well as low salt ones. As a rule the phosphate uptake was determined and occasionally the nitrate uptake. In some experiments the growth was determined by tracing the development of the shoots. The starting point was the examination of the course of the uptake of phosphate and the growth in light and darkness. Initially the uptake increases in light, in particular with low salt material. But with an intensive illumination the uptake by high salt mateiial also increases. After some days a constant level is attained. In darkness the uptake decreases. The extent to which this occurs with low salt material depends on the degree in which the plants have been turned into a high salt condition. This can be regulated experimentally by the use of various concentrations. The growth of the shoot increases mostly only a little during the first days of an experiment. Afterwards it remains at a constant level but shows a typical day and night rhythm in spite of constant conditions. In darkness the growth drops. Generally uptake and growth progress parallel to each other, but there are exceptions. It appeared from analysis of the plants, that a large amount of the phosphate absorbed is transferred to the shoot. With an extremely low salt condition the amounts present in the shoot and root are almost equal. If the plants are standing on a nutrient solution, a large part is transferred to the shoot. In explanation of the behaviour observed, the uptake from the external solution was assumed to depend on a number of physiological factors: fixation by growth processes in root and shoot; accumulation in the vacuoles; secretion into the vessels; loss from the shoots. The importance of accumulation and secretion is obvious. The effect of the loss from the shoot (as far as it can be studied from a single experiment) could not be obtained. On the other hand growth proved to be of primary importance. In order to show this, high nitrate, low phosphate plants were grown. By lack of phosphorus, growth was checked. Some nitrate absorption was possible but it soon came to a standstill, the plants coming in a nitrate saturated condition as a result of the daily renewal of the solutions. By phosphate supply the synthetic processes could get started. This leads on the one hand to a renewed nitrate absorption, on the other hand to the promotion of the visible growth. All processes mentioned are connected with metabolism.