Absorption and Transport by the Tentacles of Drosera capensis. V. Influence on the transport of substances inhibiting enzymatic processes

The tentacles of the leaves of Drosera have the function of secreting to the leaf substances which are liberated by the disintegration of the insects. An extensive survey has been given of the method of research. The difficulties met have been summed up in VIII pp. 98 and 99 and in the methodical part it has been stated to what extent it has been possible to find a working method giving reliable results. The principal results of two previous publications, which had been published in Dutch in war time, have been summarized and supplemented with new data. The tentacles of Drosera capensis are genuine transport organs, which themselves retain the transport substance in hardly analysable quantities, but pass it on to the leaf. Important is the dependence on oxygen in the medium. Some substances are not transported in an anaerobic medium others only inhibited. The first set of substances is absorbed from a low concentration and accumulated in the leaf in a changed or unchanged form. We have called this active transport. In the latter case we have spoken of activated transport since a diffusion process acts an important part; pure diffusion, however, was not found for any substance, as withdrawal of oxygen always effects the transport somewhat. This points to influence of processes in the plasm, connected with metabolism. Amino acids, asparagine, glutamine, phosphates and ammonium are transported actively. For urea, thiourea, ammonium carbonate, caffeine, and others activation of the transport occurs in a different degree. The transport of amino acids, asparagine and glutamine on the one side and that of phosphate on the other side have in common that these substances are transported actively, but the nature of the transport differs for these two groups of substances. This specificity of the transport appears from summation experiments. For each substance the uptake depends on the concentration in the medium; already in fairly low concentrations a maximal rate of uptake is reached. Combination of different amino acids or of asparagine with an amino acid gives as long as the concentration is limiting summation until the saturation level for amino acids and asparagine has been reached. This indicates that they are all absorbed by the same system. Combination of an amino acid or asparagine with phosphate, however, gives of each of these substances absorption till saturation is attained. These systems must work independently. This led us in 1944 to draw up the hypothesis that during the transport the substances are combined with the plasm. Chemical reactions between the substances and the plasmatic particles must take place rendering absorption and transport possible. The summation experiments indicate that the nature of the binding of amino acids and asparagine is different from that of phosphates. The theory of the transport through combining the substances with the protoplasm based on these data (Arisz 1944) has been discussed in VIII pp 100 and 101. Some substances such as caffeine, antipyrine, and ammoniumcarbonate inhibit especially in a higher concentration the active transport of phosphates and amino acids. These substances inhibit aggregation as well. With the aid of substances inhibiting enzymatic processes, the relation of transport to metabolism has been investigated. Such investigations have, for instance, been made by Thimann and collaborators for the growth, the protoplasmic streaming and the active absorption of water and for instance by Lundegardh, Machlis and Robertson for the uptake of salts. The results of our experiments was that the wellknown inhibitors of glycolysis and respiration, KCN, Na-azide, jodoacetate and Na-arsenate all inhibit the transport of phosphate and asparagine. Dinitrophenol likewise inhibits the transport of these two substances, which points to the influence of energyrich phosphates on the transport process. Na-arsenate inhibits the asparagine transport. This likewise points to the significance of energyrich phosphates for the transport processes. As phosphate competes with arsenate, it is to be understood that arsenate has no influence on the phosphate transport. More specific is the behaviour of phloridzin and penicillin. The first substance only inhibits the uptake of phosphate, the last only the uptake of asparagine. These specific inhibitions prove that the theory previously formulated that the combination of phosphate with the plasm is of a different nature from that of asparagine and amino acids is correct. The glands of the tentacles can be cut off with a pair of scissors. Marginal tentacles treated in such a way behave essentially in the same way as tentacles with glands. They transport phosphate as well as tentacles without glands; this transport is likewise dependent on oxygen. The glands of the tentacles are, therefore, not essential to the active transport of phosphates. The transport of asparagine by the tentacles, however, is dependent on the presence of glands. For a low asparagine concentration 1/100 M, the transport is very slight. For a higher concentration, for instance 1/20 M, it may be greater, but the height of the transport in intact tentacles is not reached. The gland, therefore, has a specific influence on the uptake of asparagine. This reminds us of the influence of the gland on aggregation (Coelingh). Inhibitors of the respiration have partly the same influence on the transport of phosphate in tentacles without glands as with intact tentacles. KCN, Na-azide and Na-arsenite inhibit this transport. This proves that the transport in the tentacle pedicel is of the same nature as the transport in the intact tentacles. Various inhibitors gave no inhibition or a weaker one in tentacles without glands than in intact tentacles. This phenomenon has not yet been explained. It may be connected with the wounding or point to the fact that certain reactions are localized in the gland. Eosin is a dye which is used to render transport in the sieve tubes impossible. Eosin gives a complete inhibition of the transport in Drosera tentacles already in a very low concentration. Fluorescein has been used as an indicator of the transport in parenchyma cells and in sieve tubes. It causes a distinct inhibition of the transport in Drosera tentacles in a low concentration.