| Abstract: | Summary Structural viscosity of plasm in plants varies over a wide range under the influence of a number of different stimuli, as both internal and surrounding factors are bound to affect it. If viscosity is regarded as an index of the dispersion degree of plasmatic colloids, it will be easily gathered that, parallel with it, also the reactive surface of these is subject to both quantitative and qualitative variations. The result is that such stimuli as determine the aforesaid variations in the living plasm structure, ultimately should have a bearing on the intensity of all such functions as are controlled by plasm. Of all the stimuli bound to exert the effects referred to above, the Authors have devoted their special attention to auxins. Under their influence the plasm structure undergoes such modifications — which can be appraised with the plasmolysis method — that an increase in viscosity is noted, the latter phenomenon being followed — in the Authors' opinion — by an increase in the dispersion degree of the plasmatic colloids. Consequently, several functions are enhanced, the most evident of these being the cells' growth. On the other hand, in such cells where the membrane have reached such a degree of evolution as to be no longer extensible, the auxins cause the same phenomena as in the plasm, without this being, however, accompanied by a resumption of the growing process. The Authors have expressed the opinion that plants may have a way to regulate the rate of such functions as are controlled by plasm not only by producing some substances wich, by causing a higher dispersion of the plasmatic colloids, act as stimulants, but also by producing some other substances having an opposite action; these substances, by exerting the contrary effect on the plasmatic colloids, would act as inhibiting agents. According to this assumption the auxin-type substances would be offest by some anti-auxinic substances, the actual extent of all functions, as well as the reaction to surrounding stimuli, would thus be controlled by a system of two classes of regulators having opposite effects, and by their relative amount. In the last few years several researchers have investigated the anti-auxin field; the Authors, however, specifically refer to the ascorbic acid (AA) as the mos widely diffused an the one having the most general significance. In this paper the Authors propose to study antagonist relation between auxins and AA under the limited standpoint of the effect that the two substances exert on the plasm's structural viscosity. Their experimental results have shown that a) the administration of AA, no matter which technique has been used, cuts the plasmolisys time (if concave in the controls, the latter become convex in the tissues treated), consequently decreasing the plasm viscosity. Such a reduction, which is noted in both the stem and roots, is, at least to a certain extent, proportional to the amount of AA actually to be found in the organs; b) the very same result is obtained when a variation is introduced in the surrounding conditions which, by affecting the photosynthetic process, influence the amount of AA which is present in the organ. More particularly, it has been found that, after being kept for a certain number of hours in the dark, the vegetal organs — notably the leaves and green stems — contain far lower amounts of AA than those which could be found when the same organs were exposed to the light. Likewise, the plasm viscosity is far higher in the dark than in the light. Etiolated plants, too, contain a far lesser amount of AA than the controls which have grown in the light, and their plasm is far more viscous than in the green controls. The experimental introduction of AA, anyway, lowers the plasmatic viscosity both in the etiolated specimens and in the controls. The roots, wich are extremely poor in AA contents as compared with the green organs, also have a far more viscous plasm; c) the antagonist relation between the action of the AA and the substances having an auxinic action is also indirectly evidenced by the AA being capable of cutting or even offsetting the action of the auxinic type substance. As a matter of fact, in such plants as have been experimentally enriched in their AA contents the plasm viscosity undergoes only a very slight variation subsequent to the administration of substances exerting an auxinic action. It is, anyway, a well-know fact that roots, being extremely poor in AA as compared with the stem, are influenced to a far larger extent than the latter by the action of all growth-promoting substances; d) AA is not a specific antagonist of the auxins. As a matter of fact, it has been found that it opposes the action developed by indoleacetic and indolebutyric acids, as well as the action exerted by some other substances, such as xanthine, uric acid and colchicine whose auxin-like action on both plasm viscosity and cellular enlargement has already been detected. |
