Pretreatment and Chloride Uptake in Vallisneria Leaves. Influence of light, sugar, salts and pH on subsequent Chloride accumulation

The results of the preceding research show that the rate of uptake of chloride ions by Vallisneria leaves, may be influenced by various pretreatments of the material during a shorter or longer period. By the method described in Chapter 2 the chloride uptake per hour was determined. If during a pretreatment in water the Vallisneria leaves are exposed to light, the rate of chloride uptake increased, irrespective of the fact whether the uptake occurs in the light or in the dark. By our aerating with air free from C02 during the pretreatment as well as during the uptake the formation of carbohydrates in the light has been inhibited as much as possible. The effect of the light pretreatment is comparatively strongest if subsequent uptake takes place in the dark. If this effect is due to the formation of a specific substance during the pretreatment in the light, it follows from this investigation that it continues to be active for at most 24 hours. Sometimes there is not any effect left after 12 hours. A pretreatment of 3-5 hours in water in the light is sufficient to give an appreciable increase in chloride uptake. Administration of sugar during the pretreatment or during the uptake influences the course of subsequent uptake. The effect of the specific substance formed under the influence of light during the pretreatment is not changed by this addition of sugar. Sugar administered during the pretreatment may influence the subsequent chloride uptake in two ways; 1) by an inhibitory action during the first few hours of the uptake period, 2) by a stimulating influence after this initial period. The first effect may be due to a dehydration of the plasm, which alters the conductivity for ion transport. The second effect may be a metabolic influence. The absorbed sugar might supply energy via metabolism for the accumulation of chloride ions. Also carbohydrates formed in photosynthesis can stimulate the chloride uptake. This appears to depend on the amount of sugar already present in the material and on the products formed from this sugar. By a pretreatment with different salt solutions the chloride uptake is sometimes inhibited, sometimes it is not. The following salts have an inhibitory effect: NaCl, LiCl, CaCl2, MgCl2, SrCl2, LaCl3 and K2S04. Other salts such as KNOs, NaNOs, Ca(N03)2, Mg(N03)2, Sr(N03)2, 0aSO4 and Na2S04 have no effect. From this it appears that the chloride uptake is inhibited, when there is a particular combination of an anion and a cation present during the pretreatment. The strength of the inhibition decreases according to the sequences La > Ca > Na, Li > Na > K and Sr > Mg = Ca. Though the inhibition is due to an influence of the cations, yet there must also be a certain influence of the anions. They may be significant through theire influence on the absorption or non absorption of the cations. The inhibitions due to these cations appear to be entirely or partly reversible. Only LaCl3 causes an irreversible inhibition. Light is an important factor for these inhibition phenomena. Only by a pretreatment in the light these ions have an effect on the subsequent uptake. Here too this may be due to the penetration of the cations into the plasm. From the experiments with various calcium chloride concentrations it appears that the inhibition grows stronger according as the concentration increases. Also the duration of this CaCl2 pretreatment is significant. This indicates an influence of the amount of ions absorbed in the plasm. The pH during the pretreatment proves to influence the subsequent chloride uptake. Only at pH 3 chloride is released during the pretreatment. Calcium inhibits this release but it has no influence on the effects of various pH’s on subsequent chloride absorption.