90 THE SYNTHESIS OF PROTEINS 



angiosperms of varied affinity the power to bring about the 

 reduction, the best results being given by the potato, tubers 

 and shoots, and shoots of Solatium dulcamara. There is in 

 some instances a seasonal variation, thus Solatium dulcamara 

 was just active in October, but in June the same species, gath- 

 ered from various localities and at all times, gave good positive 

 results. The " reductase " is a thermolabile oxidizable sub- 

 stance precipitated from its solution by saturation with am- 

 monium sulphate. The best conditions for the manifestation 

 of its ability are a temperature of 45 C* and the presence of 

 an accelerator, such as acetaldehyde, which, obviously, are 

 artificial conditions ; at ordinary temperatures in the absence 

 of an accelerator the reaction is very slow. In the majority 

 of its properties it resembles the aldehydase of animal 

 origin, e.g. that of milk. If this be the mechanism for the 

 reduction of nitrate to nitrite in the plant, it must be assumed 

 that the conditions obtaining in the living cell are much more 

 favourable for the reaction to take place. The elucidation 

 of the problem was carried further by the concurrent work of 

 Eckerson f on tomato plants ; he found that the plant juice 

 in the presence of fructose, or glucose, and free oxygen easily 

 reduced nitrate to nitrite in a slightly alkaline medium, the 

 best reaction occurring at pH 7-6 ; the juice of nitrogen high 

 plants, containing nitrates and sugars in abundance, rapidly 

 reduced nitrate at 50 C. at pH j-6, and in these conditions 

 boiled juice was as effective as unboiled. In carbohydrate 

 high plants, containing much sugar but no nitrate, the re- 

 duction of added nitrates was localized to those regions which 

 gave a slightly alkaline reaction, i.e. the stem tip just behind 

 the growing region, cells of the leaves especially near the 

 phloem, cortical cells of the petioles, phloem parenchyma 

 of the stem bundles and adjacent cortical cells in the nodal 

 regions. It was also observed that newly formed amines 

 and amino acids, aspartic acid, asparagine, alanine, etc., ap- 

 peared in the regions of the nodes ; and in the petioles, in the 



* In experiments with plant juices, especially if continued over rela- 

 tively long periods of time, due precaution must be taken against bacterial 

 activity which may give rise to nitrite. 



t Eckerson : " Bot. Gaz.," 1924, 77, 377. 



