Physiological Studies in Plant Nutrition

Abstract

A survey by means of paper chromatography of the free amino-acids in barley leaves at different stages of development is described. The plants were grown in sand culture, using a variety of nutrient solutions, the most important variable being potassium supply. In general, the amino-acid distribution is not greatly affected by nutritional differences. Potassium deficiency results in much increased contents of the amides, especially asparagine, and reduced amounts of the corresponding acids. Other acids increased under these conditions are serine, leucine, tyrosine, and phenylalanine, but the most characteristic changes occur in -the basic constituents; lysine and arginine are increased, and an unknown basic substance accumulates very characteristically. Accumulation of this substance (probably an amine) is checked by the presence of either sodium or rubidium in the culture solution, almost as effectively as by increased potassium supply. Extreme potassium deficiency yields chromatograms closely resembling those from more moderately deficient plants. When a low rubidium supply accompanies potassium shortage the disturbances occasioned by potassium deficiency, both in growth and in amino-acid distribution, are diminished, but a higher rubidium supply leads to toxic symptoms in the plant; large increases in the contents of the two amides and of their parent acids are then found, this being the only condition encountered that leads to simultaneous accumulation of both these types of substances.