Effect of uracil, thiouracil, & guanine on cold resistance & nitrogen metabolism of alfalfa.

Persistence of plants under conditions of low temperature is related to their inherent ability to make metabolic adjustments conducive to the maintenance of their living processes, a phenomenon referred to as cold resistance. For ages efforts have been directed toward illucidation of the mechanism(s) which enables certain plants to live during periods of sub-freezing temperatures. Investigations (2, 3, 5, 8, 10-12) have revealed close associations between cold resistance and specific nitrogenous constituents of alfalfa. Inasmuch as certain mineral constituents (4, 6) and carbohydrate fractions (1, 3, 5, 9) have been shown to be closely associated with cold resistance in alfalfa, it has been difficult to evaluate the role and importance of the nitrogenous constituents during cold resistance development. Kessler (7) reported that the free amino acids and the protein nitrogen content of olive trees and grape vines sprayed with uracil increased whereas a concomitant decrease was noted with the use of thiouracil. That similar changes might be induced in alfalfa with these metabolites was very suggestive. It also seemed reasonable to believe that this might be a means of studying in detail the relationship between nitrogenous constituents and cold resistance development. Experimental work began in 1957 on a preliminary basis. Early fall spray applications of several chemicals were made on a 4 year old stand of Vernal alfalfa. Stand counts the following spring indicated that guanine (0.3 lb/acre) significantly (5 % level) reduced the percentage of winter killing. With uracil, the reduction in winter killing was not quite significant at the 5 % level. No chemical analyses were made on the plant tissue. This report describes the results of the study designed to investigate the influence of uracil, guanine, and thiouracil on the cold resistance and nitrogen metabolism of alfalfa. Specific objectives were to determine A, whether cold resistance development and nitrogen metabolism would be affected by these chemicals, and B, if any association existed between certain nitrogen fractions and cold resistance development.