Methionine and cystine content of two strains of alfalfa as influenced by different concentrations of the sulfate ion

Two clonal lines of alfalfa, C-3 and C-10, which were suspected of having different methionine and cystine content under identical growth conditions were grown in the greenhouse in flint-shot quartz sand in nutrient solutions with concentrations of the sulfate ion varying from 0 to 81 ppm. The plants were analyzed for the two sulfur-containing amino acids, methionine and cystine, and also for total sulfur and total nitrogen. Similar studies were conducted on the selfed progenies of these two clones. The yields of the C-3 plants were generally higher than those of the C-10 in both clones and S1 plants. Also, the C-3 plants had a much better appearance at the lower levels of sulfur. The data indicate that there is a considerable difference in the ability of these two strains to synthesize both methionine and cystine with a given amount of sulfur, C-10 having the higher efficiency of the two. These differences, on the average, tend to be more marked at the lower levels of sulfur. This relationship exists in both the clonal lines and the selfed progeny. However, there is no consistent relationship between the clones and their progeny with respect to total sulfur and total nitrogen. Total nitrogen was higher at the lower levels of sulfur, decreasing as the concentration of sulfur increased. The per cent methionine and cystine increased with increasing concentrations of sulfur. However, there was a tendency for these percentages of the amino acids to level off at the higher concentrations. Even at the highest concentration of sulfur the methionine and cystine were too low to make alfalfa a balanced protein. The results show that the total nitrogen or total sulfur is not always a criterion of quality in alfalfa. Total nitrogen was highest at the low levels of sulfur. Conversely the methionine and cystine were lowest at these lower levels. This suggests that erroneous conclusions concerning quality may be drawn from total nitrogen analysis.