Distribution of cellular amino acids, protein, and total organic nitrogen during fruitbody development in Flammulina velutipes. I. Growth on sawdust medium

Abstract

Dry weights of stipes and pilei of Flammulina velutipes grown on nutrient-supplemented sawdust increased throughout the growth period. The pilei weighed only slightly less than the stipes. Amounts of total organic nitrogen, α-amino nitrogen, and alkali-soluble protein increased in the whole pileus and stipe as the fruitbodies elongated, but the concentrations on a dry weight basis decreased although they were always highest in the pileus. The concentration of alkali-insoluble nitrogen increased in both structures and was highest in the stipe. Concentrations of total nitrogen and protein in surface mycelium did not change significantly when fruitbodies formed but increased markedly when their growth ceased. An average of 8.3 mg dry weight of spores containing about 0.6 mg of nitrogen was released during the life of the fruitbody. Changes in 18 free and 17 protein amino acids were followed quantitatively in the pileus and stipe. Glutamic and aspartic acids and alanine were always among the four predominant free amino acids. Lysine and arginine concentrations remained low in the stipes but increased considerably in the expanding pilei. Ornithine levels increased strongly in the stipe during the early part of rapid elongation but remained almost constant and low in the pilei. Free proline was detected only in traces. Valine became the most abundant protein amino acid during elongation, especially in the stipe. There was very little bound methionine and cystine. In surface mycelium levels of free amino acids were low before fruiting and close to the end of fruitbody growth. Protein amino acids increased during that interval but their proportions remained virtually unchanged and valine was not predominant. The concentration of urea remained very low in both pilei and stipes during their growth.