Changes in the Individual Free Amino Acid Concentrations in the Petals of Carnations during the Vase Life of the Flowers

Abstract

Changes in the concentrations of individual free amino acids of petal tissue of carnations (Dianthus caryophyllus L. cv. «White Sim») were studied. In addition, the respiration rate and moisture content of petals were determined as indicators of metabolic activity and degree of senescence. The concentrations of glutamine, glycine, histidine, methionine, phenylalanine, proline, serine, threonine and valine increased throughout the vase life of the flowers. The concentrations of arginine, aspartic acid, isoleucine, leucine, lysine and tyrosine increased initially but decreased thereafter. There was a noticeable decline in the concentration of α-alanine, γ-aminobutyric acid and asparagine immediately prior to the climacteric maximum of respiration, whereas during all other times an increase was evident. The concentration of all other free amino acids fluctuated. During the early stages of the vase life of the flowers the increase in free amino acid content is probably due to a de novo synthesis. Proteolysis may contribute significantly to the accumulation of free amino acids during the later stages of the vase life. The decrease in concentration of certain free amino acids towards the end of the vase life may be ascribed to their assimilation as respiration substrates and/or their incorporation during the synthesis of degrading enzymes. The observed accumulation of free ammonia may give rise to an accumulation of asparagine and glutamine with a resultant decrease in aspartic and glutamic acids. Wilting could stimulate the synthesis of α-alanine and γ-aminobutyric acid, whilst inhibiting the synthesis of others such as aspartic acid. Inhibition of amino acid synthesis and the loss of cell integrity may also play an important role in the observed changes in free amino acid concentration.