Composition and Distribution of Free Amino Acids in Flatpea (Lathyrus sylvestrisL.) as Influenced by Water Deficit and Plant Age

Abstract

Drought-stressed flatpea (Lathyrus sylvestris L.) plants from 8 to 22 weeks old were analysed for nitrogen, soluble protein and free amino acids. An increase in nitrogen and free amino acid concentrations and a decrease in soluble protein level were observed in roots of plants up to 16 weeks old. The cumulative concentration of free amino acids increased with drought stress. Tissue concentrations of 2, 4-diaminobutyric acid (1.6–2.6% of the dry weight) were highest in leaves. Levels increased steadily, nearly doubling, in leaves and stems between weeks 10 and 16. Levels in drought-stressed leaves were, on average, 11.9% higher than those of controls. Estimated concentrations of a mixture of 4-aminobutyric acid and an unknown amino acid were highest in stems, increased in this tissue with age and tended to increase in stems and leaves and decrease in roots in response to water deficit. Levels of the mixture of homoserine and another unidentified amino acid were not influenced by age or water status of the plants. Root concentrations of asparagine, arginine, glutamine, aspartate, and another prominent, unidentified amino acid increased with plant age and reached a peak at the time of flowering (14 to 18 weeks). Only the concentration of the unknown compound was elevated following drought stress. Concentrations of valine, isoleucine, leucine, phenylalanine, and methionine also increased during this period and were elevated in drought-stressed plants. Proline levels increased with plant age and drought stress, but proline accounted for only about 10% of the total free amino acids in the drought-stressed plants.