The sources of free proline and asparagine in field bean plants, Vicia faba L., during and after a short period of water withholding

Abstract

Interconversions between free and bound amino acids were studied in the organs of 8-weeks-old field bean plants during two days of water withholding and one day after re-supply of water. At the end of the period of water stress, the increase in proline concentration in the vegetative parts was 10- to 25-fold but in the generative parts not more than 3-fold. The largest amount of proline was found in the lower part of the stem and in the roots; most protein was broken down in the young leaves. During the first day of water deficit, the existing pool of free and bound amino acids served as sources of accumulated proline and asparagine. The amounts of proline and asparagine which accumulated during the second day, came for 15% from the amino-transfering components (total of glutamine, glutamate, aspartate, alanine, serine and glycine), derived from protein. Of the total amount 85 % was newly synthesized from sources other than the amino acid pool. After re-supply of water, protein synthesis resumed. Asparagine proceeded to accumulate and the amount of proline decreased slightly. It is concluded that the system of amino-transfering components is directly involved in the reactions of the plant to water stress.