Free and protein amino acids of vicia faba l

Abstract

Sources of carbon for the developing fruits Of Vicia faba L. variety triple white were investigated. Attached leaves and pods were allowed to photosynthesis in [(^14)C]-labelled carbon dioxide. Leaves, pods and seeds were extracted separately with trichloroacetic acid. Amino acid and radioactive analyses were carried out on both the trichloroacetic acid soluble (non-protein) and insoluble (protein) fractions. Quantitative analysis of 90 min leaf photosynthesis indicated that a proportion of new photosynthate is rapidly exported from the leaf. Retention in the leaf of some labelled carbon was demonstrated during a 16 hour chase period. Evidence for protein synthesis from newly formed photosynthate is presented, together with evidence for the rapid turnover of such protein. Labelled amino acids and sugars were shown to be present in the petiole of a leaf photosynthesising in [(^14)C] – CO(_2). Leaves near the plant base contributed carbon to xylem sap amino acids. The bloom node leaf was shown to export preformed sugars and amino acids to the developing (20-35 day old) pod and seeds. Some translocate from the leaf entered the seed directly, but more than half was metabolised in the pod before being re-exported to the seeds. Pod photosynthesis was shown to involve labelling patterns like those of leaf photosynthesis, but to provide the seed with a different, and partly complementary, set of amino acids. Seeds were shown to have a carbon source during the night when transpiration and photosynthesis are negligible. The likelihood of stem tissue functioning as this carbon source is discussed. Bleeding sap from decapitated plants was analysed, and its relationship to xylem sap discussed. Sap contribution to the developing seeds is considered. Quantitative estimates are made of the carbon contribution from leaves and pods to seeds, and these are compared with the results of other workers. Seeds are shown to be capable of amino acid synthesis and interconversion, particularly of compounds readily synthesised from respiratory intermediates. Protein synthesis in leaves, pods and seeds is demonstrated, and the nature of the seed protein is discussed.