| Popis: |
Summary Net sucrose and amino acid efflux from excised seed-coat halves and cotyledons of developing seeds of Pisum sativum L. into a bathing medium (pH 5.5) was measured over a period of 5 h, after uptake from a solution containing a mixture of 3 H - and 14 C-labelled solutes. Net efflux of amino acids (α-aminoisobutyric acid, valine and asparagine) from seed-coat halves and cotyledons was strongly inhibited by p -chloromercuribenzenesulfonic acid (PCMBS). Net efflux of labelled sucrose was not markedly inhibited by a treatment with PCMBS; under certain conditions it was enhanced by PCMBS. The effect of a low-temperature (0 °C) treatment did not differ much from the effect of a treatment with PCMBS. Net efflux of labelled solutes from seed-coat halves and cotyledons was enhanced by KCN, but this effect was much more pronounced in the case of sucrose than in the case of amino acids. The parallel between seed-coat halves and cotyledons illustrates the point that the seed coat contains tissues with ≪cotyledon characteristics≫ (e.g. intensive resorption of sucrose). After unloading into the seed coat apoplast from the seed-coat unloading sites, amino acids encounter less resorption activity than sucrose. |
