Characteristics of Sugar, Amino Acid and Phosphate Release from the Seed Coat of Developing Seeds ofVicia fabaandPisum sativum

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Abstract
After removal of the embryo from developing seeds of Vicia faba L. and Pisum sativum L., the ‘empty’ ovules were filled with a standard solution (pH 5.5). Seed coat exudates of both species were collected during relatively long experiments (up to about 12 h) and the concentration of sugar (mainly sucrose), amino acids and phosphate in the exudate measured. A discussion is presented on the amino acid/sugar ratio and the phosphate/sugar ratio in the seed coat exudate. A pretreatment (15 min) with p-chloromercuribenzenesulphonic acid (PCMBS) reduced the release of sugar, amino acids and phosphate from broad bean seed coats. After excision of ‘empty’ ovules of Vicia faba and Pisum sativum from the maternal plant, 2–4 h after this treatment a strong difference became visible between sucrose release from excised seed coats and sucrose release from attached seed coats. Similarly, when the rate of phloem transport of sucrose into an ‘empty’ ovule of Vicia faba or Pisum sativum was reduced by a sub-optimal mannitol concentration in the solution, a reduced rate of sugar release from the seed coat could be observed. Excision and treatment with a sub-optimal mannitol concentration reduced the release of amino acids to a lesser extent than for sucrose. These treatments did not reduce the rate of phosphate release from the seed coat.