Enzymes concerned with sucrose synthesis and transformations in seeds of maize, broad bean and castor bean

Abstract

A comparative study of the activities of sucrose synthetase, sucrose phosphate synthetase, sucrose phosphatase and other enzymes in developing and germinating plant seeds was carried out to gain further information on the pathways involved in sucrose synthesis and transformation. Sucrose phosphatase has not previously been detected in seeds. In developing cotyledons of broad bean ( Vicia faba L.) and developing endosperm of maize ( Zea mays L.), tissues in which sucrose conversion to reducing sugars or sugar nucleotides is the predominant reaction involving sucrose, there was high activity of sucrose synthetase and relatively low activities of sucrose phosphate synthetase and sucrose phosphatase. In the cotyledons of germinating broad bean seeds, the scutella of germinating maize seeds and the endosperm of germinating castor bean seeds ( Ricinus communis L.), tissues in which sucrose synthesis is more rapid than sucrose breakdown, there were high activities of sucrose phosphate synthetase and sucrose phosphatase. Sucrose synthetase activity was also high in the scutella of maize and endosperm of castor bean. The activity of invertase was very low in all tissues. The results support the hypothesis suggested by several workers that in some plant tissues sucrose synthetase catalyses the breakdown of sucrose and that sucrose phosphate synthetase and sucrose phosphatase catalyse the synthesis of sucrose via sucrose phosphate. However, sucrose synthesis catalysed by sucrose synthetase cannot be dismissed since tissues also contain this enzyme.