Abstract:

Guar (Cyamposis Tetragonoloba (L.) Taub.) is an important raw material for guar gum, in which galactomannan (GM) is the active component. GM is a main storage carbohydrate in guar seeds, which is an analogue to that of starch in cereal grains. Sucrose is a common precursor for the biosynthesis of GM and starch. Studies were made on the changes in sucrose synthetic enzymes and carbohydrate contents in guar plants, to understand the effect of soluble sugar biosynthesis on accumulation of endospermic polysaccharides in this special plant. Sucrose synthetase (SS) and sucrose phosphate synthetase (SPS) activities, compositions and contents of carbohydrates in guar leaves, seeds and pod peels were determined. The results showed that SS and SPS activities in leaves, pod peels and seeds decreased with the development of seeds. SS and SPS activities in the seeds were higher than those in leaves and pod peels. SS activity showed a positive correlation with SPS activity in seeds. Glucose content was significantly higher than sucrose content in leaves. Contents of soluble sugar and sucrose increased in pod peels, till the diameter of seed was about 5 mm, and then decreased quickly, they were well correlated with each other. Soluble sugar of seeds decreased gradually during seed development. Sucrose content in pod peels showed a negative correlation with total carbohydrate contents (soluble sugar + polysaccharides) in seeds, and it is an important source of the carbohydrate in the seeds. It took part in the carbohydrate synthesis and also the establishment of seed sink. Carbohydrates in the leaves, as sucrose transported to and temporarily deposited in the pod peels in the early period of seed development, and then transported rapidly from pod peels into seeds at the seed diameter of about 5 mm. However, there was less sucrose in seeds than in pod peels, it suggested that sucrose was inverted into other reduced sugars after transported into seeds. Starch accumulated quickly in the seeds when the seed diameter was about 4 to 5 mm, a critical period for pod peels changing from ‘sink’ to ‘source’, and galactomannan increased dramatically in the seeds after that.

Key words: Cyamposis tetragonoloba (L.) Taub., Sucrose, Soluble sugar, Galactomannan, Sucrose synthetase, Sucrose phosphate synthetase