Galactomannan, soluble sugar and starch mobilization following germinationof Trigonella foenum-graecum seeds

Galactomannan reserves in the endosperm of intact fenugreek (Trigonella foe num-graecum) seeds were mobilized in part by endo-beta-D-mannanase (mannan endo-1,4-beta mannosidase, E beta M, EC 3.2.1.78) activity. The hydrolytic products, mannose and galactose, applied to isolated endosperms at physiolo gically relevant concentrations enhanced E beta M activity; but at higher c oncentrations, E beta M activity and its secretion were inhibited. Increase s in glucose, fructose, and sucrose in the embryo reflected the mobilizatio n of the galactosyl-sucrose sugars therein and, presumably, the uptake of t he hydrolytic products of galactomannan breakdown from the endosperm. Concu rrent with the accumulation of both axial and cotyledonary starch, with tim e and with the incubation of isolated seedlings in sugar solutions, there w ere increases in the steady state amounts of transcripts of both the large and small subunits of adenosine diphosphate glucose pyrophosphorylase (gluc ose-1 -phosphate adenylyl-transferase, EC 2.7.7.27), the key regulatory enz yme of starch synthesis. The corresponding sugar, adenosine diphosphoglucos e, accumulated only within the cotyledons after starch began to decrease. A ctivity of the starch degradative enzyme Fenugreek (TrigoMelln foenum-gmecu m L.) seedlings present an interesting opportunity to study the regulation of carbohydrate mobilization following germination because three different types of carbohydrates (galactomannans, soluble sugars including the,oalact osyl-sucrose sugars, and starch) are utilized dur ing their establishment [ 15-18]. The major source of stored carbohydrate reserves in the dry fenugre ek seed is the galactomannan contained within the endosperm cell walls [16] . These are mobilized during early seedling growth following the production and secretion of hydrolytic enzymes (agalactosidase (EC 3,2,1.22), P-manno sidase (EC 3.2.1.25), and mannan endo-1,4-P mannosidase (EC beta-amylase (E C 3.2.1.2) increased in the cotyledon as starch started to decline, althoug h low amounts of alpha-amylase (EC 3.2.1.1) were constitutively present. (C ) Elsevier, Paris.