Role of β‐amylase in starch metabolism during soybean seed development and germination

Differences in starch metabolism during seed development and germination of two soybean [Glycine max (L.) Merrill] genotypes with normal seed β‐amylase activity [‘Williams’ (Sp1^b and ‘Altona’ (Sp1^b)] and two soybean genotypes with undetectable seed β‐amylase activity [‘Chestnut’ (Sp1^au) and ‘Altona’ (Sp1)] were investigated. Starch and soluble sugar profiles were essentially the same during seed development and germination. Total amylase activity of Williams and Altona (Sp1^b) peaked just prior to seed maturity and then dropped off slowly; whereas, the total amylase activity of Chestnut and Altona (sp1) was very low throughout seed development and germination. The differences in amylase activity between Altona (Sp 1 ^b) and Altona (sp 1) was also seen in leaves. α‐Amylase activity was similar in the four genotypes when β‐amylase was inhibited with Hg²⁺ but was higher in the two genotypes with normal β‐amylase activity when β‐amylase was inhibited with heat plus Ca²⁺. Low levels of starch phosphorylase activity were detected throughout seed development and germination, and the activity was similar in three of the genotypes and higher in Altona (sp 1). The protein, oil and oligosaccharide contents of mature seeds of the four genotypes were similar. Altona (sp 1 ^b) and (sp 1), which appear to be near isogenic lines, were not different in any morphological character or yield. Altona (Sp 1 ^b) showed greater hydrolysis of soybean seed starch than Altona (sp 1), but the evidence indicates that the mutation resulting in greatly reduced or missing β‐amylase activity has no effect on starch metabolism of developing and germinating soybean seeds.