PHYSIOL. PLANT. 53: 429-434. Cupenhagen 1981 Role of p-amylase im starch metabolism during soybean seed development and germination D. F. Hildebrand and T. Hymowitz Hildebrand, D, F. and Hymowitz, T. 1981. Role of P-amylase in starch metabolism during soybean seed development and germination, -Physiol. Plant. 53: 429^34. Differences in starch metabolism during seed development and germination of two soybean [Glycine max (L.) Merrill] genotypes with normal seed P-amyiase activity {'Williams' (Sp,") and 'Altona' (Sp,'')] and two soybean genotypes with undelectable seed p-amylase activity ['Chestnut' (5/1/") and 'Altona' (sp,)] were investigated. Starch and soluble sugar profiles were essentially the same during seed development and germination. Total amyiasc activity of Williams and Aitona (Spi'') peaked just prior to seed maturity and then dropped off slowly; whereas, the total amylase activity of Chestnut and Altona {sp J was very low throaghout seed development and germination. The differences in amylase activity between Altona {Spi") and Altona (sp i) was also seen in leaves, a-Amylase activity was similar in the four genotypes when P-amylase was inhibited with Hg^* but was higher in the two genotypes with normal P-amylase activity when P-amylase was inhibited with heat plus Ca^"', 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 i). The protein, oil and ohgosaccharide contents of mature seeds of the four genotypes were similar, Altona {sp i") and (sp J, which appear to be near isogenic lines, were not different in any morphological character or yield. Altona (Sp,") showed greater hydrolysis of soybean seed starch than Altona {sp,), bot the evidence indicates that the mutation resulting in greatly reduced or missing p-amylase activity has no effect on starch metabolism of developing and germinating soybean seeds. Additionai kev-^ s: Glycine max — a-,amylase — phosphorylase — sugars. D. f. Hildebrand and T. Hymowitz, Department of Agronomy, University of Illinois, Urbana, Hiinois 61801, U.S.A. Introduction Amottg the main enzymes itivolved in starch breakdown in plants are a- and P-amylase and starch phos- phorylase. Juliano and Varner (1969) investigated the role of these enzytnes in the starch metabolism of ger- tninating peas and concluded that a-amylase was the major enzyme responsible for initiating the degradation of the starch granules and that p-amylase and starch phosphorylase acted on the products of hydrolysis of the starch by a-amylase. Dunn (1974) found that native starch granules prepared frotn maize seed were not sus- ceptible to hydrolysis by barley p-amylase, and that barley P-amylase only very weakly stimulated the pro- duction of reducing sugars by Bacillus subtiUs a-amylase. Wilson et al (1978), however, found that P-anaylase from barley was capable of hydrolyzing iso- lated starch granules,from soybean seeds imbibed for 18 h. Mature soybean seeds contain high levels of p-amylase (Adams et al. 1980, Birk and Waldman 1965)i, but the a-amylase and starch phosphorylase levels are very low (Peat etal. 1949, Yin and Son 1948). Although soybean seeds contain very httle starch at maturity (Wilson et al. 1978), they contain 10 to 15% starch at earlier stages of development and during ger- mination (Adams et al. 1980, Yazdi-Samadi et al. 1977). Received 4 May, 1981 29 Physiol. Plaoi. 53 0031-9317/81/120429-06 $03.00/0 ©1981 Physiologia Plantarum 429