Comparative Biochemical and Morphological Studies of Acacia sophorae (Labill.) R. Br. And A. longifolia (Andrews) Willd

Abstract

Biochemical as well as morphological differences justify the retention of Acacia sophorae (Labill.) R.Br. as a distinct species rather than a variety of Acacia longifolia (Andrews) Willd. The seeds of A. sophorae are larger, with a water content between 6 and 7 %. The water content of A. longifolia seeds may be higher (6-10%). The seed coat accounts for c. 40% of the seed mass, but this value also is more variable for A. longifolia (33-43 %). Although the salt-extractable protein content of the seed is similar in both on a dry weight basis (12-13% whole seed, 19-20% embryo), qualitative and quantitative differences are evident in the electrophoretic patterns of albumin and globulin fractions, which were studied in a range of gels of different acrylamide contents (4.0-7.0%). Slopes of mobility (as 100 x log₁₀(RF x 100)) v. acrylamide content of gel were obtained for more than half the protein bands observed. These data indicate that proteins of comparatively low molecular weight (50,000-100,000) constitute a major proportion of the total protein stored in the cotyledons of A. sophorae, whereas proteins of intermediate to high molecular weight occupy a much greater proportion of the total reserve protein in A. longifolia cotyledons.

The globulin designated G6, of molecular weight c. 250,000, was found to exhibit differences in subunit composition on s~s-polyacrylamide gel analysis. Subunits of molecular weight 72,000, 61,000, 45,000, 36,000, 31,000, 16,000 and 11,000 are present in apparently equal proportions in the G6 globulin from A. longifolia. By comparison, the G6 globulin from A. sophorae lacks subunit IV, consisting of subunits of molecular weight 72,000, 61,000, 45,000, 31,000, 16,000 and 11,000 in the ratio 1/1/2/1/1/1.

No differences were observed in the profile of non-protein amino acids from the seeds. The flavonoid composition of the seeds also appeared to be identical for both acacias, with five areas resolved by two-dimensional chromatography for each. In contrast, the flavonoid composition of the phyllode is more complex in A. sophorae; a maximum of 11 areas were resolved from extracts of A. sophorae phyllodes, compared with only five areas for A. longifolia.