SEED GALACTOMANNAN IN THE CLASSIFICATION AND EVOLUTION OF THE LEGUMINOSAE

The galactomannans from seeds of 28 Brazilian legume species were extracted and analysed, and these data were added to those of 23 others previously presented. Among the species of the subfamily Caesalpinioideae studied, 84.6% contain galactomannan in their seeds, whereas this polysaccharide was found in 52 and 46.6% of the Mimosoideae and Faboideae, respectively. Higher galactomannan yields were found in seeds of Caesalpinioideae than in those of Mimosoideae and Faboideae. Furthermore, the galactomannans of Caesalpinioideae presented higher mannose:galactose ratios. This pattern did not change when further data available for 71 species were added. Considering the evolutionary pattern accepted for the Leguminosae in which Mimosoideae and Faboideae are derived from Caesalpinioideae, the data obtained suggest that in the course of evolution there was a decrease in galactomannan content, together with an increase in the proportion of galactose present. These features of galactomannan are also reproduced both at subfamilial and tribal levels. The yield and composition of seed galactomannans from tropical legume species are discussed in terms of the possibility that this multifunctional polysaccharide could be an important factor for the adaptation (through different strategies) of these species to the tropical humid, semi-arid and arid climates.