Acacieae Ingeae

Yield 0%

Dimorphandra group

Yield j 8% M/G 4.4 * Ceralonia siliqua grou

Amherstieae

Peltophorum Caesalpinia grou

Yield 21%

Cassiiriae

Yield 23%

Sclerolobium group

Tropic a I tribes

Temperate

i enum-graecu

Genistoid aHianc

Yield 13%

Bauhiniinae

Cercidinae

understand the fine structure of the polymers. They found a direct correlation between the extent of hydrolysis of galactomannans with P-mannanase and the degree of gelling interactions with xanthan gum. The author suggested that gelling interaction was not absolutely dependent on long sections of unbranched main chains, as had been proposed by Morris et al. [35], since a mannose:galactose ratio of 2 provides conditions for interaction. More recently, Bressolin et al. [36] found that galactomannans with fully substituted main chains were still able to interact with xanthan.

Using isolated P-mannanases from guar and from Aspergillus niger, McCleary et al. [37] performed a thorough study on the fine structure of carob and guar galactomannans, associating data produced by controlled hydrolysis by the enzymes with a computer simulation of the process. They found that the galactose distribution in carob galactomannan is non-regular, with a high proportion of substituted couplets, lesser amount of triplets and absence of block substitution. This feature seems to be reasonably constant, since those authors reported that the patterns of oligosaccharides produced from galactomannans from guar and carob of different varieties were constant.

Because the fine structure of other legume species apart from guar and carob are not studied yet, it is not possible to make generalisations for the patterns of distribution of galactose branches in galactomannans of species of the whole family. Thus, in order to recognise how galactomannan structure varies within the species of the family Leguminosae, one has to rely on the proportion between mannose and galactose (M/G ratio). Such comparisons can be quite useful as will be discussed below.

4.2. Chemotaxonomy: occurrence of galactomannans in different legume species

Galactomannans are particularly abundant in the endosperm of seeds of Leguminosae (or Fabaceae), a family with the third largest number of species in the Plant Kingdom (ca. 18,000). This is permitting the utilisation of galactomannan as a taxonomic marker, the yield and mannose:galactose ratio being used for this purpose. As the number of analysed species increases, a better grouping is becoming possible and also a better understanding of the relationship of species with their habitats becomes feasible.

Table 1 shows a list of species distributed within the tribes of Leguminosae for which data on galactomannans are presently available in the literature. Some new data on recently analysed Brazilian native species mainly from the subfamilies Caesalpinioideae and Mimosoideae, are presented in Figure 1. In few publications, however, information on

Figure 1. Radiation of the main groups of the Leguminosae and relationships between yield and mannose:galactose ratio (M/G). The tree was drawn according to Polhill and Raven (1981) and the means were calculated based on the data compiled in Table 1. The lower part of the figure contains more primitive groups and at the top the more advanced ones. The gradual change in shades of grey from black to white indicate a gradual decrease in galactomannan yields and M/G ratios. White indicate that attempts of extraction resulted in absence of galactomannan. Names in normal font refer to groups in Caesalpinioideae, bold to Mimosoideae and italic to Faboideae. Names of the most studied species (Ceratonia siliqua, Cyamopsis tetragonolobus and Trigonella foenum-graecum) were added for general reference and are marked with (*). (**)Two of the main radiation groups (Dialiinae and Sclerolobium) do not have species studied yet. Xg=Xyloglucan.

species which do not contain galactomannan is provided. These are included in table 2 in order to broaden the view of galactomannan distribution throughout the tribes of the Leguminosae.

Although the proportion of studied species in relation to the total number in the Leguminosae is relatively low, most of the important taxonomic groups of the family are represented in published data (Table 1). The examination of the data arranged according to what are believed to be the evolutionary relationships in the Leguminosae as a whole [38], is shown in figure 1.

The three main radiation groups in the subfamily Caesalpinioideae (Ceratoniinae, Gleditsia and Cercidinae) tend to present higher yields and high M/G ratios. In the branch of Ceratoniinae, the high yields and relatively debranched galactomannans appear to be preserved during evolution.

In the branch that led from Caesalpinioideae to Mimosoideae a decrease in yield seems to be coupled with an increase in galactosylation (decreasing M/G ratio). In the more advanced tribes of Mimosoideae (Acacieae and Ingeae), galactomannan is virtually not present in mature seeds, whereas large frequency of occurrence is observed in the more primitive tribe Mimoseae.

Another group pointed as important in the radiation of Caesalpinioideae is the Sclerolobium group. Although no attempts appear to have been made to extract galactomannan from seeds of this group, many species of the directly derived group of Peltophorum and Caesalpinia have relatively higher yields and lower degree of branching with galactose, which are comparable to the ones from Cassiinae. On the other hand, the radiation leading to Amherstieae and Detarieae present species with very high contents of xyloglucan instead. In a separate branch of Caesalpinioideae, Cercidinae also displays very low degrees of branching (M/G=5.5), leading to Bauhiniinae, with similar yield averages (1012%) and higher degree of branching.

Comparing the main groups of Faboideae, the yield seems to have been maintained from the most primitive Sophoreae (11%) to the more advanced species of the Genistoid alliance (13%) and to the tropical and temperate advanced tribes through the Galegoid complex (10%), whereas the degree of branching increased (M/G ratios from 3.8 to 1.3 in temperate tribes). Among the groups classified by Polhill et al. (1981) as advanced tropical and temperate tribes, the degree or branching became very high whereas yield decreased in the temperate species and although galactose branching is approximately the same, the yield is higher in tropical species.

Altogether, the compiled results suggest that a general trend towards decreasing yield and increasing galactose branching (decreasing M/G ratio) is apparent in the Leguminosae during evolution (Figure 1)

The analysis of the changes in yield and M/G ratio within the subfamilies revealed a similar and clearer picture (Figure 3). As previously pointed out by Buckeridge et al. [56], there is a tendency towards decrease in yield and increase of galactose branching from the more primitive Caesalpinioideae to the more advanced species of Faboideae. The addition of data gathered from 1995 up to now indicate bimodal curves of yield and unimodal curves of mannose:galactose ratio. In Caesalpinioideae, one mode occurs between yields of 25-30% and corresponds to approximately 25% of the studied species in the subfamily. A second mode can be observed between 10 and 20% which contains almost 40% of the species (Figure 3A). In Mimosoideae a wider distribution of the species according to yield is

Table 1.

Compilation of published and original data on galactomannan yields (percentage of the dry weight of the seed) and mannose:galactose ratios for seeds species of Leguminosae. Species are taxonomically distributed according to Polhill and Raven [38]._

Table 1.

Compilation of published and original data on galactomannan yields (percentage of the dry weight of the seed) and mannose:galactose ratios for seeds species of Leguminosae. Species are taxonomically distributed according to Polhill and Raven [38]._

Subfamily/Tribe/Species

Yield %

M/G ratio

Reference

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