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|dc.contributor.author||Powrie, Leslie Ward||-|
|dc.title||The Distribution of Free Amino Acids in Diastella Salisb. and Leucopsermum R.Br. and some other members of the Proteaceae||en_ZA|
|dc.journal.institution||University of the Witwatersrand||en_ZA|
|dc.journal.contents||SUMMARY Diastella is a small Proteaceous genus endemic in the South Western Cape. Hall and Veldhuis (1985) list D. buekii as endangered, D. myrtifolia as critically rare, D. parilis and D. proteoides as vulnerable, and consequently the opportunity was taken to obtain some information regarding the chemical components of the species of Diastella. Diastella species had been placed variously in Protea, Leucadendron and Mimetes prior to the genus Diastella being formally accepted in 1911. Johnson & Briggs (1975) suggest that Leucospermum and Diastella have nearly parallel phylogenetic lines. Rourke (1976) suggests that Diastella probably arose from a member of Leucospermum section Diastelloidea. The occurrence in nature of a fertile putative bigeneric hybrid between D. thymelaeoides and L. (Sect. Crinitae) oleifolium corroborates some of Rourke's arguments. A phytochemical investigation was undertaken with a view to using the data obtained in a chemotaxonomic study to investigate the relationship between Diastella, Leucospermum, and the putative hybrid. Bell (1981) reports that free amino acids have been found to be reliable chemotaxonomic characters in plants and consequently free amino acids were used in the present study. Very little chemotaxonomic work has been done on the Proteaceae, and as it was important to compare the relationship between Diastella and Leucospermum with that of Diastella with other members of the family, the free amino acids in several other genera originating both within and without South Africa were analysed. Some duplicate and triplicate tests were carried out to confirm the reliability of the extraction in a methonol:chloroform:water mixture. Tests were carried out to determine suitable post-harvest conditions which were to be used to prevent the variation in the free amino acid composition of a sample so that reliable data could be obtained for use in this chemotaxonomic study. It was found that lyophilising, or short term storage in polythene bags at sub-zero or ambient (15°C to 25°C) temperatures prevented changes in the free amino acid composition of the leaves of L. oleifolium. Amino acids were detected using paper chromatography (solvents butanol:acetic acid:water (90:10:29) and water-saturated phenol) and by using the LKB 4150 Alpha automatic amino acid analyser. The original intention had been to analyse flower material from each species, but instrument failure caused a long delay after which the flowering season had passed for most of the taxa. Therefore, most of the analyses were done using leaf material. Consequently the data were not suitable for a proper taxonomic study using numerical taxonomic systems. Nevertheless, as a matter of interest, sixty-eight taxa were compared using a cluster analysis program which I wrote for use on the IBM PC XT computer, using the correlation coefficient (r) to compare species, and another program after Spencer (1984) using standard deviations to compute dissimilarity coefficients. The groupings obtained in the cluster analyses of the data showed that Diastella and Leucospermum were grouped with each other more frequently than with other genera. The other indigenous genera were frequently grouped together or with the exotic genera, and the exotic genera were frequently grouped with each other. Visual inspections of the tabular presentations of the data indicate some trends within taxonomic groupings, but these appear to indicate seasonal variation and probably have little taxonomic significance. From these data one cannot say that Diastella should be sunk into the genus Leucospermum, although when comparing taxa using the cluster analyses, a closer relationship with Leucospermum may have been indicated than that with other taxa which were compared with these two genera. Perold (1984b) indicates that while the phenolic lactones in Diastella and Leucospermum (Sect. Diastelloidea) are generally different, there was greater similarity between Diastella and L. (sect. Crinitae) oleifolium which is one of the presumed parent species of the putative bigeneric hybrid. For this reason it is felt that future work should investigate the chemical similarities between Diastella and Leucospermum section Crinitae as well as section Diastelloidea. The free amino acid data did not show any specific value, in this case, as a means of identifying the parent species of hybrids. Some differences were noted in the free amino acid compositions of the different sexes of Leucadendron and Aulax which may mean that one can use the free amino acid composition of a plant to identify its sex. Further investigation needs to be done in these areas as this could be economically important to the growers of these plants if they could determine the sex of a seedling. In conclusion, the chemical data indicate a similarity between Proteaceous genera in that there do not appear to be prominent novel free amino acids such as is the case among some members of the Fabaceae (i.e. a similarity by absence rather than by presence). Thus I do not feel that one can use the data obtained in this work to make any conclusions about the value of using free amino acids as taxonomic characters in the Proteaceae, other than that they can vary between organs, they change with the seasons, and they can alter between harvest and extraction and one must work within these limitations. There are better similarities observed between the flavonoid compositions than the free amino acid compositions of Diastella and L. oleifolium, the one presumed parent of the putative bigeneric hybrid and further study should be undertaken into the compositions of these and other chemical compounds in Diastella and sections Diastelloidea and Crinitae of the genus Leucospermum.||en_ZA|
|dc.journal.shorttitle||The Distribution of Free Amino Acids in Diastella Salisb. and Leucopsermum R.Br. and some other members of the Proteaceae||en_ZA|
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