Michelle van der Bank

A review of the use of allozyme electrophoresis in plant systematics.

Abstract The role of electrophoretic data is discussed as it applies to plant taxonomy and systematic studies. Neis (Am. Nat. 106 (1972) 283–292; Genetics 89 (1978) 583–590) genetic distances calculated for a large number of populations, species and genera were taken from published data. The relation between Neis genetic identity measures and taxonomic rank (populations, species and genera) are shown graphically. The graphs obtained in this way (from 3021 pairs of plant taxa) differ substantially from previous graphs published by Thorpe (Ann. Rev. Ecol. Syst. 13 (1982) 139–168; in: G.S. Oxford, D. Rollinson (Eds.), Protein Polymorphism: Adaptive and Taxonomic Significance, Academic Press, London, 1983, pp. 131–152) and Thorpe and Sole-Cava (Zool. Scripta 23 (1994) 3–18). These authors suggested that the divergence between the different taxonomic ranks is roughly similar across a wide range of taxa. The latter was based on values for 2664 (Thorpe, 1982) and 8060 (Thorpe, 1983) pairs of animal and plant taxa, but the plant data contributed little to the total. For any given taxonomic rank, we found that plants are genetically more closely related than animals (possibly with the exception of birds). This result is important because the empirical relationships of genetic distance measures, to different levels of taxonomic separation, is often used for distinguishing and identifying cryptic or sibling species where conventional methods are unable to resolve systematic problems.

Allozyme and DNA sequence comparisons of nine species of Encephalartos (Zamiaceae)

Phylogenetic relationships between Encephalartos altensteinii Lehmann, E. arenarius R.A. Dyer, E. horridus (Jacquin) Lehmann, E. latifrons Lehmann, E. lehmannii Lehmann, E. longifolius (Jacquin) Lehmann, E. princeps R.A. Dyer and E. trispinosus (Hooker) R.A. Dyer were studied, using E. ferox Bertoloni f. as outgroup. Three continuous and one discontinuous buffer systems were used and gene products of 14 enzyme coding loci were examined by horizontal starch gel-electrophoresis. Genetic variation was studied in a cultivated population of E. lehmannii and the average heterozygosity value for this population is 13.5%, which falls within the range reported for other cycad species. Fixed allele differences between the species studied was not found at any of the loci studied, which suggest that these species are closely related. DNA sequence analysis of rbcL and ITS 1 & 2 genes (1428 and 895 basepairs, respectively) confirmed the close genetic relationships between these taxa. According to ITS and rbcL sequences E. altensteinii and E. princeps are sibling taxa which form a sister group to E. arenarius, E. horridus, E. latifrons, E. lehmannii, E. longifolius, and E. trispinosus. The genetic distances between both groups were 0.12-0.47% for ITS and 0.08-0.16% for rbcL DNA. The results indicate recent (probably pleistocenic) speciation for this group of cycads, and the relationships are discussed with reference to affinities based on morphology and distribution.

Biochemical genetic variation in four wild populations of Aspalathus linearis (Rooibos Tea)

Abstract Four morphologically different populations of Aspalathus linearis were examined by horizontal starch gel electrophoresis to assess levels and patterns of genetic variation and to estimate the amount of genetic differentiation within and between populations. Leaf extracts were surveyed for 13 enzymes, and gene products revealed genetic variation at six (40%) of 15 protein coding loci. The percentages of polymorphic loci range from 6.67 to 26.67% (0.95 criterion), values of 1.07–1.40 were obtained for the mean number of alleles per locus, and average heterozygosities per locus were calculated at 0.016–0.096. The mean genotypic distance index (Nei, 1978) between populations was 0.034. Enzyme electrophoresis appears to be a suitable method for studying genetic variation in A. linearis .

Evolution of sprouting versus seeding inAspalathus linearis

We have tested the hypothesis that reseeding is a plesiomorphic character state and that sprouting is a derived state inAspalathus linearis, and that the latter is an adaptation to ensure fire-survival in a fireprone environment. Samples of five seeder and four sprouter populations of A.linearis were examined by horizontal starch gel electrophoresis to assess the amount of genetic differentiation within and between sprouting and seeding populations, and to determine the extent of gene flow between the populations. Leaf extracts were surveyed for ten enzymes and gene products revealed genetic variation at 13 (76%) of 17 protein coding loci. Allele frequency differences were found between sprouting and seeding populations and genetic distance values show that the sprouters are grouped separate from the seeders, thus providing support for the morphological data on which the above mentioned hypothesis is based. It is evident that evolution operates at the population level inA. linearis.

Lack of genetic differentiation between 19 populations from seven taxa of Sutherlandia Tribe: Galegeae, Fabaceae

Abstract Horizontal starch gel-electrophoresis was used to examine genetic diversity between geographically isolated populations of Sutherlandia tomentosa, S. frutescens, S. frutescens var. incana, S. microphylla, S. speciosa, S. humilis and S. montana at 18 enzyme coding loci. Astragalus atropilosulus subsp. burkeanus and a Lessertia species were used as outgroups to root dendrograms. Gene product of 32 enzyme coding loci revealed genetic variation at 18 (56.3%) thereof. The percentage of polymorphic loci ranged from 0 to 20.6% (0.95 criterion), values between 1.0 (±0.00) and 1.3 (±0.09) were obtained for the mean number of alleles per locus, and average heterozygosity values per locus ranged from 0 to 0.097 (±0.034). The average genetic distance between populations (0.077) was higher than between taxa (0.032); the overlap in the cluster analyses of genetic distance data indicated that Sutherlandia taxa are not easily distinguished genetically. Although preliminary results showed that it was possible to identify some sympatric taxa, the analysis of additional populations annuled this result. There is remarkable lack of agreement between morphological and allozyme patterns within the genus Sutherlandia and the low allozyme differentiation between populations and taxa could be the result of the breeding systems of this genus.

Genetic polymorphism in wild and cultivated Siphonochilus aethiopicus (Zingiberaceae)

Abstract Horizontal starch gel-electrophoresis was utilized to estimate genetic diversity within a natural population of wild ginger ( Siphonochilus aethiopicus ) and individuals of the species cloned for commercial purposes. The aim of this study was to determine if electrophoresis is useful in studying genetic variation in S. aethiopicus . In the wild population, 50 plants revealed genetic variation at 11 (50%) of the 22 enzyme coding loci studied. The percentage of polymorphic loci ( P ) was 50, a value of 1.55 (±0.13) was obtained for the mean number of alleles per locus ( A ) and the average heterozygosity per locus ( H ) was calculated at 0.177 (±0.044). These values were 4.55, 1.05 (±0.05), and 0.023 (±0.023), respectively, for the cultivated clones. Allozyme data for the wild population is compared with that of two sources of cultivated specimens, showing that genetic fingerprinting of S. aethiopicus clones can be achieved by using only 11 polymorphic loci and that the two cultivated clones probably originated from the same source. The exceptionally high allelic heterogeneity obtained for individuals (clonal polymorphism) may be due to the synergistic effects of vegetative and sexual reproduction.

Electrophoretic evidence for an undescribed species of Barleria L.

Allozyme data confirmed the existence of a new species of Barleria L., Barleria sp. nov, aff. B. obtusa. The following loci displayed unique alleles in at least one of the species studied: AAT-1 *95, AAT-2 *50, AAT-3 *60, ACP*-110, EST *105, MDH-1 *95, MDH-2 *100, MNR-1 *100, MNR-2 *100, PEP-D2 *105, PER-1 *60, PER-1 *80, PGM *100 and SOD *-98. Four were unique for the new species: ACP*-110, EST *105, MNR-1 *100 and PER-1 *80. Genetic distance values between this species and S. bremekampii Obermeyer, B. heterotricha Lindau and B. obtusa Nees ranged from 0 389 to 0.670 This compares favourably with values estimated for congeneric species. This was also confirmed by fixation index values. In a dendrogram constructed using Nei’s genetic distances, Barleria sp, nov. aff. B. obtusa and B. obtusa are grouped together and these species are more closely related to S. bremekampii than to B. heterotricha We present a biochemical key to identify the species studied.

Speciation inVirgilia (Fabaceae): Allopatric divergence followed by introgression?

Levels of variation revealed by starch gel-electrophoresis were compared with morphological and chemical variation within and among the species and subspecies ofVirgilia:V. oroboides subsp.oroboides, V. oroboides subsp.ferruginea andV. divaricata. The data sets exhibited concordance in that all point to a very close relationship between the taxa. Differences are mostly quantitative and an overlapping east-west gradient of character variation is indicated. Analysis of morphological and chemical characters showed thatV. oroboides subsp.ferruginea andV. divaricata are relatively distinct, whereas allozyme analysis indicated a high degree of genetic similarity among populations of these two taxa. The observed pattern of variation suggests relatively recent speciation with subsequent introgressive hybridisation resulting in a geographical and ecological gradient.