Geographic patterns of morphological variation in Turnera sidoides subsp. pinnatifida (Turneraceae)

With the objective of contributing to understanding the patterns of variation within the Turnera sidoides complex, a detailed evaluation of morphological variation along the range of T. sidoides subsp. pinnatifida was performed. A multivariate analysis based on leaf traits and flower colour data enabled differentiation of five morphotypes. Common-garden experiments demonstrated that the morphological variants have a strong genetic basis. It was also found that the morphotypes are geographically structured along the subspecies range, display different habitat preferences, and occur in regions with different climatic regimes. Although these results are suggestive of adaptive differentiation of T. sidoides subsp. pinnatifida, comparisons between morphological and bioclimatic ordinations showed that the patterns observed cannot be fully explained by current climatic conditions. It is proposed that Miocene–Pleistocene events may explain the origin of the five morphotypes and that current climatic and ecological factors may be contributing to the maintenance of the extent and patterns of morphological differentiation in T. sidoides subsp. pinnatifida.     

Cyanogenesis variation in the Turnera sidoides L. polyploid complex (Turneraceae)

This study constitutes the first investigation of cyanogenesis variation within the Turnera sidoides autopolyploid complex. The qualitative and quantitative analysis carried out in 38 populations showed that the five subspecies of the complex are cyanogenic, although the levels of cyanide released varied both between and within subspecies. Between the subspecies, carnea , holosericea and integrifolia showed higher values of HCN released than subspecies pinnatifida and sidoides . Within subspecies, there is a tendency toward an increment of mean cyanide values with ploidy levels and different hypotheses are considered in order to explain this variation. The study of cyanogenesis in populations from different geographical areas cultivated under uniform greenhouse conditions showed that, in the widespread subspecies pinnatifida , HCN variation may also reflect the action of different selection pressures, since populations having dissimilar cyanide levels grow in different phytogeographical provinces with different climatic regimes. On the other hand, the fact that the variation of HCN released was greater between populations from different geographical areas than that observed between diploid and tetraploid populations of the same area provides additional evidence for the multiple origins of polyploids of the T. sidoides complex.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 85–94.     

Karyotypic studies in Turnera sidoides complex (Turneraceae, Leiocarpae)

Turnera sidoides, with the most southerly distribution of all Turnera species in America, is a complex of obligately outcrossing perennial herbs. Karyotypes of the five subspecies of T. sidoides (x = 7) are described for the first time utilizing root-tip mitotic metaphases. Different ploidy levels were found for all of the subspecies, ranging from diploid to octoploid. The results obtained, coupled with available meiotic and preliminary biosystematic data, support the hypothesis of autopolyploidy within this species complex. Although detailed karyotype analysis shows a high degree of intraspecific uniformity, subspecies may be differentiated by the number, type, and position of satellites, suggesting that chromosome rearrangements may also be involved in the karyotypic evolution of T. sidoides. Karyotype data, coupled with morphological and anatomical features, suggest the removal of T. sidoides from series Leiocarpae.     

Cytogeography of the South American Turnera sidoides L. complex (Turneraceae, Leiocarpae)

New chromosome number determinations are presented for 48 populations of five subspecies of Turnera sidoides. Chromosome counts in sspp. carnea, holosericea, integrifolia and sidoides confirm previous data while, in ssp. pinnatifida , the numbers 2n=2x = 14 and 2n = 6x = 42 are reported for the first time. The results show that polyploidy is a very frequent phenomenon. Populations are primarily tetraploids (2n = 4x = 28), while diploids (2n = 2x = 14), hexaploids (2n = 6x =42) and octoploids (2rc = 8x = 56) are less frequent. Diploid, tetraploid and hexaploid cytotypes occur in sspp. carnea and pinnatifida , whereas tetraploids and hexaploids are known in ssp. holosericea. Turnera sidoides ssp. integrifolia shows a polyploid series with ploidy levels from 2x to 8x. The ssp. sidoides appears to be uniformly tetraploid, with the exception of an isolated pentaploid (2rc = 5x = 35). On the basis of these counts and previous reports the geographical distribution of the cytotypes has been determined and related to climatic and ecological factors.     

Chloroplast DNA variation in the Turnera sidoides L. complex (Turneraceae): biogeographical implications

Aim To analyse the current geographical structure of chloroplast DNA variation in the Turnera sidoides L. complex in order to establish historical biogeographical hypotheses for the mid‐latitude South American lowlands. During the Quaternary, the climate shifted from tropical humid to cold dry, and the vegetation cover has not been stable. The consequences of these processes on the current distribution of the vegetation of this area have received very little attention. Location The mid‐latitude South American lowlands extend between c. 20 and 40°S and include Uruguay, northern, central and eastern Argentina, southern Brazil, and parts of southern Paraguay and Bolivia. They are surrounded by higher‐elevation systems. Methods Turnera sidoides is a well‐studied polyploid complex of perennial rhizomatous herbs occurring throughout the area of interest. We analysed 321 individuals from 79 populations of the five recognized subspecies. We also included progenies from artificial crosses in order to analyse chloroplast inheritance. After screening sequences for four non‐coding chloroplast DNA regions, the trnL–trnF spacer was selected to characterize the collection. Results Three haplotypes can be easily identified, with each differing from the others in two independent characters. A clear geographic structure is revealed when haplotypes are plotted for the complex as a whole regardless of subspecies and cytotype. Three distinct regions can be identified. Main conclusions We propose three putative refugial areas for the Turnera sidoides complex, which are associated with the orographical systems of the region. Ravines and slopes in the Haedo Cuchilla system in northern Uruguay, the elevations of the western side of the area in Argentina, and the eastern Serranías system in south‐eastern Uruguay may each have served as refugia in which the A, B and C haplotypes became fixed during the drier climatic phases. Biogeographical patterns in the area covered by T. sidoides, particularly east of the Uruguay River, have not previously been analysed from a historical perspective.     

Inheritance of plastid DNA in the Turnera ulmifolia complex (Turneraceae)

We used PCR to amplify most of the rbcL gene and identified restriction fragment length polymorphisms to study the inheritance of chloroplast DNA (cpDNA) in the cross between two taxonomic varieties of the Turnera ulmifolia L. complex, vars. angustifolia and velutina. We identified an Alu I restriction site polymorphism that distinguished the parental plants. All 23 progeny from the cross var. angustifolia × var. velutina, where var. angustifolia was the maternal parent, possessed the paternal cpDNA. Results for the reciprocal cross were more varied, and the 16 progeny showed maternal, paternal, or biparental inheritance. We believe this represents the first study of plastid inheritance for any species in the Tumeraceae. The results are unusual and warrant further investigation using other species in this family.     

Turnera ulmifolia L. (Turneraceae): preliminary study of its antioxidant activity

Turnera ulmifolia L. is used in Brazilian folk medicine as an anti-inflammatory. Since this activity may be correlated with the presence of antioxidant compounds, a leaf extract was evaluated for its radical scavenging capacity (RSC). The in vitro RSC of a 50% hydroethanolic (HE) extract was evaluated by beta-carotene/linoleic acid coupled oxidation system for the inhibition of oxidation and the lipid peroxidation inhibition in rat brain homogenates, using thiobarbituric acid reactive substances (TBARS) and chemiluminescence (CL). Results indicated, through peroxidation suppression, that this extract exhibited greater antioxidative activity (77.4% +/- 10%) than alpha-tocopherol (58.4% +/- 3.7%). TBARS and CL inhibition was concentration-dependent and Q(1/2) values were 8.2 and 6.0 microg/mL for TBARS and CL, respectively. For alpha-tocopherol these values were 7.1 microg/mL (TBARS) and 9.8 microg/mL (CL). Phenolic compounds may be responsible for this antioxidant capacity.     

Inheritance of spontaneous mutant homostyles in Turnera subulata x krapovickasii and in autotetraploid T. scabra (Turneraceae)

To explore the genetic architecture of distyly in Turnera spp., we determined the inheritance and compatibility behaviour of two spontaneous homostyled mutants. A long-homostyled mutant shoot arose on an otherwise short-styled plant that was an artificial hybrid (Turnera subulata x T. krapovickasii) between two diploid distylous species. The mutation appears to be an allele, SH, of the distyly locus with the dominance relationships, S>SH>s, where S confers the short-styled phenotype, SH confers homostyly in SHSH and SHs genotypes, and ss genotypes are long-styled. Aberrant segregation ratios were observed among some crosses and might be the result of pollen competition. Compatibility relationships are consistent with the hypothesis that a gene complex determines distyly. Infrequently, revertant short-styled flowers have appeared on cuttings of the T. subulata x T. krapovickasii mutant and on occasion, short-styled progeny have appeared in crosses where none were expected. A second mutant homostyle was discovered in autotetraploid T. scabra. The mutation is inherited as above, however, tetrasomic inheritance occurs at the locus. This homostyled mutant carries two copies of the SH allele and has the duplex genotype SHSHss. Compatibility relationships were as observed above. The occurrence of homostyled mutants is consistent with the hypothesis that a linked gene complex underlies the inheritance of distyly in Turnera but we cannot discount the hypothesis that an allelic series is responsible.     

Evidence for the existence of 2n gametes in Lotus tenuis Wald. et Kit. (2n=2x=12): their relevance in evolution and breeding of Lotus corniculatus L. (2n=4x=24)

Summary Crosses between male sterile L. corniculatus (2n=4x=24) and L. tenuis (2n=2x=12) plants were performed in order to verify the presence of 2n gametes in L. tenuis. All but one of the plants from these crosses had 2n=4x=24 and the L. corniculatus phenotype; this plant had 2n=2x=12 and the L. tenuis phenotype. The plants also showed good quantity of pollen at tripping, good pollen fertility and good percentage of seed setting in the backcross to L. corniculatus. On the whole, both cytological and morphological observations, showing that all but one of the plants from L. corniculatus x L. tenuis were normal tetraploids, suggest the existence of diploandrous gametes in L. tenuis. On the other hand, haploid parthenogenesis probably gave origin to the dihaploid plant 2n=2x=12.     

Effects of ant behaviour and presence of extrafloral nectaries on seed dispersal of the Neotropical myrmecochore Turnera ulmifolia L. (Turneraceae)

This paper describes the myrmecochory system of Turnera ulmifolia in a coastal sand dune matorral in Mexico. Turnera ulmifolia has elaiosome‐bearing seeds and extrafloral nectaries (EFNs). In ten quadrants (4 × 15 m) ant–seed interaction was monitored, and an interaction intensity index calculated and correlated with the number of seedlings. Seed removal rates by ants were surveyed every 2 h for 24 h, the ants being observed both on and beneath the plants. The role of the elaiosome in seed removal was evaluated by offering seeds with and without elaiosomes, and elaiosomes only. Finally, the effect of ant manipulation in seed germination was evaluated. There were 25 ant species associated with seeds and/or EFNs, the most frequently recorded being Monomorium cyaneum and Forelius analis. There was a positive correlation between the intensity index and seedling number per quadrant. There was significantly higher mean seed removal during the day than during the night (19.3% and 12.3%, respectively), and from beneath than on the plant (21.9% and 9.5%, respectively). The preference for elaiosomes only was also greater during the diurnal period, and when gathered on, rather than beneath, the plant. Seed manipulation by F. analis enhanced germination by T. ulmifolia. Seed removal, dispersal distances, seed predation and germination were largely determined by ant behaviour. The presence of EFNs may be influencing seed removal on the plant by attracting a specific assemblage of omnivorous ants. Among such assemblages associated with T. ulmifolia we encountered a variety of behaviours, with ant species either good at defending plants but bad at dispersing seeds, or vice versa. We discuss the way in which these two rewards, and the processes involved (defence and dispersion), could have interacted with each other and evolved. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 67–77.     

Structure of d(T)n.d(A)n.d(T)n: the DNA triple helix has B-form geometry with C2'-endo sugar pucker.

The polynucleotide helix d(T)n.d(A)n.d(T)n is the only deoxypolynucleotide triple helix for which a structure has been published, and it is generally assumed as the structural basis for studies of DNA triplexes. The helix has been assigned to an A-form conformation with C3'-endo sugar pucker by Arnott and Selsing [1974; cf. Arnott et al. (1976)]. We show here by infrared spectroscopy in D2O solution that the helix is instead B-form and that the sugar pucker is in the C2'-endo region. Distamycin A, which binds only to B-form and not to A-form helices, binds to the triple helix without displacement of the third strand, as demonstrated by CD spectroscopy and gel electrophoresis. Molecular modeling shows that a stereochemically satisfactory structure can be build using C2'-endo sugars and a displacement of the Watson-Crick base-pair center from the helix axis of 2.5 A. Helical constraints of rise per residue (h = 3.26 A) and residues per turn (n = 12) were taken from fiber diffraction experiments of Arnott and Selsing (1974). The conformational torsion angles are in the standard B-form range, and there are no short contacts. In contrast, we were unable to construct a stereochemically allowed model with A-form geometry and C3'-endo sugars. Arnott et al. (1976) observed that their model had short contacts (e.g., 2.3 A between the phosphate-dependent oxygen on the A strand and O2 in the Hoogsteen-paired thymine strand) which are generally known to be outside the allowed range.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genomic diversity in aneudiploid (2n = 38) and diploid (2n = 40) Glycine tomentella revealed by cytogenetic and biochemical methods.

Of the 15 perennial species of the subgenus Glycine Willd., G. tomentella Hayata is unique in that it has four cytotypes (2n = 38, 40, 78, and 80) and a wide range of geographical distributions. The objective of this study was to uncover the genomic diversity among accessions of aneudiploid (2n = 38) and diploid (2n = 40) G. tomentella based on crossability rate, hybrid seed and seedling viability, meiotic chromosome pairing of F1 hybrids, and seed protein and protease inhibitor profiles. Aneudiploid and diploid G. tomentella accessions were divided into two (D1 and D2) and three [D3(A,B,C), D4, and D5] groups, respectively, based on previous isozyme studies. Crossability rate, intergenomic hybrid viability, degree of chromosome pairing, total seed protein profiles, and trypsin and chymotrypsin inhibitor banding patterns confirmed the isozyme grouping with minor disagreements. A consistent variation was not observed among the aneudiploid accessions in any method of analysis used in this study. Similarly, cytogenetic analysis and the total seed protein profiles did not show dissimilarity among the accessions from Papua New Guinea (PNG; the D3 group) and north of Mitchell River in Northern Queensland [N.Qld(n)]. However, trypsin and chymotrypsin inhibitor analysis revealed that the PNG accessions were distinctly different from N.Qld(n) accessions. The D4 and D5 group accessions were clearly distinguishable by both cytogenetic and biochemical methods. Thus, this study indicates the presence of four genomic groups among G. tomentella (2n = 38, 40) accessions, including the aneudiploids D1 and D2 in one group and diploids in three groups (D3, D4, and D5). These findings will be useful in further genome analysis and add to our present understanding of the biosystematics of the genus Glycine.     

Interspecific mating in the Piriqueta caroliniana (Turneraceae) complex: effects of pollen load size and composition

Two taxa of Piriqueta (P. caroliniana and P. viridis) form a broad hybrid zone that extends over much of the central Florida peninsula. We used genetic markers to examine the strength of the isolation barriers between these taxa and the patterns of mating at the initial stages of hybridization. Regression models were employed to analyze the effects of pollen load size and the proportions of intra- and interspecific pollen on the frequency of first-generation (F1) hybrid formation. Overall, the postpollination mating barriers between these two taxa were relatively weak. However, there were significant effects of pollen load composition and size on the patterns of hybridization in both taxa with frequency-dependent responses to composition in both taxa. The frequency of F1 hybrid formation was generally lower than expected based on the frequency of each pollen type on the stigma for P. caroliniana recipients. The lower frequencies of F1 seeds in this taxon were apparently due to a greater competitive ability for intraspecific pollen, since hybrid seed formation decreased with increasing pollen load size. Pollen from P. caroliniana donors was also competitively superior on P. viridis recipients, leading to higher than expected frequencies of hybrid seed formation. Pollen from P. caroliniana did suffer higher rates of pollen-tube attrition than intraspecific pollen on P. viridis recipients, so the frequency of hybrid seed formation would be lower when pellen load sizes were small. In general, reproductive isolation mechanisms were stronger in P. caroliniana, suggesting that introgression should occur into P. viridis when these taxa come into close contact. Comparison of these expected patterns of mating to the distribution of hybrid genotypes in Florida provides insights into the relative roles of mating and selection in the evolution of hybrid populations of Piriqueta.     

Patterns of cytotype variation of <Emphasis Type="Italic">Turnera sidoides</Emphasis> subsp. <Emphasis Type="Italic">pinnatifida</Emphasis> (Turneraceae) in mountain ranges of central Argentina

Cytogeographical variability among 564 plants from 26 populations of Turnera sidoides subsp. pinnatifida in mountain ranges of central Argentina was analysed with meiotic chromosome counts and flow cytometry and is described at regional and local scales. Populations were primarily tetraploids (2n = 4x = 28), although diploid (2n = 2x = 14), hexaploid (2n = 2x = 42), and mixed populations of diploids and triploids (2n = 3x = 21) were also found. Diploids, triploids, and hexaploids were fewer in number and restricted to narrow areas, while tetraploids were the most common and geographically widespread cytotype. Diploids grew at higher altitudes and in colder and wet locations; tetraploids had the broadest ecological spectrum, while hexaploids occurred at the lowest altitudes and in drier conditions. The cytotypes were also spatially segregated at a microgeographical scale. Diploids grew in the piedmont, tetraploids were in the adjacent valley, and in the contact zone of both cytotypes, patches of diploids and triploids were found. At a regional scale, the distribution of the cytotypes may be governed by a combination of ecological and historical variables, while segregation in the contact zone may be independent of the selective environment because the cytotypes are unable to coexist as a result of reproductive exclusion. The role of triploids is also discussed.     

Retention of triplicated phytoene synthase (PSY) genes in Brassica napus L. and its diploid progenitors during the evolution of the Brassiceae

The extent of genome redundancy exhibited by Brassica species provides a model to study the evolutionary fate of multi-copy genes and the effects of polyploidy in economically important crops. Phytoene synthase (PSY) catalyzes the first committed reaction of the carotenoid biosynthetic pathway, which has been shown to be rate-limiting in Brassica napus seeds. In Arabidopsis thaliana, a single PSY gene (AtPSY) regulates phytoene synthesis in all tissues. Considering that diploid Brassica genomes contain three Arabidopsis-like subgenomes, the objectives of the present work were to determine whether PSY gene families exist in B. napus (AACC) and its diploid progenitor species, Brassica rapa (AA) and Brassica oleracea (CC); to establish the level of retention of Brassica PSY genes; to map PSY gene family members in the A and C genomes and to compare Brassica PSY gene expression patterns. A total of 12 PSY homologues were identified, 6 in B. napus (BnaX.PSY.a-f) and 3 in B. rapa (BraA.PSY.a-c) and B. oleracea (BolC.PSY.a-c). Indeed, with six members, B. napus has the largest PSY gene family described to date. Sequence comparison between AtPSY and Brassica PSY genes revealed a highly conserved gene structure and identity percentages above 85% at the coding sequence (CDS) level. Altogether, our data indicate that PSY gene family expansion preceded the speciation of B. rapa and B. oleracea, dating back to the paralogous subgenome triplication event. In these three Brassica species, all PSY homologues are expressed, exhibiting overlapping redundancy and signs of subfunctionalization among photosynthetic and non-photosynthetic tissues. This evidence supports the hypothesis that functional divergence of PSY gene expression facilitates the accumulation of high levels of carotenoids in chromoplast-rich tissues. Thus, functional retention of triplicated Brassica PSY genes could be at least partially explained by the selective advantage provided by increased levels of gene product in floral organs. A better understanding of carotenogenesis in Brassica will aid in the future development of transgenic and conventional cultivars with carotenoid-enriched oil.     

Characterization of divalent cation localization in the minor groove of the A(n)T(n) and T(n)A(n) DNA sequence elements by (1)H NMR spectroscopy and manganese(II)

The localization of Mn(2+) in A-tract DNA has been studied by (1)H NMR spectroscopy using a series of self-complementary dodecamer oligonucleotides that contain the sequence motifs A(n)(n) and T(n)A(n), where n = 2, 3, or 4. Mn(2+) localization in the minor groove is observed for all the sequences that have been studied, with the position and degree of localization being highly sequence-dependent. The site most favored for Mn(2+) localization in the minor groove is near the 5'-most ApA step for both the T(n)A(n) and the A(n)T(n) series. For the T(n)A(n) series, this results in two closely spaced symmetry-related Mn(2+) localization sites near the center of each duplex, while for the A(n)T(n) series, the two symmetry-related sites are separated by as much as one half-helical turn. The degree of Mn(2+) localization in the minor groove of the T(n)A(n) series decreases substantially as the AT sequence element is shortened from T(4)A(4) to T(2)A(2). The A(n)T(n) series also exhibits length-dependent Mn(2+) localization; however, the degree of minor groove occupancy by Mn(2+) is significantly less than that observed for the T(n)A(n) series. For both A(n)T(n) and T(n)A(n) sequences, the 3'-most AH2 resonance is the least broadened of the AH2 resonances. This is consistent with the observation that the minor groove of A-tract DNA narrows in the 5' to 3' direction, apparently becoming too narrow after two base pairs for the entry of a fully hydrated divalent cation. The results that are reported illustrate the delicate interplay that exists between DNA nucleotide sequence, minor groove width, and divalent cation localization. The proposed role of cation localization in helical axis bending by A-tracts is also discussed.