Brian G. Murray

Ribosomal DNA locus evolution in Nemesia : transposition rather than structural rearrangement as the key mechanism?

We investigated chromosome evolution in Nemesia using fluorescent in-situ hybridization (FISH) to identify the locations of 5S and 45S (18–26S) ribosomal genes. Although there was conservation between Nemesia species in chromosome number, size and centromere position, there was large variation in both number and position of ribosomal genes in different Nemesia species (21 different arrangements of 45S and 5S rRNA genes were observed in the 29 Nemesia taxa studied). Nemesia species contained between one and three pairs of 5S arrays and between two and four pairs of 45S arrays. These were either sub-terminally or interstitially located and 45S and 5S arrays were often located on the same chromosome pair. Comparison of the positions of rDNA arrays with meiotic chromosome behaviour in interspecific hybrids of Nemesia suggests that some of the changes in the positions of rDNA have not affected the surrounding chromosome regions, indicating that rDNA has changed position by transposition. Chromosome evolution is frequently thought to occur via structural rearrangements such as inversions and translocations. We suggest that, in Nemesia, transposition of rDNA genes may be equally if not more important in chromosome evolution.

Contributions to a chromosome atlas of the New Zealand flora—37. Miscellaneous families

Abstract Documented chromosome numbers are reported for 156 taxa (117 species, 3 subspecies, 8 varieties, 3 forma, 1 hybrid, and 24 of uncertain rank) from 24 families (54 genera) of angiosperms. Of these, 122 are for previously uncounted New Zealand taxa. Many of the counts are from poorly investigated families and genera, or from nationally uncommon and threatened, or newly described plants. In the majority of genera the numbers follow established patterns. Counts have now been obtained for all the New Zealand representatives of the Arecaceae and Urticaceae.

Flow cytometric determination of genome size in Pinus

Abstract The nuclear 2C DNA content of seven Pinus species and Pseudotsuga menziesii was determined by flow cytometric analysis. Conditions for nuclear isolation were adapted to optimise results for Pinus . To reduce endonuclease activity and the effect of high tannins and phenolics, 10 mM EDTA, 15 mM β-mercaptoethanol and 1% PVP-10 were added to the chopping buffer. The accessibility of propidium iodide, an intercalating stain, was improved by acid treatment of the nuclei with HCl for 1 min, leading to an increase of 10–30% in fluorescence. Using these optimised conditions, values for genome sizes of the eight species ranged from 38 to 53 pg per 2C nucleus. Little or no variation was observed between shoot apices or embryogenic cell cultures of P. radiata , except that one cell line and plants derived from it contained an additional 2 pg of DNA. Cytogenetic analysis showed this line to be trisomic, with 2n = 2x+1 = 25 chromosomes.

Low outcrossing rates and shift in pollinators in New Zealand pohutukawa (Metrosideros excelsa; Myrtaceae).

New Zealand pohutukawa (Metrosideros excelsa), a member of the Myrtaceae, is a large, mass-flowering tree endemic to northern New Zealand coastlines. Mainland populations have been reduced to fragmented stands, and the original suite of bird pollinators has been largely replaced by introduced species. The native pollinator fauna on several offshore islands is largely intact and includes three species of the New Zealand honeyeaters (Meliphagidae) and native, solitary bees. We estimated multilocus outcrossing rates for three mainland and two island populations and found that they were among the lowest in the Myrtaceae (t(m) = 0.22-0.53). The shift in pollinators had no measurable effect on the mating system. Mass-flowering facilitates geitonogamous selfing, and inbreeding depression in seedling height was detectable at 6 mo of growth. F(s) [Wrights (1965) Fixation Index] was consistently higher than F(m) in all populations, indicating that selection may eliminate selfed offspring from populations prior to achieving reproductive maturity. Results suggest that increased selfing in mainland populations due to pollinator changes is not responsible for current patterns of poor regeneration of this species.

Breeding systems and floral biology in the genus Briza

SummaryFloral morphology is shown to be closely correlated with the type of breeding system in the genus Briza L. (Gramineae). The outbreeding species have large anthers and stigmas that are well exerted at anthesis whereas in the inbreeding species anthers and stigmas are small and the flowers are frequently cleistogamous. Self-incompatibility in B. media is controlled by two genes, both with multiple alleles. Identity at both loci is necessary for pollen inhibition. Pollen control is gametophytic, incompatible pollen tubes are inhibited on the stigmatic surface. Unilateral incompatibility occurs in crosses between self-incompatible and self-compatible species. Self-compatible pollen is inhibited on self-incompatible stigmas but the reciprocal shows no inhibition.

Contributions to a chromosome atlas of the New Zealand flora ‐ 38. Counts for 50 families

Abstract Documented chromosome numbers are reported for 187 taxa (170 species, 9 subspecies, 8 varieties), 5 hybrids (four putative, one artificial), and 18 of uncertain rank from 50 families (84 genera; 2 lycophyte, 11 pterophyte and 71 anthophyte). Of these, 189 counts are new for the New Zealand flora (167 of these are from named taxa). Many of the counts reported are from more poorly investigated families (e.g., Cyperaceae, Lycopodiaceae, Pota‐mogetonaceae) and genera (e.g., Desmoschoenus, Freycinetia, Lycopodiella, Lycopodium, Potamo‐geton, Schoenus), indigenous to New Zealand, or from nationally uncommon and/or threatened taxa (e.g., Eleocharis neozelandica, Hebe societatis, Myriophyllum robustum, and Pittosporum dallii), and/or newly described plants (e.g., Gingidia gri‐sea, Olearia adenocarpa), while three counts are from naturalised species (Alternanthera sessilis, Nephrolepis cordifolia, and Senecio skirrhodon), and one from a cultivated plant of Metrosideros nervulosa. In the majority of genera the numbers follow established patterns. Counts have now been obtained for all known New Zealand representatives of the Alseuosmiaceae, Chloranthaceae, Dryopteri‐daceae, Elatinaceae, Euphorbiaceae, Geraniaceae, Hydatellaceae, Lauraceae, Linaceae, Rubiaceae, Scrophulariaceae, Nephrolepidaceae, Nyctagina‐ceae, Pandanaceae, Polypodiaceae, Sapotaceae, and Thelypteridaceae.

Climate and the evolution of annual/perennial life-histories in Nemesia (Scrophulariaceae)

The Cape Floristic Region and the Succulent Karoo in southwestern Africa are both noted for their plant species richness and high levels of endemism. The southwestern tip of Africa is one of the worlds five Mediterranean-type climate regions. The biodiversity in the Cape Floristic Region and Succulent Karoo is thought to be at least partly due to changes to the climate of these regions that have occurred since the middle Miocene. Annual species are usually a significant proportion of local flora in Mediterranean-type climate regions. Previous studies of species radiations in the Cape Floristic Region have concentrated on genera that predominantly contain perennial species. Nemesia (Scrophulariaceae) comprises c. 65 species of annual and perennial herbs and sub-shrubs that are native to southern and tropical Africa. Annuals make up a significant proportion (~75%) of Nemesia species. We have reconstructed a phylogeny of 23 Nemesia species using nucleotide sequences of the ITS, ETS and trnL-spacer regions. Species were grouped into five clades, two composed of annual species, one that contained two annual and one perennial species, one that contained one annual and two perennial species, and one that was predominantly composed of perennial species. Phylogenetic dating of the ITS + ETS based phylogenetic tree using penalised likelihood suggested the genus evolved during the Miocene, and that the majority of extant Nemesia species studied radiated during the Pliocene. Ancestral state reconstruction supports at least three separate origins of the annual habit from plants with a perennial life history. One origin can be traced to the late Miocene while the other two transitions occurred more recently during the Pliocene. The transition from perennial to annual life-histories in Nemesia may have been a response to climate change.

Contributions to a chromosome atlas of the New Zealand flora ‐ 35. Miscellaneous familie

Abstract Documented chromosome numbers are reported for 33 species, 7 subspecies, 9 varieties, 2 forma, 2 hybrids, and 14 taxa of uncertain rank from 21 families ofangiosperms. Thirty‐eight of these are for previously uncounted taxa and hybrids. The majority of the counts are for nationally uncommon and threatened, or newly described plants. In the majority of genera the numbers follow established patterns but new examples of polyploid series have been found in New Zealand species of Crassula and Gratiola.

Secondary constrictions and NORs of of Lathyrus investigated by silver staining and in-situ hybridization

A variety of karyotypic differences were seen among six Lathyrus species. In part these differences are the result of different numbers of metacentric and acrocentric chromosomes in the complement but there were also clear differences in the number(s) and position(s) of secondary constrictions. Silver staining and in-situ hybridization were used to identify the nucleolar organizer regions (NORs). Silver staining also occurred at the centromere in most species and in addition at a number of non-centromeric sites in L. tingitanus. Some of these additional sites coincide with allocyclic regions revealed by the use of air-dried preparations. Unusual ‘extended’ centromeres were observed in these air-dried preparations of two of the species.

Cytological characterization of heterochromatin and rDNA inPinus radiata andP. taeda

Fluorochrome C-banding ofPinus radiata andP. taeda metaphase chromosomes showed many pericentromeric DAPI bands and interstitial CMA bands inP. radiata, and centromeric and interstitial CMA bands inP. taeda. Giemsa C-band patterns differed between the species with centromeric bands inP. radiata but no consistent bands inP. taeda. A karyotype ofP. radiata was developed based on banding patterns that distinguished all but two of the 12 pairs of chromosomes. In situ hybridization (ISH) using probes for high-copy ribosomal DNA (rDNA) showed 10 pairs of 18S–25S sites and two pairs of 5S sites in both species. Most of the sites were interstitial or centromeric.