Recovery of plant DNA using a reciprocating saw and silica‐based columns

The time needed for hand grinding and the cost of commercially available extraction kits remain to be the major limitations in plant DNA extraction for many researchers. We present inexpensive techniques for (i) simultaneously machine grinding large numbers of plant samples for DNA extraction using a commercially available reciprocating saw; and (ii) DNA recovery using silica column‐based extractions similar to that used in some commercially available kits. Used together, these allow for the rapid recovery of plant DNA at relatively low cost. Furthermore, these methods appear to be widely applicable within plants with good yields recovered in test extractions across major plant groups (ferns, gymnosperms, monocots and eudicots).     

Influence of Photoperiod, Daylength, and Feeding Schedule on Tadpole Growth and Development

The metamorphic rate of Rana pipiens tadpoles was studied under different photoperiods, daylengths, and feeding schedules. Tail resorption and hindlimb growth and development induced by immersion in 30 μg/l thyroxine (T₄) were accelerated under longer photoperiods and continuous light when 6L: 18D, 12L: 12D, 18L: 6D, and 24L regimes were compared. Constant light exposure did not produce faster development than an 18 hr photoperiod, and initially was less effective. The rate of spontaneous and T₄-induced metamorphosis was greater the shorter the day on 9L:9D, 12L: 12D, or 15L: 15D cycles, although all groups received the same overall amount of light, but in different dosages. When feeding schedule but not the LD cycle was varied, groups of tadpoles fed on 18, 24, or 30 hr regimes showed no differences in growth and development rate on 19L: 5D, and only random variations under continuous light. Differences in metamorphic rate on 18, 24, or 30 hr days are not due to the feeding schedules, but to the LD cycles. From these experiments we conclude that illumination, particularly the length and frequency of the photoperiod, affects the utilization of T₄. Development rates independent of the total amount of illumination, but related to daylength and light schedule, suggest interaction of light with an endogenous timing mechanism.     

Catalytic RNA and RNA Splicing

The capacity of Watson-Crick base-pair complementarity to directinformational transactions basic to gene expression has longbeen appreciated. Among RNA molecules, it mediates mRNA-tRNAcodon-anticodon pairing and the 16S rRNA-mRNA Shine-Dalgarnointeraction. More recently, we have come to realize that therole of RNA may transcend that of intermolecular recognition,per se, to include catalysis. Following the tour-de-force studiesof the self-splicing Tetrahymena rRNA precursor, the stage isnow set for the primary role of RNA to be revealed in nuclearpre-RNA splicing, which is catalyzed by a large ribonucleoprotein(RNP) complex in the cell nucleus, called the spliceosome. Theremoval of introns from nuclear pre-messenger RNA (pre-mRNA)shares fundamental properties with certain RNA self-splicingreactions. It therefore seems likely that the major catalyticstrategies in nuclear pre-mRNA splicing are carried out by thesmall nuclear RNAs (snRNAs), which are major constituents ofthe spliceosome.     

Implications of community concordance for assessing stream integrity at three nested spatial scales in Minnesota,U.S.A.

1. Fish and invertebrate assemblage data collected from 670 stream sites in Minnesota (U.S.A.) were used to calculate concordance across three nested spatial scales (statewide, ecoregion and catchment). Predictive taxa richness models, calibrated using the same data, were used to evaluate whether concordant communities exhibited similar trends in human‐induced taxa loss across all three scales. Finally, we evaluated the strength of the relationship between selected environmental variables and the composition of both assemblages at all three spatial scales. 2. Significant concordance between fish and invertebrate communities occurred at the statewide scale as well as in six of seven ecoregions and 17 of the 21 major catchments. However, concordance was not consistently indicative of significant relationships between rates of fish and invertebrate taxa loss at those same scales. 3. Fish and invertebrate communities were largely associated with different environmental variables, although the composition of both communities was strongly correlated with stream size across all three scales. 4. Predictive taxa‐loss models for fish assemblages were less sensitive and precise than models for invertebrate assemblages, likely because of the relatively low number of common fish taxa in our data set. Both models, however, distinguished reference from non‐reference sites. 5. The importance of concordance, geographic context and scale are discussed in relation to the design and interpretation of stream integrity indicators. In particular, our findings suggest that community concordance should not be viewed as a substitute for an evaluation of how assemblages respond to environmental stressors.     

A rapid serological test for detecting Fusarium oxysporum f.sp. narcissi in Narcissus

Polyclonal antiserum was elicited against a strain of Fusarium oxysporum f.sp. narcissi (GCRI80/26) and a specific and sensitive enzyme-linked immunosorbent assay developed. Antiserum raised to cell wall fractions gave better recognition than that to cytoplasmic fractions. Recognition was equally good in artificially and naturally infected bulbs. Little cross-reactivity in bulb tissue was shown by three other bulb-rotting fungi. Nine isolates of F. oxysporum f.sp. narcissi from a wide geographic area gave similar results in an indirect ELISA of mycelial extracts, although some cross-reactivity was observed with two other Fusarium spp. Four Fusarium spp. and four other fungi showed little cross-reactivity. Ten days after inoculation the pathogen was readily detected in the base plate area of three Narcissus cultivars and points remote from the inoculation site in the most susceptible cultivar. A direct correlation was observed between positive results in the enzyme-linked immunosorbent assay and recovery of the pathogen on selective medium.     

EVOLUTION OF HORNS IN UNGULATES: ECOLOGY AND PALEOECOLOGY

(1) The savanna ungulate faunas of the North American Miocene were broadly similar to those of present-day East Africa in terms of overall morphological and taxonomic diversity. However, the predominant ungulates of the African faunas are bovids, which possess bony horns that are primitively sexually dimorphic in their occurrence. The predominant ungulates of the North American Tertiary were equids, camelids and oreodonts, which all lacked horns. A limited number of horned ruminants were present, but these were largely Miocene immigrants from Eurasia. Horns were also absent from the large-bodied herbivores in the endemic faunas of South America and Australia. (2) The absence of horns in equids and tylopod artiodactyls is unlikely to be due to genetic insufficiency. Bony horns were present in brontotheres, which were closely related to equids, and in protoceratids, which were closely related to camelids. Nasal horns were present in one oreodont genus. (3) Studies on living ungulates show that a strong correlation exists between habitat type, feeding behaviour, social behaviour and morphology. It is possible to use the morphological remains of extinct ungulates to reconstruct the types of feeding and social behaviour, and to use the distribution of morphologies and body sizes in a community of mammals, in conjunction with geological and paleobotanical evidence, to reconstruct the type of habitat. (4) The importance of the post-Eocene climatic changes to the history of mammalian evolution is stressed. Continents at higher latitudes have become increasingly seasonal in terms of temperature and rainfall since the equable global conditions of the early Tertiary. Savanna mosaic were the predominant biome in North America by the early Miocene, and in Eurasia by the middle Miocene. Living temperate-latitude species of ungulates may not be a reliable guide for the assessment of the interrelationship between behaviour and morphology in an evolutionary perspective, as their behaviour may have been recently adapted to a habitat type that has only been in existence since the Pleistocene. (5) The primitive condition in eupecorans and protoceratids is the absence of horns, with the presence of large sabre-like canines in the males. The first horned members of these divisions had horns in the males only. Small present-day antelope, where horns may also be present in the females of the species, are probably secondarily small. (6) Horns were acquired independently in ruminant artiodactyls at least three times, and a maximum number of seven times is not unlikely. In each case, horns first appeared at a critical body weight of about 18 kg, and in correlation with a change in habitat from closed to open woodland. (7) Horns in living ruminants are associated with territorial defence by males holding exclusive feeding and reproductive territories in woodland habitats. Such behaviour in present-day antelope is correlated with a body size of greater than 15 kg and a folivorous diet. It is argued that horns evolved in ruminant artiodactyls on the adoption of this type of territorial behaviour once the critical combination of body size, diet and habitat type had been attained in their evolution from small, essentially frugivorous, forest-dwelling animals. (8) Perissodactyls never evolved sexually dimorphic bony horns of the type seen in ruminant artiodactyls. This is because their foraging and digestive strategies necessitate a larger daily intake of food. In a woodland habitat they were never able to adopt a feeding area small enough to make exclusive territory maintenance an economical proposition. Territory holding in male perissodactyls is seen, but under the opposite conditions of habitat to territorial behaviour in ruminant artiodactyls. (9) Study of the morphology and paleoecology of oreodonts suggests that they were woodland herd-forming browsers with exclusively folivorous diets. They probably had some forestomach fermentation, but did not chew the cud. Similar studies of Tertiary camelids suggest that they were predominantly selective browsers eating herbage at a low level in open country and formed mixed-sex feeding groups. These combinations of feeding and social behaviour suggest a more open structure of the mid-Tertiary habitat in North America than in Eurasia. (10) Studies of the behaviour and morphology of living members of the Ruminantia, and of the morphology and paleoecology of their fossil ancestors, suggest that they were primitively tree browsers living in closed woodland habitats. Such habitats were abundant in the Old World, but in limited supply in North America during the Oligocene, where the protoceratids were the only ungulates to parallel the eupecoran type of feeding and social behaviour. South America appears to have had an even more open habitat in the Oligocene than North America, and no parallel to the eupecorans was seen amongst the indigenous ungulates. The radiation of the Bovidae into open grassy habitats in the Pliocene may have been dependent on the immigration of grazing equids into the Old World. (11) I conclude that there was a difference in habitat structure between North America and the Old World during the Tertiary. The food resources in North America were more widely dispersed, and this may have been the result of the trees being more widely spaced. A possible causal mechanism for this was the stable land mass of the North American continent during the Tertiary, resulting in a more continental climate, with a more severe effect of the post-Eocene seasonality on the vegetation. The faunal record of the two continents also implied a greater density of trees in the Old World. (12) Thus most endemic North American ruminants did not evolve horns because, at the critical combination of body size and diet seen in the evolution of horns in the Old World ruminants, the dispersal of the food resources within the vegetation was too great for an effective home range to be maintained as an exclusive territory. (13) Attention is drawn to the dangers of constructing evolutionary stories about living animals without primary reference to the fossil record to see if the hypotheses are upheld, and of assuming that fossil animal communities can be made to fit models of existing communities.     

Correlation between leaf growth variables suggest intrinsic and early controls of leaf size in Arabidopsis thaliana

Leaf development is affected by both internal (genetic) and external (environmental) regulatory factors. The aim of this work was to investigate how leaf growth variables are related to one another in a range of environments. The leaf growth variables of wild-type Arabidopsis thaliana and leaf development mutants (ang4, ron2-1, elo1, elo2 and elo4) were studied under different incident light treatments (light and shade). The leaves studied were altered in various leaf development variables, such as the duration of expansion, relative and absolute expansion rates, epidermal cell size, epidermal cell number and initiation rate. Final leaf area was correlated to maximal absolute leaf expansion rate and cell number, but not to duration of leaf expansion or cell size. These relationships were common to all studied genotypes and light conditions, suggesting that leaf size is determined early in development. In addition, the early variables involved in leaf development were correlated to one another, and initial relative expansion rate was negatively correlated to the duration of expansion. These relationships between the leaf development variables were used to construct a conceptual model of leaf size control.     

Chemical Composition of the Epidermal, Hypodermal, Endodermal and Intervening Cortical Cell Walls of Various Plant Roots

A survey of chemical modifications in the cells of the epidermis,hypodermis, cortical parenchyma and endodermis in roots of 27plant species was performed. Cortical parenchyma walls weregenerally free of modifying substances whereas the walls ofthe epidermis, hypodermis and endodermis were usually modifiedby the presence of lipids, phenols, suberin or lignin. In mostcases, wall-modifying components could be detected within 5mm of the root apex. lipids, phenols, suberin, lignin, ferulic acid, root, epidermis, hypodermis, cortex, endodermis, cell wall     

A new role for glutathione in the regulation of root architecture linked to strigolactones

Reduced glutathione (GSH) is required for root development, but its functions are not characterized. The effects of GSH depletion on root development were therefore studied in relation to auxin and strigolactone (SL) signalling using a combination of molecular genetic approaches and pharmacological techniques. Lateral root (LR) density was significantly decreased in GSH synthesis mutants (cad2‐1, pad2‐, rax1‐), but not by the GSH synthesis inhibitor, buthionine sulfoximine (BSO). BSO‐induced GSH depletion therefore did not influence root architecture in the same way as genetic impairment. Root glutathione contents were similar in the wild‐type seedlings and max3‐9 and max4‐1 mutants that are deficient in SL synthesis and in the SL‐signalling mutant, max2‐1. BSO‐dependent inhibition of GSH synthesis depleted the tissue GSH pool to a similar extent in the wild‐type and SL synthesis mutants, with no effect on LR density. The application of the SL analogue GR24 increased root glutathione in the wild‐type, max3‐9 and max4‐1 seedlings, but this increase was absent from max2‐1. Taken together, these data establish a link between SLs and the GSH pool that occurs in a MAX2‐dependent manner.     

Tribal Languages and the Challenges of Revitalization

Although school- and university-based language programs can help strengthen threatened Indigenous languages, language revitalization at its heart involves reestablishing traditional functions of language use in the context of everyday speaker interactions. The inherent dynamics of Native oral language traditions suggest the limitations of institutions in supporting critical language learning activities that are the key to successful language renewal efforts.