Somaclonal variation from Sorghum bicolor (L.) Moench cell culture

Plant Cell, Tissue and Organ Culture (PCTOC) - Sorghum bicolor (L.) Moench, plants were regenerated from 4 to 5 month old callus cultures originally derived from seedling explants. Somaclonal...     

Plants and insects in early old-field succession: comparison of an English site and an American site

The plant and insect communities of early, secondary succession beginning with bare ground in an Old World site (southern Britain) and a New World site (Iowa, U.S.A.) shared a number of characteristics. Both sites showed similar temporal patterns of plant species cover and species richness, although overall richness was greater at the Old World site. Annuals dominated at both sites during the first year of succession and were largely replaced by perennials in the second year. Monocotyledons were more abundant at the Old World site, especially in the second year. The two sites differed markedly in the contribution of native and introduced plant species, with the Old World site dominated by natives and the New World site by alien plant species. Insect herbivore load was greater at the Old World site, when expressed in terms of structural complexity of the vegetation, suggesting that there may be major differences in the influence of herbivores on the direction and rate of succession at the two sites.     

Evidence for the retention of genetic variation in Erodium seed dormancy by variable rainfall

Summary The periodic occurrence of summer/early autumn precipitation in the California annual grassland can result in the formation of early and late emerging cohorts of Erodium botrys and E. brachycarpum. The occurrence of early rainfall and the timing of such rainfall are highly variable from year to year. A series of field watering experiments in 1980–81 were used to simulate early emergence conditions that would result from significant rainfall (1 cm) occurring in mid-July, late August, and mid-September. Net reproduction was used to estimate fitness differentials between Erodium cohorts emerging in response to a watering treatment (early emerging cohorts) and Erodium cohorts emerging with the onset of winter rains in mid-October (late emerging cohorts). Survival was lower and gross reproduction was higher among early emerging cohorts than late emerging cohorts. For both species, net reproduction of the early cohort was lower than that of the late cohort under the July watering treatment and higher than that of the late cohort under the August watering treatment.Early cohorts, formed in response to rainfall in mid-September, 1982, were also compared demographically to later cohorts emerging in October. Compared to late cohorts, net reproduction, gross reproduction and survival were higher for the early cohorts.Common garden experiments indicate that differences in the duration of seed dormancy between the progenies of early and late emerging plants reflect a significant genetic component. Progency produced by early cohorts of E. brachycarpum from all three watering treatments possessed more extended seed dormancy than progeny of late cohorts. In E. botrys, progeny from early cohorts emerging in response to the July watering treatment were also more dormant than late progeny. In contrast, early cohorts of E. botrys emerging in response to the September watering treatment produced seed less dormant than seed produced by late cohorts. When combined with demographic data, indicating that fitness differentials between early and late cohorts varied with changes in the date of early emergence, genetic results suggest that year to year variation in early rainfall may act to retain genetic variation in the duration of seed dormancy.     

Effects of clonal variation of the host plant,interspecific competition,and climate on the population size of a folivorous thrips

Summary The effects of clonal variation, interspecific competition, and climate upon the population size of Apterothrips secticornis was assessed by a series of observations and experimental manipulations. Three clones of the host plant, Erigeron glaucus, consistently supported different numbers of thrips during monthly censuses. When rosettes of the three clones were transplanted to a common garden, relative numbers of thrips on the clones remained the same as those observed where the clones grew in situ. The presence or absence of other hervivores had no effect on thrips numbers in the common garden. Plume moth caterpillars and thrips were observed to co-occur less often than expected in the field but this was caused by differences in habitat selection by these two species rather than being the result of interspecific competition. Populations of thrips were affected by climate, but analyses suggest that the host clone was a more important factor.     

Comparisons of tests for aneuploidy

The fundamental problems that face us in the development of suitable assay systems for the detection of potentially aneugenic (aneuploidy-inducing) chemicals include: (a) the diversity of cellular targets and mechanisms where perturbations of structure and function may give rise to changes in chromosome number, and (b) the phylogenetic differences that exist between species in their mechanism and kinetics of cell division and their metabolic profiles. A diverse range of assay systems have been developed, which have been shown to have potential for use in the detection of either changes in chromosome number or of perturbations of the events which may be causal in the induction of aneuploidy.

Chromosome number changes may be detected cytologically by karyotypic analysis, or by the use of specialised strains in which aneuploid progeny may be observed due to phenotypic differences with aneuploid parental cells or whole organisms. Techniques for the detection of cellular target modifications range from in vitro studies of tubulin polymerisation to observations of the behaviour of various cellular organelles and their fidelity of action during the division cycle.

The diversity of mechanisms which may give rise to aneuploidy and the qualitative relevance of events observed in experimental organisms compared to man make it unlikely that the detection and risk assessment of the aneugenic activity of chemicals will be possible using a single assay system. Optimal screening and assessment procedures will thus be dependent upon the selection of an appropriate battery of predictive tests for the measurement of the potentially damaging effects of aneuploidy induction.     

The control of chloroplast number in wheat mesophyll cells

Chloroplast number per cell and mesophyll cell plan area were determined in populations of separated cells from the primary leaves of different wheat species representing three levels of ploidy. Mean chloroplast number per cell increases with ploidy level as mean cell size increases. But in addition the analysis of individual cells clearly shows that cells of a similar size but from species of different ploidies have similar numbers of chloroplasts. We conclude that the number of chloroplasts within a cell is closely correlated (P<0.001) with the size of the cell and this relationship is consistent for species of different ploidies over a wide range of cell sizes. These results are discussed in relation to the hypothesis that chloroplast number in leaf mesophyll cells is determined by the size of the cell.     

Localization by in situ hybridization of a low copy chimaeric resistance gene introduced into plants by direct gene transfer

Summary An in situ hybridization method was developed for detecting single or low copy number genes in metaphase chromosomes of plants. Using as a probe ³H-labelled plasmid pABDI, which confers kanamycin resistance (Km^r) to transformed cells. DNA introduced into the plant genome by direct gene transfer was detected with a high efficiency: about 60% to 80% of interphase and metaphase plates showed a strong signal. The insertion site of the Km^r gene in two independent transformants was localised on different homologous chromosome pairs. This result independently confirmed previous genetic data which had indicated that transformed DNA was integrated into plant chromosomes in single blocks.     

Structure of T-DNA in plants regenerated from roots transformed by Agrobacterium rhizogenes strain A4

Summary The structure of the T-DNA in Ri-transformed plants of Brassica napus, Nicotiana plumbaginifolia and Nicotiana tabacum was analysed. All the plants studied present a particular phenotype with wrinkled leaves. The T-DNA is composed of two parts: TL and TR. The size of the TL-DNA (19–20 kb) seems to be almost constant, except in N. tabacum where it is shorter. The TR-DNA can be absent, and its size varies from about 5–28 kb, with two predominant lengths. The smaller size does not include the region homologous to the tms genes of the pTi T-DNA. The copy number varies from one to four copies per plant genome. TL and TR-DNA are not always present in the same copy number, but in some cases are linked together.     

Genetic diversity within and among 11 juvenile populations of green alder (Alnus crispa) in Canada

Germinated seeds from 11 populations of green alder [ Alnus crispa (Ait.) Pursh] sampled in four Canadian provinces were analysed for electrophoretically demonstrable diversity of 10 enzymes encoded by 15 structural loci. Of these, nine were polymorphic, and on average, 52% of the loci per population were polymorphic. Assuming a diploid model of expression, average level of expected heterozygosity was 0.11 with nearly all populations in Hardy-Weinberg equilibrium for the set of polymorphic loci analysed. No significant inbreeding and associated subpopulation structuring were noted. Rates of gene flow appeared high within and among populations. Although little divergence was observed among populations, genetic and geographical distances between populations were related. Discriminant and cluster analyses revealed a pattern of genetic variation associated with geography. Populations from northern Quebec were poorly differentiated, whereas western populations from Alberta exhibited a larger degree of genetic differentiation. Introgresive hybridization with the sympatric species Alnus sinuata (Regel) Rydberg and partial isolation in the West are suggested as an explanation for this larger differentiation. The occurrence and significance of rare alleles is discussed in relation to the importance of geographical distance in the process of population differentiation in this species.