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To avoid negative effects of transposable element (TE) proliferation, plants epigenetically silence TEs using a number of mechanisms, including RNA-directed DNA methylation. These epigenetic modifi ...

Plant performance is correlated with element concentrations in plant tissue, which may be impacted by adverse chemical soil conditions. Antibiotics of veterinary origin can adversely affect plant performance. They are released to agricultural fields via grazing animals or manure, taken up by plants and may be stored, transformed or sequestered by plant metabolic processes. We studied the potential effects of three antibiotics (penicillin, sulfadiazine, and tetracycline) on plant element contents (macro-and microelements). Plant species included two herb species (Brassica napus and Capsella bursa-pastoris) and two grass species (Triticum aestivum and Apera spicaventi), representing two crop species and two noncrop species commonly found in field margins, respectively. Antibiotic concentrations were chosen as to reflect in vivo situations, that is, relatively low concentrations similar to those detected in soils. In a greenhouse experiment, plants were raised in soil spiked with antibiotics. After harvest, macro-and microelements in plant leaves, stems, and roots were determined (mg/g). Results indicate that antibiotics can affect element contents in plants. Penicillin exerted the greatest effect both on element contents and on scaling relationships of elements between plant organs. Roots responded strongest to antibiotics compared to stems and leaves. We conclude that antibiotics in the soil, even in low concentrations, lead to low-element homeostasis, altering the scaling relationships between roots and other plant organs, which may affect metabolic processes and ultimately the performance of a plant.

Summary The variation among isolates of beet mild yellowing luteovirus (BMYV), collected from commercial crops of sugar beet during 1990, 1992 and 1993, was studied using monoclonal antibodies and transmissions to indicator species. The common strain of BMYV, which occurs throughout the sugar-beet root growing area, reacts with monoclonal antibodies MAFF 24, BWYV-BC-510H and BYDV-PAV-IL-1, and infects Capsella bursa-pastoris. A second strain, which failed to react with monoclonal antibody BYDV-PAV-IL-1 and which did not infect C. bursa-pastoris, was identified in 11% of sampled infected plants. The implications of the properties of this strain for the epidemiology of BMYV are discussed.

In the vineyards of Rhineland-Palatinate (Germany), two different types of Shepherd’s Purse (Capsella bursa-pastoris) coexist: (1) the common type called ‘wild type’, and (2) the decandric type called Capsella apetala or ‘Spe’ with four stamens in place of the four petals. In this study, we compare the anatomical and physiological characters of rosette leaves of the respective types. Progeny of individual plants was cultivated in growth chambers under low- and high-light conditions. Under low-light conditions, the stomata densities of the adaxial and abaxial epidermis did not differ between the two types. When grown under high-light conditions, wild type and Spe, both exhibited increased stomata densities compared to low-light conditions, but Spe to a lesser extent than the wild type. The maximal photosynthetic capacity of Spe was lower in both, low-light and high-light conditions compared to wild-type plants. Under all CO2 concentrations, Spe seemed to be less productive. The less effective CO2 assimilation of the Spe mutant C. apetala was accompanied by later flowering. This fact prolonged the vegetative phase of Spe by about two weeks and was sufficient for the maintenance of both populations stably over years.

Presentation of CAPSELLA project at EC after invitation from SC2 during November 2017

This presentation took place in Rome, during 1 & 2 February 2017 on the scope of the DSI Fair.

Hybridization of closely related plant species is frequently connected to endosperm arrest and seed failure, for reasons that remain to be identified. In this study, we investigated the molecular events accompanying seed failure in hybrids of the closely related species pairCapsella rubellaandC.grandiflora. Mapping of QTL for the underlying cause of hybrid incompatibility inCapsellaidentified three QTL that were close to pericentromeric regions. We investigated whether there are specific changes in heterochromatin associated with interspecific hybridizations and found a strong reduction of chromatin condensation in the endosperm, connected with a strong loss of CHG and CHH methylation and random loss of a single chromosome. Consistent with reduced DNA methylation in the hybrid endosperm, we found a disproportionate deregulation of genes located close to pericentromeric regions, suggesting that reduced DNA methylation allows access of transcription factors to targets located in heterochromatic regions. Since the identified QTL were also associated with pericentromeric regions, we propose that relaxation of heterochromatin in response to interspecies hybridization exposes and activates loci leading to hybrid seed failure.

Many plants derive nutrients by attracting, ensnaring and killing invertebrates, a process that is described as “protocarnivory”. This has been observed in seeds of the weed Capsella bursa-pastoris, but it is unclear as to whether it confers any material benefit in terms of germination, establishment and development. In the present study, seeds were germinated in zero, low, medium and high nutrient soils in both the presence and absence of nematodes (Steinernema feltiae). Nematodes were attracted to the seeds, with many dying within three days. Germination rates and seedling fresh masses were higher at all nutrient levels, and seedling fresh lengths were higher in all but the zero nutrient treatment, in the presence of nematodes. After transplantation, young plant fresh root lengths and dried leaf and root masses were generally higher in plants that had been germinated in the presence of nematodes across all nutrient levels, with the majority of significant differences being observed in the low-nutrient treatment. Our findings suggest that protocarnivory may play a role in the germination, establishment and early development of C. bursa-pastoris, and that this process may be facultative, since differences between nematode and non-nematode treatments were generally more pronounced in soils with low nutrient levels.

Presentation of CAPSELLA project at EC after invitation from SC2 during November 2017

NUMEROUS physiologically active polypeptides have been found in animals and bacteria, but little has been reported about such substances in plants. A purified substance from an alcohol extract of the herb Capsella bursa-pastoris (Cruciferae), however, exerted contractile activity on the rat uterus which was similar to that of oxytocin and had some characteristics of a polypeptide. Few studies have been made of the chemical composition and pharmacology of this herb, although it has been eaten and used medicinally for haemostasis, diuresis and as an antipyretic in China and Japan for many centuries.

PREVIOUSLY, I have directed attention to the prevalence of intermittent germination as a feature of the most successful of our annual garden weeds and suggested that human cultivation activities have probably effected an artificial selection of strains that has accentuated this feature1. Attention was there directed to the need for sowing freshly ripened seeds from individual plants to avoid the concealment of this feature, through overlap of the germination flushes from seeds of different individuals or seeds stored for varying periods. These conditions, however, frequently impose a severe limitation on the number of seeds available for any one test and it might therefore be suggested that if a considerably augmented number of seeds were simultaneously ripened the intermittence would be appreciably diminished or might actually disappear.

SUMMARY (1) Monocultures of Capsella bursa-pastoris and Poa annua were sown at high density and grown in the presence and absence of the slug Agriolimax caruanae. The slug showed strong dietary preference for Capsella just as it had done in laboratory tests, and ate Poa only after starving for c. 66 h. (2) The populations of Capsella exhibited linear survivorship curves, individuals being lost from the populations at an approximately constant rate. (3) The rate of self-thinning and the growth made by survivors were such that populations conformed to the - 3/2 power thinning law, though stands of the two species had different carrying capacity. (4) Slugs behaved quite differently towards the two plant species. The) ate whole, or parts of, leaves of Capsella bursa-pastoris but rarely, if ever, killed the plants. They ate Poa annua (after the starving threshold) by chewing through shoots at ground level, 'felling' but not consuming the shoots. Many of the damaged plants of Poa died. (5) The effect of slugs was therefore generally to change the size of plants of Capsella but not their number and to change the number of plants of Poa rather than their size, at least in the early stages of the study. (6) There was some evidence that defoliation decreased the reproductive potential of the grazed monocultures. (7) The results are discussed in the context of the compensatory effects of competition and predation, the differential effect of herbivores on plants with different biology, and caveats for other work where grazing trials are involved.

Beet western yellows virus (BWYV) was isolated from potato cultivars showing leaf roll in Tasmania. Twenty-four of 25 plants representing 11 cultivars selected from the field as showing typical leaf roll symptoms contained virus that infected Capsella bursa-pastoris. Serological tests with two isolates showed them to be closely related to several Californian BWYV isolates. Because of strict plant quarantine and certification schemes operating in Tasmania since the early 1930s, these isolates of BWYV are probably representative of leaf roll isolates that were common before world-wide certification schemes. The occurrence of BWYV in potatoes during these early periods strongly indicates a world-wide significance of BWYV in potato culture. The wide spread occurrence of BWYV associated with leaf roll in Tasmanian potatoes could have very important consequences for the potato certification scheme. These are discussed together with the use of sensitive serological tests to detect luteoviruses in potato and facilitate their control.

bute to the main bulk of the seed population are very similar. Two of the most important of these species are Capsella bursa-pastoris and Senecio vulgaris. We chose them for study in order to gain further insight into the germination characteristics which lead to the success of annual weeds in cultivated or disturbed soil. This paper describes a laboratory investigation into the dormancy and germination behaviour of the two species in relation to some of the major factors which are likely to affect seed germination in the soil. As Koller (1964) has pointed out that there are difficulties in relating petri dish experiments to field conditions. Nevertheless it is believed that laboratory studies under controlled conditions are an essential beginning to an understanding of the behaviour of seeds in response to the complex and fluctuating conditions in the field. In the second paper, an attempt will be made to relate field behaviour to the physiological responses investigated here. MATERIALS AND METHODS Source of seed Seeds were collected in Cheshire in September 1965: those of Capsella bursa-pastoris (L.) Medik. from the Experimental Grounds, Jodrell Bank, and those of Senecio vulgaris L. from Morton's Rose Nursery, Alderley Edge. They were dried to about 800 moisture content in a stream of dry air at room temperature and were then stored in Kilner jars at 4 + 20 C until needed. Occasional checks on viability and dormancy during the 2-year period of these investigations showed that there were no changes, except for a slight loss of dormancy in the case of Senecio.

Circumstantial evidence suggests that Albugo is heterothallic and that coincident infection with Peronospora may induce selfing of Albugo. Meiosis occurs immediately before gamete formation in both species. Conclusive evidence for this is the observation of chromatid exchanges at pachytene and of multivalents at metaphase in Albugo. Stages of nuclear division between meiotic prophase and fertilization are illustrated in Albugo. Nuclei from the developing oospore and other vegetative nuclei are illustrated and shown to be much larger than the haploid nuclei resulting from meiosis in the gametangia. The haploid chromosome number of P. parasitica is 18–20 and that of Albugo lies between 25 and 40. If the basic number of the group is 9 or 10, Peronospora is tetraploid and Albugo hexaploid or octoploid. The strain of Albugo on Lunaria has larger chromosomes than that on Capsella, indicating a genetic difference between the two strains.

In the ecology of annual weeds, it is the characteristics of the seeds which are most important in determining the distribution of the plants in both space and time. The weed plant itself lives for less than 9 months but its seeds can remain alive in the soil for many years. Furthermore, because weeds live in temporary habitats, they are always exposed to the risk of total elimination from a locality and therefore the vast reservoir of seeds in the soil is necessary to ensure survival. In the soil, germination and subsequent emergence of weed seedlings is an irregular process. Usually, at intervals throughout the year, large numbers of seeds germinate within a few days of each other and then each burst of activity is followed by a quiescent period during which only a few seeds germinate. This has been observed in natural seed populations (Chancellor 1965) and in artificially introduced populations derived from bulk seed collections (Roberts 1964). Small flushes of germination of Senecio and Capsella were observed by both these authors throughout the year but the biggest flushes occurred in May and in August and September. Salisbury (1964) confirmed this pattern of germination in Capsella using an artificially introduced population derived from a single plant. Such a pattern of seed germination would appear to be of great advantage to the species because even if an entire crop of plants is destroyed, more seedlings will soon emerge to replace those which were lost. The causes of these intermittent flushes of germination are often obscure. In some cases it has been shown that a population of seeds, even from a single plant, contains distinct groups with different physiological responses which may (or may not) be correlated with morphological differences. This phenomenon has been exposed largely by Harper and his colleagues and is referred to as seed polymorphism (Williams & Harper 1965; Cavers & Harper 1966). To be useful, the term should be restricted to those cases where it can be shown that there is a discontinuous distribution of some germination mechanism amongst the seeds, or that, when subjected to constant conditions, the distribution of the onset of germination in time contains more than one distinct mode. Even in homozygous, cultivated cereals there is great variation in the distribution of dormancy periods in a single population of seeds, even from the same plant. For example, if a population of rice seeds is stored under constant conditions after harvest and samples subjected to germination tests at regular intervals, it has been shown that the distribution of dormancy periods amongst the individual seeds is normal and that the standard deviation is relatively large (Roberts 1961, 1965): from these published data it may be calculated that the coefficient of variation