Dynamics of callose deposition and beta-1,3-glucanase expression during reproductive events in sexual and apomictic Hieracium

Callose accumulates in the walls of cells undergoing megasporogenesis during embryo sac formation in angiosperm ovules. Deficiencies in callose deposition have been observed in apomictic plants and causal linkages between altered callose deposition and apomictic initiation proposed. In apomictic Hieracium, embryo sacs initiate by sexual and apomictic processes within an ovule, but sexual development terminates in successful apomicts. Callose deposition and the events that lead to sexual termination were examined in different Hieracium apomicts that form initials pre- and post-meiosis. In apomictic plants, callose was not detected in initial cell walls and deficiencies in callose deposition were not observed in cells undergoing megasporogenesis. Multiple initial formation pre-meiosis resulted in physical distortion of cells undergoing megasporogenesis, persistence of callose and termination of the sexual pathway. In apomictic plants, callose persistence did not correlate with altered spatial or temporal expression of a β-1,3-glucanase gene (HpGluc) encoding a putative callose-degrading enzyme. Expression analysis indicated HpGluc might function during ovule growth and embryo sac expansion in addition to callose dissolution in sexual and apomictic plants. Initial formation pre-meiosis might therefore limit the access of HpGluc protein to callose substrate while the expansion of aposporous embryo sacs is promoted. Callose deposition and dissolution during megasporogenesis were unaffected when initials formed post-meiosis, indicating other events cause sexual termination. Apomixis in Hieracium is not caused by changes in callose distribution but by events that lead to initial cell formation. The timing of initial formation can in turn influence callose dissolution. Received: 18 April 2000 / Accepted: 10 July 2000     

Optimum reproduction and dispersal strategies of a clonal plant in a metapopulation: a simulation study with Hieracium pilosella

Clonal spread is favoured in many plants at the expense of seed production in order to expand rapidly into open habitats or to occupy space by forming dense patches. However, for the dynamics of a population in a patchy landscape seed dispersal remains important even for clonal plants. We used a spatially explicit individual-based metapopulation model to examine the consequences of two trade-offs in Hieracium pilosella L: first, between vegetative and sexual reproduction, and second, between short and far-distance dispersal of seeds. Our main question was, what are the environmental conditions that cause a mixed strategy of vegetative and sexual reproduction to be optimal. The model was parameterised with field data on local population dynamics of H. pilosella. Patch dynamics were given firstly by disturbance events that opened patches in a matrix of a clonal grass that were colonisable for H. pilosella, and secondly by the gradual disappearance of H. pilosella patches due to the expanding grass. Simulations revealed opposing selection pressures on traits determined by the two trade-offs. Vegetative reproduction is favoured by local dynamics, i.e. the need for maintenance and expansion of established populations, whereas seed production is favoured by the necessity to colonise empty habitats. Similar pressures act on the proportion of seeds dispersed over short and far distances. Optimum reproductive and dispersal strategies depended on habitat quality (determined by seedling establishment probability), the fraction of dispersed seeds, and the fraction of seeds lost on unsuitable ground. Under habitat conditions supporting moderate to low seedling establishment, between 20% and 40% of reproductive effort in H. pilosella should be devoted to sexual reproduction with at least 10% of the seeds dispersed over distances suitable to attain empty patches. We conclude that in a spatially heterogeneous landscape sexual seed production in a clonal plant is advantageous even at the expense of local vegetative growth.     

Streamlining 'search and destroy': cost-effective surveillance for invasive species management

Invasive species surveillance has typically been targeted to where the species is most likely to occur. However, spatially varying environmental characteristics and land uses may affect more than just the probability of occurrence. Biodiversity or economic value, and the ease of detection and control are also likely to vary. We incorporate these factors into a detection and treatment model of a low-density invader to determine the surveillance strategy that minimizes expected management costs. Sites with a high probability of invader occurrence and great benefits associated with detection warrant intensive surveillance; however, the optimum investment is a nonlinear function of these factors. Environments where the invader is relatively easy to detect are prioritized for surveillance, although only a moderate investment is necessary to ensure a high probability of detection. Intensive surveillance effort may be allocated to other sites if the probability of occurrence, budget and/or expected benefits is sufficiently high.     

Methanol Extracts of 28 Hieracium Species from the Balkan Peninsula – Comparative LC–MS Analysis,Chemosystematic Evaluation of their Flavonoid and Phenolic Acid Profiles and Antioxidant Potentials

Introduction

Hieracium s. str. represents one of the largest and most complex genera of flowering plants. As molecular genetics seems unlikely to disentangle intricate relationships within this reticulate species complex, analysis of flavonoids and phenolic acids, known as good chemosystematic markers, promise to be more reliable. Data about pharmacological activity of Hieracium species are scarce.

Objective

Evaluation of the chemosystematic significance of flavonoids and phenolic acids of methanol extracts of aerial flowering parts of 28 Hieracium species from the Balkans. Additionally, investigation of antioxidant potentials of the extracts.

Methods

Comparative qualitative and quantitative analysis of flavonoids and phenolic acids was performed by LC–MS. Multivariate statistical data analysis included non‐metric multidimensional scaling (nMDS), unweighted pair‐group arithmetic averages (UPGMA) and principal component analysis (PCA). Antioxidant activity was evaluated using three colorimetric tests.

Results

Dominant phenolics in almost all species were luteolin type flavonoids, followed by phenolic acids. Although the investigated Hieracium species share many compounds, the current classification of the genus was supported by nMDS and UPGMA analyses with a good resolution to the group level. Hieracium naegelianum was clearly separated from the other investigated species. Spatial and ecological distances of the samples were likely to influence unexpected differentiation of some groups within H. sect. Pannosa. The vast majority of dominant compounds significantly contributed to differences between taxa. The antioxidant potential of the extracts was satisfactory and in accordance with their phenolics composition.

Conclusions

Comparative LC–MS analysis demonstrated that flavonoids and phenolic acids are good indicators of chemosystematic relationships within Hieracium, particularly between non‐hybrid species and groups from the same location. Copyright © 2017 John Wiley & Sons, Ltd.     

Predicting the Impact of the Biocontrol Agent Aulacidea subterminalis (Cynipidae) on Growth of Hieracium pilosella (Asteraceae) under Differing Environmental Conditions in New Zealand

A gall wasp, Aulacidea subterminalis, was released into the field in New Zealand in 1999 for biocontrol of the grassland weed Hieracium pilosella. To predict its likely impact in the field, the effect of the gall wasp on plant growth was measured under stress-free conditions in a shade house trial with potted plants. Plants with galls showed a reduction in stolon length of 75%. They had slightly lower total dry matter and reduced root weight. In a glasshouse experiment to measure the impact of water stress, nutrient stress, and plant competition on growth of H. pilosella and performance of the gall wasp, the number and mean diameter of gall clusters were not significantly different between treatment and control plants. However, galled plants produced more, but shorter, stolons in all stress treatments, and stolons that were more branched in nutrient- and water-stressed plants, than ungalled plants. Under the plant competition treatment, total stolon length relative to biomass was greater with, than without, wasps, indicating that stolons were thinner. Galling by A. subterminalis is likely to reduce vegetative reproduction of H. pilosella whether or not the plants are stressed, indicating that the wasp may be a successful biocontrol agent.     

Eight new species of Hieracium sect. Tridentata (Asteraceae) from southern and northern Sweden

Eight new species of Hieracium sect. Tridentata, namely H. antrorsum, H. quercifolium, H. stenianum, H. vestrogothicum, and H. vetlandaënse are described from the Götaland region (southern Sweden), H. grothii from Norrbotten in the Norrland region (northeast Sweden), and H. sparsifolium var. suppansum Johanss. and H. adampliatum var. pilosius Ohlsén are raised to specific rank as H. suppansum and H. gothiciferum respectively.     

A DEFICIENS homologue is down-regulated during apomictic initiation in ovules of Hieracium

 Hieracium is a member of the Asteraceae family, and contains sexual species in addition to apomictic species that reproduce by apospory and produce seed without fertilization. A homologue of the floral organ-identity gene DEFICIENS (DEF) was isolated from an apomictic line of Hieracium piloselloides (Vill.) following differential display between mature ovules and those initiating autonomous embryogenesis. The gene termed HPDEF has 93% amino acid identity with GDEF2, a DEF homologue isolated from Gerbera hybrida (D. Yu et al., 1999, Plant J. 17: 51–62), another member of the Asteraceae. In-situ analysis showed that early in floral development HPDEF is expressed in stamen and petal primordia, indicating expected B-function activity, according to the ABC model of floral organ identity (J. L. Bowman et al., 1991, Development 112: 1–20; E. S. Coen and E. M. Meyerowitz, 1991, Nature 353: 31–37). However, HPDEF expression was also observed in ovule primordia and expression continued in developing ovules until anthesis, indicating that this gene may have a role in ovule development. Expression of HPDEF was not detected in megaspore mother cells, or in sexual or aposporous embryo sacs. In sexual Hieracium, HPDEF was uniformly expressed throughout the ovule integument until anthesis. In most ovules of the apomict, however, HPDEF expression was transiently down-regulated in a specific zone in the chalazal region where cells initiating aposporous embryo sac formation differentiate. Uniform low-level HPDEF expression was subsequently observed prior to anthesis in ovules from sexual and apomictic plants. HPDEF may be down-regulated as a consequence of apomictic initiation and/or its down-regulation may facilitate progression of apomictic events. Received: 15 September 1999 / Accepted: 12 October 1999