Archives - Allelopathy Journal

Laboratory and pot experiments were done to determine the autotoxicity potential of aqueous extracts (rhizomes, shoots, soil extracts) and rhizome exudates of Angelica sinensison its own seed germination and seedling growth. Inlaboratory experiments, aqueous extracts (rhizomes, shoots, soilextracts) and rhizome exudates inhibited its own seed germination and seedling growth and this inhibitory effect increased with increase in aqueous extracts concentrations. The extracts from A. sinensisrhizomes were less inhibitory than those from shoots. The extracts of rhizome and shoot collected at the rhizome thickening stage were more inhibitory than those collected at seedling stage. The radicle growth was more sensitive to extract than shoot growth and seed germination. These results showed that A. sinensishad autotoxicity potential. The pot experiments showed that plant parts and sterilized soil (previously cropped with A. sinensis) inhibited the seedling growth at 1.5% concentrations (g plant material/g soil), and confirmed the autotoxicity potential ofA. sinensis. Thus autotoxicity is the main problem in continuous cropping of A. sinensis.

The allelopathic effects of extracts of leaf litterand live roots of three Eucalyptusspecies [Eucalyptus urophylla Blake (Myrtaceae), Eucalyptus citriodora Hook. andEucalyptus camaldulensisDehnh] were determined on the following crops: radish [Raphanus raphanistrumvar. sativusL. G. Beck, Brassicaceae), cucumber (Cucumis sativus L., Cucurbitaceae), and Chinese cabbage (Brassica rapavar. glabra Regel, Brassicaceae)]. The extracts of leaf litter and live roots were inhibitory or stimulatory to test species. However, the effects of leaf litter extracts at lower concentrations were similar to natural concentration in fields and were more pronounced than live roots. When litterfall were removed, Chinese cabbage should be a good candidate crop grown under Eucalyptus urophyllaand cucumber should be a good candidate crop grown under all tested Eucalyptusspecies in the tree-crop agroforestry systems.

To develop models for pollen-pollen interactions, the effects of allelochemicals secreted by foreign pollen i.e. donor pollens were studied in vitro or in vivo on the germination of acceptor-pollen and autofluorescence. Both acceptor and donor pollens were choosen from the indoor (greenhouse) and outdoor grown plants. Microspores from Hippeastrum hybridum, Philadelphus grandiflorus, Knautia arvensis, Plantago major and Oenothera biennis were used as pollen-acceptors, while other pollen grains from 42 spp. - as donor pollens. The significant negative effects of donor pollen were observed on 3 acceptor pollen: Hippeastrum hybridum, Philadelphus grandiflorus and Knautia arvensis. Their germination was inhibited by forein pollen grains from 18 spp. In mixtures of pollen from various species, 4 donors pollens (Alstroemeria aurantiaca, Anthriscus sylvestris, Solidago virgaurea and Tagetes patula) stimulated the microspores’ germination, whereas, microspores from Aloe vera, Lilium mortagon, Filipendula ulmaria and Hypericum perforatum showed no significant responses to foreign pollen. The rate of the pollen tube formation was also changed in donor pollens themselves in the presence of acceptor pollen grains. Coloured excretions from donor pollen of Hypericum perforatum and Calendula officinalis stained the Colourless pollens of Plantago major and Oenothera biennis. Autofluorescence of acceptor and donor pollens in mixtures was changed to blue-green and red spectral regions that may serve as the indicator response on forein microspores. Generally increased blue-green and occasionally red emission indicated the decrease in rate of pollen germination. However, red fluorescence was not related to germination and depended more on species used.

The chemosignaling in allelopathy uses plant microspores as unicellular models. Possible mechanisms were compared for pollen and vegetative microspores. Development of pollen (generative microspores) from knights’ star (Hippeastrum hybridum) and vegetative microspores of Equisetum arvense were analyzed after treating with blockers of ion channels and anticontractile agents for 24 h (short-time experiments) and 25-28 days (long-time experiments). The blockers of Na+, K+, Ca2+ ion channels (relatively a-bungarotoxin; tetraethylammonium; verapamil) or anti-conractile agents (cytochalasin B or colchicine, except papaverine or clofelin), depressed the germination (30-60 % in short-time exposures) of both types of microspores to different degrees depending on the concentration. Moreover in long-time experiments, the normal fruits were not formed from the pollens after pollination, while, in vegetative microspores the gamethophyte (thallus) and antheridia (male sexual organs) formation were inhibited. However, the actin from rabbit muscle, restored the vegetative microspore germination after the blockade of cholinoreceptor (related to Na+/K+ channels) by a-bungarotoxin or the intracellular binding with cytochalasin B, inhibitor of actin polymerization. The similar effects were observed in preliminary blockade of Ca 2+ channels with verapamil in pollen of knights’ star. Thus, the pathways of chemosignal transduction from the cell are discussed in relation to possible mechanism of allelopathy.

The compounds present in pollen excretions (which participates in allelopathy), have been analyzed in model systems of generative microspores (pollen) from Hippeastrum hybridum and vegetative microspores of horsetail (Equisetum arvense). These compounds were proteins and substances related to reactive oxygen species (oxidants and antioxidants) found in pollens and vegetative microspores. Both types of microspores contained high-molecular (< 2000 kDa and subunits with SDS near 90-94 kDa) and low-molecular (< 30 kDa) proteins having cholinesterase, peroxidase and superoxide dismutase activity. The effects of pollen proteins (monoamine oxidase, peroxidase, hexokinase, a- amylase, pepsin, trypsin, cytochrome C, ferritin, haemoglobin, cholinesterase and lysozyme) were tested on microspores development. Among the proteins, cytochrome C, ferritin, haemoglobin, subtilisin and trypsin strongly inhibited the pollen germination, whereas, the inhibition in vegetative microspores was observed with pepsin and amylase. The other analyzed peptides either weakly stimulated or had no effect on spore’s germination. Reactive oxygen species (peroxides or superoxide) formed anion radical from the catecholamines [(dopamine and noradrenaline), transamine and iprazide (inhibitors of monoamine oxidases)], stimulated the germination (20-100 % increase) of both spore types. While antioxidants (dithionite,mannitol, ascorbate, peroxidase, superoxide dismutase, ecdysone, caffeic and chlorogenic acids, austricine, gaillardine and grosshemine) inhibited the germination. However, high concentration of ozone (0.2 ml/L) inhibited the reaction and damaged the cells. Therefore role of reactive oxygen species for growth enhancement and antioxidants retardation may be important in pollen-pollen and pollen-pistil interactions. Possible mechanisms of cell-cell interactions with identified compounds have been discussed.

We determined the contents of endogenous phytohormones and flavonols on in vitro germinating petunia (Petunia hybrida L.) male gametophyte and their effects on petunia pollen germination and pollen tube growth. The germination and growth of pollen tubes on the cultivation medium (containing 0.4 M sucrose and 1.6 mM H3BO3) increased the contents of IAA, ABA, gibberellins, cytokinins and flavonols (quercetin and kaempferol). The qualitative effects of exogenous compounds depended on their nature and concentration. All test compounds were most stimulatory at 10-12 M concentration. The applied exogenous ABA and gibberellin A3 stimulated the germination and growth of male gametophyte at all test concentrations (10-12–10-3 M). Gibberellin A3, proved most stimulatory to growth of pollen tubes. IAA stimulated the germination and growth of male gametophyte at 10-12 – 10-8 M concentrations, whereas, the inhibition was observed at 10-4 – 10-3 M concentrations. The test flavonols, stimulated both processes at 10-12–10-10 M concentrations and caused inhibition at 10-6–10-3 M concentrations. Synthetic cytokinin 6-BAP at 10-12–10-3 M concentrations inhibited both the germination and growth of pollen tubes. The 2,4-chlorphenoxy-2-methylpropionic acid (inhibitor of IAA transport) completely blocked both the processes, while the fluridone and paclobutrasol (known inhibitors of synthesis of ABA and gibberellins respectively), only inhibited the germination and growth of male gametophyte. In the presence of 2,4-chlorphenoxy-2-methylpropionic acid (inhibitor of IAA transport), exogenous ABA, gibberellin A3 and flavonols did not stimulate pollen germination.

We tested the in situ pollen transfers and allelopathic impacts of the putative pollen allelopathic spp. [Alliaria petiolata L. and Hesperis matronalis L. on the sympatric concurrently flowering spp. Alyssum alyssoides (L.), Cardamine diphylla (Michx.) Willd., Lepidium campestre (L.) R. Br. and Sisymbrium altissimum L]. Pearson product moment and Mann Whitney U tests indicated that regardless of whether Coulter Counters or microscope counts were used to count pollen, there was sufficient pollen transfer from the Alliaria petiolata and Hesperis matronalis to all spp. except Cardamine diphylla, where its pollinator is more fidelous. When there was a relatively low maximum of 10 pollen grains of either Alliaria petiolata or Hesperis matronalis on stigmas of Alyssum alyssoides, Lepidium campestre and Sisymbrium altissimum, the pollen tube generation declined by 80% and the difference compared to stigmas with no heterospecific pollen was significant (Pearson product moment tests, P < 0.001). While this is typical for pollen allelopathic impacts, our conclusion is more cautious, because after 5-days in a sterilized environment, fungi that already existed on pollen and stigmas began to grow. This is unlike the situation in our research group’s previous studies, where there was no “contamination” from fungi or any other organism or chemical. As such, we conclude that while there is evidence of pollen allelopathic impacts, it is still possible that the declines in pollen tube generation in species receiving pollen from Alliaria petiolata or Hesperis matronalis may be due to immediate exudation from fungal spores carried on pollen or stigmas rather than pollen.

Pollen allelopathy plays key role in normal plant fertilization in biocenosis. Allelochemicals released from the pollens of foreign spp. on the stigma of other spp. interferes with the pollen germination or tube growth, stigma or style receptivity, ovule development, respiration, seedling germination and/or growth), leaf chlorophyll, seed set and non-specialist pollinators or nectarivores. Besides these allelochemicals also affects the reproductive success or failure of recipient plant spp. and leads to weed-crop and crop-weed interactions, when many crops and weeds exist together. Pollen allelopathy may delay the flowering in weeds to less favourable season or diurnal period to reduce the weeds pressure, hence, it may be used in Ecological Weed Management. This review provides the Current Status of Allelopathy Research

During repeated and long term experiments using in vitro and field tests, we examined the identity of the pollen allelochemical in Hieracium x dutillyanum Lepage & its ecological impacts on a Conyza canadensis and Sonchus arvensis dominated community in southern Ontario, Canada. We found that H. x dutillyanum had significant numbers of pollen grains transmitted to both Conyza canadensis and Sonchus arvensis in the field. Further, we determined that the field impacts matched the in vitro tests and that the number of pollen grains or equivalent extract concentrations was ecologically relevant. We confirmed that the chemical responsible for the pollen allelopathic effect is phenylacetic acid - similar to Ana Luisa Anaya lab’s finding for a cultivar of Zea mays. During 1997-2008, flowering populations of H. x dutillyanum caused declines in populations of both Conyza canadensis and Sonchus arvensis. In contrast, if we manipulated fields by bagging H. x dutillyanum inflorescences, then the populations of Conyza canadensis and Sonchus arvensis rose significantly during this time period. Because the fields were otherwise similar and not manipulated further, we conclude that the long-term population responses in Conyza canadensis (L.) Cron.and Sonchus arvensis L. are explained solely by the presence or absence of allelopathic pollen (using phenylacetic acid) from Hieracium x dutillyanum. This is the first comprehensive and long term study examining the identity of the pollen allelopathic chemical, the in vitro response, the in situ response, and the population and community responses.