ROS Metabolism Perturbation as an Element of Mode of Action of Allelochemicals

The allelopathic interaction between plants is one of the elements that influences plant communities. It has been commonly studied by applying tissue extracts onto the acceptors or by treating them with isolated allelotoxins. Despite descriptive observations useful for agricultural practice, data describing the molecular mode of action of allelotoxins cannot be found. Due to the development of -omic techniques, we have an opportunity to investigate specific reactive oxygen species (ROS)-dependent changes in proteome or transcriptome that are induced by allelochemicals. The aim of our review is to summarize data on the ROS-induced modification in acceptor plants in response to allelopathic plants or isolated allelochemicals. We present the idea of how ROS are involved in the hormesis and plant autotoxicity phenomena. As an example of an -omic approach in studies of the mode of action of allelopatic compounds, we describe the influence of meta-tyrosine, an allelochemical exudated from roots of fescues, on nitration—one of nitro-oxidative posttranslational protein modification in the roots of tomato plants. We conclude that ROS overproduction and an induction of oxidative stress are general plants’ responses to various allelochemicals, thus modification in ROS metabolisms is regarded as an indirect mode of action of allelochemicals.

Revisiting Theron’s hypothesis on the origin of fairy circles after four decades: Euphorbias are not the cause

Background The Euphorbia hypothesis on the origin of fairy circles (FCs) in Namibia dates back to 1979. It proposes that the remains of decaying shrubs would induce an allelopathic interaction with the grasses and thereby cause bare-soil FCs. Here, we investigated this hypothesis based on revisiting marked Euphorbias after four decades, comparing the typical size distribution of dead Euphorbia damarana and FCs, and analyzing the spatial patterns of Euphorbias and FCs within the same drone-mapped study plots in three regions of Namibia. Results We found four dead Euphorbias in the southern Giribes that were marked by G.K. Theron about 40 years ago. Those locations did not develop into FCs over this time span. However, for the four dead Euphorbias, we provide photographic evidence that grass tufts were growing at the metal pins of those decaying shrubs, agreeing with previous research findings that the soil taken from beneath dead E. damarana shrubs was stimulating rather than inhibiting the growth of grasses. In the Giribes, there were very large FCs that ranged in diameter from 13.0 to 19.1 m. By contrast, the measured dead E. damarana, including the largest plants that we could find, ranged in size only between 4.2 and 11.7 m. At Brandberg, we found particularly small FCs with diameters between 2.4 and 2.7 m but the dead E. damarana, including the smallest dead shrubs in the area, ranged in size between 4.1 and 7.2 m. Hence given these size mismatches, the decaying Euphorbias cannot induce such observed FCs in the two regions. Spatial patterns of E. damarana and FCs in the two regions Giribes and Brandberg, as well as of E. gummifera and FCs near Garub, showed a strong mismatch within the same habitat: in four out of five plots the patterns differed significantly. FCs were regularly distributed while Euphorbias were predominantly clustered. Conclusions We reject the Euphorbia hypothesis based on the fact that grass growth was not prevented under decaying shrubs, the size of dead Euphorbias cannot explain the size of observed FCs and the spatial distribution of Euphorbias cannot cause the specific pattern signature of FCs.

Inhibition of growth rate and cylindrospermopsin synthesis by Raphidiopsis raciborskii upon exposure to macrophyte Lemna trisulca (L)

Impact of macrophyte Lemna trisulca on the growth rate and synthesis of cylindrospermopsin (CYN) by cyanobacterium Raphidiopsis raciborskii was determined. The presence of L. trisulca inhibited the biomass accumulation of the cyanobacterium by 25% compared to the control during co-cultivation. The simultaneous cultivation of these organisms slightly affected the inhibition of macrophyte growth rate by 5.5% compared to the control. However, no morphological changes of L. trisulca after incubation with cyanobacteria were observed. It was also shown that the long-term (35 days) co-cultivation of R. raciborskii and L. trisulca led to a decrease in CYN concentration in media and cyanobacterial cells by 32 and 38%, respectively, compared to the values obtained for independent cultivation of cyanobacterium. Excessive absorption of phosphate ions by L. trisulca from the medium compared to nitrate ions led to a significant increase in the nitrate:phosphate ratio in the media, which inhibits the development of cyanobacterium. The obtained results indicate that L. trisulca in the natural environment may affect the physiology of cyanobacteria. The presented study is the first assessment of the allelopathic interaction of macrophyte and R. raciborskii.

Effect of Aqueous Extracts from Solidago Canadensis L. Leaves on Germination and Early Growth Stages of Three Cultivars of Raphanus Sativus L. Var. Radicula Pers

Solidago canadensis L. is an expansive perennial that forms persistent, species-poor plant communities. It often spreads in fallow areas, displacing native floristic ingredients. Its expansiveness is largely due to morphological features, but it can also be the effect of allelopathic interaction. The aim of the experiment was to investigate the effect of aqueous extracts (decoction, infusion, and maceration) from dry S. canadensis leaves on germination and early growth stages of Raphanus sativus L. var. radicula Pers., in three cultivars: ‘Rowa’, ‘Półdługa’, and ‘Krakowianka’. In comparison to the control, the percentage of germinated radish seeds of ‘Rowa’ cultivar was statistically lower on the infusion and macerate. Regardless of the cultivar, the smallest changes in germination were found in seeds watered with decoction, and the largest with macerate. Seedlings length was most inhibited on macerate substrates, and least with infusion. Regardless of the form of the extract, each of them negatively affected the initial growth of radish seedlings. A fresh mass of ‘Rowa’ seedlings was inhibited by all Canadian goldenrod extracts. In relation to the control, the ‘Krakowianka’ cultivar was the least sensitive to S. canadensis extracts. The total chlorophyll content was the lowest in the seedlings of the ‘Rowa’ and ‘Półdługa’ cultivars germinated on macerate, compared to the control and two others extracts. The percentage of electrolyte leakage depended on the type of extract used and the radish cultivar. The study showed that depending on the cultivar, the aqueous extracts from S. canadensis leaves decreasing of germination and early growth of R. sativus.

Study of Allelopathic Interaction of Essential Oils from Medicinal and Aromatic Plants on Seed Germination and Seedling Growth of Lettuce

Medicinal and aromatic plants have the ability to transmit volatile allelochemicals and affect their surrounding organisms. In this regard, their interaction should also be considered. The inhibitory effects of 112 essential oils on lettuce seed and seedling were investigated by cotton swab method. Germination (G%), Mean germination time (MGT), Lethal of embryo (L%), dormancy (D%), radicle growth (R%), and hypocotyl growth (H%) were measured. Two methods were used for evaluating allelopathic interaction effects: the simplified modified dilution check-board technique (SMCT) and the isobologram. Thymus daenensis had the highest inhibitory effect on G% (IC50 = 2.9 ppm) and the most lethal effect on the embryo (LC50 = 7.2 ppm). Thymus transcaspicus, Dracocephalum moldavica, Artemisia sieberi and Amomum subulatum had the greatest effect on MGT. Ziziphora tenuior, Trachyspermum ammi and Pelargonium graveolens had the highest effect on D%. Origanum vulgare was the strongest growth inhibitor. The highest synergistic effect on G% was in A. subulatum + Mentha suaveolens, on H% was related to Perovskia abrotanoides + T. daenensis, and on R% was observed in Artemisia vulgaris + M. suaveolens. The results of this study can lead to identification of new phytotoxic compounds in EOs and control weeds more effectively.