Physiological and cell ultrastructure disturbances in wheat seedlings generated by Chenopodium murale hairy root exudate.

Chenopodium murale L. is an invasive weed species significantly interfering with wheat crop. However, the complete nature of its allelopathic influence on crops is not yet fully understood. In the present study, the focus is made on establishing the relation between plant morphophysiological changes and oxidative stress, induced by allelopathic extract. Phytotoxic medium of C. murale hairy root clone R5 reduced the germination rate (24% less than control value) of wheat cv. Nataša seeds, as well as seedling growth, diminishing shoot and root length significantly, decreased total chlorophyll content, and induced abnormal root gravitropism. The R5 treatment caused cellular structural abnormalities, reflecting on the root and leaf cell shape and organization. These abnormalities mostly included the increased number of mitochondria and reorganization of the vacuolar compartment, changes in nucleus shape, and chloroplast organization and distribution. The most significant structural changes were observed in cell wall in the form of amoeboid protrusions and folds leading to its irregular shape. These structural alterations were accompanied by an oxidative stress in tissues of treated wheat seedlings, reflected as increased level of H2O2 and other ROS molecules, an increase of radical scavenging capacity and total phenolic content. Accordingly, the retardation of wheat seedling growth by C. murale allelochemicals may represent a consequence of complex activity involving both cell structure alteration and physiological processes.This is a post-peer-review, pre-copyedit version of an article published in Protoplasma. The final authenticated version is available online at: [http://dx.doi.org/10.1007/s00709-018-1250-0

Cyanamide mode of action during inhibition of onion (Allium cepa L.) root growth involves disturbances in cell division and cytoskeleton formation

Cyanamide is an allelochemical produced by hairy vetch (Vicia villosa Roth.). Its phyotoxic effect on plant growth was examined on roots of onion (Allium cepa L.) bulbs. Water solution of cyanamide (2–10 mM) restricted growth of onion roots in a dose-dependent manner. Treatment of onion roots with cyanamide resulted in a decrease in root growth rate accompanied by a decrease in accumulation of fresh and dry weight. The inhibitory effect of cyanamide was reversed by its removal from the environment, but full recovery was observed only for tissue treated with this chemical at low concentration (2–6 mM). Cytological observations of root tip cells suggest that disturbances in cell division may explain the strong cyanamide allelopathic activity. Moreover, in cyanamide-treated onion the following changes were detected: reduction of mitotic cells, inhibition of proliferation of meristematic cells and cell cycle, and modifications of cytoskeleton arrangement

Allelopathy for Weed Management

A large number of plant and weed species produce secondary metabolites known as allelochemicals, and the process is known as allelopathy. Allelochemicals can be used to control weeds in agricultural systems by using allelopathic crops for intercropping, crop rotation, or mulching. A few important examples of crop species with high allelopathic potential may include (but not limited to) wheat, rice, sorghum, rye, barley, and sunflower. The naturally produced allelochemicals in these crops could be manipulated to suppress weeds and witness an environment-friendly and sustainable agricultural production system. © 2020, Springer Nature Switzerland AG

Stimulation Versus Inhibition—Bioactivity of Parthenin, A Phytochemical From Parthenium hysterophorus L.

Parthenium hysterophorus L. is an invasive weed that biosynthesizes several phytochemi-cals. The sesquiterpene lactone parthenin receives most attention regarding allelopathy of the plant or potential herbicidal properties. Since parthenin exhibits dose-dependent phy-totoxicity with low dose stimulation, this study investigated the occurrence and temporal features of parthenin hormesis in Sinapis arvensis L. sprayed with parthenin under semi-natural conditions. Dose/response studies showed that the occurrence and the magnitude of hormesis depended on climatic conditions and the parameter measured. Within the tested dose range, stimulatory responses were only observed under less-stressful conditions and were most pronounced for leaf area growth [138 % of control; 13 days after treatment (DAT)]. Temporal assessment of leaf area development showed that doses causing a stimulatory response at the end of the experiment (< 0.42 ± 0.04 kg/ha; 13 DAT) were initially inhibitory up to ED50 values (2 DAT). This clearly demonstrated an over-compensatory response. Inhibition of leaf area at 13 DAT reached ED50 values on average at 0.62 ±0.12 kg/ha, and S. arvensis was completely inhibited at doses exceeding 1.81 ±0.56 kg/ha (ED90). Based on these findings, implications of parthenin hormesis are discussed with respect to allelopathy of P. hysterophorus and exploitation of growth stimulatory responses in agriculture

Physiological and biochemical parameters: new tools to screen barley root exudates allelopathic potential (*Hordeum vulgare* L. subsp. *vulgare*

peer reviewedMorphological markers/traits are often used in the detection of allelopathic stress, but optical signals including chlorophyll a fluorescence emission could be useful in developing new screening techniques. In this context, the allelopathic effect of barley (Hordeum vulgare subsp. vulgare) root exudates (three modern varieties and three landraces) were assessed on the morphological (root and shoot length, biomass accumulation), physiological (Fv/Fm and F0), and biochemical (chlorophyll and protein contents) variables of great brome (Bromus diandrus Roth., syn. Bromus rigidus Roth. subsp. gussonii Parl.). All the measured traits were affected when great brome was grown in a soil substrate in which barley plants had previously developed for 30 days before being removed. The response of receiver plants was affected by treatment with activated charcoal, dependent on barley genotype and on the nature of the growing substrate. The inhibitory effect was lower with the addition of the activated charcoal suggesting the release of putative allelochemicals from barley roots into the soil. The barley landraces were more toxic than modern varieties and their effect was more pronounced in sandy substrate than in silty clay sand substrate. In our investigation, the chlorophyll content and Fv/Fm were the most correlated variables with barley allelopathic potential. These two parameters might be considered as effective tools to quantify susceptibility to allelochemical inhibitors in higher plants