Adela M. Sánchez-Moreiras

The natural compound benzoxazolin-2(3H)-one selectively retards cell cycle in lettuce root meristems

Benzoxazolin-2(3H)-one (BOA) is a natural plant product that is phytotoxic to target plant species, inhibiting germination and growth and causing oxidative damage. We investigated its effects on the root meristems of seedlings of lettuce (Lactuca sativa) by means of light and transmission electron microscopy, flow cytometry, and conventional determination of mitotic index. Flow cytometry analyses and mitotic index showed a retard of cell cycle in BOA-treated meristems with selective activity at G2/M checkpoint.

Citral Induces Auxin and Ethylene-Mediated Malformations and Arrests Cell Division in Arabidopsis thaliana Roots

Citral is a linear monoterpene which is present, as a volatile component, in the essential oil of several different aromatic plants. Previous studies have demonstrated the ability of citral to alter the mitotic microtubules of plant cells, especially at low concentrations. The changes to the microtubules may be due to the compound acting directly on the treated root and coleoptile cells or to indirect action through certain phytohormones. This study, performed in Arabidopsis thaliana, analysed the short-term effects of citral on the auxin content and mitotic cells, and the long-term effects of these alterations on root development and ethylene levels. The results of this study show that citral alters auxin content and cell division and has a strong long-term disorganising effect on cell ultra-structure in A. thaliana seedlings. Its effects on cell division, the thickening of the cell wall, the reduction in intercellular communication, and the absence of root hairs confirm that citral is a strong phytotoxic compound, which has persistent effects on root development.

Early senescence induced by 2-3H-benzoxazolinone (BOA) in Arabidopsis thaliana

Measurements of chlorophyll a fluorescence, nutrient and trace elements, total protein content and malonyldialdehyde in leaves of Arabidopsis thaliana between 1 and 192 h after treatment with 0, 1 or 3 mM 2-3H-benzoxazolinone (BOA), together with imaging of chlorophyll a fluorescence and of the distributions of hydrogen peroxide and superoxide anion, suggested that the primary phytotoxic action of BOA is the induction of premature senescence, and that oxidative stress is a secondary effect that sets in a day or two later.

Terpenoid trans-caryophyllene inhibits weed germination and induces plant water status alteration and oxidative damage in adult Arabidopsis

trans-Caryophyllene (TC) is a sesquiterpene commonly found as volatile component in many different aromatic plants. Although the phytotoxic effects of trans-caryophyllene on seedling growth are relatively explored, not many information is available regarding the phytotoxicity of this sesquiterpenes on weed germination and on adult plants. The phytotoxic potential of TC was assayed in vitro on weed germination and seedling growth to validate its phytotoxic potential on weed species. Moreover, it was assayed on the metabolism of Arabidopsis thaliana adult plants, through two different application ways, spraying and watering, in order to establish the primary affected organ and to deal with the unknown mobility of the compound. The results clearly indicated that TC inhibited both seed germination and root growth, as demonstrated by comparison of the ED50 values. Moreover, although trans-caryophyllene-sprayed adult Arabidopsis plants did not show any effect, trans-caryophyllene-watered plants became strongly affected. The results suggested that root uptake was a key step for the effectiveness of this natural compound and its phytotoxicity on adult plants was mainly due to the alteration of plant water status accompanied by oxidative damage.

Loss of Gravitropism in Farnesene-Treated Arabidopsis Is Due to Microtubule Malformations Related to Hormonal and ROS Unbalance

Mode of action of farnesene, a volatile sesquiterpene commonly found in the essential oils of several plants, was deeply studied on the model species Arabidopsis thaliana. The effects of farnesene on the Arabidopsis root morphology were evaluated by different microscopic techniques. As well, microtubules immunolabeling, phytohormone measurements and ROS staining helped us to elucidate the single or multi-modes of action of this sesquiterpene on plant metabolism. Farnesene-treated roots showed a strong growth inhibition and marked modifications on morphology, important tissue alterations, cellular damages and anisotropic growth. Left-handed growth of farnesene-treated roots, reverted by taxol (a known microtubule stabilizer), was related to microtubule condensation and disorganization. As well, the inhibition of primary root growth, lateral root number, lateral root length, and both root hairs length and density could be explained by the strong increment in ethylene production and auxin content detected in farnesene-treated seedlings. Microtubule alteration and hormonal unbalance appear as important components in the mode of action of farnesene and confirm the strong phytotoxic potential of this sesquiterpene.

The Phytotoxic Potential of the Terpenoid Citral on Seedlings and Adult Plants

Abstract Citral is a monoterpene commonly found as volatile component in many different aromatic plants. Although many studies have identified the presence of citral in phytotoxic essential oils, this work determines for the first time the potential herbicidal effect of citral on weeds. The use of citral against weeds and crops resulted in the potential for the management of barnyardgrass, redroot pigweed, and ribwort. Clear morphological differences were observed between adult thale cress plants exposed to citral in two different application methods: spraying and watering. Citral-sprayed and citral-watered thale cress plants showed completely different effects after treatment, suggesting that foliar or root absorption can determine the effectiveness of this compound. This work demonstrates that citral is effective not only on seedling metabolism but also on adult plants by inhibiting growth and development altering the plant oxidative status. Nomenclature: Citral, 3,7-dimethyl-2,6-octadienal, CAS 5392-40-5; barnyardgrass, Echinochloa crus-galli L. (Beauv.) ECHICRU; redroot pigweed, Amaranthus retroflexus L. AMARE; buckhorn plantain, Plantago lanceolata L. PLANLAN; thale cress, Arabidopsis thaliana L. ARATH.

Individual and joint activity of terpenoids, isolated from Calamintha nepeta extract, on Arabidopsis thaliana

Four terpenoids, camphor, pulegone, trans-caryophyllene and farnesene, previously found in Calamintha nepeta (L.) Savi methanolic extract and essential oils were assayed on germination and root growth of Arabidopsis thaliana (L.) Heynh. None of the terpenes, singularly or in combination, was able to inhibit the germination process. Farnesene and trans-caryophyllene caused a strong inhibitory effect on root growth, and pulegone, at the highest concentrations, reduced lateral root formation. Although the mixture of camphor–trans-caryophyllene with or without farnesene did not cause any effect on root growth, the addition of pulegone induced a marked synergistic activity. Moreover, the addition, at low concentration, of farnesene to pulegone–camphor–trans-caryophyllene mixture further increased the inhibitory effect on root elongation. These results suggested that the inhibitory effects caused by C. nepeta methanolic extract may depend on the combined action of different molecules.

Phytotoxic Potential of Trans-chalcone on Crop Plants and Model Species

Chalcones are flavonoid precursors that recently have been found to disrupt mitochondrial function and induce apoptosis in Arabidopsis radicles. However, whether they are potentially useful for weed control as selective herbicides depends on whether they are phytotoxic for important weeds and are not toxic for crops. This work determines the phytotoxicity of chalcone for the germination and early development of a variety of crop species and associated weeds. Also, the phytotoxic potential was investigated in chalcone-watered or sprayed adult plants of Arabidopsis, a common model in phytotoxicity assays. Chalcone was detrimental mainly to the germination of Plantago lanceolata and Lactuca sativa and to the early root growth of Amaranthus retroflexus, Echinochloa crus-galli, and P. lanceolata, and likewise detrimental to the development of adult Arabidopsis. The morphology and physiology of adult Arabidopsis plants watered or sprayed with chalcone confirmed that this metabolite is also phytotoxic for adult plants and showed that the mechanism of its action on plant metabolism depends on whether it is administered by spraying or watering. These results support the role of chalcone as a plant growth regulator and its potential use in weed management in the field.

Early photosynthetic response of Arabidopsis thaliana to temperature and salt stress conditions

Temperature changes and salt accumulation are among the most common abiotic factors affecting plants in agricultural and natural ecosystems. The different responses of plants to these factors have been widely investigated in previous works. However, detailed mechanism of the early photosynthetic response (first 24 h) has been poorly studied. The aim of the work was to monitor the early response of adult Arabidopsis thaliana plants exposed to different thermal (cold and heat) and salt conditions. Detailed evaluation of the efficiency of photosystem II was done, and the various routes of energy output as well as measurements of the contents of H2O2, proline, and photosynthetic pigments at different times during the first 24 h of treatment were examined. The conditions used in the study were those that caused a weak stress with time of exposure. Cold-treated plants showed the most continuous inhibitory effect on photosynthetic activity, with a fast metabolic slowdown (reduced PSII efficiency and decreased pigment contents), although they also demonstrated clear acclimation responses (increased heat dissipation and protein content). Heat-treated plants showed a late but stronger effect on photosynthesis with significantly increased quantum yield of nonregulated energy dissipation (ΨNO) and H2O2 content at the last measurements. Finally, salt-induced oxidative stress (increased H2O2 content), decreased PSII efficiency and pigment content.

The role of peroxidases on the mode of action of chalcone in Arabidopsis roots

Chalcone is a secondary metabolite belonging to the group of flavonoids. It has shown strong phytotoxic activity on Arabidopsis roots, as inductor of programmed cell death, and inhibitor of root growth and root hair formation. Peroxidases are particularly abundant in root meristems and are involved in the formation and interconversion of reactive oxygen species (ROS), which play a critical role on root and root hair development. Therefore, we report here the role of peroxidases in Arabidopsis root development during chalcone treatment. A strong inhibition of peroxidase activity was detected in the apical root meristems after chalcone treatment, which reflects the important role of these enzymes on the mode of action of this secondary metabolite.