Phytotoxic effects of Cerbera manghas L. leaf extracts on seedling elongation of four monocot and four dicot test species

Exploration of allelochemicals with phytotoxic effects is intended to minimize a current dependency on synthetic herbicides in weed management. Several allelochemicals from the tropical tree Cerbera manghas (sea mango) have been reported as termiticides and bactericides. The present study investigated possible phytotoxic effects of C. manghas leaf extracts under laboratory conditions. Four monocots: barnyard grass (Echinochloa crus-galli), foxtail fescue (Vulpia myuros), Italian ryegrass (Lolium multiflorum), and timothy (Phleum pratense) and four dicots: alfalfa (Medicago sativa), garden cress (Lepidium sativum), lettuce (Lactuca sativa), and rapeseed (Brassica napus) were used as test species. Elongation of both shoots and roots of seedlings was measured to assess any phytotoxic effects. The results showed that the sensitivities of shoots and roots were different between the test species, and the inhibition of seedling elongation significantly increased with increasing concentration of leaf extracts of C. manghas for all the test species. The IC50 (50% inhibitory concentration) values showed that 8.50–32.30 and 4.26–34.67 mg dry weight equivalent extract mL−1 of C. manghas inhibited seedling elongation by 50%, for shoots and roots respectively. Isolation and identification of the phytotoxic substances from C. manghas are suggested for future investigation

Phytotoxic property of the invasive plant Tithonia diversifolia and a phytotoxic substance

Tithonia diversifolia (Hermsl.) A. Gray is a perennial invasive plant and spreads quickly in the invasive areas. The extracts of T. diversifolia were found to be toxic to several crop plant species such as rice, maize, sorghum, lettuce and cowpea, and several putative allelopathic substances were identified. However, there is limited information available for the effects of T. diversifolia on wild plants including weed plant species. We investigated the allelopathic potential of T. diversifolia extracts on weed plants, and searched for phytotoxic substances with allelopathic activity. An aqueous methanol extract of T. diversifolia leaves inhibited the growth of weed plants, Lolium multiflorum Lam., Phleum pretense L., Echinochloa crus-galli (L.) Beauv. The extract was then purified by several chromatographic runs and a phytotoxic substance with allelopathic activity was isolated and identified by spectral analysis as tagitinin C. The substance inhibited the growth of Lolium multiflorum, Phleum pratense and Echinochloa crus-galli at concentrations greater than 0.1 – 0.3 mM. The present results suggest that T. diversifolia may possess allelopathic potential on weed plants and tagitinin C may be responsible for the allelopathic effects of T. diversifolia. The allelopathic potential of T. diversifolia may contribute to its invasive characteristics

Isolation and identification of a growth inhibitory substance from Heliotropium indicum L.

Heliotropium indicum L. belongs to the family Boraginaceae. The plant has been used as a folk medicine because it contains substances of various biological activities. It is also identified as a common weed which grows wildly in crop fields in tropical and subtropical regions of the world. However, there is little information on the allelopathic effect in this plant. Therefore, this study was undertaken to investigate the growth inhibitory effect and to identify the growth inhibitory substances in H. indicum. An aqueous methanol extract of H. indicum inhibited shoot and root growth of barnyard grass, foxtail fescue, timothy, cress, lettuce and rapeseed at concentrations higher than 10 mg dry weight equivalent extract/mL. The concentrations required for 50% growth inhibition (I50) of those test plants ranged from 3–282 mg dry weight equivalent extract/mL. The extract was then separated using a sequence of chromatographic fractionations and a growth inhibitory substance was isolated and identified by spectral analysis as methyl caffeate. Methyl caffeate inhibited the growth of lettuce and foxtail fescue at concentrations higher than 1.0 mM. The results suggest that methyl caffeate may contribute to the growth inhibitory effect of H. indicum and may play an important role in the allelopathic effect of H. indicum

The potency of lemon ( Citrus limon L.) essential oil to control some fungal diseases of grapevine wood

This study aimed to evaluate the in vitro antifungal activity (AA) of the essential oil (EO) of lemon (Citrus limon L.) against three pathogenic fungi attacking grapevine wood. The composition of the EO was also studied. Ten volatile components were identified by gas chromatography–mass spectrometry. The results showed that the EO consists of volatile components where monoterpene hydrocarbons are the most abundant ones. Four major components were identified, which represent 99.9% of the total EO (limonene, neral, ß-pinene, and ?-terpinene). The AA of the EO was evaluated against three pathogenic fungi attacking grapevine wood (Eutypa sp., Botryosphaeria dothidea, and Fomitiporia mediterranea). The results showed that the EO exerts AA against all tested fungi and significantly inhibits their growth. Eutypa sp. is the most sensitive fungus. These results show, for the first time, a new use for the EO of lemon (C. limon L.) to control fungal diseases of grapevine wood. Résumé Cette étude examine l’activité antifongique in vitro (AA) de l’huile essentielle (EO) de citron (Citrus limon L.) contre trois champignons pathogènes du bois de la vigne. La composition de l’EO a également été étudiée. Dix composants volatiles ont été identifiés par chromatographie en phase gazeuse–spectrométrie de masse. Les résultats ont montré que l’EO est constituée de composants volatils où les hydrocarbures de monoterpènes sont majoritaires. Quatre composants principaux ont été identifiés, ce qui représente 99,9 % de l’EO totale (limonène, néral, ß-pinène et ?-terpinène). L’AA de l’EO a été évaluée contre trois champignons pathogènes du bois de vigne (Eutypa sp., Botryosphaeria dothidea et Fomitiporia mediterranea). Les résultats ont montré que l’EO exerce une AA contre tous les champignons testés et inhibe de manière significative leur croissance. Eutypa sp. a été le plus sensible. Ces résultats montrent, pour la première fois, une nouvelle utilisation pour l’EO du citron pour lutter contre les maladies fongiques du bois de vigne

Light-induced structural changes and the site of O=O bond formation in PSII caught by XFEL

Photosystem II (PSII) is a huge membrane-protein complex consisting of 20 different subunits with a total molecular mass of 350 kDa for a monomer. It catalyses light-driven water oxidation at its catalytic centre, the oxygen-evolving complex (OEC). The structure of PSII has been analysed at 1.9 Å resolution by synchrotron radiation X-rays, which revealed that the OEC is a Mn4CaO5 cluster organized in an asymmetric, 'distorted-chair' form. This structure was further analysed with femtosecond X-ray free electron lasers (XFEL), providing the 'radiation damage-free' structure. The mechanism of O=O bond formation, however, remains obscure owing to the lack of intermediate-state structures. Here we describe the structural changes in PSII induced by two-flash illumination at room temperature at a resolution of 2.35 Å using time-resolved serial femtosecond crystallography with an XFEL provided by the SPring-8 ångström compact free-electron laser. An isomorphous difference Fourier map between the two-flash and dark-adapted states revealed two areas of apparent changes: around the QB/non-haem iron and the Mn4CaO5 cluster. The changes around the QB/non-haem iron region reflected the electron and proton transfers induced by the two-flash illumination. In the region around the OEC, a water molecule located 3.5 Å from the Mn4CaO5 cluster disappeared from the map upon two-flash illumination. This reduced the distance between another water molecule and the oxygen atom O4, suggesting that proton transfer also occurred. Importantly, the two-flash-minus-dark isomorphous difference Fourier map showed an apparent positive peak around O5, a unique μ4-oxo-bridge located in the quasi-centre of Mn1 and Mn4 (refs 4,5). This suggests the insertion of a new oxygen atom (O6) close to O5, providing an O=O distance of 1.5 Å between these two oxygen atoms. This provides a mechanism for the O=O bond formation consistent with that proposed previousl

Submergence Acclimation to Low-Temperature Stress in Rice Roots

A low temperature (10ºC, 48 h) inhibited primary root growth of rice seedlings (Oryza sativa L.). However, the inhibition was significantly mitigated by submergence for 24 h before the exposure to low temperatures, which induced alcohol dehydrogenase and increased the ethanol concentration in roots. Exogenous application of ethanol also had a similar mitigating effect. These results suggest that submergence pretreatment increases the tolerance to low temperature in rice roots due to ethanol accumulation in the roots

Allelopathy in Maize II.: Allelopathic potential of a new benzoxazolinone, 5-chloro-6-methoxy-2-benzoxazolinone and its analogue

To characterize the allelopathic activity of a new benzoxazolinone, 5-chloro-6-methoxy-2-benzoxazolinone (Cl-MBOA), seeds or seedling of monocotyledonous and dicotyledonous plants were exposed to Cl-MBOA for two or three days in a Petri dish, and effects of Cl-MBOA on the seed germination and the plant growth were determined and compared to those of its analogues, 6-methoxy-2-benzoxazolinone (MBOA) and benzoxa-zolinone (BOA). Cl-MBOA, MBOA and BOA dose-dependently inhibited the seed germination and growth of roots and shoots of cockscomb (Amaranthus caudatus L.), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), crabgrass (Digitaria sanguinalis L.), timothy (Phleum pratense L.) and ryegrass (Lolium multiflorum Lam.). A new benzoxazolinone, Cl-MBOA was the most active in all bioassays followed in order by MBOA and BOA. The results that the attachment of CI at C-5 position on MBOA leads to an increase in the activity

Isolation of Allelopathic Substances in Rice Seedlings

In order to evaluate the allelopathic potential of the early developmental stage of rice plants (Oryza sativa L.), a search for allelopathic substances was undertaken in acetone extract of 10-d-old rice seedlings. Two growth-inhibiting substances were found in the neutral fraction of the extract after silica gel column chromatography, and one substance was further purified by thin layer chromatography, C18 Sep Pack cartridge and HPLC. The purified substance inhibited the growth of lettuce (Lactuca sativa L.) at concentrations greater than 0.3 μgmL–1. These two substances may be released into the environment, either as exudates from living tissues or leachates from residues of the plant, and act as allelochemicals to other plants, which should be investigated further in the laboratory and the field