M. Iftikhar Hussain

Allelochemical stress inhibits growth, leaf water relations, PSII photochemistry, non-photochemical fluorescence quenching, and heat energy dissipation in three C3 perennial species

In this study, the effect of two allelochemicals, benzoxazolin-2(3H)-one (BOA) and cinnamic acid (CA), on different physiological and morphological characteristics of 1-month-old C3 plant species (Dactylis glomerata, Lolium perenne, and Rumex acetosa) was analysed. BOA inhibited the shoot length of D. glomerata, L. perenne, and R. acetosa by 49%, 19%, and 19% of the control. The root length of D. glomerata, L. perenne, and R. acetosa growing in the presence of 1.5 mM BOA and CA was decreased compared with the control. Both allelochemicals (BOA, CA) inhibited leaf osmotic potential (LOP) in L. perenne and D. glomerata. In L. perenne, Fv/Fm decreased after treatment with BOA (1.5 mM) while CA (1.5 mM) also significantly reduced Fv/Fm in L. perenne. Both allelochemicals decreased ΦPSII in D. glomerata and L. perenne within 24 h of treatment, while in R. acetosa, ΦPSII levels decreased by 72 h following treatment with BOA and CA. There was a decrease in qP and NPQ on the first, fourth, fifth, and sixth days after treatment with BOA in D. glomerata, while both allelochemicals reduced the qP level in R. acetosa. There was a gradual decrease in the fraction of light absorbed by PSII allocated to PSII photochemistry (P) in R. acetosa treated with BOA and CA. The P values in D. glomerata were reduced by both allelochemicals and the portion of absorbed photon energy that was thermally dissipated (D) in D. glomerata and L. perenne was decreased by BOA and CA. Photon energy absorbed by PSII antennae and trapped by ‘closed’ PSII reaction centres (E) was decreased after CA exposure in D. glomerata. BOA and CA (1.5 mM concentration) decreased the leaf protein contents in all three perennial species. This study provides new understanding of the physiological and biochemical mechanisms of action of BOA and CA in one perennial dicotyledon and two perennial grasses. The acquisition of such knowledge may ultimately provide a rational and scientific basis for the design of safe and effective herbicides.

Salt and drought stresses in safflower: a review

Safflower is one of the oldest cultivated crops, usually grown at a small scale. Safflower is grown for flowers used for coloring, flavoring foods, dyes, medicinal properties, and livestock feed. Safflower is underutilized but gaining attention due to oil yield potential and the ability to grow under high temperatures, drought, and salinity. Salinity and drought have negative effects by disrupting the ionic and osmotic equilibrium of the plant cells. The stress signal is perceived by membranes then transduced in the cell to switch on the stress responsive genes. This review discusses on stress tolerance mechanisms in safflower. Strategies are proposed for enhancing drought and salt resistance in safflower.

Seedling growth, leaf water status and signature of stable carbon isotopes in C3 perennials exposed to natural phytochemicals

Inthepresentstudy,weevaluatedtheseedlinggrowth,waterstatusandsignatureofstablecarbonisotopesinC3 perennial species exposed to natural phytochemicals. Three perennial species, cocksfoot (Dactylis glomerata), perennial ryegrass (Lolium perenne) and common sorrel (Rumex acetosa), were grown for 30 days in perlite, watered with Hoagland solution and exposed to the phytochemicals benzoxazolin-2(3H)-one (BOA) and cinnamic acid (CA) at 0, 0.1, 0.5, 1.0 and 1.5mM concentrations. BOA markedly decreased the leaf and root fresh weights of D. glomerata and L. perenne in a concentration-dependentmanner.Theleaffreshweight(LFW)ofplantstreatedwithCA(1.5mM)wassimilarlyaffectedby showing a decrease of LFW, being the lowest in L. perenne (56%) followed by D. glomerata (46%). The relative water contents of L. perenne, D. glomerata and R. acetosa were decreased while maximum RWC reduction was observed in L.perenne.CarbonisotopediscriminationinL.perenne,D.glomerataandR.acetosawerereducedfollowingtreatmentwith BOAandCAat1.5mM.BOAat1.5mMdecreasedtheratioofintercellulartoambientCO2concentrationrelativetocontrol in L. perenne, D. glomerata and R. acetosa. There was an increase in water-use efficiency in L. perenne, D. glomerata and R. acetosa after treatment with BOA and CA. The dry weight of plants treated with CA (1.5mM) showed different patterns ofvariation,beinglowestinL.perenne(33%)followedbyD.glomerata(3%)andR.acetosa(2%).Phytotoxicitywashigher for the perennial grass than for the perennial broadleaf. These results clearly demonstrate a widespread occurrence of phytotoxicity among the three species, their tolerance and relationship between carbon isotope discrimination and intrinsic water-use efficiency. Additional keywords: benzoxazolin-2(3H)-one, cinammic acid, intrinsic water use efficiency, leaf-water relationship.

Role of Allelopathy During Invasion Process by Alien Invasive Plants in Terrestrial Ecosystems

Biological invasion is causing serious current biodiversity loss in different parts of the world and involves different stages: introduction, establishment, naturalization, and fast dispersion outside the normal ranks. Invasion may cause a reduction in abundance of native species or the elimination of populations of a particular species. Exotic species have to surpass different biological filters to get to be invaded in a new habitat. Importance of allelopathy in the invasion process may include the release of secondary chemical metabolites into the surrounding environment to inhibit the seedling establishment and other ecophysiological attributes of native biota. Temperature, drought, cold, association, and feedback from soil microorganism can also adversely affect the biological nutrient cycle, and other aspects that can favor the invading capacity of exotic species. Environmental problems generated by invading species can become serious in naturally protected and sensitive areas, where climatic circumstances may evolve in the shape of global warming. The purpose of this chapter is to highlight the role of allelopathy during the invasion process with special emphasis to ecophysiological relationships between exotic and native plants, and soil microorganisms.

Higher peroxidase activity, leaf nutrient contents and carbon isotope composition changes in Arabidopsis thaliana are related to rutin stress.

Rutin, a plant secondary metabolite that is used in cosmetics and food additive and has known medicinal properties, protects plants from UV-B radiation and diseases. Rutin has been suggested to have potential in weed management, but its mode of action at physiological level is unknown. Here, we report the biochemical, physiological and oxidative response of Arabidopsis thaliana to rutin at micromolar concentrations. It was found that fresh weight; leaf mineral contents (nitrogen, sodium, potassium, copper and aluminum) were decreased following 1 week exposure to rutin. Arabidopsis roots generate significant amounts of reactive oxygen species after rutin treatment, consequently increasing membrane lipid peroxidation, decreasing leaf Ca(2+), Mg(2+), Zn(2+), Fe(2+) contents and losing root viability. Carbon isotope composition in A. thaliana leaves was less negative after rutin application than the control. Carbon isotope discrimination values were decreased following rutin treatment, with the highest reduction compared to the control at 750μM rutin. Rutin also inhibited the ratio of CO2 from leaf to air (ci/ca) at all concentrations. Total protein contents in A. thaliana leaves were decreased following rutin treatment. It was concluded carbon isotope discrimination coincided with protein degradation, increase lipid peroxidation and a decrease in ci/ca values may be the primary action site of rutin. The present results suggest that rutin possesses allelopathic potential and could be used as a candidate to develop environment friendly natural herbicide.

Evaluation of photosynthetic performance and carbon isotope discrimination in perennial ryegrass (Lolium perenne L.) under allelochemicals stress

Ferulic (FA) and p-hydroxybenzoic acid (pHBA) are commonly found as phenolic compounds (PHC) in many forage and cereal crops. Although the effects of these PHC on seedling growth are relatively explored, not many information is available regarding the phytotoxicity on ecophysiological processes of perennial ryegrass adult plants. The experiment was conducted with the aim to evaluate the phytotoxic potential of PHC on the seedling growth, leaf water relation, chlorophyll fluorescence attributes and carbon isotope discrimination adult plants of perennial ryegrass (Lolium perenne L.). The results clearly indicated that PHC behaved as potent inhibitors of chlorophyll fluorescence yield (Fv/Fm) in leaves of L. perenne and plants showed poor tolerance against allelochemicals stress. Quantum yield (ΦPSII), chlorophyll fluorescence quenching (qP) and non-photochemical quenching (NPQ) were decreased following exposure to FA and pHBA. The portion of absorbed photon energy that was thermally dissipated (D) in L. perenne was decreased. Exposure of the L. perenne seedlings to FA and pHBA stress led to a decrease in fresh/dry weight, relative water content and leaf osmotic potential. Carbon isotope composition ratio (δ13C) was significantly less negative than the control following treatment with FA or pHBA. The results suggested that PHC uptake was a key step for the effectiveness of these secondary metabolites and their phytotoxicity on L. perenne adult plants was mainly due to the alteration of leaf water status accompanied by photosystem II damage. Acquisition of such knowledge may ultimately provide a better understanding about the mode of action of the tested compounds.

Characterization of xanthophyll pigments, photosynthetic performance, photon energy dissipation, reactive oxygen species generation and carbon isotope discrimination during artemisinin-induced stress in Arabidopsis thaliana.

Artemisinin, a potent antimalarial drug, is phytotoxic to many crops and weeds. The effects of artemisinin on stress markers, including fluorescence parameters, photosystem II photochemistry, photon energy dissipation, lipid peroxidation, reactive oxygen species generation and carbon isotope discrimination in Arabidopsis thaliana were studied. Arabidopsis ecotype Columbia (Col-0) seedlings were grown in perlite and watered with 50% Hoagland nutrient solution. Adult plants of Arabidopsis were treated with artemisinin at 0, 40, 80, 160 μM for one week. Artemisinin, in the range 40–160 μM, decreased the fresh biomass, chl a, b and leaf mineral contents. Photosynthetic efficiency, yield and electron transport rate in Arabidopsis were also reduced following exposure to 80 and 160 μM artemisinin. The ΦNPQ and NPQ were less than control. Artemisinin treatment caused an increase in root oxidizability and lipid peroxidation (MDA contents) of Arabidopsis. Calcium and nitrogen contents decreased after 80 and 160 μM artemisinin treatment compared to control. δ13C values were less negative following treatment with artemisinin as compared to the control. Artemisinin also decreased leaf protein contents in Arabidopsis. Taken together, these data suggest that artemisinin inhibits many physiological and biochemical processes in Arabidopsis.

Evidences of Bryophyte Allelochemical Interactions: The Case of Sphagnum

In most terrestrial ecosystems, allelochemical interactions are involved in vascular plants. Nevertheless, bryophytes represent also a crucial group found in many ecosystems with a specific morphology and physiology (e.g. secondary metabolism). Among bryophytes, Sphagnum genus is of particular interest because they form a dense homogeneous carpet which is slowly decomposed (the peat) in peatlands. Such ecosystems represent a terrestrial sink of carbon and so are crucial to be studied, especially under a climate change. Objectives of this chapter were (1) to synthesize current bryophyte allelochemical interactions and (2) to illustrate recent research on Sphagnum with the case of Sphagnum fallax phenolics (production and degradation) recovered in a french peatland. The top layer of living Sphagnum represents the active allelopathic part where water-soluble phenolics were mostly recovered. Their concentrations were found to change along the seasons. The transformation of phenolic compounds is performed by an enzymatic system O2 (phenoloxidases) or H2O2 (peroxidases) dependent. Sphagnum-peroxidases constituted the main oxidative system and fungal phenoloxidases were proposed to be regulated by phenolics. Moreover, Sphagnum was able to regulate its secondary metabolism under a climate forcing by decreasing its phenolic concentrations. Allelopathic potential of Sphagnum phenolics was stated with their role in the microdistribution of associated Sphagnum microorganisms. Finally, Sphagnum extracts also strongly delayed Pine and Lolium germination seeds and inhibited Lolium radicle growth and delayed Raphanus and Pinus radicles. Ecological and agronomic perspectives of Sphagnum extracts are discussed.