Design, Synthesis, and Herbicidal Evaluation of Pyrrolidinone-Containing 2-Phenylpyridine Derivatives as Novel Protoporphyrinogen Oxidase Inhibitors.

In this work, a series of pyrrolidinone-containing 2-phenylpyridine derivatives were synthesized and evaluated as novel protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) inhibitors for herbicide development. At 150 g ai/ha, compounds 4d, 4f, and 4l can inhibit the grassy weeds of Echinochloa crus-galli (EC), Digitaria sanguinalis (DS), and Lolium perenne (LP) with a range of 60 to 90%. Remarkably, at 9.375 g ai/ha, these compounds showed 100% inhibition effects against broadleaf weeds of Amaranthus retroflexus (AR) and Abutilon theophrasti (AT), which were comparable to the performance of the commercial herbicides flumioxazin (FLU) and saflufenacil (SAF) and better than that of acifluorfen (ACI). Molecular docking analyses revealed significant hydrogen bonding and π-π stacking interactions between compounds 4d and 4l with Arg98, Asn67, and Phe392, respectively. Additionally, representative compounds were chosen for in vivo assessment of PPO inhibitory activity, with compounds 4d, 4f, and 4l demonstrating excellent inhibitory effects. Notably, compounds 4d and 4l induced the accumulation of reactive oxygen species (ROS) and a reduction in the chlorophyll (Chl) content. Consequently, compounds 4d, 4f, and 4l are promising lead candidates for the development of novel PPO herbicides.

ß-Resorcylic Acid Derivatives, with Their Phytotoxic Activities, from the Endophytic Fungus Lasiodiplodia theobromae in the Mangrove Plant Xylocarpus granatum.

Nine new ß-resorcylic acid derivatives, (15S)-de-O-methyllasiodiplodin (1), (13S,15S)-13-hydroxy-de-O-methyllasiodiplodin (2), (14S,15S)-14-hydroxy-de-O-methyllasiodiplodin (3), (13R,14S,15S)-13,14-dihydroxy-de-O-methyllasiodiplodin (4), ethyl (S)-2,4-dihydroxy-6-(8-hydroxynonyl)benzoate (5), ethyl 2,4-dihydroxy-6-(8-hydroxyheptyl)benzoate (6), ethyl 2,4-dihydroxy-6-(4-methoxycarbonylbutyl)benzoate (7), 3-(2-ethoxycarbonyl-3,5-dihydroxyphenyl)propionic acid (8), and isobutyl (S)-2,4-dihydroxy-6-(8-hydroxynonyl)benzoate (9), together with a known ethyl 2,4-dihydroxy-6-(8-oxononyl)benzoate (10) were obtained from Lasiodiplodia theobromae GC-22. The structures of these compounds were elucidated by extensive spectroscopic analyses. Compounds 1, 3, and 6 showed growth inhibitory effects against Digitaria ciliaris. Conversely, treatment with compounds 5, 6, 7, 9, and 10 stimulated elongation activity toward the root of Lactuca sativa. These data expand the repertoire of new ß-resorcylic acid derivatives that may function as lead compounds in the synthesis of new agrochemical agents.

Herbicidal Characteristics and Structural Identification of the Potential Active Compounds from Streptomyces sp. KRA17-580.

Weeds are notorious plant species exhibiting a harmful impact on crops. Biological weed control is an efficient and environmentally friendly technique, usually constitutes naturally derived compounds, including bioherbicidal metabolites produced by Streptomyces sp. The isolation and structural identification of phytotoxic compounds from Streptomyces have recently been proposed as an effective way to the discovery of novel bioherbicides. In the screening of bioherbicidal agents, isolated Streptomyces strain KRA17-580 demonstrated significant phytotoxic activity against Digitaria ciliaris. Phylogenetic analysis of the 16S rRNA sequence indicated that isolated KRA17-580 is similar to Streptomyces olivochromogenes. The bacterial culture conditions were optimized for temperature, agitation, and initial pH. Streptomyces strain KRA17-580 showed intense phytotoxic activity and high cell mass at an initial pH of 5.5-7.0, more than 150 rpm, and 25-30 °C. The herbicidal compounds isolated from the culture filtrate of strain KRA17-580 were purified by solvent partition, C18, Sephadex LH20 column chromatography, and high-performance liquid chromatography. By 1D-NMR, 2D-NMR, and electrospray ionization mass spectrometry analysis, the 580-H1 and 580-H2 compounds were identified as a cinnoline-4-carboxamide (MW, 173.0490; C9H7N3O2) and cinnoline-4-carboxylic acid (MW, 174.0503; C9H6N2O2), respectively. Only these two herbicidal compounds showed strong phytotoxic activity against D. ciliaris in foliar applications. However, compound 580-H2 was more phytotoxic than 580-H1 and the toxicity was dose-dependent. The herbicidal metabolite KRA17-580 produced by Streptomyces sp. is a new bioherbicidal candidate that may provide a new lead molecule for more efficient phytotoxic compounds.

Synthesis of Pyranopyrans Related to Diplopyrone and Evaluation as Antibacterials and Herbicides.

Stereoselective syntheses of new pyranopyrans that are related to the natural product diplopyrone, which is a phytotoxin implicated in cork oak decline, have been achieved from carbohydrate starting materials in two approaches that are based on C-glycosides as key intermediates. A C-alkynyl glycoside prepared by Ferrier rearrangement was used as the precursor to a new pyranopyran alkyne that showed potent antibacterial activity against the common bacterial pathogen Edwardsiella ictaluri that causes enteric septicemia in catfish. The C-alkynyl glycoside also showed herbicidal activity. New bioassay data for the pyranopyran nitrile (4aR,6S,8aR)-6-cyano-6,8a-dihydropyrano-[3,2-b]pyran-2(4aH)-one, the most potent of the pyranopyrans synthesized to date, were obtained in greenhouse studies that revealed additional herbicidal activity. Other new analogues that were synthesized included desmethylpyranopyrans that were prepared by Isobe C-alkynylation-rearrangement/reduction and RCM-based pyranopyran construction. The antibiotic and phytotoxic activities of the new pyranopyrans synthesized in this study highlight the importance of substituents on the nonlactone ring and demonstrate the potential of such compounds as antibiotics and herbicides.

Cytisus scoparius and Ulex europaeus Produce Volatile Organic Compounds with Powerful Synergistic Herbicidal Effects.

New herbicides based on natural products are claimed to address weed resistance and environmental concerns related to synthetic herbicides. In our previous studies, certain volatile organic compounds (VOCs) produced by Ulex europaeus and Cytisus scoparius were argued to be responsible for the phytotoxicity of both shrub species. Interactions among VOCs were hypothesized to explain the inconsistency between the effects of the identified pure compounds and those naturally emitted from fresh plant material. In this work, eugenol, verbenone, terpinen-4-ol, α-terpineol, and linalool were assayed as binary mixtures of Amaranthus retroflexus and Digitaria sanguinalis. Powerful synergistic inhibitory effects were revealed for germination and early growth. Only 3.1 ppm of verbenone was enough to inhibit A. retroflexus germination when paired to other VOCs. Eugenol was capable of exacerbating the effects of terpinen-4-ol on A. retroflexus, even though it was innocuous when acting alone at 12.5 ppm. The verbenone and linalool pair produced very significant synergistic effects in terms of D. sanguinalis germination. The synergistic effects were predominantly irreversible for D. sanguinalis, since seeds exposed to paired VOCs were unable to recover their germination capacity after removing the phytotoxins or produced damaged seedlings. Both shrub species have been revealed as sources of natural herbicide molecules, with promising synergistic modes of action that deserve to be studied in depth.

Do silicon and nitric oxide induce resistance to Mahanarva spectabilis (Hemiptera: Cercopidae) in forage grasses?

BACKGROUND: Great efforts have been made to identify grasses that are resistant to spittlebugs (Hemiptera: Cercopidae). However, the time required to develop and launch new cultivars is relatively long. The employment of resistance inducers is a current strategy that may be useful for the control of insect pests. This analysis evaluates the feasibility of using the chemical inducers silicon and nitric oxide to increase spittlebug resistance based on changes in forage grass vegetative characteristics and the biological traits of Mahanarva spectabilis (Distant, 1909). RESULTS: Mahanarva spectabilis nymphs and adults can cause significant damage to forage grasses. Furthermore, silicon and nitric oxide inducers were not sufficient to lessen this damage by positively influencing the growth and development of forage grasses. These inducers did not negatively alter the biological parameters of M. spectabilis or diminish its population. However, phenolic compound concentrations increased when forage grasses were treated with silicon or attacked by adult insects, but this parameter was not useful to predict spittlebug resistance. This fact suggests that the physiological and biochemical changes caused by silicon should be further studied. CONCLUSION: The current analysis demonstrated that application of the chemical inducers silicon and nitric oxide is currently not a viable strategy for the effective and economic management of M. spectabilis on Brachiaria ruziziensis, Pennisetum purpureum and Digitaria sp. © 2019 Society of Chemical Industry.

Novel aryloxyphenoxypropionate derivates containing benzofuran moiety: Design, synthesis, herbicidal activity, docking study and theoretical calculation.

A series of novel aryloxyphenoxypropionate (APP) herbicides containing benzofuran moiety were designed, synthesized and tested for herbicidal activity. The bioassay results indicated that most of target compounds possessed moderate to good herbicidal activity against monocotyledonous weeds. Compounds 5a-5d and 6a-6d showed 100% control efficiency against crabgrass (Digitaria sanguinalis) and barnyard grass (Echinochloa crus-galli) in both pre-emergence and post-emergence treatments at the dosage of 1500 g a.i. ha-1. Compound 6c was the most promising, with herbicidal activity better than clodinafop-propargyl. Molecular docking for compound 6c and its hydrolysis acid 1c were performed. ACCase activities of some compounds were also tested. Theoretical calculations for corresponding hydrolysis products 1a-1ewere carried out. Based on the results of molecular docking, enzyme activity test and theoretical calculation, the potential mechanism for herbicidal activity of these compounds was evaluated.

On the bioherbicide potential of Ulex europaeus and Cytisus scoparius: Profiles of volatile organic compounds and their phytotoxic effects.

The phytotoxic potential of the legume shrubs Ulex europaeus L. (gorse) and Cytisus scoparius (L.) Link. (Scotch broom) is studied in this work for the first time. On the basis of their richness in active principles, the previous evidence of biological activity, and the abundance of biomass in their native range and invaded areas, a question arose: can U. europaeus and C. scoparius be considered as potential sources of natural herbicides for sustainable agriculture? By means of volatile bioassays, the flowering fresh plant material of both shrub species was shown to produce and emit volatile organic compounds (VOCs) able to inhibit the germination and/or early growth of two agricultural weeds: Amaranthus retroflexus and Digitaria sanguinalis. Novel complete VOCs profiles from the volatile extracts of the shrub species were obtained by GC and GC/MS. A total of 20 compounds were identified from U. europaeus flowering biomass, theaspirane and eugenol, among others, being described in gorse for the first instance. The chemical profile of C. scoparius yielded 28 compounds and was rich in oxygenated monoterpenes such as terpinen-4-ol, verbenol, α-terpineol, and verbenone, which were also identified in this species for the first time. Using dose-response bioassays with pure compounds, these VOCs were argued to be involved in the phytotoxicity observed for the plant materials, even at very low concentrations. The phytotoxic effects were predominantly irreversible, particularly for D. sanguinalis, since the seeds exposed to the VOCs produced damaged seedlings, were unable to recover germination capacity after removing the phytotoxin or, when recovered, produced unviable seedlings. Our results extend the interest of the abundant U. europaeus and C. scoparius for the obtention of natural products with bioherbicide potential, or to be used as allelopathic biomass in the development of new sustainable agricultural practices.

Investigation of resistance levels and mechanisms to nicosulfuron conferred by non-target-site mechanisms in large crabgrass (Digitaria sanguinalis L.) from China.

Large crabgrass is a major grass weed widely distributed across China. This weed infests maize fields and has evolved resistance to the acetolactate synthase (ALS)-inhibiting herbicide nicosulfuron due to continuous and intensive use. In this study, a total of 25 out of 26 large crabgrass populations collected from maize field demonstrated resistance to nicosulfuron. Amino acid modifications in ALS known to confer resistance to ALS-inhibiting herbicides in other weeds, were not found in the 9 tested resistant populations. The P450 inhibitor malathion significantly reversed resistance to nicosulfuron in 3 tested populations, indicating one or more P450s may be involved. Nicosulfuron was metabolized more rapidly in one resistant large crabgrass population than in a susceptible biotype. This demonstrates that the metabolic resistance mechanisms involving one or more P450s may be responsible for large crabgrass resistance to nicosulfuron in this biotype.

Acetyl-CoA carboxylase overexpression in herbicide-resistant large crabgrass (Digitaria sanguinalis).

BACKGROUND: The occurrence of herbicide-resistant weed biotypes is increasing and this report of an acetyl-CoA carboxylase (ACCase) inhibitor-resistant Digitaria sanguinalis L. Scop. from southwestern Ontario is another example. The identified weed escaped control in an onion and carrot rotation in which graminicides were used for several consecutive years. Our goal was to characterize the level and mechanism of resistance of the biotype. RESULTS: The biotype was resistant to all five ACCase inhibitor herbicides tested. Gene-expression profiling was performed because none of the mutations known to confer resistance in the ACCase gene were detected. RNASeq and quantitative reverse-transcriptase PCR (qRT-PCR) results indicated that transcription of ACCase was 3.4-9.3 times higher in the resistant biotype than the susceptible biotype. ACCase gene copy number was determined by qPCR to be five to seven times higher in the resistant compared with the susceptible biotype. ACCase gene overexpression was directly related to the increase of the ACCase gene copy number. CONCLUSION: Our results are consistent with the hypothesis that overexpression of the herbicide target gene ACCase confers resistance to the herbicide. This is the first reported case of target gene duplication conferring resistance to a herbicide other than glyphosate. © 2017 Society of Chemical Industry See related Article.

A novel amino acid substitution Trp574Arg in acetolactate synthase (ALS) confers broad resistance to ALS-inhibiting herbicides in crabgrass (Digitaria sanguinalis).

BACKGROUND: Crabgrass (Digitaria sanguinalis) is an annual monocotyledonous weed. In recent years, field applications of nicosulfuron have been ineffective in controlling crabgrass populations in Shandong Province, China. To investigate the mechanisms of resistance to nicosulfuron in crabgrass populations, the acetolactate synthase (ALS) gene fragment covering known resistance-confering mutation sites was amplified and sequenced. RESULTS: Dose-response experiments suggested that the resistant population SD13 (R) was highly resistant to nicosulfuron (resistance index R/S = 43.7) compared with the sensitive population SD22 (S). ALS gene sequencing revealed a Trp574Arg substitution in the SD13 population, and no other known resistance-conferring mutations were found. In vitro ALS enzyme assays further confirmed that the SD13 population was resistant to all tested ALS-inhibiting herbicides. The resistance pattern experiments revealed that, compared with SD22, the SD13 population exhibited broad-spectrum resistance to nicosulfuron (43.7-fold), imazethapyr (11.4-fold) and flumetsulam (16.1-fold); however, it did not develop resistance to atrazine, mesotrione and topramezone. CONCLUSIONS: This study demonstrated that Trp574Arg substitution was the main reason for crabgrass resistance to ALS-inhibiting herbicides. To our knowledge, this is the first report of Trp574Arg substitution in a weed species, and is the first report of target-site mechanisms of herbicide resistance for crabgrass. © 2017 Society of Chemical Industry.

EPSPS variability, gene expression, and enzymatic activity in glyphosate-resistant biotypes of Digitaria insularis.

Weed resistance to herbicides is a natural phenomenon that exerts selection on individuals in a population. In Brazil, glyphosate resistance was recently detected in Digitaria insularis. The objective of this study was to elucidate mechanisms of weed resistance in this plant, including genetic variability, allelism, amino acid substitutions, gene expression, and enzymatic activity levels. Most of these have not previously been studied in this species. D. insularis DNA sequences were used to analyze genetic variability. cDNA from resistant and susceptible plants was used to identify mutations, alleles, and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) expression, using real-time quantitative reverse transcription-polymerase chain reaction. In addition, EPSPS activity was measured. We found a decrease in genetic variability between populations related to glyphosate application. Substitutions from proline to threonine and tyrosine to cysteine led to a decrease in EPSPS affinity for the glyphosate. In addition, the EPSPS enzymatic activity was slightly higher in resistant plants, whereas EPSPS gene expression was almost identical in both biotypes, suggesting feedback regulation at different levels. To conclude, our results suggest new molecular mechanisms used by D. insularis to increase glyphosate resistance.

Synthesis and herbicidal activity evaluation of novel α-amino phosphonate derivatives containing a uracil moiety.

A series of novel α-amino phosphonate derivatives containing a uracil moiety 3a-3l were designed and synthesized by a Lewis acid (magnesium perchlorate) catalyzed the Kabachnik-Fields reaction. The bioassays {in vitro, in vivo [Glass House 1 (GH1) and Glass House 2 (GH2)]} showed that most of compounds 3 exhibited excellent and selective herbicidal activities; for example, in GH1 test, compounds 3b, 3d, 3f, 3h and 3j showed excellent and wide spectrum herbicidal activities at the dose of 1000 g/ha, and compounds 3b and 3j exhibited 100% inhibition activities against the four plants in both post- and pre-emergence treatments. Moreover, most of compounds 3 showed higher inhibition against Amaranthus retroflexus and Digitaria sanguinalis than Glyphosate did in pre-emergence treatment. In GH2 test, the four compounds (3b, 3d, 3h and 3j) exhibited 100% inhibition against Solanum nigrum, Amaranthus retroflexus and Ipomoea hederacea in post-emergence treatment and displayed 100% inhibition against Solanum nigrum, Amaranthus retroflexus in pre-emergence treatment at the rate of 250 g/ha, and compound 3b showed the best and broad spectrum herbicidal activities against the six test plants. However, the four compounds displayed weaker herbicidal activities against Lolium perenne and Echinochloa crus-galli than the other four plants at the rate of 250 g/ha in both pre- and post-emergence treatments. So, compounds 3 can be used as a lead compound for further structure optimization for developing potential selective herbicidal agent. Their preliminary structure-activity relationships were also investigated.

Pool of resistance mechanisms to glyphosate in Digitaria insularis.

Digitaria insularis biotypes resistant to glyphosate have been detected in Brazil. Studies were carried out in controlled conditions to determine the role of absorption, translocation, metabolism, and gene mutation as mechanisms of glyphosate resistance in D. insularis. The susceptible biotype absorbed at least 12% more (14)C-glyphosate up to 48 h after treatment (HAT) than resistant biotypes. High differential (14)C-glyphosate translocation was observed at 12 HAT, so that >70% of the absorbed herbicide remained in the treated leaf in resistant biotypes, whereas 42% remained in the susceptible biotype at 96 HAT. Glyphosate was degraded to aminomethylphosphonic acid (AMPA), glyoxylate, and sarcosine by >90% in resistant biotypes, whereas a small amount of herbicide (up to 11%) was degraded by the susceptible biotype up to 168 HAT. Two amino acid changes were found at positions 182 and 310 in EPSPS, consisting of a proline to threonine and a tyrosine to cysteine substitution, respectively, in resistant biotypes. Therefore, absorption, translocation, metabolism, and gene mutation play an important role in the D. insularis glyphosate resistance.

Synthesis, herbicidal activities and comparative molecular field analysis study of some novel triazolinone derivatives.

A series of novel triazolinones were synthesized and their structures were characterized by (1)H NMR, elemental analysis and single-crystal X-ray diffraction analysis. The herbicidal activities were evaluated against Echinochloa crusgalli (L.) Beauv., Digitaria adscendens, Brassica napus and Amaranthus retroflexus. The herbicidal activity data indicated that the title compounds had higher activities with substituted benzyl group moieties than with other groups such as sulfonyl, alkyl, etc. To further investigate the structure-activity relationship, comparative molecular field analysis was performed on the basis of herbicidal activity data. Both the steric and electronic field distributions of comparative molecular field analysis are in good agreement in this work. The results showed that a bulky and electronegative group around the ortho- or para-positions of the benzene ring would possibly lead to higher activity. Based on the comparative molecular field analysis, compound I-23 was designed and synthesized, which display as good herbicidal activities as the commercial herbicide, carfentrazone-ethyl. The activity against Digitaria adscendens is 66.1% under pre-emergence at 300 g of a.i./ha.

Design, synthesis, and biological activities of novel 2-cyanoacrylates containing oxazole, oxadiazole, or quinoline moieties.

A series of novel 2-cyanoacrylates containing an oxazole, oxadiazole, or quinoline moiety were designed and synthesized, and their structures were characterized by (1)H NMR and elemental analysis (or high-resolution mass spectrometry). Their herbicidal activities against four weeds were evaluated, and the result indicated that some of the title compounds showed excellent herbicidal activities against rape and amaranth pigweed in postemergence treatment at a dose of 375 g/ha. Furthermore, most of these cyanoacrylates exhibited interesting plant growth regulatory activities.

Mesotrione control and pigment concentration of large crabgrass (Digitaria sanguinalis) under varying environmental conditions.

BACKGROUND: Mesotrione is a carotenoid biosynthesis-inhibiting herbicide currently labeled for crabgrass (Digitaria spp.) control. Mesotrione control of large crabgrass has been reported to vary with temperature and relative humidity; however, the effect of irradiance on mesotrione efficacy has not previously been reported. Likewise, little is known about pigment concentrations of Digitaria spp. The present research investigated the effects of mesotrione on large crabgrass, Digitaria sanguinalis (L.) Scop., control and pigment concentrations under varying irradiance at three temperatures. RESULTS: Mesotrione (0.28 kg ha(-1)) control of large crabgrass did not differ between temperature levels (18, 26 and 32 degrees C). Control was similar at tested irradiance levels (600, 1100 and 1600 micromol m(-2) s(-1)). Mesotrione reduced large crabgrass chlorophyll a, chlorophyll b and total carotenoid concentrations, as well as chlorophyll a to b ratios. Treated plant bleaching was highest 7 days after treatment (DAT) but decreased by 21 DAT. Treated plants were less than 10% necrotic 3 and 7 DAT but nearly 35% necrotic 21 DAT. Treated large crabgrass bleaching was highest and photochemical efficiency was lowest 7 DAT. These results indicate that some plant recovery occurs prior to 21 DAT. CONCLUSION: Although mesotrione efficacy has previously been reported to vary according to environmental factors, mesotrione control of large crabgrass did not vary with measured temperature and irradiance levels in this study. On account of crabgrass convalescence, secondary applications of mesotrione may control large crabgrass more effectively when applied prior to 21 DAT.

Comparison of the biological properties of several marine sponge-derived sesquiterpenoid quinones.

Eight naturally occurring marine-sponge derived sesquiterpenoid quinones were evaluated as potential inhibitors of pyruvate phosphate dikinase (PPDK), a C4 plant regulatory enzyme. Of these, the hydroxyquinones ilimaquinone, ethylsmenoquinone and smenoquinone inhibited PPDK activity with IC50's (reported with 95% confidence intervals) of 285.4 (256.4-317.7), 316.2 (279.2-358.1) and 556.0 (505.9-611.0) microM, respectively, as well as being phytotoxic to the C4 plant Digitaria ciliaris. The potential anti-inflammatory activity of these compounds, using bee venom phospholipase A2 (PLA2), was also evaluated. Ethylsmenoquinone, smenospongiarine, smenospongidine and ilimaquinone inhibited PLA2 activity (% inhibition of 73.2 +/- 4.8 at 269 microM, 61.5 +/- 6.1 at 242 microM, 41.0 +/- 0.6 at 224 microM and 36.4 +/- 8.2 at 279 microM, respectively). SAR analyses indicate that a hydroxyquinone functionality and a short, hydroxide/alkoxide side-chain atC-20 is preferred for inhibition of PPDK activity, and that a larger amine side-chain at C-20 is tolerated for PLA2 inhibitory activity.

Screening marine fungi for inhibitors of the C4 plant enzyme pyruvate phosphate dikinase: unguinol as a potential novel herbicide candidate.

A total of 2,245 extracts, derived from 449 marine fungi cultivated in five types of media, were screened against the C(4) plant enzyme pyruvate phosphate dikinase (PPDK), a potential herbicide target. Extracts from several fungal isolates selectively inhibited PPDK. Bioassay-guided fractionation of one isolate led to the isolation of the known compound unguinol, which inhibited PPDK with a 50% inhibitory concentration of 42.3 +/- 0.8 muM. Further kinetic analysis revealed that unguinol was a mixed noncompetitive inhibitor of PPDK with respect to the substrates pyruvate and ATP and an uncompetitive inhibitor of PPDK with respect to phosphate. Unguinol had deleterious effects on a model C(4) plant but no effect on a model C(3) plant. These results indicate that unguinol inhibits PPDK via a novel mechanism of action which also translates to an herbicidal effect on whole plants.

Photochemical and antioxidant responses in the leaves of Xerophyta viscosa Baker and Digitaria sanguinalis L. under water deficit.

In this study, photochemical and antioxidant responses of the monocotyledonous resurrection plant Xerophyta viscosa Baker and the crab grass Digitaria sanguinalis L. under water deficit were investigated as a function of time. Water deficit was imposed by withholding irrigation for 21 d. Gas exchange and chlorophyll a fluorescence analyses indicated that the dehydration treatment caused photoinhibition in both species. The reduction in the photosynthesis rate in both species during water deficit probably contributed to the decline in the photochemical efficiency of PSII and electron transport rate. However, the stomatal conductance of both species did not change during treatment whereas the intercellular CO2 pressure increased after 10 d of water deficit treatment. These observations could be related to nonstomatal limitations. The increasing net transpiration rate of both species may have contributed to leaf cooling because of water limitations. Prolonged water deficit resulted in photosynthetic pigment chlorophyll (a + b) and carotenoids content loss in only D. sanguinalis. Both species especially D. sanguinalis had increased the level of anthocyanin after 15 d of treatment, possibly to prevent the damaging effect of photooxidation. The total SOD activity of D. sanguinalis was significantly different from X. viscosa during the treatment. The total peroxidase activity in D. sanguinalis was significantly higher than in X. viscosa. X. viscosa acclimated to water deficit with no ultimate apparent oxidative damage due to endogenous protective mechanisms of resurrection. In case of D. sanguinalis, water deficit induced considerable stress and possibly caused some oxidative damage, despite the upregulation of protection mechanisms.