多胺及其转运体在杂草对百草枯抗性机制中的作用研究进展

通过对多胺在植物体内的形态分布、转运、代谢及其参与植物生长发育和胁迫反应的作用机制,以及杂草对百草枯的抗性机制最新研究进展进行综述,重点围绕多胺对百草枯毒性的缓解作用及多胺转运体在杂草对百草枯抗性机制中的作用进行评述,揭示了多胺及其转运体将是杂草对百草枯抗性机制研究的重要领域。     

Direct measurement of paraquat in leaf protoplasts indicates vacuolar paraquat sequestration as a resistance mechanism in Lolium rigidum

Sequestration of paraquat away from its target site in the chloroplast has been proposed as a mechanism of paraquat resistance. However, no consensus has been reached as to where paraquat is sequestered. This study quantifies paraquat in leaf protoplasts of paraquat resistant (R) and susceptible (S) Lolium rigidum. Intact protoplasts were prepared from plants treated with commercial dose of paraquat for 2 h. Paraquat absorbed by the leaf protoplasts was determined by light absorption of reduced paraquat following concentration and purification using a cation-exchange resin. Leaf protoplasts from treated paraquat resistant plants contained 2- to 3-fold more paraquat than leaf protoplasts isolated from susceptible plants. Since paraquat is not metabolised in L. rigidum and paraquat readily enters chloroplasts of both R and S plants, this greater amount of paraquat in leaf protoplasts of R plant must be kept away from the target site (chloroplast). This result indicates that paraquat resistance in L. rigidum is associated with a cytoplasmic mechanism, most likely a greater rate of vacuolar sequestration.     

Polyamines can inhibit paraquat toxicity and translocation in the broadleaf weed Arctotheca calendula

Reduced paraquat transport from the site of application to the site of action in the chloroplast seems a likely mechanism for paraquat resistance in several weed species including Arctotheca calendula. Recently, it has been shown that paraquat translocation in A. calendula is correlated with paraquat-induced injury and is reduced in paraquat-resistant A. calendula. Studies with leaf slices have shown that some polyamines when applied concomitantly with paraquat can reduce the toxic effects of paraquat. This study examined the effects of three polyamines, putrescine, cadaverine, and spermidine, on paraquat translocation to examine the possibility that paraquat translocation in susceptible plants would be reduced in the presence of polyamines due to competition of the polyamines with cellular paraquat uptake. Two polyamines, spermidine and cadaverine were effective in reducing paraquat translocation in susceptible A. calendula inducing these plants to perform more like resistant A. calendula in terms of translocation. Quantification of the polyamine contents of resistant and susceptible A. calendula showed that resistant plants have higher constitutive spermidine levels than susceptible plants, which infers a possible role of either polyamines or a polyamine transporter in paraquat resistance.     

Activity of fungicides and modulators of membrane drug transporters in field strains of Botrytis cinerea displaying multidrug resistance

In Botrytis cinerea, multidrug resistant (MDR) strains collected in French and German vineyards were tested in vitro, at the germ-tube elongation stage, towards a wide range of fungicides. Whatever the MDR phenotype, resistance was recorded to anilinopyrimidines, diethofencarb, iprodione, fludioxonil, tolnaftate and several respiratory inhibitors (e.g., penthiopyrad, pyraclostrobin). In MDR1 strains, overproducing the ABC transporter BcatrB, resistance extended to carbendazim and the uncouplers fluazinam and malonoben. In MDR2 strains, overproducing the MFS transporter BcmfsM2, resistance extended to cycloheximide, fenhexamid and sterol 14α-demethylation inhibitors (DMIs). MDR3 strains combined the overexpression of both transporters and exhibited the widest spectrum of cross resistance and the highest resistance levels. The four transport modulators, amitriptyline, chlorpromazine, diethylstilbestrol, and verapamil, known to affect some ABC transporters, were tested in B. cinerea. In our experimental conditions, the activity of several fungicides was only enhanced by verapamil. Interestingly, synergism was only recorded in MDR2 and/or MDR3 isolates treated with tolnaftate, fenhexamid, fludioxonil or pyrimethanil, suggesting that verapamil may inhibit the MFS transporter BcmfsM2. This is the first report indicating that a known modulator of ABC transporters could also block MFS transporters.     

Metabolism, uptake and translocation of 14C-paraquat in resistant and susceptible biotypes of Crassocephalum crepidioides (Benth.) S. Moore

The metabolism, uptake and translocation of paraquat in resistant (R) and susceptible (S) biotypes of Crassocephalum crepidioides (Benth.) S. Moore (redflower ragleaf) at the 10-leaf stage was investigated. A study on the properties of leaf surface was carried out to examine the relationship between leaf surface characters and paraquat absorption. The extractable paraquat was not metabolized by the leaf tissue of either the resistant or susceptible biotypes. Differential metabolism, therefore, does not appear to play a role in the mechanism of resistance. Both biotypes did not show any significant difference in the amount of cuticle and trichome densities. Furthermore, both biotypes are identical in the structure of stomata, trichomes and epicuticular wax. The results of the leaf surface studies are in agreement with the findings of the uptake study. Both biotypes demonstrated no significant difference in absorption between the resistant and susceptible biotypes. However, 10% of the absorbed ¹⁴C-paraquat into the S biotype was translocated basipetally, but not in the R biotype. The results of this study suggest that in C. crepidioides , differential translocation may contribute to the mechanism of resistance at the 10-leaf stage.     

Significance of ABC transporters in fungicide sensitivity and resistance

ATP-binding cassette (ABC) transporters are members of a protein superfamily which can be responsible for efflux of drugs from cells of target organisms. In this way, the transporters may provide a mechanism of protection against cytotoxic drugs. In laboratory-generated mutants of fungi, overproduction of ABC transporters can cause multi-drug resistance to azoles and other non-related toxicants. The impact of this mechanism of resistance in field populations with decreased sensitivity to azoles remains to be established. Inhibitors of ABC transporter activity may synergize activity of azoles to populations of both sensitive and azole-resistant pathogens. The natural function of ABC transporters in plant pathogenic fungi may relate to transport of plant-defence compounds or fungal pathogenicity factors. Therefore, inhibitors of ABC transporter activity may act as disease control agents with an indirect mode of action. ©1997 SCI     

Characterisation of Avena fatua populations with resistance to multiple herbicides

Avena fatua (wild oat) populations with resistance (R) to one or more herbicides have been described in numerous cropping systems worldwide. We previously reported that the R3 and R4 wild oat populations from Montana, USA, were resistant to four herbicides representing three different modes of action: tralkoxydim [acetyl‐CoA carboxylase (ACCase] inhibitor), imazamethabenz and flucarbazone [acetolactate synthase (ALS) inhibitors] and difenzoquat (growth inhibitor). We now quantify resistance levels of these populations to triallate [very long chain fatty acid (VLCFA) biosynthesis inhibitor], pinoxaden (ACCase inhibitor) and paraquat (photosystem I inhibitor). Glasshouse dose–response experiments showed that, compared with the means of two susceptible (S) populations, the R3 and R4 populations were 17.5‐ and 18.1‐fold more resistant to triallate, 3.6‐ and 3.7‐fold more resistant to pinoxaden, respectively, and 3.2‐fold (R3) more resistant to paraquat. Pre‐treatment of R plants with the cytochrome P450 inhibitor malathion partially reversed the resistance phenotype for flucarbazone (both populations), imazamethabenz (R4), difenzoquat (R4) and pinoxaden (R3), but not for tralkoxydim, fenoxaprop‐P‐ethyl or triallate. Target site point mutations known to confer resistance to ALS or ACCase inhibitors were not detected via DNA sequencing and allele‐specific PCR assays in R plants, suggesting the involvement of non‐target site resistance mechanism(s) for these herbicides. Together, our results complete the initial characterisation of wild oat populations that are resistant to seven (R3) or six (R4) herbicides from five or four mode of action families respectively.     

Perspective: root exudation of herbicides as a novel mode of herbicide resistance in weeds

The evolution of resistance to herbicides in weeds has become a great challenge for global agricultural production. Weeds have evolved resistance to herbicides through many different physiological mechanisms. Some weed species are known to secrete herbicide molecules from roots into the rhizosphere upon being treated. However, root exudation of herbicides as a mechanism of resistance has only recently been identified in two weed species. Root exudation pathways have been investigated in Arabidopsis, and this work suggested that ATP‐binding cassette (ABC) and multidrug and toxic compound extrusion (MATE) transporters play a role in the secretion of primary and secondary plant products from roots. We hypothesize that the mechanisms involved in root exudation of herbicides that result in resistance are mediated by overactive or overexpressed transporters, probably similar to those found for the exudation of primary and secondary compounds from roots. Elucidating the molecular and physiological basis of root exudation in herbicide‐resistant weeds would improve our understanding of the pathways involved in herbicide root secretion mediated by transporters in plants. © 2020 Society of Chemical Industry     

Resistance pattern and antioxidant enzyme profiles of protoporphyrinogen oxidase (PROTOX) inhibitor-resistant transgenic rice

We quantified the resistance levels of transgenic rice plants, expressing Myxococcus xanthus protoporphyrinogen oxidase (PROTOX) in chloroplasts and mitochondria, to PROTOX inhibitors, acifluorfen, oxyfluorfen, carfentrazone-ethyl, and oxadiazon. We also determined whether active oxygen species-scavenging enzymes are involved in the resistance mechanism of transgenic rice. The transgenic rice line M4 was about >200-fold more resistant to oxyfluorfen than the wild-type (WT). M4 was also resistant to acifluorfen, carfentrazone-ethyl, and oxadiazon, but did not show multiple resistance to imazapyr and paraquat, which have different target sites. Acifluorfen, oxyfluorfen, carfentrazone-ethyl, and oxadiazon reduced the chlorophyll content in leaves of WT, but had minimal or no effect on M4. The PROTOX inhibitors also caused significant lipid peroxidation in the treated leaves of WT rice. However, the malondialdehyde production in M4 was not affected by these herbicides. The WT rice had higher activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase than M4 after treatment with PROTOX inhibitors. A similar response was observed in all cases of antioxidant isozyme profiles analyzed. However, the induction in antioxidant activity in WT was not enough to overcome the toxic effects of a PROTOX inhibitor so the plant eventually died.     

Reduced paraquat translocation in paraquat resistant Arctotheca calendula (L.) Levyns is a consequence of the primary resistance mechanism, not the cause

Resistance to paraquat has been studied in detail in many weed species for more than a decade, with the precise mechanism of resistance still unclear. Several studies have indicated that reduced movement of the herbicide to the site of action in the chloroplast is at least partly responsible for endowing resistance. Although paraquat translocation studies have been performed in the past it has been rare for these studies to have been conducted on whole plants in the light, despite early observations which clearly showed that paraquat translocation is minimal unless treated plants are exposed to light. This study has addressed this issue in Arctotheca calendula by tracing the movement of ¹⁴C-paraquat in resistant and susceptible plants in both the dark and light. Differences in paraquat translocation between the resistant and susceptible biotypes of A. calendula were only observed when treated plants were exposed to light. It was observed that paraquat translocation was significantly reduced in the resistant compared to the susceptible biotype when plants were exposed to light but not in the dark. It is postulated that paraquat translocation is dependent on light mediated damage. As paraquat-induced damage is less severe in paraquat resistant plants, overall paraquat translocation is reduced in the resistant biotype.     

A review of physiological and biochemical aspects of resistance to atrazine and paraquat in Hungarian weeds

The most important results in the field of atrazine and paraquat resistance research by Hungarian researchers are reviewed. Pleiotropic effects accompanying atrazine resistance were investigated in atrazine-resistant (AR) and susceptible (S) biotypes of horseweed (Conyza canadensis (L) Cronq). No significant difference in carbon dioxide assimilation rate was found between the AR and S plants. The rates of the Hill reaction of the AR and S chloroplasts exhibited different temperature dependence. The thylakoid membrane lipids contained a lower amount of polar lipid and the fatty acid content exhibited a higher degree of unsaturation in the AR biotype. Photosynthetic apparatus of the AR biotype had better adaptive ability at low temperature and showed enhanced susceptibility to high-temperature stress. AR horseweed plants had reduced activity of xanthophyll cycle, limited capacity of light-induced non-photochemical and photochemical quenching, higher photosensitivity and susceptibility to photo-inhibition. In the case of paraquat resistance, horseweed found in Hungary exhibited a resistance factor of 450; the resistance is not based on an elevated level and activity of the antioxidant enzyme system. The suggested role of polyamines in the resistance mechanisms can be excluded. The higher putrescine and total polyamine content of paraquat-treated R leaves can be regarded as a general stress response rather than as a symptom of paraquat resistance. A paraquat-inducible, nuclear-coded protein, which presumably functions by carrying paraquat to the vacuole, is supposed to play a role in resistance.     

Contact activity of difenzoquat differs from that of paraquat

Difenzoquat herbicide is used for post-emergence control of wild oat (Avena fatua L) in small grain crops. Its mechanism of action is not known, but appears to have both paraquat-like contact activity and systemic growth-inhibition activity. Experiments were conducted in vitro to compare the contact activity of difenzoquat and paraquat, to examine the contact activity of difenzoquat in difenzoquat-resistant (accession LCS) and -susceptible (accession SB 18) A fatua biotypes and -tolerant 'Ernest' and -susceptible 'Verde' hard red spring wheat (Triticum aestivum L) cultivars, and to investigate the role of differential DNA synthesis as a mechanism for difenzoquat resistance. Difenzoquat at 1 mM induced significant electrolyte leakage from resistant and susceptible A fatua leaf tissue in both light and dark, but paraquat at 1 mM induced electrolyte leakage only in light and not in dark. Difenzoquat at 1 mM under light induced more electrolyte leakage from resistant and susceptible A fatua than from tolerant 'Ernest' and susceptible 'Verde' wheat. Paraquat under light conditions induced more electrolyte leakage than difenzoquat, but no significant differences among A fatua accessions and wheat cultivars were detected. Difenzoquat under light did not decrease chlorophyll levels for either A fatua accessions or wheat cultivars, whereas paraquat decreased chlorophyll content of all four plant types. Inhibition of DNA synthesis was not significantly different between susceptible and resistant A fatua, but was significantly greater in susceptible 'Verde' than tolerant 'Ernest' wheat. These data suggest that difenzoquat and paraquat, have different modes of contact activity.     

Multiple resistance across glufosinate,glyphosate, paraquat and ACCase‐inhibiting herbicides in an Eleusine indica population

An Eleusine indica population was previously reported as the first global case of field‐evolved glufosinate resistance. This study re‐examines glufosinate resistance and investigates multiple resistance to other herbicides in the population. Dose–response experiments with glufosinate showed that the resistant population is 5‐fold and 14‐fold resistant relative to the susceptible population, based on GR₅₀ and LD₅₀ R/S ratio respectively. The selected glufosinate‐resistant subpopulation also displayed a high‐level resistance to glyphosate, with the respective GR₅₀ and LD₅₀ R/S ratios being 12‐ and 144‐fold. In addition, the subpopulation also displayed a level of resistance to paraquat and ACCase‐inhibiting herbicides fluazifop‐P‐butyl, haloxyfop‐P‐methyl and butroxydim. ACCase gene sequencing revealed that the Trp‐2027‐Cys mutation is likely responsible for resistance to the ACCase inhibitors examined. Here, we confirm glufosinate resistance and importantly, we find very high‐level glyphosate resistance, as well as resistance to paraquat and ACCase‐inhibiting herbicides. This is the first confirmed report of a weed species that evolved multiple resistance across all the three non‐selective global herbicides, glufosinate, glyphosate and paraquat.     

Initial report of glufosinate and paraquat multiple resistance that evolved in a biotype of goosegrass (Eleusine indica) in Malaysia

Field and glasshouse studies have confirmed the presence of a glufosinate‐ and paraquat‐resistant goosegrass biotype that has infested a bitter gourd field in Air Kuning, Perak, Malaysia. Glufosinate and paraquat had been applied at least six times per year to the affected fields (originally a rubber plantation) for more than four consecutive years. Paraquat had been used since 1970 for weed control in the rubber plantation. An on‐site field trial revealed that the control of the goosegrass plants, measuring 20–35 cm in height, ranged from 20 to 35% 3 weeks after being treated with each herbicide at twice the recommended rate. Dose–response tests were conducted in the glasshouse, using seedlings at the three‐to‐four‐leaf stage that had been obtained from the plants that had received repeated exposure to these herbicides and a biotype with no history of any herbicide resistance. The comparison of the GR₅₀ (the herbicide rate that is required to reduce the shoot fresh weight by 50%) of the seedlings indicated that the resistant biotype of goosegrass is 3.4‐fold and 3.6‐fold more resistant than the susceptible biotype following treatment with glufosinate and paraquat, respectively. This study has demonstrated the world's first field‐evolved instance of multiple resistance in goosegrass to two non‐selective herbicides, glufosinate and paraquat.     

Reduced translocation is involved in resistance to glyphosate and paraquat in Conyza bonariensis and Conyza canadensis from California

Resistance to glyphosate and paraquat has evolved in some populations of Conyza spp. from California, USA. This study evaluated whether herbicide absorption and translocation were involved in the mechanism of resistance to both herbicides. Three lines of each species were used: glyphosate‐paraquat‐susceptible (GPS), glyphosate‐resistant (GR) and glyphosate‐paraquat‐resistant (GPR). Radiolabelled herbicide was applied to a fully expanded leaf, and absorption and movement out of the treated leaf were monitored for up to 24 h for paraquat and 72 h for glyphosate. Plants treated with paraquat were incubated in darkness for the first 16 h and then subjected to light conditions. More glyphosate was absorbed in C. bonariensis (52.9–58.3%) compared with C. canadensis (28.5–37.6%), but no differences in absorption were observed among lines within a species. However, in both species, the GR and GPR lines translocated less glyphosate out of the treated leaf when compared with their respective GPS lines. Paraquat absorption was similar among lines and across species (71.3–77.6%). Only a fraction of paraquat was translocated in the GPR lines (3% or less) when compared with their respective GPS or GR lines (20% or more) in both species. Taken together, these results indicate that reduced translocation is involved in the mechanism of resistance to glyphosate and paraquat in C. bonariensis and C. canadensis.     

Resistance to paraquat in Mazus pumilus

Mazus pumilus is an annual self‐pollinating weed that is commonly found in arable land, vegetable gardens and roadsides. This weed harbours insects and pathogens that attack vegetables. The mechanism of resistance to paraquat of M. pumilus found in Ohita, Japan, was studied. Whole plant bioassays revealed that the resistant (R) biotypes were four to six times less susceptible than controls. Chlorophyll destruction of leaf discs by paraquat treatment in R biotypes was 4–20 times lower than those of susceptible (S) biotypes. Ferric reducing antioxidant power (FRAP) values in R biotypes were higher than those of S biotypes before and after paraquat treatments. The activity of superoxide dismutase (SOD) was also higher in R biotypes than those of S biotypes before and after treatment with paraquat, but the activities of ascorbate peroxidase (APX) and catalase (CAT) were not different between R and S biotypes. Change of ascorbate (AsA) contents before and after paraquat treatment was equivalent in both biotypes. These results indicate that the increased SOD activity and antioxidant capacity in R biotypes contribute to the resistance to paraquat of M. pumilus.     

Paraquat-resistant biotypes of Hordeum glaucum from zero-tillage wheat

There has been a significant increase in the area seeded to minimum- and zero-tilled crops worldwide over the past two decades. These cropping systems rely primarily on the non-selective herbicides glyphosate or paraquat/diquat to control weeds before seeding the crop. Both glyphosate and paraquat/diquat are regarded as low-risk herbicides in the ability of target weeds to develop resistance to them. Following 10–15 years of once annual applications of paraquat and diquat for weed control in zero-tilled cereals, failure of these herbicides to control Hordeum glaucum Steud. in two separate fields occurred. Dose–response experiments demonstrated high-level resistance to paraquat and diquat in both populations; however, the resistant biotypes are susceptible to other herbicides. This is the first report, worldwide, of paraquat resistance following the use of this herbicide in zero-tillage cropping systems and is therefore a harbinger of future problems in minimum-tillage systems when there is exclusive reliance on a contact herbicide for weed control.     

杂草对乙酰乳酸合成酶抑制剂抗药性研究进展

乙酰乳酸合成酶(ALS)抑制剂类除草剂已经成为一类广泛使用的除草剂。综述了杂草对ALS抑制剂类除草剂抗药性的产生与发展、抗性机理、抗性基因应用等方面的研究进展。其抗性产生机理主要有杂草对除草剂代谢能力增强、ALS基因突变导致对除草剂敏感性降低和ALS含量提高等。