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Fil: Longas, Maria de Las Mercedes. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; Argentina. Universidad Nacional del Sur. Departamento de Agronomia; Argentina

Mepiquat chloride (MC) priming alleviates the effects of salt stress during seed germination in cotton (Gossypium hirsutum L.), but the mechanisms underlying its effects are unknown. We found that MC priming increases salt tolerance, as evidenced by marked increases in seed vigor and germination rates, and alleviated salt toxicity by reducing Cl− accumulation in germinating seeds. Consistently, electrophysiological experiments revealed that the seeds with MC priming displayed superior Cl− exclusion ability in the root apex. These beneficial effects of MC priming were abolished by the abscisic acid (ABA)-synthesis blocker fluridone under salt stress. MC priming induced an early response to acclimatization and stress, as indicated by rapidly increasing ABA content during initial exposure to salt stress. Transcriptome analyses revealed that MC priming induced an array of differentially expressed genes (DEGs) in germinating seeds. The most noticeable changes in germinating seeds were MC priming-induced increases in the expression of DEGs encoding components of ABA biosynthesis, ABA catabolism, and ABA signaling pathways under salt stress. MC priming also increased the expression of some DEGs encoding Cl− ion transporters (e.g. CCC, SLAC1/SLAH1/SLAH3, CLC, and ALMT9) in germinating seeds. These results indicate that MC priming-induced ABA contributes to Cl− homeostasis in tissues and acts as a positive regulator of salt tolerance via regulation of Cl− transporters (particularly CCC and SLAC1/SLAH1/SLAH3). Taken together, these findings shed light on the molecular mechanism underlying MC-mediated tolerance to salt stress during seed germination.

Cadmium (Cd) is a highly toxic heavy metal. Abscisic acid (ABA) is a regulator that has various functions in plants. To further explore the mechanism by which ABA alleviates Cd damage in plants, ABA and fluridone, which inhibits ABA biosynthesis, were separately sprayed on the leaves of Malus hupehensis Rehd. (M. hupehensis) seedlings treated with Cd. The root Cd2+ flux in vivo, the accumulation and transport of Cd2+ in roots, the cell death in roots and the transpiration rate in leaves were then analyzed. The results showed that the amount of cell death in roots gradually increased from 6 to 72 h in the Cd treatment. After spraying ABA on M. hupehensis leaves in the Cd treatment, the number of root cell deaths, the accumulation of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in roots and the transpiration rate in leaves decreased significantly compared with those in the samples in the Cd-only treatment. In addition, the influx rate of Cd2+ in roots, the content of Cd in plants and the migration rate of Cd from the roots to the aerial parts were also significantly reduced. In contrast, all of these parameters increased significantly in M. hupehensis sprayed with fluridone under the Cd treatment. These results indicate that spraying ABA on leaves alleviates Cd damage in M. hupehensis roots by decreasing cell death as well as the contents of H2O2 and MDA in roots. Given that transpiration is the main driving force for the absorption and transport of inorganic salts in plants, our results showed that the alleviation of Cd damage in roots resulted from the reduced leaf transpiration rate, which decreased the influx and accumulation of Cd2+ in roots.

Drought stress is a limiting factor for wheat production and food security. Drought priming has been shown to increase drought tolerance in wheat. However, the underlying mechanisms are unknown. In the present study, the genes encoding the biosynthesis and metabolism of abscisic acid (ABA) and jasmonic acid (JA), as well as genes involved in the ABA and JA signaling pathways were up-regulated by drought priming. Endogenous concentrations of JA and ABA increased following drought priming. The interplay between JA and ABA in plant responses to drought priming was further investigated using inhibitors of ABA and JA biosynthesis. Application of fluridone (FLU) or nordihydroguaiaretic acid (NDGA) to primed plants resulted in lower chlorophyll-fluorescence parameters and activities of superoxide dismutase and glutathione reductase, and higher cell membrane damage, compared to primed plants (PD) under drought stress. NDGA + ABA, but not FLU + JA, restored priming-induced tolerance, as indicated by a finding of no significant difference from PD under drought stress. Under drought priming, NDGA induced the suppression of ABA accumulation, while FLU did not affect JA accumulation. These results were consistent with the expression of genes involved in the biosynthesis of ABA and JA. They suggest that ABA and JA are required for priming-induced drought tolerance in wheat, with JA acting upstream of ABA.

Copper‐based antimicrobial compounds are widely and historically used to control plant diseases, such as late blight caused by Phytophthora infestans, which seriously affects the yield and quality of potato. We previously identified that copper ion (Cu2+) acts as an extremely sensitive elicitor to induce ethylene (ET)‐dependent immunity in Arabidopsis. Here, we found that Cu2+ induces the defence response to P. infestans in potato. Cu2+ suppresses the transcription of the abscisic acid (ABA) biosynthetic genes StABA1 and StNCED1, resulting in decreased ABA content. Treatment with ABA or inhibitor fluridone made potato more susceptible or resistance to late blight, respectively. In addition, potato with knockdown of StABA1 or StNCED1 showed greater resistance to late blight, suggesting that ABA negatively regulates potato resistance to P. infestans. Cu2+ also promotes the rapid biosynthesis of ET. Potato plants treated with 1‐aminocyclopropane‐1‐carboxylate showed enhanced resistance to late blight. Repressed expression of StEIN2 or StEIN3 resulted in enhanced transcription of StABA1 and StNCED1, accumulation of ABA and susceptibility to P. infestans. Consistently, StEIN3 directly binds to the promoter regions of StABA1 and StNCED1. Overall, we concluded that Cu2+ triggers the defence response to potato late blight by activating ET biosynthesis to inhibit the biosynthesis of ABA., Cu2+‐mediated late blight resistance activates ET signalling, subsequently suppressing ABA biosynthesis. This recalls two tips when using copper‐based antimicrobial compounds: water in advance; avoid strong sunshine and drought.

Graptopetalum paraguayense E. Walther is an edible succulent plant that is native to Mexico. When leaves of G. paraguayense are detached from the mother plant, shoots and roots regenerate from the leaf base. To investigate the endogenous hormonal regulation of plant regeneration in G. paraguayense, we evaluated the effects of applying gibberellin (GA), abscisic acid (ABA), and phytohormone biosynthesis inhibitors to leaves detached from the mother plant. GA3 and paclobutrazol did not affect plant regeneration of G. paraguayense, whereas ABA treatment significantly suppressed plant regeneration. When leaves were treated with the ABA biosynthesis inhibitor fluridone at 10 μM, the frequency of shoot regeneration was more than twice that of the control on the 6th day after leaf detachment. In addition, when both fluridone and ABA were applied at the same time, the frequency of plant regeneration decreased to control levels or below. Endogenous ABA in leaves was approximately 1.3 ng gFW−1 just after leaf detachment, decreased to 0.3 ng gFW−1 by the 1st day after leaf detachment, and increased to 3.0 ng gFW−1 by the 9th day after leaf detachment. These findings indicate that ABA plays an important role in suppression of plant regeneration in G. paraguayense. Although plant regeneration during storage and transportation currently reduces the economic value of G. paraguayense, our findings may provide a method to delay unwanted plant formation at the leaf base.

Background Diflufenican resistance has been reported in wild radish populations since 1998, but the resistance mechanisms have not been investigated. Recently, we identified a wild radish population (H2/10) from the Western Australian grain belt that is resistant (R) to the phytoene desaturase (PDS)-inhibiting herbicide diflufenican. Results Dose-response results showed this R population is 4.9-fold more resistant than the susceptible (S) population based on the LD50 R/S ratio. In addition, the R population also exhibits cross-resistance to the PDS-inhibiting herbicide fluridone. The cytochrome P450 inhibitor malathion reversed diflufenican resistance and partially reversed fluridone resistance in the R population. The full coding sequences of the PDS gene were cloned from the S and R plants and there are natural variations in the PDS gene transcripts/alleles with no correlation to resistance. In addition, the R plants had a level of PDS gene expression that is not significantly different from the S plants. Conclusion These results demonstrated that diflufenican resistance in this R wild radish population is likely due to non-target-site based enhanced herbicide metabolism involving cytochrome P450s. © 2019 Society of Chemical Industry.

Residual herbicides are routinely applied to control troublesome weeds in pumpkin production. Fluridone and acetochlor, Groups 12 and 15 herbicides, respectively, provide broad-spectrum PRE weed control. Field research was conducted in Virginia and New Jersey to evaluate pumpkin tolerance and weed control to PRE herbicides. Treatments consisted of fomesafen at two rates, ethalfluralin, clomazone, halosulfuron, fluridone, S-metolachlor, acetochlor emulsifiable concentrate (EC), acetochlor microencapsulated (ME), and no herbicide. At one site, fluridone, acetochlor EC, acetochlor ME, and halosulfuron injured pumpkin 81%, 39%, 34%, and 35%, respectively, at 14 d after planting (DAP); crop injury at the second site was 40%, 8%, 19%, and 33%, respectively. Differences in injury between the two sites may have been due to the amount and timing of rainfall after herbicides were applied. Fluridone provided 91% control of ivyleaf morningglory and 100% control of common ragweed at 28 DAP. Acetochlor EC controlled redroot pigweed 100%. Pumpkin treated with S-metolachlor produced the most yield (10,764 fruits ha–1) despite broadcasting over the planted row; labeling requires a directed application to row-middles. A separate study specifically evaluated fluridone applied PRE at 42, 84, 126, 168, 252, 336, and 672 g ai ha–1. Fluridone resulted in pumpkin injury ≥95% when applied at rates of ≥168 g ai ha–1; significant yield loss was noted when the herbicide was applied at rates >42 g ai ha–1. We concluded that fluridone and acetochlor formulations are unacceptable candidates for pumpkin production.Nomenclature: Acetochlor; clomazone; ethalfluralin; fomesafen; fluridone; halosulfuron; Smetolachlor; common ragweed; Ambrosia artemisiifolia L.; ivyleaf morningglory, Ipomoea hederacea Jacq.; redroot pigweed, Amaranthus retroflexus L.; pumpkin, Cucurbita pepo L.

An improved understanding of seed quality and germination control can contribute effectively to the use and conservation of neglected native species with ecological and economic value, such as Trichocline catharinensis, an endemic Asteraceae species from southern Brazil. We investigated the effects of applying gibberellin (GA3), abscisic acid (ABA) and their biosynthesis inhibitors, paclobutrazol (PAC) and fluridone (FLU), respectively, on T. catharinensis seed germination, and on polyamine (PA) content and antioxidant enzyme activities in germinating seeds. FLU and GA3 increased seed germination speed compared to treatment with H2O only. ABA inhibited both germination speed index and percentage, while PAC severely inhibited seed germination. The stimulatory effect of GA3 and FLU was associated with increased contents of putrescine (PUT) and spermidine (SPD) relative to spermine (SPM). As a result, high ratio (PUT + SPD/SPM) as well as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) enzyme activities were observed when seed germination occurs. In contrast, in low or no seed germination treatment (ABA and PAC), low ratio (PUT + SPD/SPM) was observed, while the antioxidant enzymes, mainly SOD activity, tended to increase. Application of PAs at 200 μM stimulated germination through improving the speed and uniformity, and this effect was associated with antioxidant enzyme activity. Our results suggest a relationship between PA and the antioxidant system with the physiological mechanism of seed germination. These results improve the physiological knowledge of seed germination control in Asteraceae and contribute to the biological groundwork for future studies on the use and conservation of native species.

Field and greenhouse studies were conducted in 2016 and 2017 to determine sweetpotato tolerance to herbicides applied to plant propagation beds. Herbicide treatments included PRE application of flumioxazin (107 g ai ha−1),S-metolachlor (800 g ai ha−1), fomesafen (280 g ai ha−1), flumioxazin plusS-metolachlor (107 g ai ha−1+ 800 g ai ha−1), fomesafen plusS-metolachlor (280 g ai ha−1+ 800 g ai ha−1), fluridone (1,120 or 2,240 g ai ha−1), fluridone plusS-metolachlor (1,120 g ai ha−1+ 800 g ai ha−1), napropamide (1,120 g ai ha−1), clomazone (420 g ai ha−1), linuron (560 g ai ha−1), linuron plusS-metolachlor (560 g ai ha−1+ 800 g ai ha−1), bicyclopyrone (38 or 49.7 g ai ha−1), pyroxasulfone (149 g ai ha−1), pre-mix of flumioxazin plus pyroxasulfone (81.8 g ai ha−1+ 104.2 g ai ha−1), or metribuzin (294 g ai ha−1). Paraquat plus non-ionic surfactant (280 g ai ha−1+ 0.25% v/v) POST was also included. After plants in the propagation bed were cut and sweetpotato slip number, length, and weight had been determined, the slips were then transplanted to containers and placed either in the greenhouse or on an outdoor pad to determine any effects from the herbicide treatments on initial sweetpotato growth. Sweetpotato slip number, length, and/or weight were affected by flumioxazin with or withoutS-metolachlor,S-metolachlor with or without fomesafen, clomazone, and all fluridone treatments. In the greenhouse studies, initial root growth of plants after transplanting was inhibited by fluridone (1,120 g ai ha−1) and fluridone plusS-metolachlor. However, by 5 wk after transplanting few differences were observed between treatments. Fomesafen, linuron with or withoutS-metolachlor, bicyclopyrone (38 or 49.7 g ai ha−1), pyroxasulfone with or without flumioxazin, metribuzin, and paraquat did not cause injury to sweetpotato slips in any of the studies conducted.

Stevia is a herbaceous plant containing non-sugar sweeteners that could be regarded as a successor to sugar for diabetics. However, there are some problems with the cultivation of stevia, especially in the greenhouse, including unbranching and low sweetening agents. To overcome this issue, an experiment was designed to increase not only the branching and leaf production but also the sweetness. Therefore, a novel strategy using abscisic acid (0, 50, 100, 150 μM), its inhibitor, i.e. fluridone (0, 50, 100, 150 μM) and decapitation of plant apical meristems was applied. Results showed that when stevia was decapitated, dormant buds responded to the application of abscisic acid and fluridone. Under these conditions, axillary buds were developed to branches. As well leaf, total dry weight, soluble sugars and steviol glycosides (SGs) were significantly increased. In addition, the interaction of abscisic acid (50 and 100 μM) and fluridone (50 μM) had the highest positive effects on plant growth and steviol glycosides production rather than their sole applications. Results also indicated that decapitation removed a terminal dominance over a limited period of time and the terminal dominance was re-established with the growth of the terminal branches, whereas the influence of 50 µM fluridone on stevia was long term and the number of shoots was greater. Since stevia is a costly sweetener, the results of this study could be used in greenhouses, where the cultivation of stevia seems to be reasonable in terms of economic aspects.

Arabidopsis ACYL-COENZYME-A-BINDING PROTEIN1 (ACBP1) plays a positive role in abscisic acid (ABA) signaling during seed dormancy and germination. As a putative component of the ABA signaling pathway, its potential role in salt and osmotic signaling was tested using ACBP1pro::GUS transgenic lines, ACBP1-overexpressors (ACBP1-OXs), the acbp1 mutant and ACBP1-complemented lines (acbp1-COM). ACBP1-OXs were more sensitive than the wild type to NaCl and mannitol during seed germination and seedling establishment, while the acbp1 mutant was less sensitive during seed germination. Germination assays were conducted using the ABA biosynthesis inhibitor, fluridone, to determine whether the ACBP1 response was ABA-related. The germination potential of Col-0, acbp1, ACBP1-OXs, and acbp1-COM recovered to a level similar to the water control when fluridone was applied to NaCl- and mannitol-treated seeds, indicating that phenotypic variation amongst these lines was related to de novo ABA biosynthesis. Furthermore, yeast two-hybrid, bimolecular complementation assays and pull-down assays showed that ACBP1 interacted with ABA-RESPONSIVE ELEMENT BINDING PROTEIN1 (AREB1) via its ankyrin repeats. The target genes of AREB1 were up-regulated in ACBP1-OXs but down-regulated in acbp1; and the localization of DsRed-AREB1 was affected in ACBP1-OX. These results indicate that ACBP1 promotes ABA signaling under salt and osmotic stress during seed to seedling transition.

Abscisic acid (ABA) and nitric oxide (NO) are both extremely important signalling molecules employed by plants to mediate plant tolerance under abiotic stresses. In the present study, the role of NO in ABA-induced photosynthesis and antioxidant system in leaves of tall fescue (Festuca arundinacea Schreb.) seedlings was investigated. Low-light (LL) stress increased intercellular CO2 concentration (Ci), as well as decreased plant height, leaf width, tiller number, biomass, chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), the maximum quantum yield of photosystem photochemistry (Fv/Fm), actual photochemical efficiency of photosystem II (ΦPSII), photochemical quenching (qP), the apparent electron transport rate (ETR), enzymatic activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) and glyceraldehyde phosphate dehydrogenase (GADPH) and phosphoribulokinase (PRK), which were substantially alleviated by exogenous ABA application. Moreover, application of these leaves with exogenous ABA resulted in reduced LL stress induced ion leakage and reduced contents of MDA, H2O2 and superoxide radicals O 2 • - , as well as higher activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). Expression of genes coding antioxidant enzymes increased in tall fescue in the presence of ABA under LL stress. These responses could be reversed by treatment with fluridone (the ABA biosynthesis inhibitor). The application of ABA elevated NO level, enhanced nitric oxide synthase (NOS)-like activity and up-regulated the tall fescue nitric oxide synthase-associated gene, NITRIC OXIDE ASSOCIATED 1 (FaNOA1) expression level. In addition, neither exogenous NO nor specific NO scavenger 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) or NO synthase (NOS) specific inhibitor Nω-nitro-L-arginine (LNNA) treatments had no effect on endogenous ABA concentration and ABA receptors transcript levels (FaPYR1 and FaPYL1), implying that the protective effect of ABA under LL stress might be mediated by NO. These results indicated that NO was involved in the ABA-mediated LL tolerance via regulating the antioxidant defense system and keeping a high level of photosynthetic rate in tall fescue.

Fomesafen provides effective control of glyphosate-resistant Palmer amaranth in cotton. However, cotton seedlings can be injured when fomesafen is applied PRE. Therefore, greenhouse and field experiments were conducted at Athens, GA, and at six locations in Alabama and Georgia in 2013 and 2016 to evaluate cotton growth and yield response to fomesafen applied PRE at 70, 140, 280, 560, 1,120, or 2,240 g ai ha-1, and in combination with pendimethalin, diuron, acetochlor, and fluridone at 1× label rates. Greenhouse bioassays indicated that fomesafen reduced cotton height and dry weight with increasing rate in Cecil sandy loam and Tifton loamy sand but not in Greenville sandy clay loam--possibly as a result of this soil's higher organic matter (OM) and clay content. Fomesafen applied at 2,240 g ai ha-1 reduced cotton stand by as much as 83% compared to the nontreated check (NTC) at all field locations except Alabama's Macon and Baldwin counties, and 1,120 g ai ha-1 reduced cotton stand only at Pulaski County, GA, by 52%. Cotton height was reduced by the two highest rates of fomesafen at all locations except Clarke County, GA, and Baldwin County, AL. Injury data indicated more visual injury followed increasing fomesafen rates, and high-rate treatments produced more injury in sandier soils. Cotton yield was unaffected by herbicide treatments at any location, except for the 1,120 g ai ha-1 rate at Pulaski County (49% yield loss compared to NTC), 2,240 g ai ha-1 at Pulaski County (72% yield loss), and Tift County (29% yield loss). These data indicated cotton yield should not be negatively affected by fomesafen applied PRE alone within label rates or in combination with pendimethalin, diuron, acetochlor, and fluridone at 1× label rates, although some visual injury, or stand or height reduction may occur early in the growing season.Nomenclature: Acetochlor; diuron; fluridone; fomesafen; glyphosate; pendimethalin; Palmer amaranth, Amaranthus palmeri S. Wats.; cotton, Gossypium hirsutum L.

Research was conducted to evaluate the sensitivity of cover crops to a low rate of soil-applied herbicides and investigate the likelihood of herbicide carryover to fall-seeded cover crops following an irrigated corn crop. In the sensitivity study, herbicides were applied at a 1/16× rate (to simulate four half-lives) 1 d after cover crop planting, whereas for the carryover study residual herbicides were applied at a 2× rate at the maximum label corn height or growth stage and cover crops sown immediately after corn harvest. In the sensitivity experiment, atrazine, diuron, fluridone, fomesafen, metribuzin, pyrithiobac, and sulfentrazone reduced emergence of the leguminous cover crops Austrian winterpea, crimson clover, and hairy vetch. However, reduced biomass production of leguminous cover crops in the spring was only observed for atrazine, fluridone, and pyrithiobac. For rapeseed, atrazine, flumioxazin, fluridone, pyrithiobac, pyroxasulfone, sulfentrazone, and tembotrione reduced emergence, but biomass production was reduced only by atrazine and fluridone. Conversely, wheat, cereal rye, barley, oats, and triticale were not affected by soil-applied herbicides. Barley was the only cereal cover crop that showed biomass reduction due to the application of flumioxazin, fluridone, mesotrione, S-metalochlor, and sulfentrazone. In the carryover study, with the exception of crimson clover, Austrian winterpea, cereal rye, hairy vetch, rapeseed, and wheat showed no negative affect on biomass production following a 2× rate of postemergence-applied residual herbicide in corn.Nomenclature: Atrazine; diuron; flumioxazin; fluridone; mesotrione; metribuzin; pyrithiobac; pyroxasulfone; S-metolachlor; sulfentrazone; tembotrione; Austrian winterpea, Lathryrus hirsutus L.; barley, Hordeum vulgare L.; cereal rye, Secale cereale L.; corn, Zea mays L.; crimson clover, Trifolium incarnatum L., hairy vetch, Vicia villosa Roth; oats, Avena sativa L.; rapeseed, Brassica napus L.; triticale, Triticale hexaploide Lart.; wheat, Triticum aestivum L.

Fluridone (FLU) is widely used as a herbicide and interferes with photosynthesis via induction of leaf bleaching. However, the mechanism of FLU-induced leaf bleaching remains elusive. In this study, the effects of FLU on the metabolism of leaf pigments, including chlorophyll and carotenoids, were investigated. Our results demonstrate that FLU induced rice leaf bleaching in a dose-dependent manner. Treatment with 5 µM FLU strongly induced leaf bleaching by decreasing pigment content, with carotenoids and chlorophyll decreased by 98 and 95%, respectively, in the second leaves of rice seedlings. Our results indicate that the transcription levels of leaf pigment biosynthetic and catabolic genes were significantly downregulated by 5 µM FLU treatment. These results suggest that FLU induces leaf bleaching by decreasing leaf pigment content via downregulation of the transcription levels of leaf pigment biosynthetic genes, and that the downregulation of transcription levels of leaf pigment catabolic genes is a result of feedback inhibition mediated by FLU-decreased leaf pigment content. In addition, to test whether FLU-induced leaf bleaching is due to FLU-induced abscisic acid (ABA) deficiency, the effect of FLU treatment on endogenous ABA content and the recovery effect of ABA on FLU-induced leaf bleaching were investigated. Application of FLU significantly decreased endogenous ABA content, but FLU-induced leaf bleaching was not rescued by ABA application, thus FLU-induced leaf bleaching is not due to FLU-induced ABA deficiency.

Herbicide resistance has increased the need for novel weed control strategies. Fluridone has herbicidal as well as potential germination stimulant activity. The objectives of this study were to evaluate fluridone as a fall-applied germination stimulant for weed control and to assess rotational crop tolerance. Fall-applied fluridone was compared with a nontreated control in areas established with false cleavers, volunteer canola, and wild oat at Lacombe, AB, in 2014–2015 and 2015–2016, and at St Albert, AB, in 2015–2016. In the fall, there was a trend for weed densities to be higher in fluridone treatments than in untreated controls across site-years. The stimulatory effect of fluridone on weed germination was not statistically significant in fall assessments, while the weed control effect was significant in 33% of spring assessments. While fluridone reduced weed biomass for some site-years, it also reduced canola crop emergence and biomass at St Albert in 2015–2016, and caused injury symptoms on wheat and field pea. Risk of carryover to subsequent crops outweighed the benefits of using fluridone in the fall to stimulate weed germination in this study.Nomenclature: Fluridone; false cleavers, Galium spurium L. GALSP; canola, Brassica napus L. BRSNN; wild oat, Avena fatua L. AVEFA; field pea, Pisum sativum L.; wheat, Triticum aestivum L.

In plants, sugar acts as an essential signaling molecule that modulates various aspects of metabolism, growth and development, which are also controlled by phytohormones. However, the molecular mechanism of cross-talk between sugar and phytohormones still remains to be elucidated. We have identified gsm1 (glucose-hypersensitive mutant 1) as a mutant with impaired cotyledon development that shows sensitivity to exogenous abscisic acid (ABA). The addition of fluridone can reverse the glucose (Glc) inhibitory effect in gsm1, implying that endogenous ABA is involved in the Glc response of gsm1. In 4.5% Glc, the expression of Glc-induced ABA-responsive genes in gsm1-1 was nearly two times higher than that in the wild type. Compared to gsm1-1, the gsm1-1 abi4-1 double mutant exhibited reduced sensitivity to Glc and ABA, which was similar to the Glc and ABA insensitive phenotype of abi4-1, suggesting that ABI4 is epistatic to GSM1. In the treatment with 4.5% Glc, the GSM1 transcript level was greatly increased in abi4-1 by almost 4-fold of that in the wild type. These data suggest that GSM1 plays an important role in the ABI4-regulated Glc-ABA signaling cascade during Arabidopsis early seedling growth.

Suberin biosynthesis involves a large number of genes, and many of them are induced by abscisic acid (ABA). However, the regulation of transcription factor (TF) in response to ABA on suberin biosynthetic genes in kiwifruit has been unexplored. In this study, two genes, AchnCYP86A1 and AchnFAR respectively encoding a fatty acid ω-hydroxylase and fatty acyl-CoA reductase involved in suberin monomer biosynthesis were demonstrated in transient overexpressed tobacco (Nicotiana benthamiana). Notably, the negative regulation of AchnMYB4 on AchnCYP86A1 and AchnFAR was identified. AchnMYB4 could repress AchnCYP86A1 and AchnFAR transcript by directly binding to the gene promoter in yeast one-hybrid and dual-luciferase assays. These results were further confirmed in transient overexpressed tobacco leaves in that AchnMYB4 significantly down-regulated suberin biosynthetic genes including CYP86A1, FAR2 and FAR3, and reduced accumulation of ω-hydroxyacids and primary alcohols. Moreover, exogenous ABA could induce the expression of AchnCYP86A1 and AchnFAR, and the accumulation of corresponding suberin monomers by inhibition of AchnMYB4 in wound-tissue of kiwifruit. However, fluridone (an inhibitor of ABA biosynthesis) was found to counter the inductive effects of ABA. Taken together, the results suggest that ABA activates AchnCYP86A1 and AchnFAR to promote suberin monomers biosynthesis by inhibiting AchnMYB4.

We elucidated the effect of increased planting density (single and grouped competing plants) on concentrations of auxin, abscisic acid, and cytokinins in normal lettuce plants and in those with ethylene perception inhibited by 1-methylcyclopropene (1-MCP). An attempt was made to relate the changes in hormone concentration induced by competition and inhibition of ethylene sensitivity to growth responses of lettuce planting. The results showed changes in concentrations of auxins, cytokinins, and ABA in the response of lettuce to crowding. Accumulation of ABA in shoots was likely to contribute to inhibition of transpiration of the plants grown in the presence of neighbors. This assumption was supported by the results of application of an inhibitor of ABA synthesis (fluridone and carotenoid biosynthesis herbicide) resulting in increased transpiration of grouped, but not single plants. Increased planting density led to the decline in root auxins paralleled by inhibition of root growth. This effect was likely to be due to decreased auxin transport to the roots from the shoots suggested by accumulation of auxins in the shoots and inhibition of root growth by application of the auxin transport inhibitor [N-(1-naphtyl)phtalamic acid (NPA)]. Importance of the changes in hormone concentrations was confirmed by data showing that disturbance of auxin and cytokinin distribution detected in MCP-treated plants was accompanied by corresponding modification of the growth response.

Flumioxazin and fomesafen are commonly used to control glyphosate-resistant Palmer amaranth in cotton and other crops, thus increasing risk to select for Palmer amaranth biotypes resistant to protoporphyrinogen oxidase (PPO) inhibitors. A field experiment was conducted to determine the potential for fluridone and acetochlor to substitute for soil-applied PPO inhibitors in a Palmer amaranth management system with glufosinate applied twice POST and diuron plus MSMA POST-directed in conservation tillage cotton. Fluridone and flumioxazin applied preplant 23 to 34 d prior to planting were similarly effective. Fluridone and acetochlor plus diuron applied PRE controlled Palmer amaranth as well as fomesafen plus diuron PRE. All systems with preplant and PRE herbicides followed by glufosinate POST and diuron plus MSMA layby controlled Palmer amaranth well. Cotton yield did not differ among herbicide treatments. This research demonstrates that fluridone and acetochlor can substitute for soil-applied PPO-inhibiting herbicides in management systems for Palmer amaranth.

Potassium (K+) plays an important role in the regulation of plant growth and development. However, how potassium works in K+ channels in strawberry fruit development is yet unknown. Here, a 2205 bp potassium channel cDNA encoding 734 amino acids, named FaKAT1, was cloned from strawberry fruits. Bioinformatics analysis showed that the cis-element ABRE responsive to ABA and conserved domains characteristic to the KAT1 superfamily were found in the promoter and encoding protein of FaKAT1. Transcription analysis revealed that FaKAT1 was expressed higher in stems and leaves, followed by fruits, but was less in roots and flowers, and that coupled with the fruit red-coloring, its transcripts increased rapidly, suggesting that FaKAT1 might play a role in ripening. Using tobacco rattle virus-induced gene silencing, downregulation of the FaKAT1 transcripts resulted in significant unripening of fruits, which is consistent with changes of the ripening-related events and genes, such as fruit firmness, contents of titratable acid, sugar, anthocyanin, and abscisic acid (ABA), as well as transcripts of PYR1, ABI1, SnRK2, GAL6, PE5, EXP2, XYL2, CA4H, CHS, CHI, DFR, and 4CL. Furthermore, ABA and the ABA inhibitor, fluridone, promoted and inhibited the mRNA expression levels of FaKAT1, respectively. Importantly, a K+ channel blocker, tetraethylammonium, also inhibited FaKAT1 expression and fruit red coloring. In conclusion, FaKAT1 is an ABA-induced K+ channel, which regulates strawberry fruit ripening.

The development of wound periderm is vital to prevent water vapor loss and pathogen invasion in wounded fruit. The effect of abscisic acid (ABA) on wound-healing in harvested tomato fruit was evaluated in this study. Wounded tomato fruit were treated with ABA or fluridone (FLD, an inhibitor of ABA biosynthesis), respectively, and allowed to wound-heal at 20 °C in darkness for 4 days. Weight loss of tomato fruit reflected the intuitionistic effects of different treatments during wound-healing. Autofluorescence and histochemical staining demonstrated the development of suberized wound periderm in harvested tomato fruit at 3–4 day after wounding. Alkanoic acids, n-alkanes, unsaturated fatty acids and pentacosane represented the major components in the suberin. ABA-treated fruit showed enhanced autofluorescence, histochemical intensity and suberin deposition along with increased activities of phenylalanine ammonia-lyase (PAL) and peroxidase (POD). FLD treatment, however, alleviated the features of suberization and enzyme activities during wound-healing. The results suggest that ABA is involved in the stimulation of wound-induced suberization in harvested tomato fruit.

The herbicide fluridone is a soil-residual herbicide that should provide effective control of several problematic agronomic weeds, but because of herbicide persistence, injury to rotational crops is possible. In this experiment, multiple rates of fluridone were applied PRE to cotton at four irrigated locations across Arkansas to determine the risk of fluridone persisting and injuring subsequently planted wheat, corn, soybean, rice, grain sorghum, and sunflower. The multiple rates of fluridone were compared with fluometuron and evaluated for percentage of crop injury, crop density, and potential yield loss for each crop at the end of the subsequent growing season. Regardless of the location, wheat exhibited the greatest injury with 13 to 26% at Fayetteville (silt loam), 8 to 15% at Pine Tree (silt loam), 2 to 7% at Keiser (silty clay), and 3 to 8% at Rohwer (silty clay). Along with high levels of injury to wheat, fluridone at 900 g ai ha−1caused loss of wheat stands to 29 plants m−1row compared with fluometuron, which had stands of 49 plants m−1row. Although injury occurred in wheat at all locations, no rate of fluridone reduced wheat yields compared with fluometuron. Injury to grain sorghum ranged from 5 to 10% from all rates of fluridone at Pine Tree. Fluridone at 900 g ha−1(11 plants m−1row) also reduced grain sorghum stands at Pine Tree over that of fluometuron (19 plants m−1row). A decrease in grain sorghum yield was also observed from fluridone at 448, 673, and 900 g ha−1compared with fluometuron at Pine Tree. At Keiser, rice exhibited significant levels of injury (1 to 13%) from fluridone 393 d after treatment. In conclusion, injury to a wheat rotational crop is more likely following an application of fluridone in cotton than is injury to other rotational crops, but yield reductions are not expected for most rotational crops when fluridone is applied to cotton at an anticipated labeled rate of 224 g ha−1.

We have studied the influence of pretreatment of wheat seedlings ( Triticum aestivum L.) with 50 μM salicylic acid (SA) on plant resistance to subsequent action of 1 mM cadmium acetate. SA pretreatment decreased the extent of detrimental effect of cadmium on wheat plants, as judged by the decline in the level of stress-induced accumulation of MDA and electrolyte leakage. Furthermore, SA-pretreatment contributed to maintenance of growth characteristics of wheat seedlings at the level close to the control under stress conditions and to acceleration of growth recovery during post-stress period. Detected defense effect of SA may be due to a decline in the amplitude of cadmium-induced accumulation of abscisic acid (ABA) and to reduced fall of indoleacetic acid (IAA) and cytokinins (CK) in stressed plants. In the course of one day treatment, SA activated phenylalanine ammonia-lyase (PAL), the key enzyme of lignin biosynthesis, in roots of seedlings under normal growth conditions contributing to the strengthening of carrier functions of cell walls. This assumption is supported by the data showing significant decline in cadmium accumulation in SA-pretreated plants, especially in the shoots. Cd-treatment was shown to result in accumulation of dehydrins with molecular mass 22, 28, 55 and 69 kDa in wheat seedlings, although low molecular weight dehydrins (22 and 28 kDa) showed greater stress sensitivity. It is noteworthy that SA-pretreatment by itself led to 1.5-fold increase in the content of low molecular weight dehydrins. Nevertheless, SA-pretreated seedlings were characterized by significantly lower Cd-induced accumulation of all of the four dehydrins, apparently due to inhibition of cadmium flow into the plants. The obtained data suggest involvement of dehydrins in the range of defense reactions induced by SA-treatment contributing significantly to development of plant resistance to subsequent action of stress. The use of fluridone allowed us to demonstrate the key role of endogenous ABA in SA-induced changes in the level of dehydrins as well as in the protective effect of SA on wheat plants under cadmium stress resulting from development of defense responses in the course of SA-treatment.

Seed dormancy is a critical mechanism that delays germination until environmental conditions are favorable for growth. Plant hormones gibberellin (GA) and abscisic acid (ABA) have long been recognized as key players in regulating dormancy and germination. Recent data have increased interest in brassinosteroid (BR) hormones that promote germination by activating GA downstream genes and inactivating ABA signaling. Exposure of imbibed seeds to low temperature (cold stratification) is widely used to release seed dormancy and to improve germination frequency. However, the mechanism by which cold stratification overcomes the inhibitory role of ABA is not completely understood. In the present study, we show delayed germination of seeds of the BR insensitive mutant, bri1-5, that was largely reversed by treatment with fluridone, an inhibitor of ABA biosynthesis. In addition, the bri1-5 seeds were markedly less sensitive to the cold stratification release of dormancy. These results suggest that BR locates upstream of ABA signaling and downstream of cold stratification signaling in dormancy and germination pathways. Consistent with this notion, BR biosynthetic genes, DWF4 and DET2, were upregulated by cold stratification. The transcripts of the GA biosynthesis gene, GA3ox1, and cold responsive genes, CBF1 and CBF2, increased in response to cold stratification in wild type seeds but not in bri1-5 seeds. Conversely, transgenic seeds overexpressing BRI1 germinated more rapidly than wild type in the absence of cold stratification. Thus, we propose that BR signaling plays a previously unrecognized role in the cold stratification pathway for seed dormancy and germination.

The methionine residues of proteins are the preferred targets of oxidation by reactive oxygen species resulting in the formation of methionine sulfoxide (MetSO), which impairs protein function. Methionine sulfoxide reductase A and B (MSR) catalyze the reduction of the MetSO S and R epimers back to Met residues, respectively. The roles of abscisic acid (ABA) and nitric oxide (NO) on the transcript levels of methionine sulfoxide reductase (MSR; EC 1.8.4.6) in the roots of 2-d-old etiolated rice (Oryza sativa L.) seedlings exposed to NaCl were examined. The OsMSR transcript levels increased upon exposure to NaCl, which increased as the NaCl concentrations increased. Fluridone (Flu) pretreatment inhibited the increases in ABA and NO contents and the OsMSRA4, OsMSRA5, OsMSRB1.1, OsMSRB3 and OsMSRB5 transcripts by NaCl, while ABA application reversed the effects of Flu. Flu did not affect the OsMSRA2 and OsMSRB1.2 transcripts. The application of the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), to NaCl-treated roots inhibited the increase in all of the OsMSRs transcripts with the exception of OsMSRB1.2. Treatment with the NO donor sodium nitroprusside (SNP) increased all the OsMSRs transcripts. The inhibitory effect of Flu on the increase of the OsMSRA4, OsMSRA5, OsMSR1.1, OsMSRB 3, and OsMSRB5 transcripts in the NaCl-treated roots was reversed by SNP. cPTIO inhibited the expression of all the OsMSR genes. The OsMSRA2.1 and OsMSRB1.2 transcripts can be increased by SNP. The Flu-inhibited internal ABA contents cannot be recovered by treatment with cPTIO or SNP. In addition, NaCl-induced NO production can be divided into ABA-dependent and ABA-independent routes. Therefore, the ABA-dependent NO route regulated the expression of OsMSRA4, OsMSRA5, OsMSRB1.1, OsMSRB 3, and OsMSRB5 in the NaCl-treated rice roots, while the ABA-independent NO pathway modulated OsMSRA2.1, and the ABA-independent and NO-independent pathway modulated OsMSRB1.2 expression in response to NaCl treatment.

SUMMARYProlonged inability of yam tubers to sprout/germinate is associated with the expression of tuber dormancy, and the start of dormancy in tubers is linked to the onset of tuber formation. Although the plant hormone, abscisic acid (ABA) is known to regulate the onset and maintenance of dormancy in tubers, there are no known method(s) of inducing shoot growth (sprouting) on seed yam tubers that are harvested at 240 days after vine emergence or earlier. Therefore, this study was conducted to: (1) determine whether the absorption of fluridone, a reputed ABA inhibitor, prior to or during early seed yam tuber formation would induce sprouting, and (2) determine the effect of fluridone on early shoot growth. The study was a 2×4 factorial experiment arranged in a Completely Randomized Design (CRD) with eight treatment combinations replicated three times. Two species of yam with long dormancy durations were used: D. rotundata var TDr 131 and D. alata var TDa 98/01166; and three concentrations of fluridone were tested (30, 50, 100 µM). Young plants (69 days after vine emergence) of TDr 131 and TDa 98/01166 were grown in a coco coir medium hydroponics system using Hoagland's Nutrient Solution, with or without the test fluridone concentrations. In all fluridone treatments, most leaves of both species of yam had 30–90% of their surface bleached while the stems appeared purplish. In both Controls, all the newly formed seed tubers that were harvested at 90 and 104 days after vine emergence were dormant (devoid of any new shoots/sprouts). In contrast, over 70% of the seed tubers that developed in 30 and 100 µM fluridone had at least one new shoot, particularly in TDa 98/01166. The fluridone treatments did not significantly affect tuber weight or vegetative growth parameters like dimensions and number of leaves. This study has shown that the duration from vine emergence of the old tuber to sprouting of the new tuber can be reduced by more than half if young plants absorbed fluridone during early tuber development.

Fluridone has been used to successfully manage Eurasian watermilfoil since the late 1980s. However, recent documentation of hybrid watermilfoils and the resulting potential for reduced herbicide sensitivity necessitate the need for an assay to determine individual population response to fluridone. A known fluridone-resistant hybrid watermilfoil population from Townline Lake in Michigan was compared to 11 Eurasian and hybrid watermilfoil populations in laboratory experiments to develop a method for determining response to fluridone. Apical shoot tips were exposed to increasing concentrations of fluridone (0 to 48μg L−1) for 3, 5, and 7 d. Chlorophyll fluorescence (Fv/Fm) was evaluated using a pulse-amplitude modulated fluorometer at each interval along with pigment analysis of chlorophyll and β-carotene at the 7-d interval. Fv/Fmand pigment analysis yielded the same results. A fluridone concentration of 12μg L−1and an analysis interval of 7 d were found to be optimal in determining invasive watermilfoil response to fluridone. Use of such small-scale assays can provide resource managers a rapid tool to cost-effectively evaluate invasive watermilfoil response to fluridone.

The effects of plant growth regulators (PGRs) and nitrogenous compounds on alleviating salinity stress on seed germination of Leymus chinensis in light (12 h light/12 h dark) and dark (24 h dark) conditions were determined in a laboratory experiment. Seed germination was compared at various combinations of salinity and germination-promoting compounds. Seed germination percentages were 57 and 74% under nonsaline conditions in light and dark, respectively, suggesting that germination was light-inhibited. Germination decreased significantly with increasing salinity level in both light and dark conditions, and the reduction was greater in light than in dark at each salinity level. Seed germination percentage decreased to 22 and 7% in light but only to 51 and 27% in dark, in 100 and 200 mM NaCl solutions respectively. The influence of PGRs and nitrogenous compounds in alleviating salinity stress varied with light and salinity condition; e.g., gibberellins (GA(4 + 7)) significantly increased germination percentages from 22%, 7% and 0.3% to 47%, 23% and 15% in light at 100, 200 and 300 mM NaCl, respectively, while they showed no effect on germination in darkness. In contrast, sodium nitroprusside and cytokinin significantly increased germination percentage in darkness at all salinity levels, but showed no effect on germination in light at 200 and 300 mM NaCl. Fluridone was very effective in alleviating salinity stress on germination in both light and dark; however, it was lethal to seedlings. Thiourea had no effect in alleviating salinity stress in either light or dark. Thus, alleviation of salinity stress on seed germination of L. chinensis by germination-promoting compounds is strongly dependent on chemicals and light conditions.

Invasive watermilfoils, specifically Eurasian watermilfoil and the interspecific hybrid of Eurasian watermilfoil × northern watermilfoil, continue to be problematic for water resource managers. Herbicides are often used to control these nuisance weeds and have been historically successful in controlling Eurasian watermilfoil. A population of hybrid watermilfoil from Townline Lake in Michigan has shown increased tolerance to the herbicide fluridone. The objective of this work is to determine if cross- and multiple tolerance have also developed in this population. Eurasian watermilfoil plants collected from multiple sites and plants from Townline Lake were treated with 0, 5, 10, 20, 40, or 80 µg L−1of fluridone, norflurazon, or topramezone. Fluridone and norflurazon inhibit phytoene desaturase, whereas topramezone is a 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide. Chlorophyll fluorescence (Fv/Fm) and pigment content was measured at 10 d after treatment. Townline Lake plants responded differently from susceptible plants when treated with fluridone, norflurazon, and topramezone at 40 µg L−1. These results indicate that the Townline population of hybrid watermilfoil has inherent tolerance to multiple herbicide modes of action. These results are especially significant as topramezone has recently been labeled for aquatic use. Screening of additional herbicides to determine potential herbicide tolerance of the Townline Lake population is recommended.

Seed dormancy facilitates to endure environmental disadvantages by confining embryonic growth until the seeds encounter favorable environmental conditions for germination. Abscisic acid (ABA) and gibberellic acid (GA) play a pivotal role in the determination of the seed dormancy state. ABA establishes seed dormancy, while GA triggers seed germination. Here, we demonstrate that MYB96 contributes to the fine-tuning of seed dormancy regulation through the coordination of ABA and GA metabolism. The MYB96-deficient myb96-1 seeds germinated earlier than wild-type seeds, whereas delayed germination was observed in the activation-tagging myb96-1D seeds. The differences in germination rate disappeared after stratification or after-ripening. The MYB96 transcription factor positively regulates ABA biosynthesis genes 9-CIS-EPOXYCAROTENOID DIOXYGENASE 2 (NCED2), NCED5, NCED6, and NCED9, and also affects GA biosynthetic genes GA3ox1 and GA20ox1. Notably, MYB96 directly binds to the promoters of NCED2 and NCED6, primarily modulating ABA biosynthesis, which subsequently influences GA metabolism. In agreement with this, hyperdormancy of myb96-1D seeds was recovered by an ABA biosynthesis inhibitor fluridone, while hypodormancy of myb96-1 seeds was suppressed by a GA biosynthesis inhibitor paclobutrazol (PAC). Taken together, the metabolic balance of ABA and GA underlies MYB96 control of primary seed dormancy.

Somatic embryogenesis (SE) in the tree fern Cyathea delgadii was first described in 2015 and since then has been used to exploration of this phenomenon in cryptogamic plants. To deepen the knowledge about the hormonal control of SE, stipe explants were cultured on media supplemented with hormone biosynthesis and transport inhibitors (HBTIs). In the presence of 30 µM 2,3,5-triiodobenzoic acid (TIBA), or 40 µM fluridone or 125 µM salicylic acid (SA), somatic embryo production was totally inhibited. The quantitative analysis of the changes in endogenous hormone and sugar contents was conducted every 2 days within 10-day-long initial culture. The results showed that the concentrations of endogenous indole-3-acetic acid (IAA), abscisic acid (ABA), cytokinins (CKs) and soluble sugars were strongly modified either by TIBA and fluridone. Under their influence, the contents of cytokinins such as c-Z, c-ZR, t-Z, t-ZR, KinR were reduced to barely detectable levels. Treatment with SA results in the changes in endogenous IAA and sugar contents. It also modifies the IAA/CKs ratio; however, excluding the first 2 days of culture, the concentrations of ABA and cytokinins were kept on the control level. All HBTIs significantly increased the kinetin (Kin) content. Our work sheds new light on the relationships between the biosynthetic inhibitors and phytohormones and sugars in the process of early SE. It can be helpful to study the role of hormones in acquisition of embryogenic competence.

Omethoate (OM) is a highly toxic organophophate insecticide, which is resistant to biodegradation in the environment and is widely used for pest control in agriculture. The effect of OM on maize seed germination was evaluated under salt stress. Salt (800 mM) greatly reduced germination of maize seed and this could be reversed by OM. Additionally, H 2 O 2 treatment further improved the effect of OM on seed germination. Higher H 2 O 2 content was measured in OM treated seed compared to those with salt stress alone. Dimethylthiourea (DTMU), a specific scavenger of reactive oxygen species (ROS), inhibited the effect of OM on seed germination, as did IMZ (imidazole), an inhibitor of NADPH oxidase. Abscisic acid (ABA) inhibited the effect of OM on seed germination, whereas fluridone, a specific inhibitor of ABA biosynthesis, enhanced the effect of OM. Taken together, these findings suggest a role of ROS and ABA in the promotion of maize seed germination by OM under salt stress.

Inhibition of lettuce plant growth under increased planting density was accompanied by accumulation of abscisic acid (ABA) in the shoots of competing plants. To check causal relationship between these responses we studied the effect of decreased synthesis of ABA on growth indexes and hormonal balance of lettuce plants under elevated density of their planting (one (single) or three (competing) plants per pot). Herbicide fluridone was used to inhibit ABA synthesis. Preliminary experiments with single plants showed that presence of fluridone in the soil solution at rather low concentration (0.001mg/L) did not affect either chlorophyll content or growth rate of shoots and roots during at least one week. Treatment of competing (grouped) plants with this concentration of fluridone prevented both accumulation of ABA and competition induced growth inhibition. These results confirm important role of this hormone in the growth inhibiting effect of increased planting density. Furthermore, as in the case of ABA, fluridone prevented allocation of indoleacetic acid (IAA) to the shoots of competing plants likely contributing to leveling off the increase in the ratio of leaf area to their mass that is characteristic effect of shading in the dense plant populations. The results suggest involvement of ABA in allocation of IAA in competing plants. Application of fluridone did not influence the concentration of cytokinins in the shoots, whose level was decreased by competition either in fluridone treated or control (untreated with fluridone) plants. Accumulation of ABA in the shoots of competing plants accompanied by inhibition of their growth and the absence of either accumulation of ABA or inhibition of their growth in fluridone treated grouped plants confirms importance of ABA synthesis for growth response to competition.

The plant hormone abscisic acid (ABA) plays an important role in fruit development. To analyze the transcriptional regulation of ABA signaling pathway-related genes during mulberry (Morus alba L.) fruit development and ripening, 17 genes participating in ABA signal transduction were isolated from the Morus notabilis genome database, including five MnPYL, six MnPP2C, and six MnSnRK2 genes. The result of multiple sequence alignment revealed that their functional amino acid residues and domains are conserved within each gene family. The expression profiles of ABA signaling pathway-related genes in the fruit of Morus atropurpurea cv. Jialing No. 40 were measured by quantitative real-time polymerase chain reaction. The transcripts of MaPYL4, MaPP2C5, and MaSnRK2.6 were expressed at a relatively higher level during the entire development process. Moreover, the transcript levels of MaPYL1/3/5, MaPP2C2/4/5/6, and MaSnRK2.3/2.6 were lower during the early-maturation stage and higher during the post-maturation stage, which suggests that they may play a vital role in regulating mulberry fruit ripening. In addition, these genes showed strong responses to exogenous ABA, fluridone, glucose, and sucrose. This study also indicated that exogenous ABA, sucrose, and glucose may promote fruit maturity, while fluridone significantly inhibits fruit ripening.

Switchgrass (Panicum virgatum L.) is a perennial warm season grass that possesses valuable characteristics as a biofuel crop. Seed dormancy can be a barrier for commercial adoption by negatively impacting stand establishment in the first year. Seed dormancy in switchgrass is classified as non-deep physiological dormancy, where the embryo condition and seed covering tissues may prevent germination. Our lab previously demonstrated that switchgrass seed dormancy was primarily caused by the pericarp/testa, and secondarily by the lemma/palea (bracts). The focus of this research was to explore embryo physiological dormancy and its interaction with environmental cues and surrounding seed layers in five switchgrass varieties with different dormancy levels. Three main objectives were involved: (1) assessing the effect of temperature and light regimes on germination of mature seeds; (2) determining the effect of exogenously applied abscisic acid (ABA), gibberellin (GA), and fluridone (FLU) on germination under either constant or alternate temperatures; and (3) examining the response of physically altered seeds to exogenously applied ABA, GA, and FLU. Incubation of both upland and lowland dormant switchgrass varieties under alternating temperatures (15/30 °C) favored germination, while incubation under a constant, warm temperature (30 °C) resulted in low percentage germination. In contrast, the low-dormancy cultivar Expresso germinated well at both temperature regimes. Germination in the dark did not differ from an alternating light/dark regime. Exogenous ABA decreased germination in all dormant cultivars studied at both temperature regimes, but the sensitivity of the seeds to ABA was less under alternating temperatures. GA increased germination at a constant temperature in all but one dormant variety. The largest effect of both GA and ABA was observed in seeds with bracts. The promoting effect of FLU on germination was not measured in intact seeds; however, FLU promoted germination at 30 °C in seeds with bracts removed, suggesting that the seed covering layers were not permeable to FLU. Collectively, results show that the effect of exogenously applied ABA, GA, and FLU was influenced by temperature, seed covering layers, and seed lot.

In somatic embryogenesis (SE) of conifers, the inability of many embryogenic cell lines to form well-developed somatic embryos may results from failure and constraints during the transition of proembryogenic masses (PEMs) to early somatic embryos. In the present work, we propose the inclusion of a preculture and prematuration steps looking at enhancing PEM III-to-early somatic embryos transition. It was further hypothesized that these results would correlate with the contents of endogenous indole-3-acetic acid (IAA), abscisic acid (ABA) and polyamines (PA). To test these hypotheses, the embryogenic culture was subjected to preculture with fluridone (FLD) and prematuration treatments with different combinations of carbon source and polyethylene glycol (PEG). The frequency of PEM III was increased after FLD preculture and the contents of IAA and ABA decreased, while the contents of PA increased. Putrescine (Put) was the most abundant PA present at this stage, followed by spermidine (Spd) and spermine (Spm). In early embryogenesis, prematuration treatments supplemented with maltose or lactose plus PEG enhanced the PEM III-to-early somatic embryos transition. IAA and ABA contents increased at this stage, while a decrease of the total free PA levels was observed. Put was the most abundant PA, followed by Spd and Spm, mainly in the treatment supplemented with PEG. This resulted in a decrease of PA ratio (Put/Spd + Spm) and, hence, PEM III-to-early somatic embryos transition. It was concluded that the preculture with FLD and prematuration treatments promote the PEM III-to-early somatic embryos transition throughout the whole early developmental process in Araucaria angustifolia.

Low temperature seriously depresses seed germination and seedling growth in winter wheat (Triticum aestivum L.). In this study, wheat plants were sprayed with abscisic acid (ABA) and fluridone (inhibitor of ABA biosynthesis) at 19 days after anthesis (DAA) and repeated at 26 DAA. The seeds of those plants were harvested, and seed germination and offspring's seedling growth under low temperature were evaluated. The results showed that exogenous ABA application decreased seed weight and slightly reduced seed set and seed number per spike. Under low temperature, seeds from ABA-treated plants showed reduced germination rate, germination index, growth of radicle and coleoptile, amylase activity and depressed starch degradation as compared with seeds from non-ABA-treated plants; however, activities of the antioxidant enzymes in both germinating seeds and seedling were enhanced from those exposed to exogenous ABA, resulting in much lowered malondialdehyde (MDA) and H2O2 concentrations and O2− production rate. In addition, the maximum quantum efficiency of photosystem II was also enhanced in ABA-treated offspring's seedlings. It is concluded that exogenous ABA treatment at later grain-filling stage could be an effective approach to improve cold tolerance of the offspring during seed germinating and seedlings establishment in winter wheat.

Plant responses to abiotic stresses are coordinated by arrays of growth and developmental programs. Phytohormones such as abscisic acid (ABA) and indole-3-acetic acid (IAA) play critical roles in developmental progresses and environmental responses through complex signalling networks. However, crosstalk between the two hormones at the biosynthesis level remains largely unknown. Here, we report that carotenoid-deficient mutants (phs1, phs2, phs3-1, phs4, and PDS-RNAi transgenic rice) were impaired in the biosynthesis of ABA and IAA. Under drought conditions, phs3-1 and PDS-RNAi transgenic rice showed larger stomata aperture and earlier wilting compared to the wild type at both seedling and panicle developmental stage. Interestingly, these carotenoid-deficient lines showed increased cold resistance, which was likely due to the combined effects of reduced IAA content, alleviated oxidative damage and decreased membrane penetrability. Furthermore, we found that IAA content was significantly declined in rice treated with fluridone (a carotenoid and ABA biosynthesis inhibitor), and expression of auxin synthesis and metabolism-related genes were altered in the fluridone-treated rice similar to that in the carotenoid-deficient mutants. In addition, exogenous IAA, but not ABA, could restore the dwarf phenotype of phs3-1 and PDS-RNAi transgenic rice. These results support a crosstalk between ABA and IAA at the biosynthesis level, and this crosstalk is involved in development and differentially affects drought and cold tolerance in rice.

Florida hydrilla populations have shown an alarming increase in resistance to fluridone, an herbicide used extensively for controlling invasive US hydrilla populations. A rapid PCR and sequencing method was developed to identify and screen hydrilla genomic DNA for three previously identified phytoene desaturase (pds) gene mutations that confer resistance to fluridone. Ninety hydrilla accessions were screened for fluridone resistant genotypes including 46 accessions from the US and 44 accessions from 15 other countries. In Florida, hydrilla from five of nine sites tested was heterozygous for wild-type and herbicide-resistant alleles. Additionally, a new resistant population was identified from Lake Seminole in Georgia, the first genetically confirmed strain of resistant hydrilla outside of Florida. All resistance-conferring mutations were located on the same homologous haplotype of US dioecious hydrilla. All other hydrilla samples tested possessed only wild type alleles, including monoecious strains that had been exposed to fluridone. Management implications are discussed.

A natural feature of freshly harvested Avena fatua L. caryopses is primary dormancy which, however, was relieved partially by putrescine (Put) (10−2 M) and completely by karrikinolide (KAR1) (3 × 10−9 M) or gibberellic acid (GA3) (10−5 M). The sensitivity of A. fatua caryopses to these stimulators was adversely affected by supraoptimal temperature (SOT) (30 °C). A reduced germinability of caryopses due to high temperature even after transferring them to lower temperatures (10 or 20 °C) indicated the induction of thermodormancy. The maintenance of relatively constant levels of abscisic acid (ABA) in embryos but not surrounding tissues during SOT treatment was observed. The application of Put either during the SOT treatment or afterwards counteracted the effects of high temperature but had no significant impact on ABA content. The action of exogenous Put in alleviating the loss of responsiveness to KAR1 and GA3 imposed by SOT treatment in A. fatua PD caryopses is discussed in reference to the interconnection between ABA and GA metabolism and signaling pathways.

Two chilling-tolerant genotypes, that is, weedy rice WR03-45 and cultivated rice Lijiangxintuanheigu and two chilling-sensitive genotypes, that is, weedy rice WR03-26 and cultivated rice Xiuzinuo were used in this study to investigate the effects of exogenous abscisic acid (ABA) on protection against chilling damage as well as on changes in physiological features. The results showed that under chilling stress the increased levels of superoxide radical (), hydrogen peroxide (H2O2) and malondialdehyde (MDA) in WR03-45 and Lijiangxintuanheigu were lower than those in WR03-26 and Xiuzinuo. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR)) and non-enzymatic antioxidants (ascorbate acid (AsA) and reduced glutathione (GSH)) were enhanced in WR03-45 and Lijiangxintuanheigu, whereas they were decreased significantly in WR03-26 and Xiuzinuo. Application of exogenous ABA reduced the chilling damage in the four genotypes. The pre-treatment with ABA decreased the levels of , H2O2 and MDA caused by chilling stress in the four genotypes through increasing the activities of SOD, CAT, APX, GR and the contents of AsA and GSH in the four genotypes under chilling stress. Moreover, pre-treatment with Fluridone, the ABA biosynthesis inhibitor, prohibited the effects of ABA through enhancing the oxidative damages and suppressing the antioxidant defence systems under chilling stress. The results indicate the mechanism for rice with chilling tolerance is to enhance the capacity of antioxidant defence systems under chilling stress. Furthermore, ABA plays important roles in the tolerance of rice against chilling stress for it could induce the capacity of whole antioxidant defence systems including enzymatic and non-enzymatic constitutions under chilling stress.

Abscisic acid (ABA) regulates many aspects of plant development, including somatic embryo (SE) initiation. However, mechanisms of ABA functions on SE initiation have remained to be investigated. In this study, we examined the endogenous ABA contents of calli in Arabidopsis during the SE inductive process. We further found that the capacity for SE initiation was strongly impaired by treatment of fluridone, a potent inhibitor of ABA biosynthesis, as well as by mutation of ABA biosynthetic gene ABA2, suggesting that ABA is required for SE initiation. Furthermore, treatment of fluridone inhibited local auxin biosynthesis and auxin polar transport in the embryonic calli, resulting in the disturbance of auxin response pattern and the decreased regeneration frequency of SEs. However, application of exogenous ABA in the medium almost recovered patterns of auxin response and SE initiation. Thus, the results suggest that ABA functions on SE initiation through mediating both auxin biosynthesis and polar transport for establishment of auxin response pattern in callus. Our study provides new information for understanding mechanisms of SE initiation.

The algae Botryococcus braunii, one of the potential renewable resources for production of liquid hydrocarbons, was used for testing the effect of selected herbicides on algal growth and hydrocarbon content. Twenty-two herbicides representing 14 modes of action were assayed. Accelerated solvent extraction (ASE) was used to extract hydrocarbon from algae and the results showed that ASE was an efficient method for algal hydrocarbon extraction at 50 °C extraction temperature, 10.3 MPa of pressure and 1 static cycle using n-hexane as extraction solvent. The photosystem II inhibitor diuron was the most toxic herbicide for algal growth, but hydrocarbon content increased from 34.9 to 42.4% of dry biomass in the presence of a 0.1 mg/L concentration of diuron. The photosystem I inhibitor diquat was inhibitory to growth of B. braunii, but hydrocarbon content increased to 43.3% of dry biomass when treated with 5 mg/L diquat. S-metalochlor, a mitosis inhibitor, reduced both algal growth and hydrocarbon content. Hydrocarbon content decreased to 16.4, 14.0 and 5.5% of dry biomass, respectively when treated with 0.1, 1, and 5 mg/L S-metalochlor. The carotenoid biosynthesis inhibitor fluridone did not affect algal growth at 0.1 mg/L, but decreased hydrocarbon content from 34.9 to 13.2%. The fatty acid and lipid biosynthesis inhibitor thiobencarb had no effect on algal growth or hydrocarbon content at 0.1 mg/L, but it inhibited algal growth and decreased hydrocarbon content from 34.9 to 7.8% at 1 mg/L. The oxidative phosphorylation uncoupler dinoterb at 0.1 mg/L reduced algal biomass by 52.8% and decreased hydrocarbon content from 34.9 to 30.0%. The use of B. braunii as a source of fuel will undoubtedly require the use of an outdoor open pond system. These results will be useful for improving algal oil production while developing management systems to control invasive algal species in outdoor open pond systems ultimately keeping the oil producing algae pure.

The gradual rise of global temperature is of major concern for growth and development of crops. Chickpea (Cicer arietinum L.) is a heat-sensitive crop and hence experiences damage at its vegetative and reproductive stages. Abscisic acid (ABA), a stress-related hormone, is reported to confer heat tolerance, but its mechanism is not fully known, especially whether it involves osmolytes (such as proline, glycine betaine and trehalose) in its action or not. Osmolytes too have a vital role in saving the plants from injurious effects of heat stress by multiple mechanisms. In the present study, we examined the interactive effects of ABA and osmolytes in chickpea plants grown hydroponically at varying temperatures of 30/25°C (control), 35/30, 40/35 and 45/40°C (as day/night (12 h/12 h)): (a) in the absence of ABA; (b) with ABA; and (c) in the presence of its biosynthetic inhibitor fluridone (FLU). The findings indicated severe growth inhibition at 45/40°C that was associated with drastic reduction in endogenous ABA and osmolytes compared to the unstressed plants suggesting a possible relationship between them. Exogenous application of ABA (2.5 μM) significantly mitigated the seedling growth at 40/35 and 45/40°C, while FLU application intensified the inhibition. The increase in growth by ABA at stressful temperature was associated with enhancement of endogenous levels of ABA and osmolytes, while this was suppressed by FLU. ABA-treated plants experienced much less oxidative damage measured as malondialdehyde and hydrogen peroxide contents. Exogenous application of proline, glycine betaine and trehalose (10 μM) also promoted the growth in heat-stressed plants and their action was not significantly affected with FLU application, suggesting that these osmolytes function downstream of ABA, mediating partially the protective effect of this hormone.

Germination of lettuce seeds has obvious thermoinhibition, but the mechanism for thermoinhibition of seed germination is poorly understood. Here, we investigated the interactions of nitrate, abscisic acid (ABA) and gibberellin on seed germination at high temperatures to understand further the mechanism for thermoinhibition of seed germination. Our results showed that lettuce (Lactuca sativa L. ‘Jianye Xianfeng No. 1’) seeds exhibited notable thermoinhibiton of germination at ≥17°C in darkness, and at ≥23°C in light, but the thermoinhibited seeds did not exhibit secondary dormancy. Thermoinhibition of seed germination at 23 or 25°C in light was notably decreased by 5 and 10 mM nitrate, and the stimulatory effects were markedly prevented by nitric oxide (NO) scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. The sensitivity of seed germination to exogenous ABA increased with increasing temperature. Thermoinhibition of seed germination was markedly decreased by fluridone (an inhibitor of ABA biosynthesis) and GA3, and was increased by diniconazole (an inhibitor of the ABA-catabolizing enzyme ABA 8′-hydroxylase) and paclobutrazol (an inhibitor of GA biosynthetic pathway). The effect of fluridone in decreasing thermoinhibition of seed germination was obviously antagonized by paclobutrazol, and that of GA3 was notably added to by fluridone, and that of nitrate was antagonized by paclobutrazol, diniconazole and ABA and was added to by GA3 and fluridone. Our data show that thermoinhibition of lettuce seed germination is decreased by nitrate in a NO-dependent manner, which is antagonized by ABA, diniconazole and paclobutrazol and added by fluridone.

Expansin protein is a component of the cell wall generally accepted to be the key regulator of cell wall extension during plant growth. Plant hormones regulate expansin gene expression as well as plant growth during drought stress. However, the relationship between expansin and plant hormone is far from clear. Here, we studied the involvement of expansin in plant cell growth mediated by the hormones indole-3-acetic acid (IAA) and abscisic acid (ABA) under osmotic stress which was induced by polyethylene glycol (PEG)-6000. Wheat coleoptiles from a drought-resistant cultivar HF9703 and a drought-sensitive cultivar 921842 were used to evaluate cell growth and expansin activity. Osmotic stress induced the accumulation of ABA. ABA induced expansin activity mainly by enhancing expansin expression, since ABA induced cell wall basification via decreasing plasma membrane H(+)-ATPase activity, which was unfavorable for expansin activity. Although ABA induced expansin activity and cell wall extension, treatment with exogenous ABA and/or fluridone (FLU, an ABA inhibitor) suggested that ABA was involved in the coleoptile growth inhibition during osmotic stress. IAA application to detached coleoptiles also enhanced coleoptile growth and increased expansin activity, but unlike ABA, IAA-induced expansin activity was mainly due to the decrease of cell wall pH by increasing plasma membrane H(+)-ATPase activity. Compared with drought-sensitive cultivar, the drought-resistant cultivar could maintain greater expansin activity and cell wall extension, which was contributive to its resultant faster growth under water stress.