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To acclimate to waterlogged conditions, wetland plants form a barrier to radial oxygen loss (ROL) that can enhance oxygen transport to the root apex. We hypothesized that one or more hormones are involved in the induction of the barrier and searched for such hormones in rice. We previously identified 98 genes that were tissue-specifically upregulated during ROL barrier formation in rice. The RiceXPro database showed that most of these genes were highly enhanced by exogenous abscisic acid (ABA). We then examined the effect of ABA on ROL barrier formation by using an ABA biosynthesis inhibitor (fluridone, FLU), by applying exogenous ABA and by examining a mutant with a defective ABA biosynthesis gene (osaba1). FLU suppressed barrier formation in a stagnant solution that mimics waterlogged soil. Under aerobic conditions, rice does not naturally form a barrier, but 24 h of ABA treatment induced barrier formation. osaba1 did not form a barrier under stagnant conditions, but the application of ABA rescued the barrier. In parallel with ROL barrier formation, suberin lamellae formed in the exodermis. These findings strongly suggest that ABA is an inducer of suberin lamellae formation in the exodermis, resulting in an ROL barrier formation in rice.

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.

Fruit development and ripening are controlled by multiple plant hormones; for strawberries, recent evidence supports the role of abscisic acid (ABA) as a promoter of fruit ripening. Fruit softening during ripening is mainly a consequence of the solubilization and depolymerization of cell wall components mediated by the action of a complex set of enzymes and proteins. In the present work, we performed a comparative study (ABA-treatment vs. control) of the changes in the physiological properties of the cell wall-associated polysaccharide contents of strawberry fruit (Fragaria x ananassa ‘Camarosa’) via analysis of thermogravimetry (TG) combined with analysis of mRNA abundance, enzymatic activity and physiological characteristics. ‘Camarosa’ did not show a decline in the fruit firmness at 48 h post-treatment; however, we observed changes in cell wall stability based on the TG and differential thermogravimetric (DTG) analysis curves, which demonstrated the degradation of the cell wall polymers after ABA hormone treatment for 48 h, principally for hemicellulose polymers. Additionally, DTG analysis showed that dried samples derived from the treatment of the fruit with the ABA biosynthesis inhibitor fluridone maintained the same thermal stability as the control samples. Finally, the existence of a relationship between thermal stability, transcriptional analysis and enzymatic activity after hormone treatment was demonstrated, which provides the basis for a model for understanding the changes in the cell wall polymers of F. x ananassa mediated by the ABA hormone during fruit ripening.

The effect of the inhibitor of endogenous ABA synthesis fluridone on the content and distribution of endogenous ABA and IAA in the calli of ABA-deficient mutant AZ34 barley and its parental cultivar Steptoe was studied using the methods of immuno-enzymatic solid-phase assay and immunolocalization of phytohormones. It was found that by the 4th week of in vitro culture, fluridone causes a significant decrease in the ABA level in calli of both genotypes compared to the control, and the inhibitory effect of fluridone in AZ34 is more pronounced than in Steptoe. In the calli of both genotypes, a significant increase in the IAA content was revealed against the background of a decrease in the ABA content upon treatment with fluridone as compared to the control. It was concluded that ABA plays an important role in the process of embryoido-genesis in vitro.

Genetic assays to identify herbicide-resistant plants are a promising tool to reduce herbicide failures. However, the genetic basis of herbicide resistance is frequently unknown. In clonal weed species, DNA fingerprinting could be a useful tool to identify known resistant versus susceptible genets (clones) that occur in multiple locations, without an immediate need for understanding the genetic mutation(s) conferring resistance. Eurasian watermilfoil (Myriophyllum spicatum L.) and hybrids with native northern watermilfoil (Myriophyllum spicatum × Myriophyllum sibiricum Kom.) are mostly clonal invasive aquatic plants, and the same clones can be found in multiple waterbodies. Previously, a clone was confirmed as resistant to the commonly used herbicide fluridone, and a recent genetic survey in Michigan identified this genotype (MG-237) in at least seven other lakes. We hypothesized that MG-237 collected from different lakes would also exhibit fluridone resistance. However, MG-237 may have accumulated resistance mutations at different times during its spread across Michigan, resulting in fluridone-resistant and fluridone-susceptible MG-237 clones distributed in different lakes. We used a herbicide assay to test the response of several accessions, including MG-237 accessions from multiple lakes, to the Michigan operational rate of 6 µg L−1 fluridone. We found that all accessions of MG-237 exhibited resistance to 6 µg L−1 fluridone. A second genotype (MG-377) was also resistant to 6 µg L−1 fluridone. The rest of the accessions were found to be significantly injured by 6 µg L−1 fluridone. Our results suggest that 6 µg L−1 fluridone would not effectively control waterbodies dominated by MG-237 or MG-377, whereas waterbodies dominated by the other genotypes in our study would likely be controlled. Although more studies are needed to identify the variation in sensitivity of the accessions tested here and the genetic basis of fluridone resistance in Myriophyllum, our results suggest that multilocus genotype data may be an effective tool to identify and track herbicide-resistant genotypes of Myriophyllum in the short term.

In plants, glucose (Glc) plays pivotal roles in development and stress responses mainly by supplying fuel for growth and regulating expression of genes essential for crosstalk with hormonal, oxidative, and defense signaling. However, the complicated relationship between Glc and plant hormones is still not very clear. In this study, gsm3 (glucose-sensitive mutant 3), an Arabidopsis mutant with Glc-sensitive phenotype, was identified. Compared to wild type, the cotyledon expansion rate of gsm3 was significantly decreased under the condition of 4.5% Glc. Fluridone was able to rescue the Glc-induced defects of gsm3 in cotyledon expansion. AAO3 and ABI4 are key genes involved in abscisic acid (ABA) biosynthesis and signaling transduction, respectively. We found that inactivation of AAO3 or ABI4 in gsm3 background led to reduced sensitivity to Glc. These results indicated that increased ABA synthesis resulted in the sensitivity of gsm3 to Glc. Moreover, our results indicated that gsm3 mutant accumulated more ROS, which made it more sensitive to the application of exogenous H2O2. Overall, GSM3 plays an important role in Glc-ABA signaling cascade during seed germination and early seedling growth.

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.

Studies were conducted during 2015 through 2018 in south-central, Coastal Bend, and Southern High Plains areas of Texas to evaluate fluridone herbicide systems for weed control and cotton response. Fluridone alone at 0.17 to 0.23 kg ai ha-1 followed by postemergence (POST) herbicides controlled Amaranthus Palmeri 82 to 100% season-long while Cucumis melo control ranged from 92 to 100%. Control of Urochloa Texana with fluridone alone ranged from 40 to 96% early-season while late-season control ranged from 37 to 96%. Fluridone plus fomesafen systems controlled A. Palmeri, C. Melo, and U. Texana at least 98% early season; however, late-season control of A. Palmeri was less than 70% while C. Melo control was 91% and U. Texana control was 80%. Adding a POST application of glyphosate to fluridone plus fomesafen improved control to at least 98% for all three weed species. Fluridone plus fluometuron combinations provided similar control to fluridone plus fomesafen. Adding glyphosate (POST) improved A. Palmeri control to at least 82% season-long. Cotton yields reflect the level of weed control with significantly better yields from fluridone systems compared with the weedy check. However, in the one year when the untreated was maintained weed-free, no differences in cotton yield were noted between the weed-free and any herbicide treatment.

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.

THE NOVEL branching regulators fluridone and imazalil (IMA) were examined for micropropagation of Paco (Zantedeschia sprengeri). IMA concentrations were 0, 4.5, 13.5 and 45µM in combination with 5µM benzylaminopurine (BAP). The shoots were transferred after 8 weeks to standard MS medium without IMA but with 5µM BAP. IMA resulted in a strong increase of new shoots from which the outgrowth was inhibited when IMA was present but that did grow out when IMA had been removed. Fluridone inhibits the biosynthesis of the endogenous regulator strigolactone. Increasing concentrations of fluridone were applied in combination with 13.5µM IMA for 8 weeks. Then the shoots were subcultured on standard medium without IMA and fluridone but with 5µM BAP for 8 weeks. Again a strong increase of new shoots occurred from which outgrowth was inhibited when IMA and fluridone were present but that did grow out when these regulators had been removed.

We examined the response of maturing tomato fruit exposed for 7 days to fluridone (1-methyl-3-phenyl-5-[3-trifluoromethyl(phenyl)]-4(1H)-pyridinone). Fluridone was applied in lanolin paste in the form of a 2–3 mm wide strip from the top to the base of the fruit. As a control, a similar stripe of lanolin was applied in the same way on the opposite side of the same fruit. The content of major carotenoids, as well as flavonoids, and free and bound phenolic acids were determined using a HPLC and HPLC-MS-MS methods. Fluridone almost completely blocked the biosynthesis of lycopene and substantial declined content of ß-carotene and lutein in the tomato fruit. The fluridone caused a decreased content of quercetin, rutin and naringenin, and increased level of epicatechin. The herbicide did not affect the content of p-coumaric acid, but reduced the level of caffeic acid, both free and ester form, and declined the content of free ferulic and chlorogenic acids. Changes in phenolics composition observed for the first time indicate that fluridone interferes with the biosynthesis of further products of the metabolism of p-coumaric acid, both flavonoids and phenolic acids.

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.

Abscisic acid (ABA) may play roles in mediating cross stress tolerance in plants. The objectives of this study were to investigate the priming effects of drought and ABA on heat tolerance and to determine how ABA may be involved in enhanced heat tolerance by drought. Focusing on the transcriptional level, two independent experiments were conducted, using a perennial grass species, tall fescue (Festuca arundinacea) and Arabidopsis. In experiment 1, tall fescue plants were exposed to mild drought by withholding irrigation for 8 days (drought priming) and foliar sprayed with ABA or an ABA-synthesis inhibitor (fluridone). After that they were subsequently subjected to heat stress (38/33°C day/night) for 25 days in growth chambers. In experiment 2, Arabidopsis Columbia ecotype (wild-type) and ABA-deficient mutant (aba3-1, CS157) were pre-treated with drought priming and then exposed to heat stress (45/40°C) for 3 days. The physiological analysis demonstrated that both drought priming and foliar application of ABA-enhanced heat tolerance in tall fescue, while drought priming had no significant effects on heat tolerance in ABA-deficient Arabidopsis plants. Application of fluridone to tall fescue and ABA-deficient mutants of Arabidopsis exhibited diminished or attenuated positive effects of drought priming on heat tolerance. ABA mediation of acquired heat tolerance by drought priming was associated with the upregulation of CDPK3, MPK3, DREB2A, AREB3, MYB2, MYC4, HsfA2, HSP18, and HSP70. Our study revealed the roles of ABA in drought priming-enhanced heat tolerance, which may involve transcriptional regulation for stress signaling, ABA responses and heat protection.

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.

Soil drying enhances root ABA accumulation and rhizosheath formation, but whether ABA mediates rhizosheath formation is unclear. Here, we used the ABA-deficient mutant Az34 to investigate molecular and morphological changes by which ABA could affect rhizosheath formation. Mild soil drying with intermittent watering increased rhizosheath formation by promoting root and root hair elongation. Attenuated root ABA accumulation in Az34 barley constrained the promotion of root length and root hair length by drying soil, such that Az34 had a smaller rhizosheath. Pharmacological experiments of adding fluridone (an ABA biosynthesis inhibitor) and ABA to drying soil restricted and enhanced rhizosheath formation respectively in Az34 and wild-type Steptoe barley. RNA sequencing suggested that ABA accumulation mediates auxin synthesis and responses and root and root hair elongation in drying soil. In addition, adding indole-3-acetic acid (IAA) to drying soil increased rhizosheath formation by promoting root and root hair elongation in Steptoe and Az34 barley. Together, these results show that ABA accumulation induced by mild soil drying enhance barley rhizosheath formation, which may be achieved through promoting auxin response. © 2021 John Wiley & Sons Ltd.

The ubiquitin system is essential for multiple hormone signaling pathways in plants. Here, we show that theArabidopsis thalianaE3 ligase BRIZ, a heteromeric ligase that consists minimally of BRIZ1 and BRIZ2 proteins, functions in abscisic acid (ABA) signaling or response.briz1andbriz2homozygous mutants either fail to germinate or emerge later than wild-type seedlings, with little cotyledon expansion or root elongation and no visible greening. Viability staining indicates thatbriz1andbriz2embryos are alive but growth-arrested. Germination ofbrizmutants is improved by addition of the carotenoid biosynthetic inhibitor fluridone or gibberellic acid (GA3), andbrizmutants have improved development in backgrounds deficient in ABA synthesis (gin1-3/aba2) or signaling (abi5-7). Endogenous ABA is not higher inbriz2seeds compared to wild-type seeds, and exogenous ABA does not affectBRIZmRNAs in imbibed seeds. These results indicate thatbrizembryos are hypersensitive to ABA and that under normal growth conditions, BRIZ acts to suppress ABA signaling or response. ABA signaling and sugar signaling are linked, and we found thatbriz1andbriz2mutants excised from seed coats are hypersensitive to sucrose. Althoughbrizsingle mutants do not grow to maturity, we were able to generate maturebriz2-3 abi5-7double mutant plants that produced seeds. These seeds are more sensitive to exogenous sugar and are larger than seeds from siblingabi5-7 BRIZ2/briz2-3plants, suggesting that BRIZ has a parental effect on seed development. From these data, we propose a model in which the BRIZ E3 ligase suppresses ABA responses during seed maturation and germination and early seedling establishment.

Background Cinnamyl alcohol dehydrogenase (CAD) is an important enzyme functions at the last step in lignin monomer synthesis pathway. Our previous work found that drought induced the expressions of CmCAD genes and promoted lignin biosynthesis in melon stems. Results Here we studied the effects of abscisic acid (ABA), hydrogen peroxide (H2O2) and jasmonic acid (JA) to CmCADs under drought stress. Results discovered that drought-induced ABA, H2O2 and MeJA were prevented efficiently from increasing in melon stems pretreated with fluridone (Flu, ABA inhibitor), imidazole (Imi, H2O2 scavenger) and ibuprofen (Ibu, JA inhibitor). ABA and H2O2 are involved in the positive regulations to CmCAD1, 2, 3, and 5, and JA is involved in the positive regulations to CmCAD2, 3, and 5. According to the expression profiles of lignin biosynthesis genes, ABA, H2O2 and MeJA all showed positive regulations to CmPAL2-like, CmPOD1-like, CmPOD2-like and CmLAC4-like. In addition, positive regulations were also observed with ABA to CmPAL1-like, CmC4H and CmCOMT, with H2O2 to CmPAL1-like, CmC4H, CmCCR and CmLAC17-like, and with JA to CmCCR, CmCOMT, CmLAC11-like and CmLAC17-like. As expected, the signal molecules positively regulated CAD activity and lignin biosynthesis under drought stress. Promoter::GUS assays not only further confirmed the regulations of the signal molecules to CmCAD1~3, but also revealed the important role of CmCAD3 in lignin synthesis due to the strongest staining of CmCAD3 promoter::GUS. Conclusions CmCADs but CmCAD4 are positively regulated by ABA, H2O2 and JA under drought stress and participate in lignin synthesis.

The phytohormone abscisic acid (ABA) inhibits seed germination and seedling growth and is required for the inception of dormancy. Xanthoxal (also known as xanthoxin) is the first specific biosynthetic precursor of ABA. In this study, a modified method to produce xanthoxal is described. I tested the ability of either xanthoxal or ABA to reinstate dormancy in dormant red rice seeds whose dormancy was broken by fluridone (an inhibitor of the synthesis of carotenoids and, subsequently, ABA). Xanthoxal was shown to have a stronger inhibitory effect on germination than ABA when exogenously provided. Although this could indicate an additional effect of xanthoxal above that expected if xanthoxal were simply converted to ABA in the seed, alternative hypotheses cannot be excluded. One alternative is that exogenous xanthoxal may be trapped inside the cells to a greater extent than exogenous ABA, resulting in an intracellular level of ABA higher than that reached with a direct application of ABA. As a further alternative, exogenous xanthoxal may interfere with ABA action in the apoplast. In this study, following germination, early seedling growth was delayed only if ABA was applied. This suggests that inhibition of early seedling growth, but not of germination, requires extracellular ABA.

The generally accepted approach for increasing plant resistance to heavy metals is the treatment by phytohormones of different natures. In particular, brassinosteroids are highly effective in decreasing the level of toxic ions damage effects on plant growth. ABA and wheat germ agglutinin (WGA) contents were measured in the same plant with the help of enzyme immunoassay method. The localization of lignin and suberin on cross sections of wheat roots stained with berberine hemisulfate/toluidine blue was performed. The mitotic index was determined as percentage of mitotic cells of the total number of the cells. It was found that 0.4 μM 24-epibrassinolide (EBR) seed pretreatment under the influence of 1 mM cadmium acetate in the presence of fluridone (Fl) inhibited the stress-induced accumulation of ABA, while the WGA content in plants stayed higher than in stressed EBR-untreated wheat roots. Moreover, EBR-pretreated wheat plants under cadmium stress formed in the root cell walls’ Casparian bands and suberin lamellae, which are the critical locations in the apoplastic barriers of endodermis and exodermis. Pre-sowing EBR-treatment promoted acceleration of Casparian bands and suberin lamellae formation without inhibiting growth processes. We have demonstrated the involvement of wheat lectin in the realization of EBR-induced protective effect on plants under cadmium stress. An important contribution to EBR-induced strengthening the barrier properties of the cell walls of the studied tissues is the ability of EBR to induce ABA-independent accumulation of WGA, which further promotes the increasing lignin and suberin biopolymers deposition in the cell walls of wheat roots.

Cadmium (Cd2 +) is among the toxic non-essential heavy metals that adversely affect plants metabolic processes and the safety of produce. However, plant hormones can improve plant’s tolerance to various stresses. This study investigated the effect of exogenous abscisic acid (ABA) on the biochemical and physiological processes and food safety of cadmium (Cd2 +)-sensitive lettuce genotype (Lüsu). Seedlings were subjected to five treatments: [(i) Control (untreated plants), (ii) 100 µM CdCl2, (iii) 100 µM CdCl2+10 µg L−1 ABA (iv) 10 µg L−1 ABA, and (v) 0.01 g L−1 ABA-inhibitor (fluridone)] for fourteen days in hydroponic system. The 100 µM CdCl2 increased the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA), decreased photosynthesis and plant biomass. Moreover, it decreased the contents of essential nutrients (except copper) in the leaves but increased the contents of toxic Cd2 + in the leaves and roots of the plants. Foliar application of fluridone (0.01 g L−1) also caused oxidative stress by increasing the contents of H2O2 and MDA. It also decreased the contents of nutrient elements in the leaves of the plants. However, exogenous ABA (10 µg L−1) mitigated the Cd2 +-induced stress, increased antioxidant enzymes activities, photosynthesis and plant biomass under CdCl2 treatment. Remarkably, exogenous ABA increased the contents of essential nutrient elements but decreased the Cd2 + content in leaves under the CdCl2 treatment. Our results have demonstrated that foliar application of ABA mitigates Cd2 + stress and increases the nutritional quality and food safety of Cd2 +-sensitive lettuce genotype under CdCl2 treatment.

Moss paraphyllia, the trichome-like or foliose structures on moss stem surfaces, are usually treated as epidermal outgrowths. However, in some taxa of the moss families Leskeaceae, Neckeraceae, and Amblystegiaceae their distribution along the stem is consistently correlated with parts of the stem surface near branch primordia. In other moss families, Climaciaceae, Hylocomiaceae, and Pseudoleskeaceae the specific paraphyllia-generating epidermal layer produces paraphyllia evenly all along the stem. These results suggest that there are at least two different types of regulation of paraphyllia development; however, both of them may be involved in the morphogenesis of paraphyllia in some families, for example in the Thuidiaceae. Exogenous abscisic acid treatment consistently increases the number of paraphyllia of the Leskea-type, and it also induces the development of proximal branch leaves that normally do not develop a lamina above the stem surface. This fact supports conclusions regarding the homology of the Leskea-type of paraphyllia with leaves.

ABA and GA metabolism during incubation rather than hormone contents in dry seeds is the key to understanding secondary dormancy and germination of Syngonanthus verticillatus seeds. The mechanism of seed dormancy cycle, although very important for preventing germination during unfavorable periods for seedling establishment, is poorly understood in tropical species. Here, we used a perennial tropical species of the Brazilian campo rupestre, Syngonanthus verticillatus (Eriocaulaceae), to investigate the involvement of ABA and GA in modulating secondary dormancy of seeds buried in situ over time and the dynamic of these hormones during the incubation of dormant and non-dormant seeds. Hormone analyses were carried out with freshly harvested seeds and on buried seeds exhumed after 3, 6 and 9 months. Dynamics of ABA and GAs in dormant and non-dormant seeds during incubation (0, 12, 24 and 36 h) under favorable conditions for germination (at 20 °C in the presence of light) were also investigated. In addition, the effects of GA4 and fluridone were evaluated for overcoming secondary dormancy. Our results showed that changes in the contents of both ABA and GA4 occurred after burial, suggesting they may be related to the modulation of secondary dormancy/germination of S. verticillatus seeds. The application of fluridone was more effective than GA4 at overcoming secondary dormancy. We conclude that during incubation, de novo ABA synthesis and its consequent maintenance at high contents regulate the inhibition of germination in dormant seeds, while GA4 synthesis and ABA catabolism modulate the germination of non-dormant seeds. ABA and GA metabolism during incubation of both dormant and non-dormant seeds rather than hormone contents of dry seeds in the field is thought to be the key to understanding secondary dormancy and germination.

Carotenoids are a group of natural tetraterpenoid pigments with essential roles in a variety of physiological processes of plants. Although carotenoid biosynthesis has been well characterized, the genetic basis of the pathway, especially in crop plants, is largely unknown. In this study, we characterized a new albino maize mutant called albino1 (alb1), which was obtained from a Mutator mutagenized population. The alb1 mutant showed defective chloroplast development and declined photosynthetic pigments, leading to a seedling-lethal phenotype. Genetic and molecular analyses indicated that ALB1 encoded a putative ζ-carotene desaturase (ZDS) involved in carotenoid biosynthesis. Measurement of carotenoids revealed that several major carotenoid compounds downstream of the ZDS were significantly reduced in alb1 mutant, indicating that ALB1 is a functional ZDS. Further transcriptome analysis revealed that several groups of nuclear genes involved in photosynthesis, such as light-harvesting complex, pigment metabolism, and chloroplast function, were significantly down-regulated in alb1 compared with wide type. Interestingly, expression of some maize plastid-localized nuclear genes, including POR, CAO, Lhcb, and RbcS, was substantially reduced in alb1 plants. Furthermore, treatment of the inhibitor fluridone significantly rescued gene transcripts of these nucleus-encoded genes in alb1 mutant, which supported the retrograde signaling of ζ-carotene/phytofluene derived molecules. These results suggested that ALB1/ZDS might function as a regulator to coordinate nuclear photosynthetic gene expression in plastid-to-nucleus retrograde signaling during development of maize plants. Together, these results have demonstrated that ALB1/ZDS is essential for carotenoids biosynthesis and plays crucial roles in chloroplast biogenesis and development in maize.

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.

THE NOVEL branching regulators fluridone and imazalil (IMA) were examined for micropropagation of Paco (Zantedeschia sprengeri). IMA concentrations were 0, 4.5, 13.5 and 45µM in combination with 5µM benzylaminopurine (BAP). The shoots were transferred after 8 weeks to standard MS medium without IMA but with 5µM BAP. IMA resulted in a strong increase of new shoots from which the outgrowth was inhibited when IMA was present but that did grow out when IMA had been removed. Fluridone inhibits the biosynthesis of the endogenous regulator strigolactone. Increasing concentrations of fluridone were applied in combination with 13.5µM IMA for 8 weeks. Then the shoots were subcultured on standard medium without IMA and fluridone but with 5µM BAP for 8 weeks. Again a strong increase of new shoots occurred from which outgrowth was inhibited when IMA and fluridone were present but that did grow out when these regulators had been removed.

In order to improve the problem of poor coloring caused by high fruit nitrogen in apple production, we studied the effects of different concentrations of abscisic acid (ABA: 0, 50, 100, and 150 mg/L) and fluridone (ABA biosynthesis inhibitor) on the fruit of 'Red Fuji' apple (Malus Domestica Borkh.) in the late stage of apple development (135 days after blooming) in 2017 and 2018. The effects of these treatments on the distribution of 13C and 15N and anthocyanin synthesis in fruit were studied. The results showed that the expression levels of ABA synthesis and receptor genes in the peel and flesh were upregulated by exogenous ABA treatment. An appropriate concentration of ABA significantly increased the expression of anthocyanin synthesis genes and transcription factors and increased the content of anthocyanin in the peel. The results of 13C and 15N double isotope labeling showed that exogenous ABA coordinated the carbon-nitrogen nutrient of apple fruit in the late stage of the development, reduced the accumulation of fruit nitrogen, increased the accumulation of fruit carbon and sugar, provided a substrate for anthocyanin synthesis, or promoted anthocyanin synthesis through the sugar signal regulation mechanism. Comprehensive analysis showed that the application of 100 mg/L ABA effectively improved the problem of poor coloring caused by high fruit nitrogen in the late stage of apple development and is beneficial to the accumulation of carbon in fruit and the formation of color.

Haematococcus pluvialis has high economic value because of its high astaxanthin-producing ability. The mutation breeding of Haematococcus pluvialis is an important method to improve the yield of astaxanthin. Fluoridone, an inhibitor of phytoene dehydrogenase, can be used as a screening reagent for mutation breeding of Haematococcus pluvialis. This study describes the effect of fluridone on the biomass, chlorophyll, and astaxanthin content of Haematococcus pluvialis at different growth stages. Five fluridone concentrations (0.00 mg/L, 0.25 mg/L, 0.50 mg/L, 1.00 mg/L, and 2.00 mg/L) were set to treat Haematococcus pluvialis. It was found that fluridone significantly inhibited the growth and accumulation of astaxanthin in the red dormant stage. In addition, transcriptome sequencing was used to analyze the expression of genes related to four metabolic pathways in photosynthesis, carotenoid synthesis, fatty acid metabolism, and cellular antioxidant in algae after fluridone treatment. The results showed that six genes related to photosynthesis were downregulated. FPPS, lcyB genes related to carotenoid synthesis are downregulated, but carotenoid β-cyclic hydroxylase gene (LUT5), which plays a role in the conversion of carotenoid to abscisic acid (ABA), was upregulated, while the expression of phytoene dehydrogenase gene did not change. Two genes related to cell antioxidant capacity were upregulated. In the fatty acid metabolism pathway, the acetyl-CoA carboxylase gene (ACACA) was downregulated in the green stage, but upregulated in the red stage, and the stearoyl-CoA desaturase gene (SAD) was upregulated. According to the transcriptome results, fluridone can affect the astaxanthin accumulation and growth of Haematococcus pluvialis by regulating the synthesis of carotenoids, chlorophyll, fatty acids, and so on. It is expected to be used as a screening agent for the breeding of Haematococcus pluvialis. This research also provides an experimental basis for research on the mechanism of astaxanthin metabolism in Haematococcus pluvialis.

Hydrogen gas (H2) regulates plant responses to abiotic and biotic stresses. Abscisic acid (ABA) might alleviate the adverse effects of drought stress. However, the mechanisms by which ABA and H2 ameliorate plant drought stress are unclear. Here, tomato “Micro-Tom” seedlings were used to investigate the interaction between H2 and ABA under drought conditions. The results showed that both hydrogen-rich water (HRW) and ABA increased plant height, stem diameter and root activity of tomato seedlings under drought stress, with optimal concentrations of 75% and 150 μM, respectively. HRW or ABA treatment was able to enhance drought tolerance by increasing photosynthesis, antioxidant enzyme activity and gene expression of antioxidant enzymes under drought stress. Fluridone (FLU), a synthetic inhibitor of ABA, significantly diminished the positive effects of HRW on plant height, stem diameter and root activity under drought stress, suggesting that ABA might play a crucial role in H2-enhanced drought resistance in tomato seedlings. The results revealed that the ABA content in the PEG + HRW treatment was 18% higher than that in the polyethylene glycol (PEG) treatment alone. Furthermore, we found that H2 enhanced endogenous ABA content by increasing zeaxanthin epoxidase (ZEP), 9-cis-epoxycarotenoid dioxygenase (NCED) and abscisic aldehyde oxidase (AAO) activities and the expression of SlZEP, SlNCED, and SlAAO. PEG + HRW treatment increased ZEP and NCED activities, which were 13% and 40% higher than those of PEG treatment, respectively. Meanwhile, the transcription levels of SlSnRK2 and SlAREB were upregulated by HRW or ABA under drought stress, whereas this upregulation was reversed by FLU. Thus, our results demonstrate that H2 was able to enhance drought resistance by regulating ABA biosynthesis and the expression of ABA signal transduction genes in tomato seedlings.

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.

ABA produced in the fig fruit triggers ethylene production in the inflorescence and induces non-climacteric ripening in the receptacle tissue., The common fig bears a unique closed inflorescence structure, the syconium, composed of small individual drupelets that develop from the ovaries, which are enclosed in a succulent receptacle of vegetative origin. The fig ripening process is traditionally classified as climacteric; however, recent studies have suggested that distinct mechanisms exist in its reproductive and non-reproductive parts. We analysed ABA and ethylene production, and expression of ABA-metabolism, ethylene-biosynthesis, MADS-box, NAC, and ethylene response-factor genes in inflorescences and receptacles of on-tree fruit treated with ABA, ethephon, fluridone, and nordihydroguaiaretic acid (NDGA). Exogenous ABA and ethephon accelerated fruit ripening and softening, whereas fluridone and NDGA had the opposite effect, delaying endogenous ABA and ethylene production compared to controls. Expression of the ABA-biosynthesis genes FcNCED2 and FcABA2, ethylene-biosynthesis genes FcACS4, FcACOL, and FcACO2, FcMADS8, 14, 15, FcNAC1, 2, 5, and FcERF9006 was up-regulated by exogenous ABA and ethephon. NDGA down-regulated FcNCED2 and FcABA2, whereas fluridone down-regulated FcABA2; both down-regulated the ethylene-related genes. These results demonstrate the key role of ABA in regulation of ripening by promoting ethylene production, as in the climacteric model plant tomato, especially in the inflorescence. However, increasing accumulation of endogenous ABA until full ripeness and significantly low expression of ethylene-biosynthesis genes in the receptacle suggests non-climacteric, ABA-dependent ripening in the vegetative-originated succulent receptacle part of the fruit.

The effects of fluridone and 1-naphthaleneacetic acid (NAA) on fruit drop and quality changes of longkong fruit after harvesting were investigated. Longkong racemes were dipped in 50 µmol L-1 of fluridone solution or dipped in 1000 µmol L-1 NAA solution for 5 min. Then, the fruits were stored at 25°C. The results showed that dipping longkong fruit in 50 µmol L-1 fluridone solution and dipping in 1000 µmol L-1 NAA solution significantly delayed fruit drop. At the same time, the results also showed that the percentages of fruit drop in the control that were dipped in distilled water increased during the storage period. Longkong fruit dipped in 50 µmol L-1 fluridone solution and dipped in 1000 µmol L-1 NAA solution showed inhibition of the ABA synthesis. Furthermore, it showed the ability to inhibit ethylene production and retard fruit color changes and browning on the peel of longkong with storage life extension for 8 days. There is no significant difference in terms of internal quality, such as total ascorbic acid content and total phenolic content in all treatments. Longkong dipped in 50 µmol L-1 fluridone solution showed lower titratable acidity, total soluble solids, and total sugar content compared with other treatments. In sum, dipping longkong raceme in fluridone solution can be used as an alternative method for minimizing the fruit drop and maintaining the quality of longkong after harvesting.

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.

Strigolactones, a novel class of phytohormones, regulate plant architecture and act as rhizosphere signals. Species-specific biosynthetic pathways convert a common precursor, carlactone, to strigolactones., Strigolactones (SLs), comprising compounds with diverse but related chemical structures, are determinant signals in elicitation of germination in root parasitic Orobanchaceae and in mycorrhization in plants. Further, SLs are a novel class of plant hormones that regulate root and shoot architecture. Dissecting common and divergent biosynthetic pathways of SLs may provide avenues for modulating their production in planta. Biosynthesis of SLs in various SL-producing plant species was inhibited by fluridone, a phytoene desaturase inhibitor. The plausible biosynthetic precursors of SLs were exogenously applied to plants, and their conversion to canonical and non-canonical SLs was analysed using liquid chromatography–tandem mass spectrometry. The conversion of carlactone (CL) to carlactonoic acid (CLA) was a common reaction in all investigated plants. Sorghum converted CLA to 5-deoxystrigol (5-DS) and sorgomol, and 5-DS to sorgomol. One sorgomol-producing cotton cultivar had the same SL profile as sorghum in the feeding experiments. Another cotton cultivar converted CLA to 5-DS, strigol, and strigyl acetate. Further, 5-DS was converted to strigol and strigyl acetate. Moonseed converted CLA to strigol, but not to 5-DS. The plant did not convert 5-DS to strigol, suggesting that 5-DS is not a precursor of strigol in moonseed. Similarly, 4-deoxyorobanchol was not a precursor of orobanchol in cowpea. Further, sunflower converted CLA to methyl carlactonoate and heliolactone. These results indicated that the biosynthetic pathways of hydroxy SLs do not necessarily involve their respective deoxy SL precursors.

In tomato fruits, chlorophyll, lycopene and ß-carotene are mostly responsible for the color. During ripening of tomato fruits, the color of the pericarp changes from green to red as chlorophyll is degraded and carotenoids accumulate. These changes are associated with an increase in respiration and ethylene production. Carotenoid biosynthesis pathway in plants can be disturbed by herbicide fluridone (1-methyl-3-phenyl-5-[3-trifluoromethyl(phenyl)]- 4(1H)-pyridinone), which inhibits the activity of phytoene desaturase, an enzyme responsible for conversion of phytoene to phytofluene. Fluridone is also used as an inhibitor of biosynthesis of abscisic acid (ABA) and strigolactones, and it reduces chlorophyll production in plants. In our research we studied the effect of fluridone on some physiological parameters, such as color, firmness, ethylene production, lycopene and chlorophyll content during ripening of the tomato fruit. Tomato plants cv. Altadena (Syngenta) were cultivated in a greenhouse in controlled temperature and both immature and mature fruits were used for the experiments, performed between August and November 2016. Fluridone at concentrations of 0.1% and 1.0% in lanolin paste was applied as a 2-3 mm stripe from the top to the base of tomato fruits, and as a control a stripe of lanolin was applied in the same way on the opposite side of the fruits. Fluridone at a concentration of 1.0% greatly inhibited lycopene accumulation in the pericarp of tomato fruits from the treated side. The measurements of fruit firmness have shown no significant differences between firmness of the part of the tomato fruits treated with fluridone, and the non-treated ones. Tomato fruits treated with fluridone produced amounts of ethylene similar to those found in control tissues on the opposite side of the same fruit. Fluridone delayed chlorophyll degradation in tomato fruits. The metabolic significance of these findings is discussed with the role of carotenogenesis inhibition in tomato fruit ripening.

Genetic engineering for heat stress tolerance can promote crop growth and improve yield. One wheat (Triticum aestivum L.) line Y16 (wild type) and two transgenic plants (Y16-3 and Y16-46) that express Hpa110-42, a functional fragment of harpin protein, were used in this study to investigate their possible abiotic stress tolerance under heat stress. Results showed that enhanced thermotolerance was observed in the Y16-3 and Y16-46 lines over the control wheat under stress conditions. However, this increased stress tolerance was significantly abolished by specific inhibitors such as fluridone or sodium tungstate (i.e., arrests abscisic acid (ABA) biosynthesis) and EGTA or La3+ (i.e., arrests Ca2+ signaling pathway) under heat exposure. By contrast, high activities of antioxidant enzymes such as superoxide dismutase, catalase, and ascorbate peroxidase (but not peroxidase) and low levels of oxidative damage (thiobarbituric acid reactive substance (TBARS) and chlorophyll) were detected in transgenic wheat lines compared with the control plant under stress exposure. However, this significant difference diminished after the addition of these specific inhibitors. Furthermore, a slight increase of H2O2 was observed in the transgenic plant, instead of the control, without the addition of chemicals under heat stress. These results suggested that antioxidant enzymes, calcium, and ABA signaling pathways were involved in this Hpa110–42-mediated thermotolerance of transgenic wheat plants under stress exposure. Finally, a hypothetical model based on H2O2 signaling was proposed to illustrate the possible mechanism of this enhanced heat stress tolerance.

Auxin is an important phytohormone which mediates diverse development processes in plants. Published research has demonstrated that auxin induces seed dormancy. However, the precise mechanisms underlying the effect of auxin on seed germination need further investigation, especially the relationship between auxins and both abscisic acid (ABA) and gibberellins (GAs), the latter two phytohormones being the key regulators of seed germination. Here we report that exogenous auxin treatment represses soybean seed germination by enhancing ABA biosynthesis, while impairing GA biogenesis, and finally decreasing GA1/ABA and GA4/ABA ratios. Microscope observation showed that auxin treatment delayed rupture of the soybean seed coat and radicle protrusion. qPCR assay revealed that transcription of the genes involved in ABA biosynthetic pathway was up-regulated by application of auxin, while expression of genes involved in GA biosynthetic pathway was down-regulated. Accordingly, further phytohormone quantification shows that auxin significantly increased ABA content, whereas the active GA1 and GA4 levels were decreased, resulting insignificant decreases in the ratiosGA1/ABA and GA4/ABA.Consistent with this, ABA biosynthesis inhibitor fluridone reversed the delayed-germination phenotype associated with auxin treatment, while paclobutrazol, a GA biosynthesis inhibitor, inhibited soybean seed germination. Altogether, exogenous auxin represses soybean seed germination by mediating ABA and GA biosynthesis.

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.

There is a growing preference for using doubled haploids (DHs) in maize breeding programs because they reduce the time required to generate and evaluate new lines to 2 years or less. However, there is an urgent need for efficient techniques that accurately discriminate between haploid and diploid maize kernels. Here, we investigate the effects of several hormones and chemicals on the germination of haploid and diploid maize kernels, including auxin, cytokinin, ethylene, abscisic acid (ABA) biosynthesis inhibitor (fluridone), ABA catabolism inhibitor (diniconazole), methyl jasmonate (MeJA), and NaCl. Ethylene effectively stimulated the germination of both haploid and diploid maize kernels. The ABA biosynthesis inhibitor fluridone, the ABA catabolism inhibitor diniconazole, and MeJA selectively stimulated the germination of haploid maize kernels. By contrast, gibberellin, 1-naphthaleneacetic acid (NAA), kinetin, and NaCl inhibited the germination of both haploid and diploid maize kernels. These results indicate that the germination of haploid maize kernels is selectively stimulated by fluridone and diniconazole, and suggest that ABA-mediated germination of haploid maize kernels differs from that of diploid maize kernels and other plant seeds.