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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The present study was undertaken to investigate the mechanism underlying NaCl-alleviated Fe (iron) deficiency in Arabidopsis thaliana Col-0 (Columbia ecotype). Six-week-old Col-0 with rosettes of similar diameters was grown in full-strength nutrient solution lacking Fe (Fe-deficient) or full-strength nutrient solution (Fe-sufficient) with or without 10 mM NaCl for 7 days. Roots were then harvested for analysis of total Fe content, soluble Fe concentration, and abscisic acid (ABA) content as well as for cell wall and RNA extraction, while shoots were harvested for total Fe content and soluble Fe concentration measurements. The total Fe content and the soluble Fe concentration were higher in roots and shoots of −Fe + NaCl-treated plants than −Fe-treated plants, whereas Fe retention in the cell wall was reduced, suggesting the presence of a cell wall Fe-reutilization mechanism. This conclusion was confirmed by the observation that less hemicelluloses Fe was found in plants under −Fe + NaCl treatment. In addition, associated to the upregulation of genes related to the long-distance transport of Fe, such as FRD3 (FERRIC REDUCTASE DEFECTIVE3), YSL2 (YELLOW STRIPE-LIKE), and NAS1 (NICOTIANAMINE SYNTHASE1) under −Fe + NaCl treatment, more Fe was available in shoots. Furthermore, endogenous ABA is involved in NaCl-alleviated Fe deficiency, as the addition of Flu (fluridone), an inhibitor of ABA biosynthesis, abolished the positive effect of NaCl on Fe deficiency. Under −Fe condition, NaCl not only is involved in the reutilization of cell wall Fe but also participates in the translocation of Fe from root to shoot in Arabidopsis, partially through its effect on ABA contents.

Despite the intensive study of xyloglucan endotransglucosylases/hydrolases, their multifaceted role in plant growth regulation in changing environmental conditions is not yet clarified. The functional role of the large number of genes encoding this group of enzymes is also still unclear. NtEXGT gene encodes one of xyloglucan endotransglucosylases/hydrolases (XTHs) of Nicotiana tabacum L. The highest level of NtEXGT gene expression was detected in young flowers and leaves near the shoot apex. Expression of the NtEXGT gene in leaves was induced by cytokinins, auxins, brassinosteroids and gibberellins. NtEXGT gene was also up-regulated by salinity, drought, cold, cadmium and 10 μM abscisic acid treatments and down-regulated in response to 0 °C and 100 μM abscisic acid. Pretreatment of leaves with fluridone contributed to smaller increase in the level of NtEXGT transcripts in response to drought stress. These data suggest that NtEXGT gene is ABA-regulated and probably implicated in ABA-dependent signaling in response to stress factors. 35S::NtEXGT plants of tobacco showed higher rate of root growth under salt-stress conditions, greater frost and heat tolerance as compared with the wild type tobacco plants.

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.

Roots are important plant organs. Lateral root (LR) initiation (LRI) and development play a central role in environmental adaptation. The mechanism of LR development has been well investigated in Arabidopsis. When we evaluated the distribution of auxin and abscisic acid (ABA) in maize, we found that the mechanism differed from that in Arabidopsis. The distribution of ABA and auxin within the primary roots (PRs) and LRs was independent of each other. Auxin localization was observed below the quiescent center of the root tips, while ABA localized at the top of the quiescent center. Furthermore, NaCl inhibited LRI by increasing ABA accumulation, which mainly regulates auxin distribution, while auxin biosynthesis was inhibited by ABA in Arabidopsis. The polar localization of ZmPIN1 in maize was disrupted by NaCl and exogenous ABA. An inhibitor of ABA biosynthesis, fluridone (FLU), and the ABA biosynthesis mutant vp14 rescued the phenotype under NaCl treatment. Together, all the evidence suggested that NaCl promoted ABA accumulation in LRs and that ABA altered the polar localization of ZmPIN1, disrupted the distribution of auxin and inhibited LRI and development.

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.

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.

In this study, we performed a comparative analysis of the physiological and biochemical parameters of wheat cultivars with contrasting drought resistance, drought-resistant Omskaya 35 (O-35) and less drought-resistant Salavat Yulaev (SYu), during 7-day germination under drought stress simulated by 5% mannitol. In addition, we evaluated the effectiveness of pre-sowing seed treatment with 0.4 μM 24-epibrassinolide (EBR) used to increase the resistance of plants of both cultivars to drought stress. It was revealed that mannitol has caused significant changes in the hormonal balance of the plants of both cultivars, associated with abscisic acid (ABA) accumulation and decrease in the contents of indoleacetic acid (IAA) and cytokinins (CKs). It should be noted that more dramatic changes in the content of phytohormones were characteristic for seedlings of SYu cultivar, which was reflected in a stronger growth inhibition of these plants. Pretreatment with EBR mitigated the negative effect of drought on the hormonal status and growth of seedlings during their germination. Furthermore, we found that drought caused accumulation of dehydrin (DHN) proteins, especially of low molecular weight DHNs, whose abundance was 2.5 times greater in O-35 cultivar than in SYu plants. EBR-pretreated plants of both cultivars were characterized by the additional accumulation of DHNs, indicating their involvement in the development of the EBR-induced wheat drought resistance. The use of fluridone allowed us to demonstrate ABA-dependent and ABA-independent pathways of regulation of low molecular mass dehydrins accumulation by EBR in wheat plants of both cultivars under drought conditions.

Some organisms have retained plastids even after they have lost the ability to photosynthesize. Several studies of nonphotosynthetic plastids in apicomplexan parasites have shown that the isopentenyl pyrophosphate biosynthesis pathway in the organelle is essential for their survival. A phytohormone, abscisic acid, one of several compounds biosynthesized from isopentenyl pyrophosphate, regulates the parasite cell cycle. Thus, it is possible that the phytohormone is universally crucial, even in nonphotosynthetic plastids. Here, we examined this possibility using the oyster parasite Perkinsus marinus, which is a plastid‐harboring cousin of apicomplexan parasites and has independently lost photosynthetic ability. Fluridone, an inhibitor of abscisic acid biosynthesis, blocked parasite growth and induced cell clustering. Nevertheless, abscisic acid and its intermediate carotenoids did not affect parasite growth or rescue the parasite from inhibition. Moreover, abscisic acid was not detected from the parasite using liquid chromatography mass spectrometry. Our findings show that abscisic acid does not play any significant roles in P. marinus.

Summary Protein farnesylation is a post-translational modification known to regulate abscisic acid (ABA)-mediated drought tolerance in plants. However, it is unclear whether and to what extent protein farnesylation affects plant tolerance to high-temperature conditions. The Arabidopsis heat-intolerant 5 (hit5) mutant was isolated because it was thermosensitive to prolonged heat incubation at 37°C for 4 d but thermotolerant to sudden heat shock at 44°C for 40 min. Map-based cloning revealed that HIT5 encodes the β-subunit of the protein farnesyltransferase. hit5 was crossed with the aba-insensitive 3 (abi3) mutant, the aba-deficient 3 (aba3) mutant, and the heat shock protein 101 (hsp101) mutant, to characterize the HIT5-mediated heat stress response. hit5/abi3 and hit5/aba3 double mutants had the same temperature-dependent phenotypes as hit5. Additionally, exogenous supplementation of neither ABA nor the ABA synthesis inhibitor fluridone altered the temperature-dependent phenotypes of hit5. The hit5/hsp101 double mutant was still sensitive to prolonged heat incubation, yet its ability to tolerate sudden heat shock was lost. The results suggest that protein farnesylation either positively or negatively affects the ability of plants to survive heat stress, depending on the intensity and duration of high-temperature exposure, in an ABA-independent manner. HSP101 is involved in the hit5-derived heat shock tolerance phenotype.

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.

application/pdf, Neospora caninum causes abortion and stillbirth in cattle. Identification of effective drugs against this parasite remains a challenge. Previous studies have suggested that disruption of abscisic acid (ABA)-mediated signaling in apicomplexan parasites such as Toxoplasma gondii offers a new drug target. In this study, the ABA inhibitor, fluridone (FLU), was evaluated for its action against N. caninum. Production of endogenous ABA within N. caninum was confirmed by ultra-performance liquid chromatography-tandem quadruple mass spectrometry. Subsequently, FLU treatment efficacy was assessed using in vitro. Results revealed that FLU inhibited the growth of N. caninum and T. gondii in vitro (IC50 143.1 +/- 43.96 mu M and 330.6 +/- 5238 mu M, respectively). However, FLU did not affect parasite replication at 24 h post-infection, but inhibited egress of N. caninum thereafter. To evaluate the effect of FLU in vivo, N. caninum-infected mice were treated with FLU for 15 days. FLU treatment appeared to ameliorate acute neosporosis induced by lethal parasite challenge. Together, our data shows that ABA might control egress in N. caninum. Therefore, FLU has potential as a candidate drug for the treatment of acute neosporosis.

The Arabidopsis thaliana T-DNA insertion mutant glucose hypersensitive (ghs) 40-1 exhibited hypersensitivity to glucose (Glc) and abscisic acid (ABA). The ghs40-1 mutant displayed severely impaired cotyledon greening and expansion and showed enhanced reduction in hypocotyl elongation of dark-grown seedlings when grown in Glc concentrations higher than 3 %. The Glc-hypersensitivity of ghs40-1 was correlated with the hyposensitive phenotype of 35S::AtGHS40 seedlings. The phenotypes of ghs40-1 were recovered by complementation with 35S::AtGHS40. The AtGHS40 (At5g11240) gene encodes a WD40 protein localized primarily in the nucleus and nucleolus using transient expression of AtGHS40-mRFP in onion cells and of AtGHS40-EGFP and EGFP-AtGHS40 in Arabidopsis protoplasts. The ABA biosynthesis inhibitor fluridone extensively rescued Glc-mediated growth arrest. Quantitative real time-PCR analysis showed that AtGHS40 was involved in the control of Glc-responsive genes. AtGHS40 acts downstream of HXK1 and is activated by ABI4 while ABI4 expression is negatively modulated by AtGHS40 in the Glc signaling network. However, AtGHS40 may not affect ABI1 and SnRK2.6 gene expression. Given that AtGHS40 inhibited ABA degrading and signaling gene expression levels under high Glc conditions, a new circuit of fine-tuning modulation by which ABA and ABA signaling gene expression are modulated in balance, occurred in plants. Thus, AtGHS40 may play a role in ABA-mediated Glc signaling during early seedling development. The biochemical function of AtGHS40 is also discussed.

Myriophyllum spicatum or Eurasian watermilfoil (hereafter, milfoil) is among the most problematic invasive aquatic plant species throughout much of North America. M. spicatum infestations can result in reduced diversity and abundance of native plant populations. Control of the invader is essential to promoting healthy ecosystems. Several treatment alternatives are available for milfoil control, although cost and efficacy vary significantly, with some treatments resulting in more harm to the native population than no treatment at all. A series of field-based microcosms containing actively growing milfoil were constructed in order to directly compare the impact of two herbicides (2,4-dichlorophenoxyacetic acid and fluridone) and the milfoil weevil (Euhrychiopsis lecontei) on weed control and plant biochemistry. Herbicide concentrations in water, plants, and sediments were monitored, as were weevil population dynamics and resulting invertebrate damage to milfoil stems. The impact of the different treatments on levels of polyphenols, carbohydrates, ash, and overall carbon and nitrogen levels in the milfoil were determined. Total biomass of the untreated milfoil increased by more than 2.7-fold during the 53-day experimental period. Conversely, the biomass of milfoil subjected to chemical or biological treatment either remained constant or decreased significantly during the experiment. The herbicide 2,4-D resulted in nearly 100% milfoil mortality by day 20, whereas fluridone toxicity was significantly slower but reached 75% by the end of the trial. Similarly, milfoil growth in the weevil-amended tanks was somewhat erratic but by the end of the trial, the total plant biomass was 71% less than that of un-amended controls. Although the total biomass remaining at the end of the fluridone and weevil treatments was similar, the carbohydrate and starch content of the shoots in the insect treatment were nearly 4.6- and 4.8-fold greater, respectively, than that of the herbicide treated plants. The higher starch content in insect-treated plants could lead to increased autofragmentation and spread of M. spicatum. However, herbicide treatments are frequently required for several years. Therefore, integrated pest management, which combines the long-term benefits of biological controls with the short-term benefits of herbicides may provide the best solution to the control of M. spicatum and the conservation of native plants.

Water stress severely reduces the production of wheat. Application of seaweed extracts have started to show promise in protecting plants from environmental stresses as they contain several biostimulants. However, the modes of action of these biostimulants are not clear. Here, we investigated the role of Gracilaria dura (GD), a red alga, in conferring stress tolerance to wheat during drought under glasshouse and agro-ecological conditions by integrating molecular studies with physiological and field investigations. GD-sap application conferred drought tolerance (as the biomass increased by up to 57% and crop yield by 70%), via facilitating physiological changes associated to maintaining higher water content. GD-sap application significantly increased ABA accumulation (2.34 and 1.46 fold at 4 and 6 days of drought, respectively) due to enhanced expression of biosynthesis genes. This followed an activation of ABA response genes and physiological processes including reduced stomatal opening, thus reducing water loss. Moreover, GD-sap application enhanced the expression of stress-protective genes specifically under water stress. Treatment with fluridone, an ABA inhibitor, further support the role of ABA in GD-sap mediated drought tolerance in wheat. The findings of this study provide insights into the functional role of GD-sap in improving drought tolerance and show the potential to commercialize GD-sap as a potent biostimulant for sustainable agriculture in regions prone to drought.

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.

Salicylic acid (SA) can induce plant resistance to biotic and abiotic stresses through cross talk with other signaling molecules, whereas the interaction between hydrogen peroxide (H2O2) and abscisic acid (ABA) in response to SA signal is far from clear. Here, we focused on the roles and interactions of H2O2 and ABA in SA-induced freezing tolerance in wheat plants. Exogenous SA pretreatment significantly induced freezing tolerance of wheat via maintaining relatively higher dark-adapted maximum photosystem II quantum yield, electron transport rates, less cell membrane damage. Exogenous SA induced the accumulation of endogenous H2O2 and ABA. Endogenous H2O2 accumulation in the apoplast was triggered by both cell wall peroxidase and membrane-linked NADPH oxidase. The pharmacological study indicated that pretreatment with dimethylthiourea (H2O2 scavenger) completely abolished SA-induced freezing tolerance and ABA synthesis, while pretreatment with fluridone (ABA biosynthesis inhibitor) reduced H2O2 accumulation by inhibiting NADPH oxidase encoding genes expression and partially counteracted SA-induced freezing tolerance. These findings demonstrate that endogenous H2O2 and ABA signaling may form a positive feedback loop to mediate SA-induced freezing tolerance in wheat.

Background Notopterygium incisum is an important Chinese medicinal plant. Its mature seeds have underdeveloped embryos and are physiological dormant. We found the seeds with full developed embryos can germinate after treated by fluridone (FL), an inhibitor of abscisic acid (ABA). In order to understand the molecular mechanisms underlying seed dormancy release by FL, we compared the transcriptomic changes in dormancy release induced by two different methods, FL and cold stratification (CS) in N. incisum. We further analyzed the gene expression patterns involved in seed germination and dormancy using quantitative reverse-transcription PCR. Results RNA-sequence analysis revealed more dramatic changes in the transcriptomes of FL than those in CS, particularly for genes involved in the biosynthesis and regulation of gibberellins (GAs) and ABA. The down-regulation of ABA biosynthesis genes and the dramatic up-regulation of NiCYP707As, an ABA catabolic gene, contributed to the reduced ABA levels in FL. The increased GA3 levels in CS-treated seeds were due to the up-regulation of NiGA3OX. Both NiABI5 (a positive ABA regulator) and NiGAI (a negative regulator of GA) were down-regulated in FL and CS. The upregulation of strigolactones (SLs; the metabolites with the same precursor as ABA) biosynthesis and regulatory genes in both FL- and CS-treated seeds indicates that SLs contribute positively to seed dormancy release in N. incisum. Conclusions Our results indicated that FL- and CS-seed dormancy release possibly depends on two totally different mechanisms: alleviation of the effects of ABA and potentiation of the effects of GA, respectively. However, NiABI5 and NiGAI probably function as common factors integrating the effects of ABA and GA on seed dormancy release. Electronic supplementary material The online version of this article (10.1186/s12870-018-1333-2) contains supplementary material, which is available to authorized users.

Heat stress at the pollen mother cell (PMC) meiotic stage leads to pollen sterility in rice, in which the reactive oxygen species (ROS) and sugar homeostasis are always adversely affected. This damage is reversed by abscisic acid (ABA), but the mechanisms underlying the interactions among the ABA, sugar metabolism, ROS and heat shock proteins in rice spikelets under heat stress are unclear. Two rice genotypes, Zhefu802 (a recurrent parent) and fgl (its near-isogenic line) were subjected to heat stress of 40°C after pre-foliage sprayed with ABA and its biosynthetic inhibitor fluridone at the meiotic stage of PMC. The results revealed that exogenous application of ABA reduced pollen sterility caused by heat stress. This was achieved through various means, including: increased levels of soluble sugars, starch and non-structural carbohydrates, markedly higher relative expression levels of heat shock proteins (HSP24.1 and HSP71.1) and genes related to sugar metabolism and transport, such as sucrose transporters (SUT) genes, sucrose synthase (SUS) genes and invertase (INV) genes as well as increased antioxidant activities and increased content of adenosine triphosphate and endogenous ABA in spikelets. In short, exogenous application of ABA prior to heat stress enhanced sucrose transport and accelerated sucrose metabolism to maintain the carbon balance and energy homeostasis, thus ABA contributed to heat tolerance in rice.

BYPASS1 (BPS1), which is a well-conserved gene in plants, is required for normal root and shoot development. In the absence of BPS1 gene function, Arabidopsis overproduces a mobile signalling compound (the BPS1 signal) in roots, and this transmissible signal arrests shoot growth and causes abnormal root development. In addition to the shoot and root meristem activities, the legumes also possess transient meristematic activity in root cortical cells during Rhizobium symbiosis. We explored the role of Phaseolus vulgaris BPS1 during nodule primordium development using an RNA-interference (RNAi) silencing approach. Our results show that upon Rhizobium infection, the PvBPS1-RNAi transgenic roots failed to induce cortical cell divisions without affecting the rhizobia-induced root hair curling and infection thread formation. The transcript accumulation of early nodulin genes, cell cyclins, and cyclin-dependent kinase genes was affected in RNAi lines. Interestingly, the PvBPS1-RNAi root nodule phenotype was partially rescued by exogenous application of fluridone, a carotenoid biosynthesis inhibitor, which was used because the carotenoids are precursors of BPS1 signalling molecules. Furthermore, we show that the PvBPS1 promoter was active in the nodule primordia. Together, our data show that PvBPS1 plays a vital role in the induction of meristematic activity in root cortical cells and in the establishment of nodule primordia during Phaseolus-Rhizobium symbiosis.

Abscisic acid (ABA) regulates the physiological and biochemical mechanisms required to tolerate drought stress, which is considered as an important abiotic stress. It has been postulated that ABA might be involved in regulation of plant phenolic compounds biosynthesis, especially anthocyanins that accumulate in plants subjected to drought stress; however, the evidence for this postulate remains elusive. Therefore, we studied whether ABA is involved in phenolic compounds accumulation, especially anthocyanin biosynthesis, using drought stressed Aristotelia chilensis plants, an endemic berry in Chile. Our approach was to use fluridone, an ABA biosynthesis inhibitor, and then subsequent ABA applications to young and fully-expanded leaves of drought stressed A. chilensis plants during 24, 48 and 72 h of the experiment. Plants were harvested and leaves were collected separately to determine the biochemical status. We observed that fluridone treatments significantly decreased ABA concentrations and total anthocyanin (TA) concentrations in stressed plants, including both young and fully-expanded leaves. TA concentrations following fluridone treatment were reduced around fivefold, reaching control plant levels. ABA application restored ABA levels as well as TA concentrations in stressed plant at 48 h of the experiment. We also observed that TA concentrations followed the same pattern as ABA concentrations in the ABA treated plants. Quantitative real-time PCR revealed that AcUFGT gene expression decreased in fully-expanded leaves of stressed plants treated with fluridone, while a subsequent ABA application increased AcUFGT expression. Taken together, our results suggest that ABA is involved in the regulation of anthocyanin biosynthesis under drought stress.

Effect of pretreatment of wheat (Triticum aestivum L.) seedlings with 0.4 μM 24-epibrassinolide (EB) on subsequent action on them of 1 mM cadmium acetate was investigated. This pretreatment decreased the extent of damage of cadmium action on wheat plants as judged by inhibition of stress-induced efflux of electrolytes from plant tissues and plant ability to maintain the growing parameters at a level close to the control. It was established that the revealed ability of EB to induce twofold increased accumulation of 28 kDa dehydrin under normal plant growth conditions and even to cause additional accumulation of this protein under the cadmium stress is of importance in development of the preadapting and protection effects of EB on wheat seedlings. Using fluridone (FD), a known inhibitor of the biosynthesis of ABA, the pathways responsible for the regulation of 28 kDa dehydrin level and both dependent and independent on ABA were revealed in wheat plants both pretreated and untreated with EB and under cadmium stress.

Saline-alkaline stress is characterized by high salinity and high alkalinity (high pH); alkaline stress has been shown to be the primary factor inhibiting rice seedling growth. In this study, we investigated the potential priming effect of abscisic acid (ABA) on tolerance of rice seedlings to alkaline stress simulated by Na2CO3. Seedlings were pretreated with ABA at concentrations of 0 (control), 10, and 50 μM by root-drench for 24 h and then transferred to a Na2CO3 solution that did not contain ABA. Compared to control treatment, pretreatment with ABA substantially improved the survival rate of rice seedlings and increased biomass accumulation after 7 days under the alkaline condition. ABA application at 10 μM also alleviated the inhibitory effects of alkaline stress on the total root length and root surface area. Physiologically, ABA increased relative water content (RWC) and decreased cell membrane injury degree (MI) and Na(+)/K(+) ratios. In contrast, fluridone (an ABA biosynthesis inhibitor) decreased the RWC and increased MI in shoots under the alkaline conditions. These data suggest that ABA has a potent priming effect on the adaptive response to alkaline stress in rice and may be useful for improving rice growth in saline-alkaline paddy fields.

Lowland rice (Nipponbare) and upland rice (Gaoshan 1) that are comparable under normal and moderate drought conditions showed dramatic differences in severe drought conditions, both naturally occurring long-term drought and simulated rapid water deficits. We focused on their root response and found that enhanced tolerance of upland rice to severe drought conditions was mainly due to the lower level of ABA in its roots than in those of the lowland rice. We first excluded the effect of ABA biosynthesis and catabolism on root-accumulated ABA levels in both types of rice by monitoring the expression of four OsNCED genes and two OsABA8ox genes. Next, we excluded the impact of the aerial parts on roots by suppressing leaf-biosynthesized ABA with fluridone and NDGA (nordihydroguaiaretic acid), and measuring the ABA level in detached roots. Instead, we proved that upland rice had the ability to export considerably more root-sourced ABA than lowland rice under severe drought, which improved ABA-dependent drought adaptation. The investigation of apoplastic pH in root cells and root anatomy showed that ABA leakage in the root system of upland rice was related to high apoplastic pH and the absence of Casparian bands in the sclerenchyma layer. Finally, taking some genes as examples, we predicted that different ABA levels in rice roots stimulated distinct ABA perception and signaling cascades, which influenced its response to water stress.

Background Ripening of fleshy fruits has been classically defined as climacteric or non-climacteric. Both types of ripening are controlled by plant hormones, notably by ethylene in climacteric ripening and by abscisic acid (ABA) in non-climacteric ripening. In pepper (Capsicum), fruit ripening has been widely classified as non-climacteric, but the ripening of the hot pepper fruit appears to be climacteric. To date, how to regulate the hot pepper fruit ripening through ethylene and ABA remains unclear. Results Here, we examined ripening of the hot pepper (Capsicum frutescens) fruit during large green (LG), initial colouring (IC), brown (Br), and full red (FR) stages. We found a peak of ethylene emission at the IC stage, followed by a peak respiratory quotient at the Br stage. By contrast, ABA levels increased slowly before the Br stage, then increased sharply and reached a maximum level at the FR stage. Exogenous ethylene promoted colouration, but exogenous ABA did not. Unexpectedly, fluridone, an inhibitor of ABA biosynthesis, promoted colouration. RNA-sequencing data obtained from the four stages around ripening showed that ACO3 and NCED1/3 gene expression determined ethylene and ABA levels, respectively. Downregulation of ACO3 and NCED1/3 expression by virus-induced gene silencing (VIGS) inhibited and promoted colouration, respectively, as evidenced by changes in carotenoid, ABA, and ethylene levels, as well as carotenoid biosynthesis-related gene expression. Importantly, the retarded colouration in ACO3-VIGS fruits was rescued by exogenous ethylene. Conclusions Ethylene positively regulates the hot pepper fruit colouration, while inhibition of ABA biosynthesis promotes colouration, suggesting a role of ABA in de-greening. Our findings provide new insights into processes of fleshy fruit ripening regulated by ABA and ethylene, focusing on ethylene in carotenoid biosynthesis and ABA in chlorophyll degradation. Electronic supplementary material The online version of this article (10.1186/s12870-018-1377-3) contains supplementary material, which is available to authorized users.

Myriophyllum spicatum or Eurasian watermilfoil (hereafter, milfoil) is among the most problematic invasive aquatic plant species throughout much of North America. M. spicatum infestations can result in reduced diversity and abundance of native plant populations. Control of the invader is essential to promoting healthy ecosystems. Several treatment alternatives are available for milfoil control, although cost and efficacy vary significantly, with some treatments resulting in more harm to the native population than no treatment at all. A series of field-based microcosms containing actively growing milfoil were constructed in order to directly compare the impact of two herbicides (2,4-dichlorophenoxyacetic acid and fluridone) and the milfoil weevil (Euhrychiopsis lecontei) on weed control and plant biochemistry. Herbicide concentrations in water, plants, and sediments were monitored, as were weevil population dynamics and resulting invertebrate damage to milfoil stems. The impact of the different treatments on levels of polyphenols, carbohydrates, ash, and overall carbon and nitrogen levels in the milfoil were determined. Total biomass of the untreated milfoil increased by more than 2.7-fold during the 53-day experimental period. Conversely, the biomass of milfoil subjected to chemical or biological treatment either remained constant or decreased significantly during the experiment. The herbicide 2,4-D resulted in nearly 100% milfoil mortality by day 20, whereas fluridone toxicity was significantly slower but reached 75% by the end of the trial. Similarly, milfoil growth in the weevil-amended tanks was somewhat erratic but by the end of the trial, the total plant biomass was 71% less than that of un-amended controls. Although the total biomass remaining at the end of the fluridone and weevil treatments was similar, the carbohydrate and starch content of the shoots in the insect treatment were nearly 4.6- and 4.8-fold greater, respectively, than that of the herbicide treated plants. The higher starch content in insect-treated plants could lead to increased autofragmentation and spread of M. spicatum. However, herbicide treatments are frequently required for several years. Therefore, integrated pest management, which combines the long-term benefits of biological controls with the short-term benefits of herbicides may provide the best solution to the control of M. spicatum and the conservation of native plants.