Explore the vast range of titles available.

• 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.

Background Heat stress is a major restrictive factor that causes yield loss in rice. We previously reported the priming effect of abscisic acid (ABA) on rice for enhanced thermotolerance at the germination, seedling and heading stages. In the present study, we aimed to understand the priming effect and mechanism of ABA on grain filling capacity in rice under heat stress. Results Rice plants were pretreated with distilled water, 50 μM ABA and 10 μM fluridone by leaf spraying at 8 d or 15 d after initial heading (AIH) stage and then were subjected to heat stress conditions of 38 °C day/30 °C night for 7 days, respectively. Exogenous ABA pretreatment significantly super-activated the ABA signaling pathway and improved the SOD, POD, CAT and APX enzyme activity levels, as well as upregulated the ROS-scavenging genes; and decreased the heat stress-induced ROS content (O 2 – and H 2 O 2 ) by 15.0–25.5% in rice grain under heat stress. ABA pretreatment also increased starch synthetase activities in rice grain under heat stress. Furthermore, ABA pretreatment significantly improved yield component indices and grain yield by 14.4–16.5% under heat stress. ABA pretreatment improved the milling quality and the quality of appearance and decreased the incidence of chalky kernels and chalkiness in rice grain and improved the rice grain cooking quality by improving starch content and gel consistence and decreasing the amylose percentage under heat stress. The application of paraquat caused overaccumulation of ROS, decreased starch synthetase activities and ultimately decreased starch content and grain yield. Exogenous antioxidants decreased ROS overaccumulation and increased starch content and grain yield under heat stress. Conclusion Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing rice grain filling capacity under heat stress at grain filling stage mainly by inhibiting ROS overaccumulation and improving starch synthetase activities in rice grain.

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 (H 2 O 2 ) and jasmonic acid (JA) to CmCADs under drought stress. Results discovered that drought-induced ABA, H 2 O 2 and MeJA were prevented efficiently from increasing in melon stems pretreated with fluridone (Flu, ABA inhibitor), imidazole (Imi, H 2 O 2 scavenger) and ibuprofen (Ibu, JA inhibitor). ABA and H 2 O 2 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, H 2 O 2 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 H 2 O 2 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, H 2 O 2 and JA under drought stress and participate in lignin synthesis.

Exogenous substances play an important role in the response of cotton to low-temperature conditions during the germination stage, but little is known about the mechanism involved. To fill this knowledge gap, experiments were conducted to clarify the effects of the application of exogenous substances on the germination, storage substances, endogenous hormones and activities of antioxidant enzymes after gibberellin (GA 3 ) treatment under low-temperature conditions. The results showed that in XinLuZao65 (L) under low-temperature conditions, all exogenous substances tested increased the germination potential (GP) and germination index (GI) and decreased the mean time of germination (MTG), but GA 3 , 2,4-epibrassinolide (EBR), methyl jasmonate, fluridone, and salicylic acid elevated the germination rate in this variety. In XinHai35 (H) at 12 °C, exogenous substances increased the GI and decreased the MTG, but only EBR, hydrogen sulfide, and nitric oxide decreased the GP of this variety, whereas exogenous GA 3 had the best effect on seed germination at low temperature. After exogenous GA 3 and low-temperature treatment, the activities of superoxide dismutase and lipase, the contents of maize riboside, GA 3 and indole-acetic acid in cotton seeds were higher than those in the control, while the peroxidase (POD), catalase (CAT), and amylase activities and the contents of abscisic acid (ABA), malondialdehyde, hydrogen peroxide (H 2 O 2 ), starch, total sugars and total proteins were lower than those of the control. Correlation analysis revealed that ABA, adipose, CAT, H 2 O 2 , POD, GA 3 and GA 3 /ABA were the main factors affecting the germination of cotton seeds at low temperature. Therefore, exogenous GA 3 regulates the balance of endogenous hormones, enhances the activities of key enzymes, and reduces the accumulation of active oxygen, thereby accelerating the metabolism and conversion of materials and improving the low-temperature tolerance of cotton seeds during the germination stage.

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.

Heat stress is a major restrictive factor that suppresses rice production. In this study, we investigated the potential priming effect of exogenous abscisic acid (ABA) on heat tolerance in rice seedlings. Seedlings were pretreated with 10 µM ABA by root-drenched for 24 h and then subjected to heat stress conditions of 40 °C day/35 °C night. ABA pretreatment significantly decreased leaf withering by 2.5–28.5% and chlorophyll loss by 12.8–35.1% induced by heat stress in rice seedlings. ABA pretreatment also mitigated cell injury, as shown by lower malondialdehyde content, relative electrolytic conductivity, and expression of cell death-related genes OsKOD1, OsCP1, and OsNAC4, while expression of OsBI1, a cell death-suppressor gene, was upregulated by ABA pretreatment. Moreover, ABA pretreatment improved antioxidant defense capacity, as shown by an obvious upregulation of ROS-scavenging genes and a decrease in ROS content (O2− and H2O2), and downregulation of the OsRbohs genes. Application of fluridone, an ABA biosynthesis inhibitor, increased membrane injury and the accumulation of ROS under heat stress. Exogenous antioxidants (proanthocyanidins) significantly alleviated leaf withering by decreasing ROS overaccumulation and membrane injury induced by heat stress. In addition, ABA pretreatment significantly superinduced the expression of ABA-responsive genes SalT and OsWsi18, the ABA biosynthesis genes OsNCED3 and OsNCED4, and the heat shock-related genes OsHSP23.7, OsHSP17.7, OsHSF7, and OsHsfA2a. Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing heat stress tolerance of rice seedlings mainly by improving antioxidant defense capacity and heat shock-related genes.

Nitric oxide (NO) and abscisic acid (ABA) play a significant role to combat abiotic stress. Application of 100 µM sodium nitroprusside (SNP, NO donor) or ABA alleviated heat stress effects on photosynthesis and growth of wheat (Triticum aestivum L.) plants exposed to 40 °C for 6 h every day for 15 days. We have shown that ABA and NO synergistically interact to reduce the heat stress effects on photosynthesis and growth via reducing the content of H2O2 and thiobarbituric acid reactive substances (TBARS), as well as maximizing osmolytes production and the activity and expression of antioxidant enzymes. The inhibition of NO and ABA using c-PTIO (2-4 carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and fluridone (Flu), respectively, reduced the osmolyte and antioxidant metabolism and heat stress tolerance. The inhibition of NO significantly reduced the ABA-induced osmolytes and antioxidant metabolism, exhibiting that the function of ABA in the alleviation of heat stress was NO dependent and can be enhanced with NO supplementation.Thus, regulating the activity and expression of antioxidant enzymes together with osmolytes production could act as a possible strategy for heat tolerance.

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. Abstract 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 order to understand more details about the role of abscisic acid (ABA) in fruit ripening and senescence of tomato, two cDNAs (LeNCED1 and LeNCED2) which encode 9-cis-epoxycarotenoid dioxygenase (NCED) as a key enzyme in ABA biosynthesis, two cDNAs (LeACS2 and LeACS4) which encode 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, and one cDNA (LeACO1) which encodes ACC oxidase involved in ethylene biosynthesis were cloned from tomato fruit using a reverse transcription-PCR (RT-PCR) approach. The relationship between ABA and ethylene during ripening was also investigated. Among six sampling times in tomato fruits, the LeNCED1 gene was highly expressed only at the breaker stage when the ABA content becomes high. After this, the LeACS2, LeACS4, and LeACO1 genes were expressed with some delay. The change in pattern of ACO activity was in accordance with ethylene production reaching its peak at the pink stage. The maximum ABA content preceded ethylene production in both the seeds and the flesh. The peak value of ABA, ACC, and ACC oxidase activity, and ethylene production all started to increase earlier in seeds than in flesh tissues, although they occurred at different ripening stages. Exogenous ABA treatment increased the ABA content in both flesh and seed, inducing the expression of both ACS and ACO genes, and promoting ethylene synthesis and fruit ripening, while treatment with fluridone or nordihydroguaiaretic acid (NDGA) inhibited them, delaying fruit ripening and softening. Based on the results obtained in this study, it was concluded that LeNCED1 initiates ABA biosynthesis at the onset of fruit ripening, and might act as an original inducer, and ABA accumulation might play a key role in the regulation of ripeness and senescence of tomato fruit.

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.