Synthesis and biological activity of photostable and persistent abscisic acid analogs

The plant hormone abscisic acid (ABA) plays a critical role in various environmental stress responses and has long been expected to be used in agriculture. However, the practical use of ABA has been limited, mainly because of its photoinstability and rapid biodegradation. We previously developed photostable ABA agonists, BP2A and Me 1',4'-trans-diol BP2A, in which the dienoic acid side chain of ABA was replaced with phenylacetic acid. This finding validated our structure-based approach in designing photostable agonists and provided a basis for developing a more potent or long-lasting ABA agonist. In this study, we synthesized novel BP2A analogs in which the cyclohexenone ring was modified to avoid catabolism by the ABA metabolic enzyme, ABA 8'-hydroxylase. All synthesized analogs showed higher photostability than BP2A under sunlight. In an Arabidopsis seed germination assay, (+)-compounds 5 and 6 with a tetralone ring displayed significantly stronger ABA agonist activity than (+)-BP2A. In contrast, in the in vitro phosphatase assays, both compounds showed comparable or weaker ABA receptor (PYL1) agonistic activity than (+)-BP2A, suggesting that the stronger ABA-like activity of (+)-5 and (+)-6 may arise from their metabolic stability in vivo. This study provides data relevant to designing photostable and persistent ABA agonists.

AtTrxh3, a Thioredoxin, Is Identified as an Abscisic AcidBinding Protein in Arabidopsis thaliana

Abscisic acid (ABA, 1) is a plant hormone that regulates various plant physiological processes such as seed developing and stress responses. The ABA signaling system has been elucidated; binding of ABA with PYL proteins triggers ABA signaling. We have previously reported a new method to isolate a protein targeted with a bioactive small molecule using a biotin linker with alkyne and amino groups, a protein cross-linker, and a bioactive small molecule with an azido group (azido probe). This method was used to identify the unknown ABA binding protein of Arabidopsis thaliana. As a result, AtTrxh3, a thioredoxin, was isolated as an ABA binding protein. Our developed method can be applied to the identification of binding proteins of bioactive compounds.

Embryogenic callus induction from immature zygotic embryos and genetic transformation of Larix kaempferi 3x Larix gmelinii 9

To date, there are few reports of the successful genetic transformation of larch and other conifers, mainly because it is difficult to transform and integrate exogenous genes. In this study, hybrid larch Larix kaempferi 3x Larix gmelinii 9 cones were collected on June 27, July 1, July 4, July 7 and July 16, 2017. Embryogenic callus induction was studied using a combination of different plant growth regulators and concentrations. The results showed that July 1 was the best stage; the highest induction rate was 10.83%, which cultured in BM medium (Button medium, which formula was listed in S1 Table) with 1.0 mg/L 2,4-D (2,4-dichlorophenoxyacetic acid) and 0.2 mg/L KT(kinetin). When cultured on a proliferation medium for 12 days, proliferation was the fastest, reaching 323.08%, which could also maintain the freshness and vitality. The suitable pre-culture medium for somatic embryogenesis was 1/4 BM medium containing 10 g/L inositol and 60 g/L sucrose. The combination of 45 mg/L ABA (abscisic acid) and 75 g/L PEG4000 (Polyethyene glycol 4000) could promote the number of somatic embryos, and reached the maximum, 210 140 per 1 g FW. The genetic transformation was carried out by the Agrobacterium-mediated transformation method with embryogenic callus cultured for 12 days. The results showed the optimal OD600 of the infection solution(suspension of A. tumefaciens) was 0.5, co-culture time was 2 days, and screening concentration of Hyg (hygromycin B) was 4 mg/L. In this study, the transformation rate of resistance callus was 32.1%. It provides a reference for low genetic transformation efficiency of larch at present. This study could be beneficial for the innovation and breeding of larch by genetic engineering and provides a certain basis for rapid propagation of excellent larch germplasm resources and genetic engineering breeding of larch and other conifers.

Effects of seed priming treatments on the germination and development of two rapeseed (Brassica napus L.) varieties under the co-influence of low temperature and drought

The present study was performed to evaluate the effects of seed priming. This was done by soaking the seeds of two rapeseed cultivars, namely, ZY15 (tolerant to low temperature and drought) and HY49 (sensitive to low temperature and drought), for 12 h in varying solutions: distilled water, 138 mg/L salicylic acid (SA), 300 mg/L gibberellic acid (GA), 89.4 mg/L sodium nitroprusside (SNP), 3000 mg/L calcium chloride (CaCl₂), and 30 mg/L abscisic acid (ABA). Primed and non-primed seeds were left to germinate at 15°C and -0.15 MPa (T₁₅W₁₅) and at 25°C and 0 MPa (T₂₅W₀), respectively. The results showed that SA, GA, SNP, CaCl₂, and ABA significantly improved the germination potential (GP), germination rate (GR), germination index (GI), stem fresh weight (SFW), stem dry weight (SDW), root length (RL), stem length (SL), and seed vigor index (SVI) under T₁₅W₁₅. For ZY15 seeds under T₂₅W₀, GA, SNP, CaCl₂, and ABA priming reduced the average germination time (96% after 5 days) compared to that of the control (88% after 5 days). For ZY15 seeds under T₁₅W₁₅, SA, SNP, CaCl₂, and ABA priming, with respect to the control and water-treated groups, shortened the average germination time (92% after 5 days) compared to that of the control (80% after 5 days). For HY49 seeds under T₂₅W₀, GA, SNP, CaCl₂, and ABA priming reduced the average germination time (92% after 5 days) compared to that of the control (85% after 5 days). Similarly, for HY49 seeds under T₁₅W₁₅, GA priming shortened the average germination time (89% after 5 days) compared to that of the control (83% after 5 days). These priming agents increased the net photosynthesis, stomatal conductivity, and transpiration rate of rape seedlings under conditions of low temperature and drought stress, while also decreasing intercellular carbon dioxide (CO₂) concentrations. Additionally, SA, GA, SNP, CaCl₂, and ABA increased superoxide dismutase concentrations (SOD) and ascorbic peroxidase (APX) activities of rape seedlings under stress conditions, while decreasing catalase (CAT) and peroxidase (POD) activities in ZY15 seedlings. In HY49, which is sensitive to low temperature and drought, all priming solutions, except for SNP, led to an increase in SOD activity levels and a decrease in CAT activity levels. Overall, SA, GA, SNP, and CaCl₂ increased the concentrations of indoleacetic acid (IAA), GA, ABA, and cytokinin (CTK) in seedlings under stress conditions. Moreover, compared to SA, CaCl₂, and ABA, GA (300 mg/L) and SNP (300 mol/L) showed improved priming effects for ZY15 and HY49 under stress conditions.

Uncovering the multi-level response of Glycine max L. to the application of allelopathic biostimulant from Levisticum officinale Koch

The interest expressed by the agriculture in the category of innovative biostimulants is due to the intensive search for natural preparations. Our study is the first ever to report a complex approach to the use of allelopathic extracts from Levisticum officinale Koch. roots in soybean cultivation, includes analyses of morphological observations, and analyses of biochemical indicators. Hot method of aqueous extraction was applied. The extracts were administered via foliar application and soil treatment. Lovage extracts had high contents of polyphenolic compounds and rich micro- and macroelemental composition. The infusions did not contain gibberellic acid and indole-3-acetic acid but the abscisic acid and saccharose, glucose, and fructose were found. The extracts modified soybean plant physiology, as manifested by changes in biometric traits. Plants responded positively by increased yield. Seeds from the treated plants had higher contents of micro- and macroelements, as well as total concentrations of lipids (with a slight decrease in protein content). In addition, they featured changes in their amino acid profile and fatty acid composition. The application of allelopathic biostimulant caused increased concentrations of isoflavones and saponins. The natural biostimulants from Levisticum officinale may become a valuable tool in the sustainable agriculture.

Action of Multiple Rice β-Glucosidases on Abscisic Acid Glucose Ester

Conjugation of phytohormones with glucose is a means of modulating their activities, which can be rapidly reversed by the action of β-glucosidases. Evaluation of previously characterized recombinant rice β-glucosidases found that nearly all could hydrolyze abscisic acid glucose ester (ABA-GE). Os4BGlu12 and Os4BGlu13, which are known to act on other phytohormones, had the highest activity. We expressed Os4BGlu12, Os4BGlu13 and other members of a highly similar rice chromosome 4 gene cluster (Os4BGlu9, Os4BGlu10 and Os4BGlu11) in transgenic Arabidopsis. Extracts of transgenic lines expressing each of the five genes had higher β-glucosidase activities on ABA-GE and gibberellin A4 glucose ester (GA4-GE). The β-glucosidase expression lines exhibited longer root and shoot lengths than control plants in response to salt and drought stress. Fusions of each of these proteins with green fluorescent protein localized near the plasma membrane and in the apoplast in tobacco leaf epithelial cells. The action of these extracellular β-glucosidases on multiple phytohormones suggests they may modulate the interactions between these phytohormones.

Effect of RIP Overexpression on Abiotic Stress Tolerance and Development of Rice

Ribosome-inactivating proteins (RIPs) are a class of cytotoxic enzymes that can inhibit protein translation by depurinating rRNA. Most plant RIPs are synthesized with a leader sequence that sequesters the proteins to a cell compartment away from the host ribosomes. However, several rice RIPs lack these signal peptides suggesting they reside in the cytosol in close proximity to the plant ribosomes. This paper aims to elucidate the physiological function of two nucleocytoplasmic RIPs from rice, in particular, the type 1 RIP referred to as OsRIP1 and a presumed type 3 RIP called nuRIP. Transgenic rice lines overexpressing these RIPs were constructed and studied for developmental effects resulting from this overexpression under greenhouse conditions. In addition, the performance of transgenic seedlings in response to drought, salt, abscisic acid and methyl jasmonate treatment was investigated. Results suggest that both RIPs can affect methyl jasmonate mediated stress responses.

Engineering Lignin Nanomicroparticles for the Antiphotolysis and Controlled Release of the Plant Growth Regulator Abscisic Acid

Lignin is the most abundant aromatic biopolymer in nature and is a major byproduct from the paper industry. The unlocking of lignin's potential for high-value applications has gained increasing attention in recent years. In this study, alkali lignin (AL), with a rigid conjugated structure and amphiphilic property, was used as a sustainable and eco-friendly encapsulation material for the protection and controlled release of photosensitive abscisic acid (ABA), an important and widely used plant growth regulator. Cetyltrimethylammonium bromide (CTAB) was used to induce the formation of AL-CTAB nanomicroparticles by self-assembly. The size and morphology of AL-CTAB particles were modified by changing the AL concentration and the dispersion agent. AL (0.3 M) dissolved in tetrahydrofuran could form a uniform size (300 nm) of particles with a regular spherical structure. Subsequently, ABA was loaded on the prepared nanomicroparticles to synthesize the capsule formulation of ABA@AL-CTAB. The controlled-release behavior and the antiphotolysis performance as well as the thermal stability of ABA@AL-CTAB were proved to be superior. Lasting inhibition of Arabidopsis and rice seed germination by ABA@AL-CTAB under light irradiations implied protection of ABA from photolysis. In addition, ABA@AL-CTAB could effectively regulate plant stomata, thereby increasing plant drought resistance. Overall, lignin is suitable for the preparation of agrochemical formulations with excellent controlled release and antiphotolysis performances.

Exogenous abscisic acid (ABA) promotes cadmium (Cd) accumulation in Sedum alfredii Hance by regulating the expression of Cd stress response genes

Sedum alfredii Hance is a zinc (Zn) and cadmium (Cd) hyperaccumulator plant. However, the regulatory role of plant hormones in the Zn or Cd uptake and accumulation of S. alfredii remains unclear. In this work, the growth, Cd accumulation, abscisic acid (ABA) synthesis and catabolism, malonaldehyde (MDA) content, and transcriptional level of some Cd stress response genes under ABA and Cd co-treatment were investigated to reveal the impact of ABA on Cd resistance and Cd accumulation of S. alfredii. The results show that 0.2 mg/L ABA and 100 μmol/L Cd co-treatment enhanced Cd accumulation and growth in S. alfredii, whereas lower or higher ABA concentrations weaken or even reverse this effect, which was positively correlated with endogenous ABA content. The increase in endogenous ABA content might be the results of the increasing ABA synthetase activities and decreasing ABA lytic enzyme, which was induced by the application of 0.2 mg/L ABA under 100 μmol/L Cd treatment. Principal component analysis (PCA) indicated that ABA impacted the expression pattern of Cd stress response genes, which coincided with the Cd accumulation pattern in the shoots of S. alfredii. Cross-over analysis of partial least squares-discriminant analysis (PLS-DA) and correlation analysis indicated that HsfA4c, HMA4 expression in roots, and HMA2, HMA3, CAD, NAS expression in shoots were correlated with endogenous ABA, which suggests that endogenous ABA improves Cd resistance of seedlings, switches the root-to-shoot transporter from HMA2 to HMA4, and transports more Cd into apoplasts to promote Cd accumulation in the shoots of S. alfredii. Taken together, ABA plays an essential role not only in Cd resistance but also in Cd transport from root to shoot in S. alfredii under Cd stress.

Inoculation with abscisic acid (ABA)-catabolizing bacteria can improve phytoextraction of heavy metal in contaminated soil

Promotion of plant capacity for accumulation of heavy metals (HMs) is one of the key strategies in enhancing phytoremediation in contaminated soils. Here we report that, Rhodococcus qingshengii, an abscisic acid (ABA)-catabolizing bacteria, clearly boosts levels of Cd, Zn, and Ni in wild-type Arabidopsis by 47, 24, and 30%, respectively, but no increase in Cu was noted, when compared with non-inoculated Arabidopsis plants in contaminated growth substrate. Furthermore, when compared with wild-type plants, R.qingshengii-induced increases in Cd, Zn, and Ni concentrations were more pronounced in abi1/hab1/abi2 (ABA-sensitive mutant) strains of Arabidopsis, whereas little effect was observed in snrk2.2/2.3 (ABA insensitive mutant). This demonstrates that metabolizing ABA might be indispensable for R. qingshengii to improve metal accumulation in plants. Bacterial inoculation significantly elevated the expression of Cd, Zn, and Ni-related transporters; whereas the transcript levels of Cu transporters remained unchanged. This result may be a reasonable explanation for why the uptake of Cd, Zn, and Ni in plants was stimulated by bacterial inoculation, while no effect was observed on Cu levels. From our results, we clearly demonstrate that R. qingshengii can increase the accumulation of Cd, Zn, and Ni in plants via an ABA-mediated HM transporters-associated mechanism. Metabolizing ABA in the plants by ABA-catabolizing bacterial inoculation might be an alternative strategy to improve phytoremediation efficiency in HMs contaminated soil.

Silicon and salicylic acid confer high-pH stress tolerance in tomato seedlings

Alkalinity is a known threat to crop plant growth and production, yet the role of exogenous silicon (Si) and salicylic acid (SA) application has been largely unexplored. Here, we sought to understand the beneficial impacts of Si and SA on tomato seedlings during high-pH (9.0) stress. Results showed that Si- and SA-treated plants displayed higher biomass, chlorophyll contents, relative leaf water and better root system than none-treated plants under alkaline conditions. Both Si and SA counteracted the alkaline stress-induced oxidative damage by lowering the accumulation of reactive oxygen species and lipid peroxidation. The major antioxidant defence enzyme activities were largely stimulated by Si and SA, and these treatments caused significantly increased K+ and lowered Na+ concentrations in shoot and root under stress. Moreover, Si and SA treatments modulated endogenous SA levels and dramatically decreased abscisic acid levels in both shoot and root. Additionally, key genes involved in Si uptake, SA biosynthesis, the antioxidant defence system and rhizosphere acidification were up-regulated in Si and SA treatments under alkaline conditions. These results demonstrate that Si and SA play critical roles in improving alkaline stress tolerance in tomato seedlings, by modifying the endogenous Na+ and K+ contents, regulating oxidative damage and key genes and modulating endogenous hormone levels. These findings will help to broaden our understanding regarding the physiological and molecular mechanisms associated with the alkaline soil tolerance in plants.

Aboveground phytochemical responses to belowground herbivory in poplar trees and the consequence for leaf herbivore preference

Belowground (BG) herbivory can influence aboveground (AG) herbivore performance and food preference via changes in plant chemistry. Most evidence for this phenomenon derives from studies in herbaceous plants but studies in woody plants are scarce. Here we investigated whether and how BG herbivory on black poplar (Populus nigra) trees by Melolontha melolontha larvae influences the feeding preference of Lymantria dispar (gypsy moth) caterpillars. In a food choice assay, caterpillars preferred to feed on leaves from trees that had experienced attack by BG herbivores. Therefore, we investigated the effect of BG herbivory on the phytochemical composition of P. nigra trees alone and in combination with AG feeding by L. dispar caterpillars. BG herbivory did not increase systemic AG tree defences like volatile organic compounds, protease inhibitors and salicinoids. Jasmonates and salicylic acid were also not induced by BG herbivory in leaves but abscisic acid concentrations drastically increased together with proline and few other amino acids. Leaf coating experiments with amino acids suggest that proline might be responsible for the caterpillar feeding preference via presumptive phagostimulatory properties. This study shows that BG herbivory in poplar can modify the feeding preference of AG herbivores via phytochemical changes as a consequence of root-to-shoot signaling.

Abscisic Acid Standardized Fig (Ficus carica) Extracts Ameliorate Postprandial Glycemic and Insulinemic Responses in Healthy Adults

Abscisic acid (ABA) can improve glucose homeostasis and reduce inflammation in mammals by activating lanthionine synthetase C-like 2 (LANCL2). This study examined the effects of two fig fruit extracts (FFEs), each administered at two different ABA doses, on glycemic index (GI) and insulinemic index (II) to a standard glucose drink. In a randomized, double-blind crossover study, 10 healthy adults consumed 4 test beverages containing FFE with postprandial glucose and insulin assessed at regular intervals over 2 h to determine GI and II responses. Test beverages containing 200 mg FFE-50× and 1200 mg FFE-10× significantly reduced GI values by -25% (P = 0.001) and -24% (P = 0.002), respectively. Two lower doses of FFE also reduced GI values compared with the reference drink (by approximately -14%), but the differences did not reach statistical significance. Addition of FFE to the glucose solution significantly reduced II values at all dosages and displayed a clear dose-response reduction: FFE-50× at 100 mg and 200 mg (-14% (P < 0.05) and -24% (P = 0.01), respectively) and FFE-10× at 600 mg and 1200 mg (-16% (P < 0.05) and -24% (P = 0.01), respectively). FFE supplementation is a promising nutritional intervention for the management of acute postprandial glucose and insulin homeostasis, and it is a possible adjunctive treatment for glycemic management of chronic metabolic disorders such as prediabetes and type 2 diabetes mellitus.

Investigating the involvement of ABA, ABA catabolites and cytokinins in the susceptibility of 'Nules Clementine' mandarin to rind breakdown disorder

BACKGROUND

'Nules Clementine' mandarin was used to investigate the potential involvement of endogenous plant hormones in mediating citrus fruit susceptibility to rind breakdown disorder (RBD). The effect of light exposure (namely canopy position and bagging treatments) on the endogenous concentration of ABA, 7'-hydroxy-abscisic acid (7-OH-ABA), ABA-glucose ester (ABA-GE) and dihydrophaseic acid (DPA), and t-zeatin was tested using four preharvest treatments: outside, outside bagged, inside and inside bagged. Phytohormones concentration was evaluated during nine weeks of postharvest storage at 8 °C.

RESULTS

The shaded fruit inside the canopy had the highest RBD score (0.88) at the end of postharvest storage, while sun-exposed fruit had the lowest score (0.12). Before storage, ABA concentration was lowest (462.8 µg kg^-1 ) for inside fruit, and highest in outside bagged fruit (680.5 µg kg^-1 ). Although ABA concentration suddenly increased from the third week, reaching a maximum concentration of 580 µg kg^-1 at week 6 in fruit from inside position, it generally reduced 1.6-fold ranging from 240.52 to 480.65 µg kg^-1 throughout storage. The increase of 7-OH-ABA was more prominent in fruit from inside canopy. Overall, the concentration of ABA-GE increased three-fold with storage time. DPA concentration of bagged fruit from inside canopy position was significantly higher compared to outside fruit. The lower ABA-GE and higher DPA concentration in inside bagged fruit throughout storage also coincided with higher RBD.

CONCLUSION

The strong positive correlations between 7-OH-ABA, DPA and RBD incidence demonstrated that these ABA catabolites could be used as biomarkers for fruit susceptibility to the disorder. © 2019 Society of Chemical Industry.

Abscisic acid enhances lead translocation from the roots to the leaves and alleviates its toxicity in Populus × canescens

To shed light on physiological mechanisms underlying abscisic-acid (ABA)-mediated lead (Pb) uptake, translocation and detoxification, we exposed Populus × canescens saplings to either 0 or 3 mM Pb²⁺ in combination with either 0 or 10 μM exogenous ABA. Pb was taken up by the roots and accumulated mainly in the cortex. A fraction of the Pb in the roots was translocated to the leaves, thereby resulting in decreased photosynthesis and biomass. Pb accumulation caused a burst of reactive oxygen species (ROS), with higher concentrations of total thiols, glutathione, and ascorbate in the roots and/or leaves. Exogenous ABA stimulated Pb uptake, decreased Pb deposition in the cortex, and enhanced Pb vascular loading in the roots. Exogenous ABA alleviated the Pb-induced reductions in photosynthesis and root biomass, and decreased Pb-triggered ROS overproduction in the roots and/or leaves. Correspondingly, exogenous ABA stimulated the mRNA levels of a few genes involved in Pb uptake, transport, and detoxification, including NRAMP1.4, ABCG40, FRD3.1, PCS1.1, and ABCC1.1. These results suggest that exogenous ABA enhances Pb uptake and translocation, and alleviates Pb toxicity in poplars through the ABA-induced movement of Pb from the root cortex to the vascular stele, and transcriptionally regulated key genes involved in Pb tolerance.

Molecular Mechanism for the Regulation of ABA Homeostasis During Plant Development and Stress Responses

The plant hormone abscisic acid (ABA) play essential roles in numerous physiological processes such as seed dormancy, seed germination, seeding growth and responses to biotic and abiotic stresses. Such biological processes are tightly controlled by a complicated regulatory network including ABA homoeostasis, signal transduction as well as cross-talking among other signaling pathways. It is known that ABA homoeostasis modulated by its production, inactivation, and transport pathways is considered to be of great importance for plant development and stress responses. Most of the enzymes and transporters involved in ABA homoeostasis have been largely characterized and they all work synergistically to maintain ABA level in plants. Increasing evidence have suggested that transcriptional regulation of the genes involved in either ABA production or ABA inactivation plays vital roles in ABA homoeostasis. In addition to transcription factors, such progress is also regulated by microRNAs and newly characterized root to shoot mobile peptide-receptor like kinase (RLKs) mediated long-distance signal transduction. Thus, ABA contents are always kept in a dynamic balance. In this review, we survey recent research on ABA production, inactivation and transport pathways, and summarize some latest findings about the mechanisms that regulate ABA homoeostasis.

Derivatization for detection of abscisic acid and 12-oxo-phytodienoic acid using matrix-assisted laser desorption/ionization imaging mass spectrometry

RATIONALE

Abscisic acid (ABA) and 12-oxo-phytodienoic acid (OPDA) play crucial roles in seed development. However, because of their low ionization efficiencies, visualization by matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) has been difficult. In this study, we used on-tissue chemical derivatization (OTCD) with the derivatization reagent Girard's T (GirT) in MALDI-IMS to visualize ABA and OPDA.

METHODS

Immature Phaseolus vulgaris L. seeds were homogenized, and frozen homogenate sections were prepared using a cryostat. The concentration of the trifluoroacetic acid (TFA) and spray volume of the GirT solution were optimized using the homogenate sections. Immature seed sections were prepared using a cryostat, and the OTCD efficiency under optimal conditions was measured using liquid chromatography/tandem mass spectrometry (LC/MS/MS). The GirT solution was sprayed on the seed sections, and then MALDI-IMS was performed.

RESULTS

The optimal TFA concentration and spray volume were 2% and 500 μL, respectively. The OTCD efficiency rates were 61 ± 10% for ABA and 45 ± 5% for OPDA. The peaks corresponding to GirT-derivatized ABA (ABA-GirT) and OPDA (OPDA-GirT) standards were detected on the optimal OTCD-treated seed sections. ABA-GirT was mainly distributed in the embryo, while OPDA-GirT was localized in the external structures. These results are in agreement with our previously published results.

CONCLUSIONS

Our results show that ABA and OPDA in the immature seeds were exactly visualized using OTCD with GirT in MALDI-IMS. Therefore, OTCD with GirT in MALDI-IMS is a promising technique for future research on the biological roles of ABA and OPDA in various immature seeds.

Lignosulfonate Improves Photostability and Bioactivity of Abscisic Acid under Ultraviolet Radiation

Abscisic acid (ABA), as a commonly used plant growth regulator, is easy to be degraded and lose its bioactivity under sunshine. To select an eco-friendly and efficient photoprotectant for the improvement of photostability and bioactivity of ABA when exposed to ultraviolet (UV) light, we tested the effects of three biodegradable natural-derived high polymers, sodium lignosulfonates 3A [molecular weight (MW) > 50000, with degree of sulfonation (DS) of 0.48] and NA (20000 < MW < 50000, with DS of 0.7) and calcium lignosulfonate CASA (MW < 20000, with DS of 0.7), on the photodegradation of ABA. Lignosulfonates 3A, NA, and CASA showed significant photostabilizing capability on ABA. Lignosulfonate 3A showed preferable photostabilizing effects on ABA compared to CASA, while NA showed an intermediate effect. That indicated that lignosulfonate with a high MW and low DS had a stronger UV absorption and the hollow aggregate micelles formatted by lignosulfonate protect ABA from UV damage. Approximately 50% more ABA was kept when 280 mg/L ABA aqueous solution was irradiated by UV light for 2 h in the presence of 2000 mg/L lignosulfonate 3A. The bioactivity on wheat (JIMAI 22) seed germination was greatly kept by 3A in comparison to that of ABA alone. The 300 times diluent of 280 mg/L ABA plus 2000 mg/L 3A after 2 h of irradiation showed 20.8, 19.3, and 9.3% more inhibition on shoot growth, root growth, and root numbers of wheat seed, separately, in comparison to ABA diluent alone. We conclude that lignosulfonate 3A was an eco-friendly and efficient agent to keep ABA activity under UV radiation. This research could be used in UV-sensitive and water-soluble agrichemicals and to optimize the application times and dosages of ABA products.

Abscisic acid-type sesquiterpenes and ansamycins from Amycolatopsis alba DSM 44262

Two new abscisic acid-type sesquiterpenes (1, 2), and one new ansamycin (3), together with four known ansamycins, namely ansacarbamitocins 4-7, were isolated from the fermentation extract of Amycolatopsis alba DSM 44262. The structures of the new compounds were elucidated to be (E)-3-methyl-5-(2,6,6-trimethyl-3-oxocyclohex-1-enyl)pent-2-enoic acid (1) and (E)-3-methyl-5-(2,6,6-trimethyl-4-oxocyclohex-2-enyl)pent-2-enoic acid (2), and 9-O-methylansacarbamitocin A1 (3), on the basis of comprehensive analysis of spectroscopic data, respectively. The antimicrobial activities were also evaluated for all seven compounds.

Transcriptome analysis of the tea oil camellia (Camellia oleifera) reveals candidate drought stress genes

BACKGROUND

The tea-oil camellia (Camellia oleifera) is the most important oil plant in southern China, and has a strong resistance to drought and barren soil. Understanding the molecular mechanisms of drought tolerance would greatly promote its cultivation and molecular breeding.

RESULTS

In total, we obtained 76,585 unigenes with an average length of 810 bp and an N50 of 1,092 bp. We mapped all the unigenes to the NCBI 'nr' (non-redundant), SwissProt, KEGG, and clusters of orthologous groups (COG) databases, where 52,531 (68.6%) unigenes were functionally annotated. According to the annotation, 46,171 (60.8%) unigenes belong to 338 KEGG pathways. We identified a series of unigenes that are related to the synthesis and regulation of abscisic acid (ABA), the activity of protective enzymes, vitamin B6 metabolism, the metabolism of osmolytes, and pathways related to the biosynthesis of secondary metabolites. After exposed to drought for 12 hours, the number of differentially-expressed genes (DEGs) between treated plants and control plants increased in the G4 cultivar, while there was no significant increase in the drought-tolerant C3 cultivar. DEGs associated with drought stress responsive pathways were identified by KEGG pathway enrichment analysis. Moreover, we found 789 DEGs related to transcription factors. Finally, according to the results of qRT-PCR, the expression levels of the 20 unigenes tested were consistent with the results of next-generation sequencing.

CONCLUSIONS

In the present study, we identified a large set of cDNA unigenes from C. oleifera annotated using public databases. Further studies of DEGs involved in metabolic pathways related to drought stress and transcription will facilitate the discovery of novel genes involved in resistance to drought stress in this commercially important plant.

Potential link between fruit yield, quality parameters and phytohormonal changes in preharvest UV-C treated strawberry

Preharvest ultraviolet-C (UV-C) treatment of strawberry is a very new approach, and little information is available on the effect of this treatment on plant growth regulators. In this study, the effect of preharvest UV-C irradiations at three different doses on strawberry yield, fruit quality parameters and endogenous phytohormones was investigated simultaneously. The overall marketable yield of strawberry was not affected by the preharvest UV-C treatments, although more aborted and misshapen fruits were found in UV-C treated groups than in the untreated control. The fruits in the high dose group were firmer and had approximately 20% higher sucrose content and 15% higher ascorbic acid content than the control, while fruits from the middle and low dose groups showed no significant changes in these parameters. The lower abscisic acid (ABA) content found in the fruits in the high UV-C group may be associated with those quality changes. The citric acid content decreased only in the low dose group (reduction of 5.8%), with a concomitant 37% reduction in jasmonic acid (JA) content, compared to the control. The antioxidant status of fruits that received preharvest UV-C treatment was considered enhanced based on their oxygen radical absorbance capacity (ORAC) and malondialdehyde (MDA) content. In terms of aroma, three volatile alcohols differed significantly among the various treatments with obvious activation of alcohol acyltransferase (AAT) activity. The observed synchronous influence on physiological indexes and related phytohormones suggests that preharvest UV-C might affect fruit quality via the action of plant hormones.

Natural Predominance of Abscisic Acid in Pongammia pinnata ("Karanj") Honey Contributed to its Strong Antimutagenicity

Various samples of raw (unprocessed) floral honey collected from different geographical locations of India were assayed for its antimutagenicity against ethyl methanesulfonate in E. coli MG1655 cells through rifampicin resistance assay. A monofloral honey ("Pongammia pinnata", local name "Karanj") displayed maximum antimutagenicity (78.0 ± 1.7; P ≤ 0.05). Solid phase extraction (using Amberlite XAD-2 resin) followed by HPLC resulted into different peaks displaying varying antimutagenicity. Peak at retention time (R_t) 27.9 min (henceforth called P₂₈) displayed maximum antimutagenicity and was further characterized to be abscisic acid (ABA) using ESI-MS and NMR. Its antimutagenicity was reconfirmed through human lymphoblast cell line (TK6) mutation assay using thymidine kinase (tk^+/-) cell line. Although ABA from this honey displayed strong antimutagenicity, it lacked any in vitro antioxidant capacity indicating noninvolvement of any radical scavenging in the observed antimutagenicity.

Design and Functional Characterization of a Novel Abscisic Acid Analog

The phytohormone abscisic acid (ABA) plays a crucial role in mediating plant growth and development by recruiting genetically redundant ABA receptors. To overcome its oxidation inactivation, we developed a novel ABA analog named 2',3'-benzo-iso-ABA (iso-PhABA) and studied its function and structural characterization with A. thaliana ABA receptors. The (+)-iso-PhABA form showed much higher ABA-like activities than (+)-ABA including inhibitory effects on the seed germination of lettuce and A. thaliana, wheat embryo germination and rice seedling elongation. The PP2C (protein phosphatases 2C) activity assay showed that (+)-iso-PhABA acted as a potent and selective ABA receptor agonist, which is preferred to PYL10. In some cases, (-)-iso-PhABA showed moderate to high activity for the PYL protein inhibiting PP2C activity, suggesting different mechanisms of action of iso-PhABA and ABA. The complex crystal structure of iso-PhABA with PYL10 was determined and elucidated successfully, revealing that (+)-iso-PhABA was better coordinated in the same binding pocket compared to (+)-ABA. Moreover, the detailed interaction network of iso-PhABA/PYL10 was disclosed and involves hydrogen bonds and multiple hydrophobic interactions that provide a robust framework for the design of novel ABA receptor agonists/antagonists.

ABA and GA3 regulate the synthesis of primary and secondary metabolites related to alleviation from biotic and abiotic stresses in grapevine

Plants are able to synthesize a large number of organic compounds. Among them, primary metabolites are known to participate in plant growth and development, whereas secondary metabolites are mostly involved in defense and other facultative processes. In grapevine, one of the major fruit crops in the world, secondary metabolites, mainly polyphenols, are of great interest for the wine industry. Even though there is an extensive literature on the content and profile of those compounds in berries, scarce or no information is available regarding polyphenols in other organs. In addition, little is known about the effect of plant growth regulators (PGRs), ABA and GA₃ (extensively used in table grapes) on the synthesis of primary and secondary metabolites in wine grapes. In table grapes, cultural practices include the use of GA₃ sprays shortly before veraison, to increase berry and bunch size, and sugar content in fruits. Meanwhile, ABA applications to the berries on pre-veraison improve the skin coloring and sugar accumulation, anticipating the onset of veraison. Accordingly, the aim of this study was to assess and characterize primary and secondary metabolites in leaves, berries and roots of grapevine plants cv. Malbec at veraison, and changes in compositions after ABA and GA₃ aerial sprayings. Metabolic profiling was conducted using GC-MS, GC-FID and HPLC-MWD. A large set of metabolites was identified: sugars, alditols, organic acids, amino acids, polyphenols (flavonoids and non-flavonoids) and terpenes (mono-, sesqui-, di- and triterpenes). The obtained results showed that ABA applications elicited synthesis of mono- and sesquiterpenes in all assessed tissues, as well as L-proline, acidic amino acids and anthocyanins in leaves. Additionally, applications with GA₃ elicited synthesis of L-proline in berries, and mono- and sesquiterpenes in all the tissues. However, treatment with GA₃ seemed to block polyphenol synthesis, mainly in berries. In conclusion, ABA and GA₃ applications to grapevine plants cv. Malbec influenced the synthesis of primary and secondary metabolites known to be essential for coping with biotic and abiotic stresses.

Assessing the Effect of Organoclays and Biochar on the Fate of Abscisic Acid in Soil

The potential use of allelopathic and signaling compounds as environmentally friendly agrochemicals is a subject of increasing interest, but the fate of these compounds once they reach the soil environment is poorly understood. This work studied how the sorption, persistence, and leaching of the two enantiomers of the phytohormone abscisic acid (ABA) in agricultural soil was affected by the amendments of two organoclays (SA-HDTMA and Cloi10) and a biochar derived from apple wood (BC). In conventional 24-h batch sorption experiments, higher affinity toward ABA enantiomers was displayed by SA-HDTMA followed by Cloi10 and then BC. Desorption could be ascertained only in BC, where ABA enantiomers presented difficulties to be desorbed. Dissipation of ABA in the soil was enantioselective with S-ABA being degraded more quickly than R-ABA, and followed the order unamended > Cloi10-amended > BC-amended > SA-HDTMA-amended soil for both enantiomers. Sorption determined during the incubation experiment indicated some loss of sorption capacity with time in organoclay-amended soil and increasing sorption in BC-amended soil, suggesting surface sorption mechanisms for organoclays and slow (potentially pore filling) kinetics in BC-amended soil. The leaching of ABA enantiomers was delayed after amendment of soil to an extent that depended on the amendment sorption capacity, and it was almost completely suppressed by addition of BC due to its irreversible sorption. Organoclays and BC affected differently the final behavior and enantioselectivity of ABA in soil as a consequence of dissimilar sorption capacities and alterations in sorption with time, which will affect the plant and microbial availability of endogenous and exogenous ABA in the rhizosphere.

Characterization of Triticum aestivum Abscisic Acid Receptors and a Possible Role for These in Mediating Fusairum Head Blight Susceptibility in Wheat

Abscisic acid (ABA) is a well-characterized plant hormone, known to mediate developmental aspects as well as both abiotic and biotic stress responses. Notably, the exogenous application of ABA has recently been shown to increase susceptibility to the fungal pathogen Fusarium graminearum, the causative agent of Fusarium head blight (FHB) in wheat and other cereals. However roles and mechanisms associated with ABA's modulation of pathogen responses remain enigmatic. Here the identification of putative ABA receptors from available genomic databases for Triticum aestivum (bread wheat) and Brachypodium distachyon (a model cereal) are reported. A number of these were cloned for recombinant expression and their functionality as ABA receptors confirmed by in vitro assays against protein phosphatases Type 2Cs. Ligand selectivity profiling of one of the wheat receptors (Ta_PYL2DS_FL) highlighted unique activities compared to Arabidopsis AtPYL5. Mutagenic analysis showed Ta_PYL2DS_FL amino acid D180 as being a critical contributor to this selectivity. Subsequently, a virus induced gene silencing (VIGS) approach was used to knockdown wheat Ta_PYL4AS_A (and similar) in planta, yielding plants with increased early stage resistance to FHB progression and decreased mycotoxin accumulation. Together these results confirm the existence of a family of ABA receptors in wheat and Brachypodium and present insight into factors modulating receptor function at the molecular level. That knockdown of Ta_PYL4AS_A (and similar) leads to early stage FHB resistance highlights novel targets for investigation in the future development of disease resistant crops.

Postharvest Application of Oligochitosan and Chitosan Reduces Calyx Alterations of Citrus Fruit Induced by Ethephon Degreening Treatment

In the present study, we investigated whether the postharvest application of oligochitosan and chitosan could be used as potential alternatives to 2,4-dichlorophenoxyacetic acid (2,4-D) treatment to prevent calyx senescence of mandarin fruits induced by degreening treatment. The results of scanning electron microscopy indicated that the ethephon degreening treatment could accelerate the formation of pedicel abscission layers. Treatments with 15 g kg^-1 oligochitosan, 5 g kg^-1 chitosan, and 50 mg kg^-1 2,4-D significantly suppressed the formation of pedicel abscission layers of ethephon degreening fruit and inhibited the browning of the calyx. These two treatments delayed the degradation of protopectin, cellulose, and lignin. Inhibition of the increase in the abscisic acid (ABA) content was also observed in these two treatments. In conclusion, these two treatments, particularly 15 g kg^-1 oligochitosan, could be potentially used as alternatives to 2,4-D to improve calyx alterations induced by the ethephon degreening treatment in mandarin fruits.

Ionone Derivatives from the Mycelium of Phellinus linteus and the Inhibitory Effect on Activated Rat Hepatic Stellate Cells

Three new γ-ionylideneacetic acid derivatives, phellinulins A-C (1-3), were characterized from the mycelium extract of Phellinus linteus. The chemical structures were established based on the spectroscopic analysis. In addition, phellinulin A (1) was subjected to the examination of effects on activated rat hepatic stellate cells and exhibited significant inhibition of hepatic fibrosis.

Abscisic Acid Induces Rapid Reductions in Mesophyll Conductance to Carbon Dioxide

The rate of photosynthesis (A) of plants exposed to water deficit is a function of stomatal (gs) and mesophyll (gm) conductance determining the availability of CO2 at the site of carboxylation within the chloroplast. Mesophyll conductance often represents the greatest impediment to photosynthetic uptake of CO2, and a crucial determinant of the photosynthetic effects of drought. Abscisic acid (ABA) plays a fundamental role in signalling and co-ordination of plant responses to drought; however, the effect of ABA on gm is not well-defined. Rose, cherry, olive and poplar were exposed to exogenous ABA and their leaf gas exchange parameters recorded over a four hour period. Application with ABA induced reductions in values of A, gs and gm in all four species. Reduced gm occurred within one hour of ABA treatment in three of the four analysed species; indicating that the effect of ABA on gm occurs on a shorter timescale than previously considered. These declines in gm values associated with ABA were not the result of physical changes in leaf properties due to altered turgor affecting movement of CO2, or caused by a reduction in the sub-stomatal concentration of CO2 (Ci). Increased [ABA] likely induces biochemical changes in the properties of the interface between the sub-stomatal air-space and mesophyll layer through the actions of cooporins to regulate the transport of CO2. The results of this study provide further evidence that gm is highly responsive to fluctuations in the external environment, and stress signals such as ABA induce co-ordinated modifications of both gs and gm in the regulation of photosynthesis.

[Effects of sodium naphthalene acetate on growth and physiological characteristics of tomato seedlings under suboptimal temperature and light condition]

Taking tomato 'Zhongza 105' as test material, the influences of sodium naphthalene acetate (SNA) on growth and physiological characteristics of tomato seedlings under suboptimal temperature and light condition were investigated. The results showed that the dry mass, vigorous seedling index, root activity, total nitrogen content, net photosynthesis rate (Pn) of tomato seedlings were significantly decreased by suboptimum temperature and light treatment. In addition, the catalase activity and zeatin riboside (ZR) concentration were also reduced. However, the superoxide dismutase, peroxidase activity and the content of abscisic acid (ABA) were increased. Compared with treatment of the same volume distilled water on tomato seedlings under suboptimum temperature and light condition, the dry mass of whole plant and vigorous seedling index of tomato seedlings were significantly increased by 16.4% and 22.9%, as the total N contents in roots and leaves and Pn were also increased by 8.5%, 28.5%and 37.0%, respectively, with the treatment of root application of 10 mg . L-1 SNA. Besides protective enzyme activity and the root activity were improved, the indole acetic acid (IAA) and ZR concentration of tomato were raised, and ABA concentration was reduced. The results indicated that root application of certain concentration of SNA could promote the growth of tomato seedlings by increasing the tomato root activity, protective enzymes activity, Pn and regulating endogenous hormone concentration under suboptimum temperature and light condition.

[Changes of endogenous hormone contents and antioxidative enzyme activities in wheat leaves under low temperature stress at jointing stage]

Low temperature stresses (-3 and -5 °C) were simulated using artificial temperature-controlled phytotrons to study the freezing rate, the contents of endogenous hormones, and the activities of antioxidative enzymes in the leaves of wheat plants of Yangmai 16 (YM 16) and Xumai 30 (XM 30) at jointing stage. The grade and index of freezing injury increased with lower temperature and longer stress. The freezing rate was at the 5th level and the main stems and tillers of both cultivars were finally dead under -5 °C lasting for 72 h. On the last day of stress initiation, the contents of abscisic acid (ABA) and zeatin riboside (ZR), and the activities of superoxide dismutase (SOD), peroxide dismutase (POD), and catalase (CAT) in leaves increased at the beginning and then declined as low temperature progressed. On the 3rd day after stress, the contents of ABA and ZR and the activities of antioxidative enzymes were higher than those on the last day of cold stress, and then reduced to the level of the control on the 6th day after stress. The content of gibberellins (GA3) was lowered by cold stress. For YM 16, GA3 content increased from the 3rd day to the 6th day after cold stress, whereas, for XM 30, it increased first and then decreased. For the treatment of -5 °C lasting for 72 h, the contents of hormones and the activities of antioxidative enzymes were significantly lower than those of the other treatments. Correlation analyses showed that higher ABA and ZR contents, and higher SOD, POD and CAT activities as well as lower GA3 content could alleviate the low-temperature injury in wheat plants under low temperature stress.

Constructing de novo H2O2 signaling via induced protein proximity

A new chemical strategy has been developed to generate de novo signaling pathways that link a signaling molecule, H2O2, to different downstream cellular events in mammalian cells. This approach combines the reactivity-based H2O2 sensing with the chemically induced protein proximity technology. By chemically modifying abscisic acid with an H2O2-sensitive boronate ester probe, novel H2O2 signaling pathways can be engineered to induce transcription, protein translocation and membrane ruffle formation upon exogenous or endogenous H2O2 stimulation. This strategy has also been successfully applied to gibberellic acid, which provides the potential to build signaling networks based on orthogonal cell stimuli.

Acclimation mechanisms elicited by sprayed abscisic acid, solar UV-B and water deficit in leaf tissues of field-grown grapevines

The independent and interactive effects of solar ultraviolet-B radiation (UV-B), moderate water deficit and sprayed abscisic acid (ABA) on leaves gas exchange and biochemical aspects of field-grown grapevines of the cv. Malbec were investigated in a high altitude vineyard (1450 m a.s.l.). Two UV-B treatments (ambient solar UV-B or reduced UV-B), two watering treatments (well watered or moderate water deficit) and two ABA treatments (no ABA and sprayed ABA) were given alone and combined in a factorial design. Gas exchange and photosynthesis were reduced by water deficit and highly impaired in the UV-B and water deficit combined treatment. UV-absorbing compounds were stimulated independently by UV-B. The monoterpenes α-pinene, 3-carene and terpinolene, and the sesquiterpene nerolidol were augmented by UV-B, water deficit or sprayed ABA. Levels of the triterpene squalene and the diterpene phytol were significantly higher in the treatment that combined UV-B, water deficit and ABA applications. Environment signals (solar UV-B and moderate water deficit) and sprayed ABA elicited mechanisms of acclimation by augmenting the content of terpenes with antioxidant and antifungal properties, thus enhancing the plant defensive mechanisms towards signals both biotic and abiotic.

Abscisic acid analogs as chemical probes for dissection of abscisic acid responses in Arabidopsis thaliana

Abscisic acid (ABA) is a phytohormone known to mediate numerous plant developmental processes and responses to environmental stress. In Arabidopsis thaliana, ABA acts, through a genetically redundant family of ABA receptors entitled Regulatory Component of ABA Receptor (RCAR)/Pyrabactin Resistant 1 (PYR1)/Pyrabactin Resistant-Like (PYL) receptors comprised of thirteen homologues acting in concert with a seven-member set of phosphatases. The individual contributions of A. thaliana RCARs and their binding partners with respect to specific physiological functions are as yet poorly understood. Towards developing efficacious plant growth regulators selective for specific ABA functions and tools for elucidating ABA perception, a panel of ABA analogs altered specifically on positions around the ABA ring was assembled. These analogs have been used to probe thirteen RCARs and four type 2C protein phosphatases (PP2Cs) and were also screened against representative physiological assays in the model plant Arabidopsis. The 1'-O methyl ether of (S)-ABA was identified as selective in that, at physiologically relevant levels, it regulates stomatal aperture and improves drought tolerance, but does not inhibit germination or root growth. Analogs with the 7'- and 8'-methyl groups of the ABA ring replaced with bulkier groups generally retained the activity and stereoselectivity of (S)- and (R)-ABA, while alteration of the 9'-methyl group afforded an analog that substituted for ABA in inhibiting germination but neither root growth nor stomatal closure. Further in vitro testing indicated differences in binding of analogs to individual RCARs, as well as differences in the enzyme activity resulting from specific PP2Cs bound to RCAR-analog complexes. Ultimately, these findings highlight the potential of a broader chemical genetics approach for dissection of the complex network mediating ABA-perception, signaling and functionality within a given species and modifications in the future design of ABA agonists.

Nitric Oxide Plays a Central Role in Water Stress-Induced Tanshinone Production in Salvia miltiorrhiza Hairy Roots

Nitric oxide (NO), a well-known signaling molecule plays an important role in abiotic and biotic stress-induced production of plant secondary metabolites. In this study, roles of NO in water stress-induced tanshinone production in Salvia miltiorrhiza hairy roots were investigated. The results showed that accumulations of four tanshinone compounds in S. miltiorrhiza hairy roots were significantly stimulated by sodium nitroprusside (SNP, a NO donor) at 100 μM. Effects of SNP were just partially arrested by the mevalonate (MVA) pathway inhibitor (mevinolin), but were completely inhibited by the 2-C-methyl-d-erythritol-4-phosphate pathway (MEP) inhibitor (fosmidomycin). The increase of tanshinone accumulation and the up-regulation of HMGR and DXR expression by PEG and ABA treatments were partially inhibited by an inhibitor of NO biosynthesis (Nω-nitro-L-arginine methyl ester (L-NAME)) and a NO scavenger (2-(4-Carboxyphenyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO)). Simultaneously, NO generation in the hairy roots was triggered by PEG and ABA, and the effects were also arrested by c-PTIO and L-NAME. These results indicated that NO signaling probably plays a central role in water stress-induced tanshinone production in S. miltiorrhiza hairy roots. SNP mainly stimulated the MEP pathway to increase tanshinone accumulation.

Light control of cellular processes by using photocaged abscisic acid

Abscisic acid (ABA) was chemically modified with a photocaging group to promote photo-induced protein dimerization. This photocontrolled chemically induced dimerization (CID) method based on caged ABA enables dose-dependent light regulation of cellular processes, including transcription, protein translocation, signal transduction, and cytoskeletal remodeling, without the need to perform extensive protein engineering. Caged ABA can be easily modified to respond to different wavelengths of light. Consequently, this strategy should be applicable to the design of light-regulated protein dimerization systems and potentially be used orthogonally with other light-controlled CID systems.

UHPLC-MS/MS based target profiling of stress-induced phytohormones

Stress-induced changes in phytohormone metabolite profiles have rapid effects on plant metabolic activity and growth. The jasmonates (JAs) are a group of fatty acid-derived stress response regulators with roles in numerous developmental processes. To elucidate their dual regulatory effects, which overlap with those of other important defence-signalling plant hormones such as salicylic acid (SA), abscisic acid (ABA) and indole-3-acetic acid (IAA), we have developed a highly efficient single-step clean-up procedure for their enrichment from complex plant matrices that enables their sensitive quantitative analysis using hyphenated mass spectrometry technique. The rapid extraction of minute quantities of plant material (less than 20mg fresh weight, FW) into cold 10% methanol followed by one-step reversed-phase polymer-based solid phase extraction significantly reduced matrix effects and increased the recovery of labile JA analytes. This extraction and purification protocol was paired with a highly sensitive and validated ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method and used to simultaneously profile sixteen stress-induced phytohormones in minute plant material samples, including endogenous JA, several of its biosynthetic precursors and derivatives, as well as SA, ABA and IAA.

[Effects of exogenous AsA and GSH on the growth of Dianthus chinensis seedlings exposed to Cd]

A pot experiment was carried out under greenhouse condition to investigate the effects of different concentrations (0, 20, 40, 60, 80 and 100 mg x L(-1)) of exogenous AsA, GSH on Dianthus chinensis seedlings which were stressed by 50 mg x kg(-1) Cd in the soil. The results indicated that 50 mg x kg(-1) of Cd significantly inhibited the growth of D. chinensis seedlings. An appropriate concentration of exogenous AsA significantly improved the biomass, plant height, tiller number, GAT and APX activities, and AsA and GSH contents. However, with the increase of exogenous AsA concentration, the ameliorating effect decreased and prooxidant effect occurred. Exogenous GSH could replenish the non-enzymatic antioxidants of D. chinensis seedlings, but the changes of antioxidant enzyme activities were relatively slight. The main mechanisms of GSH to alleviate Cd toxicity might be promoting root PCs synthesis, thereby reducing the Cd concentration in the seedlings. Both 35-45 mg x L(-1) exogenous AsA and 55-65 mg x L(-1) exogenous GSH could alleviate the Cd toxicity on D. chinensis seedlings, and the former was superior to the latter.

Synthesis, photostability and bioactivity of 2,3-cyclopropanated abscisic acid

The plant hormone abscisic acid (ABA) plays a central role in the regulation of plant development and adaptation to environmental stress. The isomerization of ABA to the biologically inactive 2E-isomer by light considerably limits its applications in agricultural fields. To overcome this shortcoming, an ABA analogue, cis-2,3-cyclopropanated ABA, was synthesized, and its photostability and biological activities were investigated. This compound showed high photostability under UV light exposure, which was 4-fold higher than that of (±)-ABA. cis-2,3-cyclopropanated ABA exhibited high ABA-like activity, including the ability to effectively inhibit seed germination, seedling growth and stomatal movements of Arabidopsis. In some cases, its bioactivity approaches that of (±)-ABA. trans-2,3-cyclopropanated abscisic acid was also prepared, an isomer that was more photostable but which showed weak ABA-like activity.

Vacuolar transport of abscisic acid glucosyl ester is mediated by ATP-binding cassette and proton-antiport mechanisms in Arabidopsis

Abscisic acid (ABA) is a key plant hormone involved in diverse physiological and developmental processes, including abiotic stress responses and the regulation of stomatal aperture and seed germination. Abscisic acid glucosyl ester (ABA-GE) is a hydrolyzable ABA conjugate that accumulates in the vacuole and presumably also in the endoplasmic reticulum. Deconjugation of ABA-GE by the endoplasmic reticulum and vacuolar β-glucosidases allows the rapid formation of free ABA in response to abiotic stress conditions such as dehydration and salt stress. ABA-GE further contributes to the maintenance of ABA homeostasis, as it is the major ABA catabolite exported from the cytosol. In this work, we identified that the import of ABA-GE into vacuoles isolated from Arabidopsis (Arabidopsis thaliana) mesophyll cells is mediated by two distinct membrane transport mechanisms: proton gradient-driven and ATP-binding cassette (ABC) transporters. Both systems have similar Km values of approximately 1 mm. According to our estimations, this low affinity appears nevertheless to be sufficient for the continuous vacuolar sequestration of ABA-GE produced in the cytosol. We further demonstrate that two tested multispecific vacuolar ABCC-type ABC transporters from Arabidopsis exhibit ABA-GE transport activity when expressed in yeast (Saccharomyces cerevisiae), which also supports the involvement of ABC transporters in ABA-GE uptake. Our findings suggest that the vacuolar ABA-GE uptake is not mediated by specific, but rather by several, possibly multispecific, transporters that are involved in the general vacuolar sequestration of conjugated metabolites.

Selection and characterization of single stranded DNA aptamers for the hormone abscisic Acid

The hormone abscisic acid (ABA) is a small molecule involved in pivotal physiological functions in higher plants. Recently, ABA has been also identified as an endogenous hormone in mammals, regulating different cell functions including inflammatory processes, stem cell expansion, insulin release, and glucose uptake. Aptamers are short, single-stranded (ss) oligonucleotidesable to recognize target molecules with high affinity. The small size of the ABA molecule represented a challenge for aptamer development and the aim of this study was to develop specific anti-ABA DNA aptamers. Biotinylated abscisic acid (bio-ABA) was immobilized on streptavidin-coated magnetic beads. DNA aptamers against bio-ABA were selected with 7 iterative rounds of the systematic evolution of ligands by exponential enrichment method (SELEX), each round comprising incubation of the ABA-binding beads with the ssDNA sequences, DNA elution, electrophoresis, and polymerase chain reaction (PCR) amplification. The PCR product was cloned and sequenced. The binding affinity of several clones was determined using bio-ABA immobilized on streptavidin-coated plates. Aptamer 2 and aptamer 9 showed the highest binding affinity, with dissociation constants values of 0.98 ± 0.14 μM and 0.80 ± 0.07 μM, respectively. Aptamers 2 and 9 were also able to bind free, unmodified ABA and to discriminate between different ABA enantiomers and isomers. Our findings indicate that ssDNA aptamers can selectively bind ABA and could be used for the development of ABA quantitation assays.

Structure and function of abscisic acid receptors

The phytohormone abscisic acid (ABA) plays a crucial role in adaptive responses to environmental stresses, such as drought and high salinity, as well as in plant development, such as seed maturation and dormancy. PYR/PYL/RCAR has been identified as a bona fide ABA receptor (ABAR) that constitutes the core regulatory component of ABA signaling networks in plants. Here, we review recent structural and functional studies of the ABAR that have elucidated its activation mechanism, early signaling components, and physiological responses. A crucial event in the receptor's activation was found to be an open-to-closed conformational change in the gate loop of the receptor protein. More recent progress has provided strategies for controlling the gate's closure using chemical agonists or protein engineering approaches.

Controlled assembly of gold nanoparticles through antibody recognition: study and utilizing the effect of particle size on interparticle distance

An assembly of gold nanoparticle through the recognition of unmodified antibody was developed. The use of peptide (Cys-Ala-Leu-Asn-Asn) as ligands to stabilize and functionalize gold nanoparticles provides technical and operational convenience. These peptide-capped particles in different sizes are recognized by antibody and assembly to form dimers and expanded hybrid material by controlling the conditions. The interparticle spacing of these assemblies was well studied with small-angle X-ray scattering measurements, and it was found that the interparticle spacing is inversely dependent on the particle size. This relationship of interparticle spacing and particle size is closely related to the structure of antibody linker. Therefore, analyzing the interparticle spacing of assemblies can reveal the equilibrium configuration of IgG. Based on the investigation, the Fab-Fab angle of IgG is obtained to be ≈102° and the Fab arms are ≈7.8 nm. These results provide new experimental data on the structure of flexible IgG.

Defective chloroplast development inhibits maintenance of normal levels of abscisic acid in a mutant of the Arabidopsis RH3 DEAD-box protein during early post-germination growth

The plastid has its own translation system, and its ribosomes are assembled through a complex process in which rRNA precursors are processed and ribosomal proteins are inserted into the rRNA backbone. DEAD-box proteins have been shown to play roles in multiple steps in ribosome biogenesis. To investigate the cellular and physiological roles of an Arabidopsis DEAD-box protein, RH3, we examined its expression and localization and the phenotypes of rh3-4, a T-DNA insertion mutant allele of RH3. The promoter activity of RH3 is strongest in the greening tissues of 3-day and 1-week-old seedlings but reduced afterwards. Cotyledons were pale and seedling growth was retarded in the mutant. The most obvious abnormality in the mutant chloroplasts was their lack of normal ribosomes. Electron tomography analysis indicated that ribosome density in the 3-day-old mutant chloroplasts is only 20% that of wild-type chloroplasts, and the ribosomes in the mutant are smaller. These chloroplast defects in rh3-4 were alleviated in 2-week-old cotyledons and true leaves. Interestingly, rh3-4 seedlings have lower amounts of abscisic acid prior to recovery of their chloroplasts, and were more sensitive to abiotic stresses. Transcriptomic analysis indicated that nuclear genes for chloroplast proteins are down-regulated, and proteins mediating chloroplast-localized steps of abscisic acid biosynthesis are expressed to a lower extent in 1-week-old rh3-4 seedlings. Taken together, these results suggest that conversion of eoplasts into chloroplasts in young seedlings is critical for the seedlings to start carbon fixation as well as for maintenance of abscisic acid levels for responding to environmental challenges.

Gibberellin-producing Promicromonospora sp. SE188 improves Solanum lycopersicum plant growth and influences endogenous plant hormones

Plant growth-promoting rhizobacteria (PGPR) producing gibberellins (GAs) can be beneficial to plant growth and development. In the present study, we isolated and screened a new strain of Promicromonospora sp., SE188, isolated from soil. Promicromonospora sp. SE188 secreted GAs into its growth medium and exhibited phosphate solubilization potential. The PGPR produced physiologically active (GA(1) and GA(4)) and inactive (GA(9), GA(12), GA(19), GA(20), GA(24), GA(34), and GA(53)) GAs in various quantities detected by GC/MS-SIM. Solanum lycopersicum (tomato) plants inoculated with Promicromonospora sp. SE188 showed a significantly higher shoot length and biomass as compared to controls where PGPR-free nutrient broth (NB) and distilled water (DW) were applied to plants. The presence of Promicromonospora sp. SE188 significantly up-regulated the non C-13 hydroxylation GA biosynthesis pathway (GA(12)→GA(24)→GA(9)→GA(4)→ GA(34)) in the tomato plants as compared to the NB and DW control plants. Abscisic acid, a plant stress hormone, was significantly down-regulated in the presence of Promicromonospora sp. SE188. Contrarily, salicylic acid was significantly higher in the tomato plant after Promicromonospora sp. SE188 inoculation as compared to the controls. Promicromonospora sp. SE188 showed promising stimulation of tomato plant growth. From the results it appears that Promicromonospora sp. SE188 has potential as a bio-fertilizer and should be more broadly tested in field trials for higher crop production in eco-friendly farming systems.

Chemical inhibition of potato ABA-8'-hydroxylase activity alters in vitro and in vivo ABA metabolism and endogenous ABA levels but does not affect potato microtuber dormancy duration

The effects of azole-type P450 inhibitors and two metabolism-resistant abscisic acid (ABA) analogues on in vitro ABA-8'-hydroxylase activity, in planta ABA metabolism, endogenous ABA content, and tuber meristem dormancy duration were examined in potato (Solanum tuberosum L. cv. Russet Burbank). When functionally expressed in yeast, three potato CYP707A genes were demonstrated to encode enzymatically active ABA-8'-hydroxylases with micromolar affinities for (+)-ABA. The in vitro activity of the three enzymes was inhibited by the P450 azole-type inhibitors ancymidol, paclobutrazol, diniconazole, and tetcyclasis, and by the 8'-acetylene- and 8'-methylene-ABA analogues, with diniconazole and tetcyclasis being the most potent inhibitors. The in planta metabolism of [(3)H](±)-ABA to phaseic acid and dihydrophaseic acid in tuber meristems was inhibited by diniconazole, tetcyclasis, and to a lesser extent by 8'-acetylene- and 8'-methylene-ABA. Continuous exposure of in vitro generated microtubers to diniconazole resulted in a 2-fold increase in endogenous ABA content and a decline in dihydrophaseic acid content after 9 weeks of development. Similar treatment with 8'-acetylene-ABA had no effects on the endogenous contents of ABA or phaseic acid but reduced the content of dihydrophaseic acid. Tuber meristem dormancy progression was determined ex vitro in control, diniconazole-, and 8'-acetylene-ABA-treated microtubers following harvest. Continuous exposure to diniconazole during microtuber development had no effects on subsequent sprouting at any time point. Continuous exposure to 8'-acetylene-ABA significantly increased the rate of microtuber sprouting. The results indicate that, although a decrease in ABA content is a hallmark of tuber dormancy progression, the decline in ABA levels is not a prerequisite for dormancy exit and the onset of tuber sprouting.

Electrolytic reduction of abscisic acid methyl ester and its free acid

Abscisic acid (ABA, 1), a plant hormone, has electrophilicity derived almost entirely from the side-chain, 3-methylpenta-2,4-dienoic acid. The electrochemical property of ABA was investigated by analysis of its cathodic reaction. ABA methyl ester (1-Me) was reduced at a peak potential of -1.6 V to give a unique and unstable bicyclic compound (5-Me) as a major product at pH 3 and 7. This finding showed that an electron was absorbed in the conjugated dienecarboxyl group, and that C-5 with a high electron density attacked C-2' through an intramolecular nucleophilic addition. At pH 10, in addition to 5-Me, a compound 4-Me was formed by isomerization of 5-Me under alkaline conditions. For a cathodic reaction of ABA at pH 3 and 7, compound 5 was a major product as well as in the case of ABA methyl ester. However, at pH 10, a dimer (6) with an epoxy group, 1'-deoxy-ABA (7) and other compounds were formed instead of compounds 4 and 5. Compounds 4 and 5 were biologically inactive, suggesting the importance of the electrophilic side-chain of ABA for biological activity.