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Global agricultural demand and the impact of fluctuating climatic conditions including global warming have catastrophically limited crop productivity and immensely outstretched the market value of agricultural products leading to acute inflation. The effect of desiccation or drought stress in plants is manifested at three levels viz. morphological, biochemical, and molecular and plants possess their own molecular and signaling arsenal to combat or ameliorate various stresses. For decades, stress-tolerant cultivars have been investigated and modulation of polyamine (PA) signaling was found to play a major role in attenuating environmental stresses including drought as major abiotic stress. PA metabolism pathways with their ability to crosstalk with both primary and secondary metabolic pathways have been correlated with several other responses such as seed germination, plant growth, development, defense, hormonal regulation, stress tolerance, and crop yield. Recent transcriptomic and metabolomic approaches have expanded the knowledge on the regulation of stress-induced biochemical, molecular, and physiological alterations. To fully comprehend the intricate biochemical network of plant stress physiology, it is necessary to identify exact responses against specific stress stimuli, interpret concurrent epigenetic alterations, and use molecular switching. The present review encompasses recent updates on drought tolerance mechanisms mediated by diverse polyamines playing significant roles in metabolic regulation, oxidative stress management, and systematic stress-reversal signaling. Besides, the drought stress-reversal role of polyamines and their cross-talks with other signaling molecules have also been documented. Gene, enzyme, and transcription factor (TF) functional features were retrieved from the published papers involving transgenic or mutant plants with over-expression or loss-of-function investigations. [ABSTRACT FROM AUTHOR]

Rice sulfite reductase (OsSiR) is important protein in reducing sulfite to sulfide. In this paper, it is aimed to shed light on OsSiR's probable structure, function, and expression using in silico methods and test its responses under drought and salt stresses. Moreover, it was also analyzed if OsSiR was structurally different from other SiR proteins. We estimated that OsSiR lacks ribbon–helix–helix DNA-binding motif allowing it to bind to DNA; therefore, it was probably localized in stroma as a non-nucleoid-type protein. Also, we found that OsSiR expression was regulated by JA in roots and by crosstalk of JA and ABA in shoots. RT-qPCR results showed that there was 20% increase in the expression of OsSiR at 3rd h of the salt treatment. However, OsSiR was downregulated when exposed to drought stress and salt stress for longer periods of time, respectively. OsSiR has a high post-translational potential because of its high phosphorylation sites. This may be originating from the most prevalent residue, Gly, facilitating its binding to phosphates in OsSiR. Our docking results showed that ligand binding residues of OsSiR (Arg159, Thr162, Gln167, and Pro501) were also active site residues of OsSiR. Both two domains of OsSiR interacted with sulfite and the number of the residues in 4Fe–4S domain (PF01077) was higher. The findings in this study are important in terms of structural and expressional studies of rice SiR (OsSiR) and can be used for SiR proteins in sorghum (Sorghum bicolor), maize (Zea mays), and foxtail millet (Setaria italica), which are closely related and highly similar to OsSiR in terms of sequence and predicted 3D structure. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deficiency is one of the critical environmental factors that induce leaf senescence, and its occurrence may cause the shorten leaf photosynthetic period and markedly lowered grain yield. However, the physiological metabolism underlying N deficiency-induced leaf senescence and its relationship with the abscisic acid (ABA) concentration and reactive oxygen species (ROS) burst in leaf tissues are not well understood. In this paper, the effect of N supply on several senescence-related physiological parameters and its relation to the temporal patterns of ABA concentration and ROS accumulation during leaf senescence were investigated using the premature senescence of flag leaf mutant rice (psf) and its wild type under three N treatments. The results showed that N deficiency hastened the initiation and progression of leaf senescence, and this occurrence was closely associated with the upregulated expression of 9-cis-epoxycarotenoiddioxygenase genes (NCEDs) and with the downregulated expression of two ABA 8′-hydroxylase isoform genes (ABA8ox2 and ABA8ox3) under LN treatment. Contrarily, HN supply delayed the initiation and progression of leaf senescence, concurrently with the suppressed ABA biosynthesis and relatively lower level of ABA concentration in leaf tissues. Exogenous ABA incubation enhanced ROS generation and MDA accumulation in a dose-dependent manner, but it decreased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in detached leaf. These results suggested that the participation of ABA in the regulation of ROS generation and N assimilating/remobilizing metabolism in rice leaves was strongly responsible for induction of leaf senescence by N deficiency. [ABSTRACT FROM AUTHOR]

Parallel to the discovery of auxin as a growth-promoting hormone in the first half of the last century, it became evident that inhibitors of auxin-induced cell elongation, seed germination and bud growth also existed in plants. Their activity was noticed first in more or less unspecific bioassays, and their natural function remained unknown for a long time. The introduction of paper chromatography in combination with bioassays enabled improved separation of plant extracts and identification of biologically active compounds. By means of these new techniques, a highly active growth inhibitory fraction named 'inhibitor β' was discovered in many plants. Evidence that this fraction seemed also to be involved in abscission processes resulted in the name 'abscisin II', whereas another research group that investigated the possible role of inhibitor β in bud dormancy proposed the name 'dormin'. Great efforts were made to identify the chemical nature of the two compounds. In 1965, it was recognized that abscisin II and dormin possessed the same chemical structure, which received the name 'abscisic acid' (ABA). Soon afterwards the extraordinary role of ABA as a hormone involved in stress reactions and in seed maturation was discovered, whereas its suggested function in abscission and bud dormancy processes has not been well established until now. The name ABA is therefore not adequate with regard to the hormonal functions, but it is acceptable with regard to priority rules. [ABSTRACT FROM AUTHOR]

To explore the fruit-cracking mechanism in nectarine, we compared three cracking-susceptible nectarine varieties ('Huaguang', 'Yanguang', and 'Zaohongzhu') and one cracking-resistant nectarine variety ('Shuguang'). Our findings indicate that 'Shuguang' nectarines exhibited significantly higher levels of calcium, calcium pectinate, total pectin, cellulose, Na2CO3-soluble pectin and CDTA-soluble pectin in the peel compared to 'Huaguang', 'Yanguang', and 'Zaohongzhu'. In contrast, the activities of polygalacturonases, pectinesterases, β-galactosidases, and cellulase were significantly lower in 'Shuguang'. Interestingly, no significant differences were observed in indole-3-acetic acid and gibberellic acid content between 'Shuguang' and the other three cracking-susceptible nectarine varieties. However, the abscisic acid content in 'Shuguang' was significantly lower. Additionally, compared with the three cracking-susceptible nectarine varieties, the expression level of PpPIP1 (encoding the plasma membrane intrinsic protein, which can improve the permeability of plant cell membranes and greatly improve the efficiency of water diffusion across membranes) in flesh was significantly lower, and the expression levels of PpExp1 and PpExp2 (encoding expansins, which play significant roles in loosening and expanding cell wall components) were significantly higher in the peels of cracking-resistant nectarine varieties. These differences can provide a basis for further study of the mechanism of nectarine fruit-cracking. [ABSTRACT FROM AUTHOR]

Plant yield is severely hampered by drought, affirming the urgent need to develop strategies to improve plant growth and drought tolerance. The synergistic application of ABA and calcium nanoparticles (Ca-NPs) has emerged as a promising approach for sustainable crop production and improved resistance to abiotic stress, although the underlying mechanism for foliar application of growth regulator ABA and Ca-NPs in regulating plant growth and drought tolerance in rapeseed (Brassica napus L.) remains poorly understood. To address this knowledge gap, the current study was conducted to investigate the protective role of 100-µM ABA and 100 ppm Ca-NPs in alleviating the drought stress (15% PEG-6000) in B. napus following further application with 100 µM solution of photosynthesis inhibitor 3-(3,4-dichlorophyllorophenyl)-1,1-dimethylurea (DCMU). Foliar application of 100 ppm Ca-NPs and 100-µM ABA significantly reduced the drought stress by increasing chl a, chl b, total chlorophyll, carotenoids, xanthophyll by 86, 63, 78, 56, 68%; nutritional profile Ca, K, P, Mg, Mn, B by 131, 108, 98, 111, 82, 67% of B. napus plants, respectively. Moreover, under drought condition the combined treatment of Ca-NPs + ABA along with the DCMU increased the Pn, Gs, Ci, Tr by 30, 24, 37, 22% and transcript abundance of transcription factors and ROS homeostasis genes (CDPK5, MYC2, TGA1, CAS, and POD), and photosynthetic proteins expressions (NCED3, PsbB, CP29, CP24, PCaA, CP26 and cytochrome f). Overall, this study provides the evidence of effectiveness of combined application of Ca-NPs and ABA in alleviating drought stress in rapeseed. [ABSTRACT FROM AUTHOR]

Acetylcholine (ACh), a potential plant growth regulator, can alleviate injury caused by NaCl and cadmium stress. However, the underlying mechanisms whereby it affects seed germination remain unclear. We pre-soaked maize (Zea mays L.) in different concentrations (1–3 μm) of ACh. Seed germination and levels of β-galactosidase, α-amylase, and starch were analyzed. ACh, abscisic acid (ABA), and gibberellic acid levels were estimated via enzyme-linked immunosorbent assay. The expression of ABA and gibberellic acid signaling-related genes was analyzed. Salt stress significantly reduced seed germination and hypocotyl elongation but increased ABA and H2O2 levels and enhanced antioxidant enzyme activity. Priming with 2 μm ACh caused a significantly higher germination rate (by 13.4%) relative to that of the seeds subjected to salt stress alone. Under salt stress, ACh effectively upregulated α-amylase and β-galactosidase activity (by 0.63- and 1.04-fold) and reduced starch content (by 34.02%). ACh treatment downregulated the expression of ZmNCED3 (involved in ABA signaling) and upregulated that of ZmKAO (involved in gibberellin signaling). The leaves of the seedlings pretreated with ACh presented higher antioxidant enzyme activity and, therefore, lower H2O2 accumulation than those of seedlings subjected to salt stress alone. Priming the maize seeds with exogenous ACh maintained seedling growth under salt stress. ACh pretreatment increased antioxidant activity, reduced ABA activity, and improved salt tolerance in maize seeds exposed to salt stress. These findings suggest that pretreatment with 2 μm ACh improves seed germination, activates ROS scavenging, and regulates phytohormone levels under salt stress, thereby improving growth. [ABSTRACT FROM AUTHOR]

This research aimed toward bioengineering of Zinc oxide nanoparticles (ZnO NPs) using Rosa canina L. aqueous extract followed by conjugation with Abscisic acid (ABA) for inducing drought-tolerant properties in Zea mays L under water stress. The impact of six different treatments using seed imbibition (SI) and foliar spray (FS) methods upon physio-morphological and biochemical properties of Z. mays L. was studied. These included ABA-SI, ABA-FS, ABA-ZnO-SI, ABA-ZnO-FS, ZnO-SI, and ZnO-FS, drought control (DC), and untreated healthy control (HC). Both ZnO and ABA-ZnO NPs showed distinct UV–Visible peaks at 438 nm and 339 nm with mean sizes of 20.17 nm and 14.05 nm, respectively. Scanning Electron Microscopy coupled with Energy-Dispersive X-ray identified 60.14% Zn in ZnO NPs with irregular surface topology and 56.72% Zn in ABA-ZnO NPs with semi-cylindrical morphology. Among treated maize plants, ABA-ZnO-SI displayed prominent results with increased root length (32.89 ± 1.25 cm), relative water content (20.4 ± 2.9%), total chlorophyll content [10.73 ± 0.18 mgg−1 Fresh weight (FW)], carotenoid content (190.4 ± 0.56 mg g−1 FW), cob length (27.94 ± 1.32 cm), cob weight (25.64 ± 0.42 g), and short anthesis-silking interval (3 days). Stomatal opening (0.95 ± 0.24%) and leaf damage index (29.86 ± 0.19%) were reduced in ABA-ZnO-SI treatment compared to DC. A significant amount of proline (4.40 ± 0.01 µmoles g−1 FW) with reduced lipid peroxidation (0.24 ± 0.02-mM malondialdehyde) and highest antioxidant activities (IC50: 332.8 ± 0.46 µg/ml) with maximum levels of catalase (2.87 ± 0.05 Uml−1), ascorbate peroxidase (3.41 ± 0.02 Uml−1), and guaiacol peroxidase (3.10 ± 0.06 Uml−1) were observed in ABA-ZnO-SI-treated plants. Given the promising outcomes, current research work has brought forward a potential drought tolerance treatment for Z. mays L. which might serve as productive agricultural progress in upcoming years. [ABSTRACT FROM AUTHOR]

Sorghum (Sorghum bicolor L. Moench) is one of the most significant cereals worldwide. Its growth and yield are threatened by different abiotic stresses, particularly drought and salinity. In this study, we performed a comprehensive meta-analysis on sorghum using RNA-seq data to discover differentially expressed genes effective in responses to drought and salinity stresses. The meta-analysis identified 2139 and 2238 genes for drought, and salinity stresses significantly differentially expressed in control and stress conditions, respectively. Also, the 1835 genes were common under drought and salinity stress conditions. Gene ontology and Kyoto encyclopedia of genes and genomes pathway enrichment analysis showed that differentially expressed genes are significantly enriched in photosynthesis and metabolic pathways, response to abiotic stimulus, phosphorus metabolic process, and biosynthesis of secondary metabolites. We found 96 transcription factor genes, all classified into 28 transcription factor families. Also, 217 protein kinase genes were recognized, with the plant receptor-like kinase (RLK-Pelle) family as the largest category. Besides, the promoter analysis identified 68 significant cis-acting elements in the hub gene's upstream regions. Known cis-acting elements participate in light-responsive, hormone-responsive, stress-related, tissue and development-related, and promoter and site-binding-related elements. Weighted gene co-expression network analysis identified 11 and 6 distinct co-expression modules for drought and salinity stresses, respectively, mainly associated with genes in response to temperature stimulus, photosynthesis, phosphorus metabolic process, and abscisic acid. The network analysis also identified hub genes, including SORBI_3001G410100, SORBI_3002G343500, SORBI_3001G426900, SORBI_3010G246000, and SORBI_3004G293500 involved in regulating the stress response. These findings provide novel insights into the abiotic stress molecular response and introduce numerous candidate genes, offering evidence for subsequent analysis of validation of their biological functions to unravel the molecular mechanisms of abiotic tolerance in sorghum. [ABSTRACT FROM AUTHOR]

Water stress is a primary abiotic stress that produces several morphological, physiological, biochemical and molecular alterations, which affect crop productivity. The aim of the present study was to evaluate and compare morphophysiological and biochemical characteristics and the hormone profiles of two sunflower inbred lines (C803 and R461-4) in response to moderate water stress at the early vegetative growth (V2) stage. Sunflower seedlings of C803 and R461-4 inbred lines obtained in pots filled with sand moistened to 60% field capacity were watered with (1) Hoagland's solution (control) or (2) mannitol 400 mM (moderate water stress) to field capacity on the fourth day after sowing. At V2, the seedlings were harvested and sectioned into the aerial part and roots. The parameters recorded for the analyses included the aerial part and root length, fresh and dry weight, leaf area and expansion rate, stomatal conductance, osmotic potential, phytohormones and total soluble carbohydrates. Among these parameters, the leaf area and stomatal conductance were the most affected by water stress. Abscisic acid and salicylic acid showed significant increases in the aerial part of water-stressed seedlings, while abscisic acid was the most abundant phytohormone in the roots. In addition, 28-Homocastasterone was the brassinosteroid with higher levels in both lines. This is the first report of teasterone in the sunflower. Finally, total soluble carbohydrates increased upon stressful conditions. Altogether, the water stress led to different parameter alterations dependent on the inbred line and its different sensitivity to water stress. [ABSTRACT FROM AUTHOR]

With the changing global climate, drought is considered one of the most devastating abiotic factors. Drought not only limits plant productivity by changing growth and development but also alters the microbiome in the rhizosphere. In addition to influencing the root microbes, drought modifies the root exudate's composition and profile in the rhizosphere. Plant health, root exudation, and abundance of soil microbes in the rhizosphere are inter-connected. The composition of root exudate is altered in terms of the abundance of primary metabolites such as sugar, amino acids, and organic acids and secondary metabolites like flavonoids, strigolactones, and terpenoids. Here, we discuss how a plethora of soil microbes may be involved in a feedback mechanism by utilizing root exudate constituents to promote drought tolerance in plants. Furthermore, plant drought tolerance is positively associated with strigolactones (SLs) exudation via coordination with ABA hormone signaling. Lastly, while the collection, sampling, and analysis of root exudates are all promising, we attempted to present advanced methodology and the development of novel processes in the review, which benefited greatly. [ABSTRACT FROM AUTHOR]

Salicylic acid (SA) has multiple functions in plants, either under optimal or environmental stress conditions. In salt-stressed plants, SA in coordination with other plant hormones (e.g., auxins, abscisic acid, gibberellins) and other signaling molecules can take part to the finely tuned regulatory network, to promote the stimulation of plant defenses aimed at counteracting the salt-triggered harmful effects. This review summarizes the most updated literature dealing with the roles of SA in salt-stressed plants with the aim to provide a comprehensive picture about physiological, biochemical and molecular mechanisms mediated by SA during salt stress, to highlight the possible beneficial effect of SA supplementation and to orientate the direction of future research on this topic. [ABSTRACT FROM AUTHOR]

Melatonin and polyamines have been broadly found in multiple physiological processes and in diverse abiotic stresses faced by plants. In various plant species, melatonin-induced regulation of polyamine metabolism has been reported to play a critical role in the manifestation of stress tolerance mechanisms. Exogenous melatonin pretreatment has been shown to elevate the levels of endogenous polyamines through enhanced expression of ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) ultimately resulting in tolerant phenotypes. The melatonin-polyamine modulation activates the antioxidant enzymatic machinery within the plant system that maintains the reactive species levels and alleviates the oxidative burst-associated damage responses. Alternatively, melatonin-mediated polyamine catabolism has been reported to be crucial in minimizing the excess reactive species accumulation under stress conditions. The melatonin-induced balance of polyamine metabolic flux maintains the ionic homeostasis in plant cells under stress conditions. Recent reports highlighted that melatonin-polyamine regulation involves crosstalk with salicylic acid, abscisic acid and ethylene that leads to a complex network of defense activation under stress conditions. This review attempts to highlight the regulatory role of melatonin in the modulation of polyamine metabolism and associated signaling components that confer stress tolerance in plants. The potential hormonal crosstalks involving melatonin-polyamine regulation have also been discussed to provide mechanistic insight into possible underlying mechanisms. This study will assist the current understanding of the uses of melatonin and polyamines as polyfunctional phytoprotectant in the crop production system. [ABSTRACT FROM AUTHOR]

Plant-derived smoke is a source of several butenolide compounds collectively termed, karrikins (KARs). These have been recognized as a recent class of plant growth regulators associated with diverse phenomena especially seed germination, seedling vigor and other photo-morphogenetic responses. Role of KARs in improving the performance of plants exposed to different environmental constraints has been recognized recently. KARs mitigate oxidative stress in plants caused by salinity, drought, shade and heavy metals by modulating antioxidative metabolism (SOD, POX, GR, APX) and up-regulating the expression of various stress related genes in plants. Such a modulation involves an interplay with different transcription factors and endogenous plant growth regulators predominantly auxins, gibberellins, ethylene and abscissic acid. The present article is an attempt to gain a comprehensive understanding regarding the KARs-induced plant responses. Moreover, role of KARs in plant abiotic stress tolerance, perception of KARs in plants, expression of different enzymes and genes involved in abiotic stress mitigation, their cross-talk with other endogenous hormones under normal and chellanging environmental circumstances. [ABSTRACT FROM AUTHOR]

Persimmon (Diospyros kaki Thunb.) contains numerous uridine diphosphate glucosyltransferases (UGT), and their roles in fruit development and quality formation have not been well studied because of limited genetic information. This study investigated a persimmon DkUGT3 which is highly expressed in young fruits and leaves during development. DkUGT3 can catalyze ABA glycosylation to form ABA-GE, thereby reducing free ABA. Tomato with overexpressed (OE) DkUGT3 significantly induces pale green color phenotypes in both transgenic young plants and fruits. DkUGT3-OE significantly weakens the tomato ABA signaling which affects the expressions of ABA-inducible transcriptional factors (TFs), such as GLK1 and GLK2 and their downstream target genes involved in chlorophyll synthesis, chloroplast development, sugar metabolism and transport, and photosynthesis, thereby impeding leaf and fruit development and quality. Conversely, DkUGT3-RNAi-treatment recovered the OE tomato fruits from yellowing phenotype to green color. This study found that chlorophyll accumulations and ABA level were increased by DkUGT3-RNAi-treatment in young persimmon leaves. These results demonstrate that DkUGT3 plays crucial roles in ABA-mediated leaf and fruit development. This study provides new evidence for the regulation of ABA in early development. [ABSTRACT FROM AUTHOR]

Thioredoxins (Trxs) are thiol-disulfide oxidoreductase proteins that play an important role in plant development and abiotic stress tolerance through redox regulation of target proteins. In plants, the individual biological functions of H-type thioredoxins (Trxhs) are still poorly known. This work is the first to identify the Trxh gene family of the trio of Brachypodium genus (B. distachyon, B. stacei, and B. hybridium) and to characterize their evolutionary patterns and expression profiles under abiotic stress. In total, 28 Trxh proteins were identified in the trio of Brachypodium species that can be divided into three groups. Interestingly, a new unusual Trxh protein (Trxh7) harboring two Cysteine (Cys) residues in its N-terminal region was discovered. Gene structure and protein-conserved motif analyses further consolidated the classification of the phylogenetic tree and highlighted the functional divergence of the Trxh family. Tandem and whole-genome duplications were found as major forces driving Trxh gene expansion in Brachypodium species. The duplicated Trxh gene pairs underwent a purifying selection during the evolution. In silico expression analysis showed the differential expression of BdTrxhs during development. Moreover, based on RT-qPCR expression analysis, target BdTrxh members were found to be induced by salt and drought stresses concomitantly with an accumulation of hydrogen peroxide (H2O2) in root tissues. The exogenous application of H2O2 modulated almost the same BdTrxh genes in root and leaf tissues. These results suggest specific roles for Trxh genes in B. distachyon beside their potential implication in abiotic stress response via redox homoeostasis. [ABSTRACT FROM AUTHOR]

Ubiquitin-specific protease (UBP) family is the largest group of deubiquitinates playing a key role in eukaryotes. Presently, we identified 41 UBP genes from Brassica rapa which were classified into three groups via phylogenetic analysis. Structural and motif analysis revealed that these genes have diverse exon–intron structures and share an equal number of conserved motifs within the same group. Cis-regulatory elements were identified for salicylic acid, abscisic acid, gibberellin, methyl jasmonate, auxin, low temperature, anaerobic, defense and stress, light, and drought. Furthermore, six br-miRNAs named br-miRN159a, br-miRN159b, br-miRN159c, br-miRN159d, br-miRN324a, and br-miRN324b were found targeting BrUBP13.1, BrUBP13.2, BrUBP12.1, BrUBP12.2, BrUBP12.3, and BrUBP17. BrUBP genes were highly expressed in stem, root, silique, flower, leaf, and callus tissues; however, leaf qRT-PCR results indicated that the genes expression was high under SA and drought stresses. Our findings provide the novel foundations for future genetic and physiological studies of BrUBPs in Brassica rapa. [ABSTRACT FROM AUTHOR]

Phytohormones have essential roles in plant growth responses under salinity. A better understanding of gibberellin (GA) function in woody plant responses under different sodium salts could help to develop new strategies to improve plant tolerance to salinity. In this study, the role of GA in morpho-physiological responses of halophytic woody Prosopis strombulifera plants under salinity was analyzed. Plants were grown in hydroponic solutions and exposed to NaCl, Na2SO4, or their iso-osmotic mixture at − 1.0, − 1.9, and − 2.6 MPa. Control (without salt) and salt-treated plants were sprayed with gibberellin A3 (GA3), or chlormequat chloride (CCC), an inhibitor of its synthesis. Growth responses, anatomical alterations and ABA, active GA forms (GA1, GA3, and GA4) and inactive GA forms (GA8 and GA34) endogenous levels were evaluated. The application of GA3 increased growth in control plants more than in salt-treated plants. Roots and leaves of salt-treated plants showed high levels of ABA and active GA forms after exposure to GA3, and lower endogenous levels of active GA when receiving the inhibitor. CCC triggered stress-alleviating responses in these plants, such as anatomical and hormonal changes that included an increase in spine length and the number of palisade cell layers, and a reduction in levels of ABA and GA4. Na2SO4-treated plants showed reduced growth, high ABA levels and an active GA metabolism to control the levels of active GA. This study indicates that the suppression of GA signaling would contribute to sodium salts tolerance in the native halophytic woody P. strombulifera plants. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) is an important phytohormone that regulates seed germination, dormancy, and plant responses to stresses such as salt, drought, and cold. Melatonin regulates ABA biosynthesis and catabolism during seed germination under various types of stress; however, the transcriptional regulation of ABA signaling genes by melatonin during cucumber seed germination under low temperature (LT, 15 °C) stress is poorly understood. Here we report that melatonin promoted seed germination under LT stress by decreasing ABA content and increasing the gibberellic acid (GA)/ABA ratio (gibberellic acid, GA). We also examined the expression levels of the ABA receptors PYR/PYL/RCAR (PYL), as well as the negative regulator protein phosphatase type 2C (PP2C) and positive regulator subfamily 2 of SNF1-related kinase (SnRK2) by real-time PCR. The expression of most tested genes increased during seed germination, showing an opposite trend to ABA level. The transcript levels of CsPYL1, CsPYL2, CsPYL3, CsPYL8, and CsPYL10 in 10 μM melatonin-pretreated seeds were significantly increased after 6 h of imbibition as a result of feedback regulation caused by the lack of ABA, and CsPP2C3, CsPP2C5, and CsSnRK2.1 exhibited higher expression levels than CK (control) treatment. The expression of most tested genes changed markedly in the initial water uptake phase (12 h after imbibition), suggesting that this period is critical for the regulation of ABA signaling during seed germination. We speculate that melatonin reduces ABA content, preventing CsPYL (CsPYL1/2/3/8/10) binding to CsPP2C and thereby enhancing the activity of CsPP2C (CsPP2C3/5) and blocking CsSnRK2.1 activation. Phosphorylation of the downstream factors ABA-responsive element-binding factor (ABF)/ABA-responsive element-binding protein (AREB) by CsSnRK2.1 is thus abolished, leading to seed germination under LT stress. [ABSTRACT FROM AUTHOR]

In the present study, an activation-tagged (AT) rice line T8-Ds-RFP3 developed has been tested for its ability to combat drought and salinity stress conditions besides analysis of its genes associated with improved productivity traits. TAIL-PCR analysis revealed the integration site of Ds element at LOC_Os03g51080 locus in the genome of the AT line. qRT-PCR analysis of glutamate decarboxylase (GAD) and F-box DUF protein-encoding genes showed more than 10- and 14-fold increased expression levels in the AT line when compared to that of wild-type (WT) plants. AT plants subjected to drought and salinity stresses exhibited enhanced stress tolerance compared to WT plants besides increased root length, tiller number and number of grains per plant. Additionally, AT plants also disclosed increased accumulation of osmolytes and antioxidants under salt and drought stress conditions owing to their enhanced ROS detoxification ability. Furthermore, AT plants also disclosed improved plant water status, photosynthetic efficiency, stomatal conductance and water use efficacy confirming their explicit stress tolerance compared to WT plants. The overall results suggest the underlying coordinated expressions of F-box DUF and GAD genes contribute to the elevated stress tolerance as well as increased productivity of the AT plants. Accordingly, the T8-Ds-RFP3 AT line can serve as a potent genetic resource for optimizing rice cultivars with increased yield potential. [ABSTRACT FROM AUTHOR]

Brassinosteroids (BRs) not only influence plant growth and development but also regulate various stress responses in plants. BRASSINOSTEROID INSENSITIVE 1 (BRI1) acts as a BR receptor, sensing BRs and then activating BR signalling. In this study, we researched how SlBRI1 regulates the drought tolerance of tomato at both the physiological and transcriptomic levels. We used SlBRI1-overexpressing and SlBRI1-weak mutant (abs) plants that were of the same background to research the mechanism underlying their drought tolerance. Physiological analyses revealed that, compared with Money Maker (MM) plants, abs plants had a greater net photosynthesis rate (Pn) and less wilting, and abs plants also accumulated lower amounts of peroxide (H2O2) and superoxide (O2−) through increased antioxidant enzyme activities under drought conditions. RNA sequencing (RNA-seq) analysis showed that the expression of 1425 and 840 genes was induced and repressed in response to drought in MM plants, respectively. However, the expression of 768 (53.9%) of drought induced 1425 genes and 418 (49.8%) of drought repressed 840 genes was induced and repressed, respectively, in abs plants under normal conditions. Moreover, the expression of 158 genes whose expression was induced in response to drought and 43 genes whose expression was repressed in response to drought was further upregulated and downregulated, respectively, in abs plants under drought conditions. In-depth analysis of these differentially expressed genes (DEGs) revealed that the expression of genes related to abscisic acid (ABA) metabolism and polyamine biosynthesis as well as oxidoreductase activity was upregulated in abs under both normal and drought conditions. Furthermore, analysis of transcription factor (TF) expression suggested that the drought tolerance of abs differed mainly through the regulation of WRKY, ERF, bHLH and MYB TFs. However, the expression of most of these genes was the same or opposite in the SlBRI1OE plants compared with the MM plants. Our results affirm that SlBRI1 expression is negatively involved in the drought response of tomato. Furthermore, our study provides valuable information for future breeding to appropriately reduce the expression of SlBRI1 and improve drought tolerance without affecting plant growth. [ABSTRACT FROM AUTHOR]

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 (GA3) 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 GA3, 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 GA3 had the best effect on seed germination at low temperature. After exogenous GA3 and low-temperature treatment, the activities of superoxide dismutase and lipase, the contents of maize riboside, GA3 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 (H2O2), starch, total sugars and total proteins were lower than those of the control. Correlation analysis revealed that ABA, adipose, CAT, H2O2, POD, GA3 and GA3/ABA were the main factors affecting the germination of cotton seeds at low temperature. Therefore, exogenous GA3 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. [ABSTRACT FROM AUTHOR]

In plants, abscisic acid (ABA)-mediated responses during abiotic stress, growth, and development have been well studied. Many chemicals which modulate ABA responses have been identified. In this study, we report that dithiothreitol (DTT), an inducer of endoplasmic reticulum (ER) stress, can overcome ABA-mediated responses in plants. In rice seedlings, combined treatment of ABA and DTT increased shoot growth compared to ABA alone. The phenotype correlated with the expression pattern of ABA and ER stress-responsive genes. In finger millet, increase in root growth was observed in combined treatment, compared to ABA treatment. Experiments using dimethyl sulfoxide indicated that the phenotype observed was specific to DTT. Priming of germinated rice seeds with DTT followed by salinity stress indicated that DTT can mask the ABA effect. In ABA bioassay using cotton petioles, an increase in intact petioles in combined treatment of ABA and DTT was observed compared to ABA treatment. The expression of OsWRKY48, an ABA-responsive gene, was down-regulated in combined treatment, indicating that the target of DTT-induced ER stress is upstream of OsWRKY48 in the ABA signaling pathway. The study demonstrated that DTT-induced ER stress can be a potential mechanism to regulate ABA-mediated responses in plants. [ABSTRACT FROM AUTHOR]

Early-spring plants are a special type of plant that complete their life cycle promptly in cold, early spring. Very little effort has been made into researching the flowering mechanism of this type. Vernalization, as an indispensable process for flowering induction at low temperature, is likely to be closely related to life cycle transition in early-spring plants. To explore the flowering strategy at low temperature, this study selected two local early-spring flowering plant species (Hylomecon japonica (Thunb.) Prantl, Smilacina japonica A. Gray) and two early-spring unflowered plants species (Cimicifuga foetida L., Veratrum nigrum L.) as subjects. Firstly, the ratio of abscisic acid (ABA), gibberellic acid (GA3), indole-3-acetic acid (IAA), and cytokinin (CTK) hormones was analyzed through high-performance liquid chromatography–mass spectrometry, results of which indicated that early-spring flowering plants have completed vernalization and thus entered the flowering stage. IAA content in early-spring flowering plants was significantly lower than that of unflowered plants, while GA3 and ABA contents were higher. Secondly, gas chromatography coupled with mass spectrometry (GC–MS) was adopted to profile metabolite richness across the two types of plants. Integrated key metabolic pathway analysis suggested that the contents of D-ribose, L-valine, L-isoleucine, alanine as well as various other compounds participating in the key pathways of early-spring flowering plants significantly reduced, demonstrating that early-spring flowering plants consume a significant amount of energy to regulate flowering, that is sourced from mass carbohydrate consumption. These results provide a greater understanding of early-spring flowering plants and their metabolic mechanism of vernalization, laying the foundation for further exploration on early-spring plants as well as the processing mechanism of the plant life cycle. [ABSTRACT FROM AUTHOR]

Plant growth and development are regulated by phytohormones, such as abscisic acid, auxins, or gibberellins. Under drought stress, melatonin and the signaling calcium (Ca2+) are involved in plant defense and stress responses by controlling phytohormone and antioxidant machineries. Exogenous melatonin (MT) promotes drought stress tolerance in plants. As an essential second messenger, the signaling molecule Ca2+ is necessary in the stress tolerance of plants and might increase stress tolerance induced by exogenous melatonin. The present study elucidated the effects of Ca2+-MT on Dalbergia odorifera seedlings under drought stress. Results showed increases in growth traits and photosynthesis indexes (pigments, net photosynthetic rate, water use efficiency, stomatal conductance, and transpiration) by MT and Ca2+ under non stress and stress conditions. Under drought stress, the water status in leaves was slightly ameliorated by MT and Ca2+ treatments, whereas the Ca2+-MT combination strongly improved water status. Comparison between combined Ca2+-MT and single Ca2+/MT treatments showed that superoxide anion was significantly lower in Ca2+-MT-treated seedlings. Lipid peroxidation was lower in Ca2+-MT-treated seedlings under drought stress. Further, relative conductivity was significantly decreased by Ca2+ and MT treatments under stress compared with seedlings untreated with Ca2+ or MT under drought. The accumulation of proline decreased by Ca2+ and MT under stress, but the carbohydrates and protein contents were increased by exogenous MT and Ca2+. Under drought, antioxidant systems (peroxidase, superoxide dismutase, and catalase activities, and glutathione [GSH] and ascorbic acid [ASA] levels) were significantly increased by the Ca2+ and MT treatments. The combined treatment showed better performance in increasing GSH and ASA levels than single MT or Ca2+ treatment. The gibberellin GA3 and cytokine ZR increased significantly under non stress and stress conditions, but exogenous Ca2+ or MT did not increase their activities compared with those in the control groups. Exogenous Ca2+ and Ca2+-MT enhanced indole-3-acetic acid (IAA) content in D. odorifera leaves under stress compared with the control. Moreover, abscisic acid (ABA) level is downregulated by MT and Ca2+-MT treatments compared with the control. The seedlings treated with Ca2+ only showed increase in ABA concentration under drought stress. This study provides an insight into a possible coordination between Ca2+ and melatonin and into drought tolerance in woody plants. [ABSTRACT FROM AUTHOR]

Citrus holds the key position in horticulture sector of Pakistan in terms of area and production. Kinnow is considered as the trademark of Pakistan's citriculture industry. Cultivation experiment was conducted to evaluate the endogenous plant hormones, leaf gas exchange, photosynthetic pigments, vegetative performance, and yield of Kinnow mandarin grafted on nine rootstocks (Rough lemon, cox mandarin, Fraser hybrid, Troyer citrange, Cleopatra mandarin, Poncirus trifoliata, Benton, C-35, and Carrizo citrange). Maximum indole acetic acid (IAA), gibberellic acid (GA3), and zeatin (ZT) levels were recorded in scion and rootstock of Poncirus trifoliata followed by Fraser hybrid. Troyer citrange rootstock depicted maximum amount of abscisic acid in scion and rootstock. Maximum leaf gas exchange in Kinnow mandarin was recorded on Fraser hybrid rootstock. Kinnow grafted on Troyer citrange rootstock had minimum stomatal conductance and photosynthetic activity because of high ABA level. Photosynthetic pigments of Kinnow mandarin were maximum on Poncirus trifoliata and minimum on Troyer citrange. A positive correlation was observed among the levels of IAA, GA, ZT, and vegetative growth of Kinnow mandarin. It is concluded that endogenous hormones modulated the growth of Kinnow mandarin. Poncirus trifoliata and Fraser hybrid rootstocks could be an alternate rootstocks of traditional Rough lemon for Kinnow mandarin. [ABSTRACT FROM AUTHOR]

BnSIP1-1 is a trihelix transcription factor family gene which functions in abiotic stress response and abscisic acid (ABA) signaling during seed germination and seedling growth of Brassica napus. In the present study, further sequence analysis and phenotype identification indicated that this gene had roles in light regulation and flowering of reproductive growth stage. Many phytohormones responsive cis-acting elements, including TC-rich repeats, GARE-motif, and TCA and TGA elements, were identified in the promoter sequence of BnSIP1-1. The expression of BnSIP1-1 was regulated by light period and remarkable higher expression level of BnSIP1-1 was detected in roots than in leaves. Overexpression of BnSIP1-1 in Arabidopsis delayed flowering time for 3–5 days in transgenic plants. In addition, we also found BnSIP1-1 can respond to abiotic and ABA stress (treated with 200 mM NaCl, 300 mM mannitol or 50 μM ABA for 0, 1, 6, and 24 h) in B. napus through adjusting not only ABA but also other endogenous hormones, including indole-3-acetic acid and salicylic acid. Moreover, jasmonates (JA) signaling pathway was found not involving in the pathway of BnSIP1-1 responding to abiotic stresses. [ABSTRACT FROM AUTHOR]

Clarifying the characteristics of photoassimilates transport and distribution to the fruits from leaves located on different branches can guide the branch composition and pruning of apple trees. A field experiment was carried out in 6-year-old 'Fuji'3/M26/Malus hupehensis Rehd. apple trees, and the 13C-labeled tracer method was used to study the growth characteristics of the leaves on different branches (vegetative branches, long branches, mid branches, short branches, bourse branches, and cluster branches) and the translocation of 13C-photoassimilates to the fruit from these leaves at the fruit enlargement stage in 2018 and 2019. Additionally, the effect of the distance between the leaf and fruit (leaves from both short and long branches that were 20, 40, and 60 cm away from the fruit) was assessed. We found that with increased branch length, the intensity of photosynthesis and the level of photoassimilates synthesis in the leaves decreased, but increased in the leaves near the fruits. Indole-3-acetic acid, gibberellic acid, and zeatin accumulated in the leaves of the longer branches, while abscisic acid accumulated in the leaves of the shorter branches. The δ values of the 13C-labeled leaves from the short branches, the short branches 20 cm away from the fruits (S20), and the bourse branches at the fruit stage were low, and the corresponding δ values of the fruits were high. The 13C absorption of the fruit was highest in the leaves of the short branches, followed by those of the bourse branches, S20, and mid branches, and was lower in the leaves of the vegetative branches, cluster branches, and 60 cm short and long branches. The leaf 13C-photoassimilates in the short branches were more greatly transported to the fruits than those from the long branches when the distance between the leaves and fruits was the same. The 13C absorption of the fruit increased by 10.91, 5.28, and 1.14 mg at the leaf–fruit spacing of 20, 40 and 60 cm, respectively, and the leaf–fruit spacing was determined to be more important than branch type in determining the 13C absorption of the fruit. [ABSTRACT FROM AUTHOR]

Anthropogenic activities in the past and present eras have created global warming and consequently a storm of drought stress, affecting both plants and animals. Being sessile, plants are more vulnerable to drought stress and consequently reduce plant growth and yield. To mitigate the effects of drought stress on plants, it is very crucial to determine the plant response mechanisms against drought stress. Drought response mechanism includes morph-physiological, biochemical, cellular and molecular processes takes place in plants underlying drought stress. These processes include improvement in root system, leaf structure, osmotic adjustment, relative water content and stomata regulation. In addition, calcium and phytohormone (Abscisic acid, Jasmonic acid, Salicylic acid, Auxins, Gibberellins, Ethylene etc.) signaling pathways and scavenging of reactive oxygen species are the key mechanisms to cope with drought stress. Moreover, microorganisms such as bacteria and fungi also have an important role in drought tolerance enhancement. To further elucidate and improve drought tolerance in plants, quantitative trait loci, transgenic approach and application of exogenous substances (nitric oxide, 24-epibrassinoide, glycine betaine and proline) are very crucial. Hereby, the present study integrates various mechanisms of drought tolerance in plants. [ABSTRACT FROM AUTHOR]

Low sunlight intensity from mid-June to mid-July in Southern China is the primary environmental factor that affects maize grain development. A field trial was conducted in 2016–2017 to investigate the effects of post-silking shading (i.e., 30% and 50% light deprivation using black net covers; ambient light as control) on grain filling, abscisic acid (ABA), and indole-3-acetic acid (IAA) contents, starch and protein contents, and enzymatic activities involved in biosynthesis by using two maize varieties, namely, the shade-sensitive Zhengdan958 (ZD958) and the shade-resistant Suyu30 (SY30). Results showed that grain filling was negatively affected by shading. Under 30% and 50% shading conditions, grain dry weight decreased by14.6% and 29.6% for ZD958, respectively, and 10.8% and 15.1% for SY30, respectively. Shading improved protein content, but restricted starch deposition. The activities of starch and protein synthetic enzymes were downregulated by shading, and the effect was severe when the plants were subjected to greater light deprivation (from 30 to 50%). Shading decreased IAA content, but increased ABA content. Under shading conditions, SY30 had higher activities of glutamine synthetase, sucrose synthase, and soluble starch synthase than ZD958. Moreover, SY30 generally had a higher IAA content, but lower ABA content than ZD958. These properties favored starch accumulation and increased grain weight. In conclusion, post-silking shading decreased IAA content and weakened the activities of starch and protein syntheses, but increased ABA content. These conditions restricted starch deposition, thereby resulting in grain weight loss. [ABSTRACT FROM AUTHOR]