Spatio-temporal dynamics of phytohormones in the tomato graft healing process

Graft healing involves a series of cytological and molecular events including wound responses, callus formation and vascular bundle remodelling. Hormones are important signalling molecules regulating plant development and responses to environmental stimuli. However,the detailed dynamics of phytohormones in graft healing remain elusive. In this research, internodes above and below the graft site were harvested from 0 to 168 h after grafting(HAG), and liquid chromatography tandem mass spectrometry(LC-MS/MS) was used to determinate jasmonic acid, auxin, cytokinin, ethylene, salicylic acid, abscisic acid and gibberellin levels during the graft healing process. Uniform manifold approximation and projection(UMAP) and k-means analyses were performed to explore hormone spatio-temporal dynamics. We found the stage-specific and asymmetric accumulation of phytohormones in the tomato graft healing process. At the early healing stage(before vascular bundle reconnection), IAA, cZ, ABA, JA and SA mainly accumulated above the graft site, while tZ and ACC mainly accumulated below the graft site. MEIAA, ICAld and IP mainly accumulated at the later stage. Comminated with the healing process, we suggested that JA is mainly involved in wound responses, IAA is beneficial to the formation of callus and vascular cell development, tZ promotes cell division, and IP is linked to vascular bundle remodelling. In addition, expression of JA-related genes SlMYC2 and SlJAZ2, IAA-related gene SlIAA1, tZ-related genes SlHP2 and SlRR8, and IP-related gene SlRR9 correlated with hormone accumulation. The findings provide important information about the hormones and genes involved in the tomato graft healing process.

Phytohormones and their metabolic engineering for abiotic stress tolerance in crop plants

Abiotic stresses including drought,salinity,heat,cold,flooding,and ultraviolet radiation causes crop losses worldwide.In recent times,preventing these crop losses and producing more food and feed to meet the demands of ever-increasing human populations have gained unprecedented importance.However,the proportion of agricultural lands facing multiple abiotic stresses is expected only to rise under a changing global climate fueled by anthropogenic activities.Identifying the mechanisms developed and deployed by plants to counteract abiotic stresses and maintain their growth and survival under harsh conditions thus holds great significance.Recent investigations have shown that phytohormones,including the classical auxins,cytokinins,ethylene,and gibberellins,and newer members including brassinosteroids,jasmonates,and strigolactones may prove to be important metabolic engineering targets for producing abiotic stress-tolerant crop plants.In this review,we summarize and critically assess the roles that phytohormones play in plant growth and development and abiotic stress tolerance,besides their engineering for conferring abiotic stress tolerance in transgenic crops.We also describe recent successes in identifying the roles of phytohormones under stressful conditions.We conclude by describing the recent progress and future prospects including limitations and challenges of phytohormone engineering for inducing abiotic stress tolerance in crop plants.

Strigolactones interact with other phytohormones to modulate plant root growth and development

Strigolactones(SLs),which are biosynthesized mainly in roots,modulate various aspects of plant growth and development.Here,we review recent research on the role of SLs and their cross-regulation with auxin,cytokinin,and ethylene in the modulation of root growth and development.Under nutrientsufficient conditions,SLs regulate the elongation of primary roots and inhibit adventitious root formation in eudicot plants.SLs promote the elongation of seminal roots and increase the number of adventitious roots in grass plants in the short term,while inhibiting lateral root development in both grass and eudicot plants.The effects of SLs on the elongation of root hairs are variable and depend on plant species,growth conditions,and SL concentration.Nitrogen or phosphate deficiency induces the accumulation of endogenous SLs,modulates root growth and development.Genetic analyses indicate cross-regulation of SLs with auxin,cytokinin,and ethylene in regulation of root growth and development.We discuss the implications of these studies and consider their potential for exploiting the components of SL signaling for the design of crop plants with more efficient soil-resource utilization.

Abiotic Stresses and Phytohormones Regulate Expression of FAD2 Gene in Arabidopsis thaliana

Modification of unsaturated fatty acid （FA） levels has been found to accompany multiple abiotic stress acclimations in many plants. Delta 12 fatty acid desaturase （FAD2） plays a critical role in the synthesis of polyunsaturated FAs in plant cells by converting oleic acid （18：1） to linoleic acid （18：2）. To better understand the relationship between polyunsaturated FAs metabolism and stress adaptation, the expression of FAD2 gene and changes in the FA compositions under various abiotic stresses and phytohormone treatments in Arabidopsis thaliana was investigated in this study. A 1 423-bp promoter of the FAD2 gene was cloned and characterized from Arabidopsis. Several putative hormone- and stress- inducible cis-elements were identified in the cloned promoter, which include salt- and pathogen-inducible GT-1 motifs, low-temperature-responsive MYC element, dehydration-responsive MYB element, and GA signaling related WRKY71OS element. To investigate the fine regulation of FAD2 gene, a recombinant FAD2 promoter-GUS construct was introduced into Arabidopsis plants. Histochemical study showed that the promoter was ubiquitously active and responsive not only to exogenous phytohormones including ABA, 24-eBL, and SA but also to darkness, temperature, salt, and sucrose stresses in Arabidopsis seedlings. Consistent with the expression change, treatments with exogenous 24-eBL, ABA, SA, and NaCl resulted in reduction in polyunsaturated FAs in Arabidopsis seedlings. These findings suggest that the FAD2 gene with a wide variety of putative response elements in its promoter is responsive to multiple phytohormones and abiotic stresses and therefore may play an important role in stress responses of Arabidopsis during plant growth and seed development.

The regulatory network behind maize seed germination: Effects of temperature, water, phytohormones, and nutrients

Seed germination is the process by which an organism grows from a seed. It requires suitable conditions and environmental factors. Maize is one of the most important crops worldwide. Germination influences both final maize yield and quality. Seed germination is regulated by a complex gene network. It is also influenced by endogenous(phytohormones and nutrients) and exogenous(temperature and water)inputs, involving molecular networks only partly identified to date. This review describes current understanding of the influence of temperature, water, phytohormones, and nutrients in regulating maize seed germination, and indicates knowledge gaps that should be addressed.

Regulation of phytohormones on root primordium initiation and adventitious root formation in the etiolated shoots of Paeonia suffruticosa'Yinfen Jinlin'

Tree peony is well known and sought after for its large, colorful flowers. Its propagation is via vegetative methods. Mech- nisms of the adventitious rooting and the regulation of rooting processes are the principles and techniques of plant propagation and improvement. Microstructures and fluctuations of phytohormones in the adventitious rooting were studied with the etiolated soft- wood shoots of Paeonia suffkuticosa ＇Yinfen Jinlin＇. There are no pre-primordia in the shoots of the cultivar. Adventitious roots are produced in five stages： shoot selection, primordium initiation, primordium growth, conducting tissue differentiation and root protru- sion. Primordia initiated in the cortex. The contents of the endogenous hormones, IAA, ABA and GA, were 5.842, 0.873 and 1.043 nmol·g^-1 FW on the bases of shoots, respectively. CTKs which included isopentenyl adenine （iPA）, zeatin riboside （ZR） and dihy- drozeatin riboside （DHZR） were 0.949, 0.695 and 2.034 nmol·g^-1 FW, respectively. DHZR is active among CTKs. The ratio of IAA to GA, CTK and ABA clearly increased at the stage of primordium initiation, while they showed low levels at the stages of primor- dium growth. The ratios were restored at the shoot levels at the stage of root protrusion. IBA provoked primordia initiation in the cortex, the vascular cambium, the pith and even in the callus induced on the base of shoots. ]AA levels in the treated shoots increased gradually to its highest level （three times of control） at the stage of conducting tissue differentiation. The ratios of IAA to GA, CTK and ABA clearly decreased at the stage of primordium initiation. The ratio of IAA to ABA is regulated at 10：1.

Characterization of the 19 Novel Cotton FLA Genes and Their Expression Profiling in Fiber Development and in Response to Phytohormones and Salt Stress

Fasciclin-like arabinogalactan proteins(FLAs),a subclass of arabinogalactan proteins(AGPs),are usually involved in cell development in plants.To investigate the expression profiling as well

Interactive Effects of Drought Stress and Phytohormones or Polyamines on Growth and Yield of Two M(<i>Zea maize</i>L) Genotypes

Two maize genotypes (Nefertiti and Bashaier) were picked up from nine maize genotypes during the early vegetative growth (25 days) to be cultivated in open field upon the crop yield under the different drought stress levels (90,70,50,30) or under the interaction effect of drought stress and phytohormones or polyamines. According to the data of growth criteria, the maize genotype Nefertiti was found to be the most drought sensitive genotype, while the genotype Bashaier was found to be the most drought resistant genotype. Additionally while the photosynthetic pigments remained more or less unchanged in genotype Bashaier, their biosynthesis destroyed earlier in the drought sensitive genotype (Nefertiti). Also while the genotype Bashaier absorbed and accumulated a sufficient amount of mono and divalent cations (K+, Ca++ and Mg++), the genotype Nefertiti did not. Accordingly while the genotype Bashaier gave a crop yield up to 50% field capacity, the genotype Nefertiti gave a crop yield only up to 70% field capacity and failed to give a crop yield beyond this level. The interaction effect of drought stress and phytohormones and polyamines improved the all above characteristics. Interestingly each of these activators considerably improved the production of crop yield only in genotype Bashaier specially polyamines they produced more than 60% field capacity and at the level of 30% field capacity (the level which did not give crop yield in this genotype). However, phytohormones in generally did not make an important effect on the crop yield in genotype Nefertiti although they improved the dry matter production during the vegetative stages. Such situation seemed to be complicated and borne many questions to be studied in the future.

Effects of Various Phytohormones on Seed Germination and Seedling Growth of Leymus Chinensis

[Objective] To explore the effects of various phytohormones at different concentrations on the seed germination and seedling growth of Leymus Chinensiss （ L. chinensis）. [ Method ] The seeds of two varieties of L. chinensis were respectively treated with four kinds of phytohormone [ gibbereUin （ GA ）, 2,4-D, naphthalene acetic acid and 6-benzyl aminopurine （6-BA） ] for the observation of seed germination. The seedling growth of natural L. chinensis was observed after the seedlings were respectively treated with these phytohormones. [Result] The germination percentage of L. chinensis was promoted by the GAs and 6-BA at low concentration and inhibited by these two kinds of phytohormone at high concentration. Moreover, they promoted the seedling growth of L. chinensis, and the GA3 had better effect. However, the NAA and 2,4-D at any concentration inhibited the seed germination and seedling growth of L. chinensis. [ Conclusion] The various phytohormones have different effects on the seed germination and seedling growth of L. chinensis.

Effect of Phytohormones on Adventitious Bud Differentiation from Bulb Scales of Oriental Lily Test-tube Plantlets

[Objective] The purpose of this study is to investigate the effects of differ- ent phytohormones on the adventitious bud differentiation of oriental lily. [Method] The bulb scales of the test-tube plantlets of Tiber, Rodina and Constanta were cul- tured in media supplemented with different cytokinin and auxin at different concen- tration, and then the adventitious buds in each treatment were calculated. [Result] Cytokinins had different influence on the adventitious bud differentiation of the three oriental lily cultivars. Among them, 6-BA had the best effect to induce the adventi- tious bud differentiation from bulb scales of Tiber and Rodina, but there was some difference in the optimal concentration. KT had the best effect to induce the adven- titious bud differentiation of Constanta. The auxins had little influence on the quality of the adventitious bud of the three oriental lily cultivars, but caused some difference in differentiation coefficients. [Conclusion] The most suitable media for the adventi- tious bud differentiation from bulb scales in vitro of Tiber, Rodina and Constanta were MS＋0.2 mg/L 6-BA＋0.2 mg/L 2,4-D, MS＋I.0 mg/L 6-BA＋0.2 mg/L IAA, MS＋ 1.0 mg/L KT＋0.5 mg/L 2,4-D, respectively.

Detection of seven phytohormones in peanut tissues by ultra-highperformance liquid chromatography-triple quadrupole tandem mass spectrometry

Development of highly sensitive and reliable method for detection of phytohormones is of great significance to study plant hormones and agricultural production.In this study,an ultra-high-performance liquid chromatography-mass spectrometry/mass spectrometry method was established for separation and quantification of trans-zeatin,trans-zeatin riboside,gibberellin A3,indol-3-acetic acid,salicylic acid,abscisic acid,and jasmonic acid(JA) without any label.The sepa ration was performed on an Agilent Explus Plus C18 column by using methanol and water as mobile phases with gradient elution.The target compounds were confirmed and quantified by mass spectrum via positive electrospray ionization for trans-zeatin,transzeatin riboside,indole-3-acetic acid,and via negative electrospray ionization for gibberellin3,salicylic acid,abscisic acid,and JA.The limits of detection ranged from 0.0127 ng L^-1 for gibberellin A3(GA3) to 33.26 ng L^-1 for JA and were lower than the currently reported values in literature.The proposed method was applied for qualitative and quantitative analyses of phytohormones in peanut gynophores and pods.The recoveries of the spiked phytohormones ranged from 80.20 to102.56%.The contents of seven endogenous hormones varied specifically in different development stages of peanuts.This study provides a highly sensitive and selective detection method for hormones and elucidates the growth and development of the gynophore and peanut fruit,which are controlled by seven endogenous hormones.

Simultaneous determination of multi endogenous phytohormones in rice tissues by GC/MS

Although at different content levels, phytohormones including auxins, gibberellins, cytokinns and ahscisic acid distribute widely over rice tissues. It has

Cloning and Expression Analysis of an AP2/ERF Gene and Its Responses to Phytohormones and Abiotic Stresses in Rice

Ethylene response factors （ERFs） play important roles in response to plant biotic and abiotic stresses. In this study, a gene encoding a putative AP2/ERF domain-containing protein was isolated by screening a SSH cDNA library from rice and designated as Oryza sativa AP2/ERF-like protein （OsAP2LP） gene. OsAP2LP is 1491 bp in length, interrupted by seven introns, and encodes a putative protein of 348 amino acids. Temporal and spatial expression analysis showed that the OsAP2LP gene was preferentially expressed in roots, panicles, mature embryos and seeds in rice. Real-time quantitative PCR analysis indicated that the expression levels of the OsAP2LP gene were increased under the treatments of drought and gibberellin but decreased under the treatments of low temperature, salt, abscisic acid （ABA） and zeatin. Taken together, these results suggest that OsAP2LP might be involved in stress responses, and probably plays roles as a transcription regulator when plants response to cold, salt and drought stresses through ABA and gibberellin pathways.

Effect of ploidy level on expression of lycopene biosynthesis genes and accumulation of phytohormones during watermelon(Citrullus lanatus) fruit development and ripening

The difference between lycopene and phytohormone levels among diploid, triploid and tetraploid plants of two watermelon cultivars during fruit growth and ripening was studied. The expression pattern of five genes（phytoene synthase（PSY1）, phytoene desaturase（PDS）, ζ-carotene desaturase（ZDS）, carotenoid isomerase（CRTISO）, and lycopene β-cyclase（LCYB）） was analyzed in details. In red-fleshed cultivar Mimei, lycopene content increased rapidly from 25 to 35 days after pollination（DAP）, and then decreased at 40 DAP. Triploid and tetraploid fruit had higher levels of lycopene than diploid. Moreover, triploid tended to contain more lycopene than tetraploid during fruit growth and ripening stages. However, little amount of lycopene（0–2 mg kg–1 fresh weight（FW）） in yellow-fleshed cultivar Huangmei was found during all fruit development stages. In Mimei, transcript level of PSY1 was generally higher than the other four genes, and LCYB gene expression was the lowest among all five genes being tested. PSY1, CRTISO and LCYB genes showed higher transcript levels in polyploid than in diploid fruit. By contrast, in Huangmei, transcript level of LCYB was not the lowest, but only lower than that of PSY1. PSY1, CRTISO and LCYB genes showed higher expression levels in diploid than in polyploid fruit. In Mimei, the negative correlation between gibberellane（GA） content and lycopene accumulation was determined in all three different ploidy fruits, while a positive correlation was observed between abscisic acid（ABA） content and lycopene accumulation only in diploid watermelon. These results indicated that different lycopene contents in different ploidy watermelons is regulated by the differential transcription expression of the lycopene metabolic genes and phytohormones.

The Effect of Phytohormones on Lavender （Lavandula Angustiflia Mill.） Organogenesis

Lavender （L. angustifolia） is a genus of flowering plants in the mint family, Lamiaceae. It is an aromatic shrub with multiple stems growing 30 to 60 cm tall. It is native to Asia, Europe and Mediterranean regions and grows on hilly areas and coastlines. The evergreen leaves are narrow and long and covered in fine hairs, which normally contain the essential oils. The leaves are also pinnately toothed, or pinnate. The plant blooms between April and June, and flowers are purple produced on violet bracts. All parts of the plant have a strong and scented odor and a bitter taste. The flowers and leaves are used as an herbal medicine. Lavender essential oil is extracted by distilling flowers and leaves, Essential oil has higher levels of linalyl acetate （40%）, butyric acid, propionic acid, valeric acid, free linalool. Considering the lack of information about lavender tissue culture, the current experiment＇ was aimed to study the effect of phytohormones on lavender callus induction and organogenesis. The lavender explants （leaf and apical meristem） were cultured onto MS media supplemented with different phytohormones. According to the observations, 5 mg/L NAA and 5 mg/L KIN treatment caused leaf and root formation, which were originally derived t^om dense and green calli. The MS medium containing 5 mg/L IBA and 5 mg/L Kin was effective just on leafy explants so that explants formed into leaves after callus induction. Application of 5 mg/L NAA and 5 mg/L BAP on apical meristem explants produced shoot and root after callus induction. However, complete plants were produced after sub-culturing the samples. In conclusion, MS medium supplemented with 5 mg/L NAA and 5 mg/L BAP was selected as the best medium for lavender tissue culture.

Phytohormones Accumulation and Distribution in Shoots and Roots of Haploid,Diploid and Tetraploid Barley Seedlings Derived from Microspore Culture

Phytohormones play important roles in plant growth and development,and polyploids are thought to be an important method for plant breeding.However,the relationship between ploidy and phytohormone is still unclear.In this study,barley at three ploidy levels were produced by microspore culture.Therefore,we further analyzed the phytohormone content in the shoots and roots of the three kinds of barley materials to study the effect of ploidy on phytohormones accumulation and distribution.The results showed that Abscisic acid(ABA),gibberellin(GA),jasmonic acid(JA),auxin(IAA),salicylic acid(SA)and cytokinin(CTK)were successfully determined in shoots and roots using LC-MS(liquid chromatography mass spectrometry).By comparing the shoots of the haploid and diploid plants,it was found that the distribution trend of the six phytohormones was consistent,and another consistent trend was found in the roots of the diploid and tetraploid plants.In addition,we further analyzed the shoot/root ratio of the different phytohormones to identify the potential differences for haploid,diploid and tetraploid.Here,the relationship between ploidy and phytohormone we provided would provide new insights into understanding the new phenotypes that occur in polyploid species.

Expression and functional analyses of the mitogen-activated protein kinase (MPK) cascade genes in response to phytohormones in wheat ( Triticum aestivum L.)

Mitogen-activated protein kinase （MPK） cascades consist of a set of kinase types （MPKKKs, MPKKs, MPKs） to establish conserved signal-transducing modules mediating plant growth, development as well as responses to internal and external cues. In this study, the expression patterns of six MPKKK, two MPKK, and 11 MPK genes in wheat in responses to external treatments of phytohormones, including naphthylacetic acid （NAA）, abscisic acid （ABA）, 6-benzyladenine （6-BA）, gibber- ellin （GA3）, salisylic acid （SA）, jasmonic acid （JA）, and ethylene （ETH）, were investigated. Expression analysis revealed that several of the MPK cascade genes are responses to the external phytohormone signaling. Of which, TaMPKKKA;3 is induced by 6-BA and NAA while TaMPK4 repressed by ETH, GA3, SA, and JA; TaMPKKKA, TaMPKKKA;3 and TaMPK1 are down-regulated by ETH and GA3whereas TaMPK9 and TaMPK12 repressed by ETH and JA in addition that TaMPK12 also repressed by GA3; TaMPK12;1 is down-regulated by ABA, GA3 and SA while TaMPK17 repressed by all exogenous phytonormones examined. TaMPK4, a MPK type gene previously characterized to mediate tolerance to phosphate （Pi） deprivation, was functionally evaluated for its role in mediation of responses of plants to exogenous GA3, ETH, SA, and JA. Results indicated that overexpression and antisense expression of TaMPK4 in tobacco dramatically modify the growth of seedlings upon treatments of GA3, SA and JA, in which the overexpressors behaved deteriorated growth feature whereas the seedlings with antisense expression of TaMPK4 exhibited improved seedling phenotype. The growth behaviors in lines overexpressing or antisensely expressing TaMPK4 are closely associated with the biomass and the corresponding hormone-associated parameters. These results demonstrated that TaMPK4 acts as a critical player in mediating the phyto- hormone signaling. Our findings have identified the phytohormone-responsive MPK cascade genes in wheat and provided a connection between the phytohormone-mediated responses and the MPK cascade pathways.

Interplay of phytohormones and epigenetic regulation:A recipe for plant development and plasticity

Both phytohormone signaling and epigenetic mechanisms have long been known to play crucial roles in plant development and plasticity in response to ambient stimuli.Indeed,diverse signaling pathways mediated by phytohormones and epigenetic processes integrate multiple upstream signals to regulate various plant traits.Emerging evidence indicates that phytohormones and epigenetic processes interact at multiple levels.In this review,we summarize the current knowledge of the interplay between phytohormones and epigenetic processes from the perspective of phytohormone biology.We also review chemical regulators used in epigenetic studies and propose strategies for developing novel regulators using multidisciplinary approaches.

Nanoparticles and their crosstalk with stress mitigators:A novel approach towards abiotic stress tolerance in agricultural systems

Plants are exposed to adverse environmental conditions,including cold,drought,heat,salinity,and heavy metals,which negatively impact plant growth and productivity of edible crops worldwide.Although the previous literature summarized the nanoparticle's involvement in abiotic stress mitigation,the interaction of nanoparticles with other stress mitigators to overcome abiotic stress from plants remains unclear.Currently,nanotechnology is considered a growing new field in agriculture for understanding plants'adapted stress tolerance mechanisms.Recent research has shown that nanoparticles can effectively mitigate abiotic stress by interacting synergistically with plant growth regulators.To address this,we comprehensively demonstrated the combined positive potential of nanoparticles in combination with plant growth regulators(signaling molecules,phytohormones,nanoparticles-nanoparticles interaction,fungi,plant growth promoting rhizobacteria and other metal salts)to improve plant growth and mitigate abiotic stresses.Their co-applications augment the plant's growth,nutrient uptake,antioxidant defense system,water absorption,cell viability,water use efficiency,and photosynthetic and biochemical attributes by reducing oxidative stressors under various abiotic stresses in different plant species.This review provides a comprehensive overview of the combined applications of nanoparticles and plant growth regulators,a novel strategy to reduce the harmful effects of abiotic stress on plants.It identifies research gaps and recommends future studies to overcome their phytotoxicity worldwide.

Mutualistic fungal endophytes produce phytohormones and organic acids that promote japonica rice plant growth under prolonged heat stress

This study identifies the potential role in heat-stress mitigation of phytohormones and other secondary metabolites produced by the endophytic fungus Paecilomyces formosus LWL1 in japonica rice cultivar Dongjin. The japonica rice was grown in controlled chamber conditions with and without P. formosus LWL1 under no stress （NS） and prolonged heat stress （HS） conditions. Endophytic association under NS and HS conditions significantly improved plant growth attributes, such as plant height, fresh weight, dry weight, and chlorophyll content. Furthermore, P. for- mosus LWL1 protected the rice plants from HS compared with controls, indicated by the lower endogenous level of stress-signaling compounds such as abscisic acid （25.71%） and jasmonic acid （34.57%） and the increase in total protein content （18.76%-33.22%）. Such fungal endophytes may be helpful for sustainable crop production under high environmental temperatures.