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Auxins regulate many aspects of plant growth and development. In pea, three of the five TIR1/AFB members (PsTIR1a, PsTIR1b, and PsAFB2) have been implicated in auxin-related responses during fruit/seed development; however, the roles of PsAFB4 and PsAFB6 in these processes are unknown. Using yeast two-hybrid assays, we found that all five pea TIR1/AFB receptor proteins interacted with the pea AUX/IAAs PsIAA6 and/or PsIAA7 in an auxin-dependent manner, a requirement for functional auxin receptors. All five auxin receptors are expressed in young ovaries (pericarps) and rapidly developing seeds, with overlapping and unique developmental and hormone-regulated gene expression patterns. Pericarp PsAFB6 expression was suppressed by seeds and increased in response to deseeding, and exogenous hormone treatments suggest that seed-derived auxin and deseeding-induced ethylene are involved in these responses, respectively. Ethylene-induced elevation of pericarp PsAFB6 expression was associated with 4-Cl-IAA-specific reduction in ethylene responsiveness. In developing seeds, expression of PsTAR2 and PsYUC10 auxin biosynthesis genes was associated with high auxin levels in seed coat and cotyledon tissues, and PsAFB2 dominated the seed tissue transcript pool. Overall, auxin receptors had overlapping and unique developmental and hormone-regulated gene expression patterns during fruit/seed development, suggesting mediation of diverse responses to auxin, with PsAFB6 linking auxin and ethylene signaling. [ABSTRACT FROM AUTHOR]

The effect of different hormones on fructan accumulation and the genes regulating biosynthesis and degradation is known; however, information on hormonal interaction mechanisms for fructan content and mean degree of polymerization (mDP) is limited.Cell suspension cultures of chicory were prepared and treated with abscisic acid (ABA), auxin (AUX), ethylene (ETH), ABA + AUX or ABA + ETH, then inulin concentration, mDP of inulin and expression of FAZY genes was determined.A low concentration of AUX and ETH increased fructan content, while a high concentration of AUX and ETH decreased it. Exogenous ABA increased mDP of inulin and this coincided with the low expression of 1‐FEHII. In hormone interactions, ABA changed and adjusted the effect of both AUX and ETH. ABA, together with a low level of AUX and ETH, resulted in a decrease in inulin content and increase in mDP, which coincided with low expression of FEHII. ABA together with a high level of AUX and ETH caused an increase in inulin content with a lower mDP, which coincided with high expression of biosynthesis (1‐FFT) and degradation (1‐FEHII) genes.The effect of both AUX and ETH was almost the same, although the effect of ETH was more severe. ABA had a modulating role in combinations with AUX and ETH. Among biosynthesis and degradation genes, the expression of 1‐FEHII was more affected by these hormones. [ABSTRACT FROM AUTHOR]

Summary: Plants have evolved an array of responses that provide them with protection from attack by microorganisms and other predators. Many of these mechanisms depend upon interactions between the plant hormones jasmonate (JA) and ethylene (ET). However, the molecular basis of these interactions is insufficiently understood.Gene expression and physiological assays with mutants were performed to investigate the role of Arabidopsis BIG gene in stress responses.BIG transcription is downregulated by methyl JA (MeJA), necrotrophic infection or mechanical injury. BIG deficiency promotes JA‐dependent gene induction, increases JA production but restricts the accumulation of both ET and salicylic acid. JA‐induced anthocyanin accumulation and chlorophyll degradation are enhanced and stomatal immunity is impaired by BIG disruption. Bacteria‐ and lipopolysaccaride (LPS)‐induced stomatal closure is reduced in BIG gene mutants, which are hyper‐susceptible to microbial pathogens with different lifestyles, but these mutants are less attractive to phytophagous insects.Our results indicate that BIG negatively and positively regulate the MYC2 and ERF1 arms of the JA signalling pathway. BIG warrants recognition as a new and distinct regulator that regulates JA responses, the synergistic interactions of JA and ET, and other hormonal interactions that reconcile the growth and defense dilemma in Arabidopsis. [ABSTRACT FROM AUTHOR]

The auxins indole-3-acetic acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA) occur naturally in pea (Pisum sativum); however, only 4-Cl-IAA mimics the presence of seeds in stimulating pericarp growth. To examine if this differential auxin effect is mediated through TIR1/AFB auxin receptors, pea TIR1 and AFB2 homologs were functionally characterized in Arabidopsis, and receptor expression, and auxin distribution and action were profiled in developing pea fruits. PsTIR1a, PsTIR1b, and PsAFB2 restored the auxin-sensitive root growth response to the mutant Arabidopsis seedlings Attir1-10 and/or Attir1-10 afb2-3. Expression of PsTIR1 or AtTIR1 in Attir1-10 afb2-3 mutants also restored the greater root inhibitory response of 4-Cl-IAA compared to that of IAA, implicating TIR1 receptors in this response. The ability of 4-Cl-IAA to stimulate a stronger DR5::GUS auxin response than IAA at the same concentration in pea pericarps was associated with its ability to enrich the auxin-receptor transcript pool with PsTIR1a and PsAFB2 by decreasing the transcript abundance of PsTIR1b (mimicking results in pericarps with developing seeds). Therefore, the markedly different effect of IAA and 4-Cl-IAA on pea fruit growth may at least partially involve TIR1/AFB receptors and the differential modulation of their population, resulting in specific Aux/IAA protein degradation that leads to an auxin-specific tissue response. [ABSTRACT FROM AUTHOR]

Search and rescue dogs are an important link in the search for missing persons. The aim of the study was to assess exam stress in search and rescue dogs and their handlers. The study included 41 rescue teams taking exams of field and rubble specialties. The level of cortisol, which is the main glucocorticosteroid modulating stress reactions in humans and dogs, was analyzed. The biological material used to assess the hormone concentration was saliva collected in a non-invasive way. In total, 164 test samples were collected: two from the dog and two from the handler before and immediately after the exam. Rescue exams were shown to significantly increase salivary cortisol in both dogs and their handlers. Strong interactions between cortisol levels in human–dog teams were also found with a more pronounced effect in female dog–female handler dyads.

In pea, the auxins 4-chloroindole-3-acetic acid (4-Cl-IAA) and indole-3-acetic acid (IAA) occur naturally; however, only 4-Cl-IAA stimulates pericarp growth and gibberellin (GA) biosynthesis, and inhibits the ethylene response in deseeded ovaries (pericarps), mimicking the presence of seeds. Expression of ovary ethylene biosynthesis genes was regulated similarly in most cases by the presence of 4-Cl-IAA or seeds. PsACS1 [which encodes an enzyme that synthesizes 1-aminocyclopropane-1-carboxylic acid (ACC)] transcript abundance was high in pericarp tissue adjacent to developing seeds following pollination. ACC accumulation in 4-Cl-IAA-treated deseeded pericarps was driven by high PsASC1 expression (1800-fold). 4-Cl-IAA, but not IAA, also suppressed the pericarp transcript levels of PsACS4. 4-Cl-IAA increased PsACO1 and decreased PsACO2 and PsACO3 expression (enzymes that convert ACC to ethylene) but did not change ACO enzyme activity. Increased ethylene was countered by a 4-Cl-IAA-specific decrease in ethylene responsiveness potentially via modulation of pericarp ethylene receptor and signaling gene expression. This pattern did not occur in IAA-treated pericarps. Overall, the effect of 4-Cl-IAA and IAA on ethylene biosynthesis gene expression generally explains the ethylene evolution patterns, and their effects on GA biosynthesis and ethylene signaling gene expression explain the tissue response patterns in young pea ovaries. [ABSTRACT FROM AUTHOR]

Angiotensin II (ANG II) is secreted by the proximal tubule resulting in a luminal concentration that is 100- to 1,000-fold greater than that in the blood. Luminal ANG II has been shown to stimulate sodium transport in the proximal tubule and distal nephron. Surprisingly, luminal ANG II inhibits NaCl transport in the medullary thick ascending limb (mTAL), a nephron segment responsible for a significant amount of NaCl absorption from the glomerular ultrafiltrate. We confirmed that addition of 10-8 M ANG II to the lumen inhibited mTAL chloride transport (220 ± 19 to 165 ± 25 pmol·mm-1·min-1, P < 0.01) and examined whether an interaction with basolateral norepinephrine existed to simulate the in vivo condition of an innervated tubule. We found that in the presence of a 10-6 Mnorepinephrine bath, luminal ANG II stimulated mTAL chloride transport from 298 ± 18 to 364 ± 42 pmol·mm-1·min-1 (P < 0.05). Stimulation of chloride transport by luminal ANG II was also observed with 10-3 M bath dibutyryl cAMP in the bathing solution and bath isoproterenol. A bath of 10-5 H-89 blocked the stimulation of chloride transport by norepinephrine and prevented the effect of luminal ANG II to either stimulate or inhibit chloride transport. Bath phentolamine, an α-adrenergic agonist, also prevented the decrease in mTAL chloride transport by luminal ANG II. Thus luminal ANG II increases chloride transport with basolateral norepinephrine; an effect likely mediated by stimulation of cAMP. Alpha-1 adrenergic stimulation prevents the inhibition of chloride transport by luminal ANG II. [ABSTRACT FROM AUTHOR]

The effects of dipping fruit in solutions made from factorial combinations of 0 and 10 ppm thidiazuron (TDZ), 0 and 50 ppm gibberellic acid (GAa3), and 0 and 20 ppm 2,4-dichlorophenoxyacetic acid (2,4-D) on fruit size and quality characteristics in Actinidia deliciosa 'Hayward' were evaluated. When the compounds were used together significant interactions, TDZ X GA3 and TDZ X GA3 X 2,4-D, were recorded for the increase in fruit weight (+42% and +94%, respectively, compared with untreated fruits that had an average weight of 82.7 g). TDZ and 2,4-D were very effective in increasing fruit weight when used alone (+31% and +32%, respectively, compared with untreated fruits) or in combination with the other compounds. GA3 only showed an appreciable effect when used in combination with TDZ or TDZ + 2,4-D. Growth regulator treatments did not affect seed weight and number per fruit. TDZ accelerated fruit ripening and caused a change in fruit shape. TDZ and GA3 did not affect the fruit carbohydrate content at harvest, whereas the use of 2,4-D slightly decreased the fruit total carbohydrate content. The results indicate that the growth potential of kiwifruit is much higher than is normally expressed. [ABSTRACT FROM AUTHOR]

This study explores the unique growth-regulatory roles of two naturally occurring auxins, indole-3-acetic acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA), and their interactions with gibberellin (GA) during early pea ( Pisum sativum L.) fruit development. We have previously shown that 4-Cl-IAA can replace the seed requirement in pea pericarp growth (length and fresh weight), whereas IAA had no effect or was inhibitory. When applied simultaneously, gibberellin (GA3 or GA1) and 4-Cl-IAA had a synergistic effect on pericarp growth. In the present study, we found that simultaneous application of IAA and GA3 to deseeded pericarps inhibited GA3-stimulated growth. The inhibitory effect of IAA on GA-stimulated growth was mimicked by treatment with ethephon (ethylene releasing agent), and the inhibitory effects of IAA and ethylene on GA-mediated growth were reversed by silver thiosulfate (STS), an ethylene action inhibitor. Although pretreatment with STS could retard senescence of IAA-treated pericarps, STS pretreatment did not lead to IAA-induced pericarp growth. Although 4-Cl-IAA stimulated growth whereas IAA was ineffective, both auxins induced similar levels of ethylene evolution. However, only 4-Cl-IAA-stimulated growth was insensitive to the effects of ethylene. Gibberellin treatment did not influence the amount of ethylene released from pericarps in the presence or absence of either auxin. We propose a growth regulatory role for 4-Cl-IAA through induction of GA biosynthesis and inhibition of ethylene action. Additionally, ethylene (IAA-induced or IAA-independent) may inhibit GA responses under physiological conditions that limit fruit growth. [ABSTRACT FROM AUTHOR]

We examined the physiological effects of brassinosteroids (BRs) on early growth of Arabidopsis. Brassinazole (Brz), a BR biosynthesis inhibitor, was used to elucidate the significance of endogenous BRs. It inhibited growth of roots, hypocotyls, and cotyledonous leaf blades dose-dependently and independent of light conditions. This fact suggests that endogenous BRs are necessary for normal growth of individual organs of Arabidopsis in both photomorphogenetic and skotomorphogenetic programs. Exogenous brassinolide (BL) promoted hypocotyl elongation remarkably in light-grown seedlings. Cytological observation disclosed that BL-induced hypocotyl elongation was achieved through cell enlargement rather than cell division. Furthermore, a serial experiment with hormone inhibitors showed that BL induced hypocotyl elongation not through gibberellin and auxin actions. However, a synergistic relationship of BL with gibberellin A[sub 3] (GA[sub 3]) and indole-3-acetic acid (IAA) was observed on elongation growth in light-grown hypocotyls, even though gibberellins have been reported to be additive to BR action in other plants. Taken together, our results show that BRs play an important role in the juvenile growth of Arabidopsis; moreover, BRs act on light-grown hypocotyl elongation independent of, but cooperatively with, gibberellins and auxin. [ABSTRACT FROM AUTHOR]

Fruit development involves a complex interplay of cell division, differentiation and expansion of sporophytic and gametophytic tissues that is carefully coordinated temporally and spatially. Plant hormones are signal molecules that regulate many processes of plant development, including fruit development leading to mature fruit and viable mature seed. Auxins, gibberellins, cytokinins, abscisic acid, and ethylene have been implicated at various stages of fruit development. In the past, hormone application studies and hormone analysis studies have supported the hypothesis that fruit development is in part regulated by hormonal interaction. More recently, biochemical, genetic, and molecular studies are beginning to unravel the complexities of how hormones affect fruit development. In the current work, we review selected studies that show the interplay between hormones during fruit development, with an emphasis on the interaction between auxin and gibberellin in pea fruit development. [ABSTRACT FROM AUTHOR]

A genomic clone for VR-ACS6, an isozyme of auxininducible ACC synthase of mungbean, was isolated, and its promoter activity was examined in transgenic tobacco. The clone contained 1,612 bp long 5′ untranscribed region and its coding sequence consisted of three exons and two introns. Genomic Southern hybridization indicated that VR-ACS6 is a single copy gene. The transcription initiation site was a cytosine present at 231-base upstream the translation start codon. The VR-ACS6 promoter contained DNA sequences homologous to various functionally identified auxin-responsive elements. To demonstrate hormonal response of the promoter region, transgenic tobacco plants carrying the 1,719 bp VR-ACS6 promoter/-glucuronidase (GUS) fusion gene were generated. Strong GUS expression occurred by auxin treatment of leaves of T0 transformants and hypocotyls of T1 etiolated seedlings. Magnitude of the response to auxin was dose-dependent, and the increased GUS activity was detected at 0.1 μM and higher concentrations of IAA. Other plant hormones did not induce GUS activity, but greatly modified the response to auxin. Cytokinin enhanced the IAA-induced expression of GUS reporter gene, whereas ABA and ethylene suppressed the expression. These characteristics of VR-ACS6 promoter activity in transgenic tobacco are in good accordance with the expression patterns of the gene in mungbean hypocotyls. Histochemical staining showed that GUS activity was evident in both etiolated and light grown seedlings treated with IAA. Cytokinin enhanced the intensity of auxin-induced GUS stain and also expanded the stained area, whereas ABA and ethylene reduced both intensity and area of the stain. [ABSTRACT FROM AUTHOR]

Cell suspension cultures derived from shoot apex or seed callus of the wild carnation Dianthus zeyheri were treated with [8-14C]benzyladenine. The metabolism of applied cytokinin was evaluated with time (30 min, 6 h, 48 h) in the presence of both low (2 mg l-1) and high (4mg l-1) levels of applied 2,4-D, Both culture types metabolised BA to produce a qualitatively similar but quantitatively different array of metabolites. The 7-glucoside of BA was the major metabolite produced by apex-derived cultures, and the second largest product after the riboside in those cultures originating from seed. In both systems higher auxin application promoted 7-glucosylation with a concurrent reduction in radioactivity associated with the 'active' cytokinins. This suggests that cytokinin-7-glucosyl transferase is stimulated by the auxin 2,4-D, and may, in part, explain the observed antagonistic interaction between these hormone classes. [ABSTRACT FROM AUTHOR]

Elongation, indolyl‐3‐acetic acid (IAA) and abscisic acid (ABA) levels, – gas chromatography‐mass spectrometry quantification –, in the elongating zone were analysed for maize (Zea mays L., Cv. LG11) roots immersed in buffer solution with or without zeatin (Z). The effect of Z depends on the initial extension rate of roots. The slower growing roots are more strongly inhibited by Z (10−7−10−5M) and they show a greater increase in IAA and ABA content. When compared to the rapidly growing roots, the larger reactivity of the 'slow’ones cannot be attributed to a higher Z uptake as shown when using [14C]‐Z. It is suggested that Z could regulate root elongation by acting on the IAA and/or ABA level. The comparative action of these two hormones is discussed. [ABSTRACT FROM AUTHOR]

Oxytocin has been associated with anxiolytic and stress reducing effects in a number of studies. Less is known about the associations of endogenous oxytocin concentrations and their interaction with other hormones such as sex hormones in relation to self-reported anxiety levels. In this study, endogenous oxytocin and sex hormone levels were analyzed in 99 high (51 women) and 100 low (50 women) socially anxious individuals. Regression analyses showed that women with high oxytocin and estradiol levels reported a lower total Liebowitz Social Anxiety Score (LSAS) as well as a lower score on the subscale LSAS Fear. This association of hormonal interaction with social anxiety scores was significant in the subsample of high socially anxious women. In men there were no significant associations for endogenous hormones with LSAS scores. These findings suggest that in women the link between oxytocin and anxiety might be dependent on basal anxiety levels as well as on individual sex hormone levels. • The link between oxytocin and anxiety in women is dependent on individual anxiety levels as well as estradiol levels. • High oxytocin and estradiol levels are associated with lower anxiety. This link is significant in highly anxious women. • Hormonal contraception use affects concentrations of oxytocin, estradiol and progesterone. [ABSTRACT FROM AUTHOR]

• We examined relationships of testosterone and corticosterone with mites and color. • These relationships differed drastically among three species of Sceloporus lizards. • Testosterone was negatively correlated with mite load in S. grammicus males. • Also in S. grammicus males, both hormones promoted brighter ventral coloration. • Corticosterone was negatively correlated with blue chroma in S. torquatus males. Testosterone, in addition to promoting the expression of sexual ornaments can negatively affect immune function, leaving individuals more susceptible to parasites (immunocompetence handicap hypothesis). Immunosuppressive effects of testosterone also can occur indirectly, through increased glucocorticoid hormones (corticosterone, cortisol). Therefore, the expression of sexual ornaments and the ability to respond to parasites and diseases may be influenced by the interaction between testosterone and corticosterone. In this study we examined correlations of both testosterone and corticosterone with ectoparasite load and with expression of colorful sexual ornaments (patches on belly and throat) in three species of Sceloporus lizards (S. grammicus , S. megalepidurus, S. torquatus). In addition, we evaluated contributions of sex, body condition, and reproductive season. We expected that individuals with higher testosterone and lower corticosterone levels would have more colorful ornaments than individuals with higher corticosterone levels. In addition, if testosterone has negative effects on immune function but only at higher corticosterone levels, individuals with higher levels of testosterone and corticosterone should have higher ectoparasite loads. Contrary to these expectations, we did not detect an interaction between testosterone and corticosterone statistically affecting either ectoparasite load or the expression of colorful ornaments. Further, we did not find a positive association of either testosterone or corticosterone on ectoparasite loads in any of the three study species. Only in S. grammicus males was a hormone statistically associated with ectoparasite load, but it was a negative association with testosterone. The relationships between both hormones and different aspects of the colorful patches (brightness and chroma) varied drastically among the three species as well as between sexes. Hence, even among congeneric species, we did not observe consistent patterns among color, steroid hormones and ectoparasites. Different associations between these variables may reflect different physiological strategies for the production of colorful signals and immune defense. [ABSTRACT FROM AUTHOR]

The increased level of endogenous abscisic acid (ABA) in brassinosteroid (BR)-deficient mutants, such as det2 and cyp85a1 ×  cyp85a2 , suggests that ABA synthesis is inhibited by endogenous BRs in Arabidopsis thaliana . Expression of the ABA biosynthesis gene ABA-deficient 2 ( ABA2 ) was negatively regulated by exogenously applied BR but up-regulated by the application of brassinazole and in det2 and cyp85a1 ×  cyp85a2 . In addition, ABA2 expression decreased in bzr1-1D , showing that ABA biosynthesis is inhibited by BR signaling via BZR1, intermediated by ABA2 , in Arabidopsis . Four cis -element sequences (E-boxes 1-4) in the putative promoter region of ABA2 were identified as BZR1 binding sites. The electrophoretic mobility shift assay and chromatin immune precipitation analysis demonstrated that BZR1 directly binds to overlapped E-boxes (E-box 3/4) in the promoter region of ABA2 . The level of endogenous ABA was decreased in bzr1-1D compared to wild-type, indicating that binding of BZR1 to the ABA2 promoter inhibits ABA synthesis in Arabidopsis . Compared to wild-type, aba2-1 exhibited severely reduced growth and development. The abnormalities in aba2-1 were rescued by the application of ABA, suggesting that ABA2 expression and ABA synthesis are necessary for the normal growth and development of A. thaliana . Finally, bzr1-KO × aba2-1 exhibited inhibitory growth of primary roots compared to bzr1-KO , verifying that ABA2 is a downstream target of BZR1 in the plant. Taken together, the level of endogenous ABA is down-regulated by BR signaling via BZR1, controlling the growth of A. thaliana .

Avocados (Persea americana Mill.) are climacteric fruits, the ripening of which during postharvest at room temperature is strongly ethylene dependent. However, the role of other phytohormones in the modulation of postharvest ripening of avocados is still poorly understood. The optimal ripening state of avocados is attained a few days after harvest depending on the genotype, growing region and initial maturity stage of the fruit, and cold temperature storage is commonly used to delay this process. Here, we hypothesized that the ripening of avocados at room temperature may be governed not only by ethylene, but also by other phytohormones. With this aim, we analyzed the hormonal profiling of avocados subjected to either 4 °C and 25 °C during 10 days of postharvest. A biphasic response was observed during postharvest ripening of avocados at room temperature. While ethylene alone appeared to govern fruit ripening during the first transfer from cold to room temperature, a complex hormonal interplay occurred during ripening of avocados leading to a progressive fruit softening at room temperatures. Aside from ethylene, auxin, gibberellins, jasmonates and ABA appeared to be involved in avocado fruit ripening during postharvest at room temperature. Cold storage for a period of 10 days inhibited this hormonal response related to ripening. Furthermore, avocados stored at cold temperatures underwent a quick response in order to tolerate cold stress leading to changes in endogenous ABA and jasmonates. We conclude that a complex hormonal interplay, rather than ethylene alone, modulates postharvest ripening of avocados and that cold storage can effectively be employed as a technique to prevent avocados from a rapid ripening thanks to the cold stress tolerance mechanisms deployed by fruits through multiple hormonal regulation. [ABSTRACT FROM AUTHOR]

Simple Summary: Stress affects both people and animals every day. Working dogs are exposed to the same stressors as their handlers during work. Our research was conducted during search and rescue dog exams. The aim of the study was to investigate if handler stress during the exam affects his or her dog's stress level. We observed a strong relationship of salivary cortisol between the dogs and their handlers, which was most prevalent in female dogs and female handlers. Search and rescue dogs are an important link in the search for missing persons. The aim of the study was to assess exam stress in search and rescue dogs and their handlers. The study included 41 rescue teams taking exams of field and rubble specialties. The level of cortisol, which is the main glucocorticosteroid modulating stress reactions in humans and dogs, was analyzed. The biological material used to assess the hormone concentration was saliva collected in a non-invasive way. In total, 164 test samples were collected: two from the dog and two from the handler before and immediately after the exam. Rescue exams were shown to significantly increase salivary cortisol in both dogs and their handlers. Strong interactions between cortisol levels in human–dog teams were also found with a more pronounced effect in female dog–female handler dyads. [ABSTRACT FROM AUTHOR]

Drought stress provokes jasmonic acid (JA) signaling, which mediates plant stress responses; moreover, growing numbers of studies suggest that JA is involved in the modulation of root development under drought stress. Recently, we showed that JA promotes differentiation of xylem from procambial cells in Arabidopsis roots. Further molecular and genetic approaches revealed that the effect of JA on xylem development is caused by suppression of cytokinin responses, suggesting that JA antagonistically interacts with cytokinin to modulate xylem development. Here, we showed that, similar to JA, drought stress promotes xylem development. This suggests that the antagonistic interaction between JA and cytokinin is involved in drought-mediated xylem development, a hypothesis supported by the observation that drought stress increases JA responses and decreases cytokinin responses. Based on these findings, we propose that drought stress promotes xylem development, and the antagonistic interaction between JA and cytokinin is deeply involved in this process.

Plant cells have a profound capacity to regenerate their full array of tissues from already differentiated organs, as best demonstrated in in vitro regeneration systems. Although critical breakthroughs in in vitro organogenesis have outlined the role of hormones and their interactions in determination of cultured plant cell developmental fates, the underlying molecular mechanisms are still largely unexplored. Investigations have recently been empowered by the identification of key genes that function in regeneration, involved in hormonal biosynthesis, transport, signaling, and hormone interactions. The establishment of differential hormone-responsive patterns in organ regeneration zones is critical for de novo organ initiation. The present review focuses on recent findings providing insights into hormone-regulated plant regeneration at the molecular level and the formation of hormonal-response environments required for de novo regeneration., (© 2014 Elsevier Inc. All rights reserved.)