Exogenous Phytohormones Research Articles

Combined effect of ultrasound treatment and exogenous phytohormones on the accumulation of bioactive compounds in broccoli florets

Postharvest treatments such as wounding, ultrasound (US) and the exogenous application of ethylene (ET) and methyl jasmonate (MJ) have been studied as an effective tool to improve the content of secondary metabolites in fresh produce. The present study evaluated the immediate and late response (storage for 72 h at 15 °C) to US treatment (20 min, frequency 24 kHz, amplitude 100 μm) alone and combined with exogenous MJ (250 ppm) and/or ET (1000 ppm) on glucosinolates, isothiocyanates, phenolic compounds and ascorbic acid content in broccoli florets. US treatment increased the extractability of glucosinolates [glucoraphanin (795%), 4-hydroxy glucobrassicin (153%), glucobrassicin (78.6%)] and phenolics [1-sinapoyl-2-feruloylgentiobiose (57.23%)] as compared with the control (CT). The combined application of MJ and US in broccoli florets, induced a synergistic effect on the accumulation of 4-hydroxy glucobrassicin (187.1%), glucoerucin (111.92%), gluconasturtiin (755.9%), neoglucobrassicin (232.8%), 3-O-caffeoylquinic acid (73.4%), 1-sinapoyl-2-ferulolylgentiobiose (56.0%), and 1,2,2-trisinapoylgentiobiose (136.7%) at 72 h of storage. Interestingly, when the three stressors were applied together the synergistic effect of US + MJ observed on the accumulation of glucosinolates and phenolics was repressed. In general, the ascorbic acid content was not affected by US treatment and decreased in most samples during storage. However, when MJ + ET were applied, the content of total ascorbic acid was significantly reduced in CT + MJ + ET and US + MJ + ET samples after 72 h of storage by 53.4% and 86.6%, respectively, as compared with CT 0 h samples. Based on the results herein obtained, the application of US can be an effective tool to enhance the extractability of certain glucocosinolate and phenolic compounds in broccoli. Moreover, due to the synergistic effect observed on the accumulation of bioactive compounds, the combined application of US and MJ could be a practical approach to yield higher levels of glucosinolates and phenolic compounds in broccoli during storage.

Methyl Jasmonate and Nitrogen Interact to Alleviate Cadmium Stress in Mentha arvensis by Regulating Physio-Biochemical Damages and ROS Detoxification

We examined effects of methyl jasmonate (MeJ), with and without N, for the alleviation of the adverse effects of 150 mg kg−1 CdCl2 stress in mentholmint (Mentha arvensis) plants. Exposure of mentholmint plants to Cd stress reduced morphological growth parameters, photosynthetic attributes, chlorophyll content and mineral nutrient assimilation rate. Cd stress significantly increased endogenous leaf and root Cd content by 67.10% and 83.05%, respectively, electrolyte leakage by 67.26%, hydrogen peroxide (H2O2) by 56.66% and malondialdehyde content by 53.97% over that of the control. Cd stress upregulated activities of antioxidant enzymes and increased osmolyte concentration. Application of 1 µM MeJ to Cd-stressed plants partially alleviated the Cd-induced oxidative stress; however, co-application of MeJ with inorganic N reversed the detrimental effects more than did MeJ or N alone. Combined application of MeJ + N further elevated the osmolyte levels and markedly increased mineral nutrient contents and nitrogen use efficiency. MeJ + N significantly reduced the production of reactive oxygen species (ROS) directly or indirectly through higher stimulation of ROS-scavenging enzymes and decreased the root-to-shoot Cd rate of translocation. Cd-induced stomatal inhibition was recovered by MeJ and N. Our study demonstrated the regulatory role of MeJ and N in overcoming Cd stress in mentholmint plants. The study is the first report of regulatory interaction of the exogenous phytohormone (MeJ) with inorganic nutrient (N) for enhancing Cd stress tolerance in mentholmint plants, the same concept can be used for remediation of toxic metal/metalloids in agricultural production.

Genome-wide identification of lipoxygenase gene family in cotton and functional characterization in response to abiotic stresses

BackgroundPlant lipoxygenase (LOX) genes are members of the non-haeme iron-containing dioxygenase family that catalyze the oxidation of polyunsaturated fatty acids into functionally diverse oxylipins. The LOX family genes have been extensively studied under biotic and abiotic stresses, both in model and non-model plant species; however, information on their roles in cotton is still limited.ResultsA total of 64 putative LOX genes were identified in four cotton species (Gossypium (G. hirsutum, G. barbadense, G. arboreum, and G. raimondii)). In the phylogenetic tree, these genes were clustered into three categories (9-LOX, 13-LOX type I, and 13-LOX type II). Segmental duplication of putative LOX genes was observed between homologues from A2 to At and D5 to Dt hinting at allopolyploidy in cultivated tetraploid species (G. hirsutum and G. barbadense). The structure and motif composition of GhLOX genes appears to be relatively conserved among the subfamilies. Moreover, many cis-acting elements related to growth, stresses, and phytohormone signaling were found in the promoter regions of GhLOX genes. Gene expression analysis revealed that all GhLOX genes were induced in at least two tissues and the majority of GhLOX genes were up-regulated in response to heat and salinity stress. Specific expressions of some genes in response to exogenous phytohormones suggest their potential roles in regulating growth and stress responses. In addition, functional characterization of two candidate genes (GhLOX12 and GhLOX13) using virus induced gene silencing (VIGS) approach revealed their increased sensitivity to salinity stress in target gene-silenced cotton. Compared with controls, target gene-silenced plants showed significantly higher chlorophyll degradation, higher H2O2, malondialdehyde (MDA) and proline accumulation but significantly reduced superoxide dismutase (SOD) activity, suggesting their reduced ability to effectively degrade accumulated reactive oxygen species (ROS).ConclusionThis genome-wide study provides a systematic analysis of the cotton LOX gene family using bioinformatics tools. Differential expression patterns of cotton LOX genes in different tissues and under various abiotic stress conditions provide insights towards understanding the potential functions of candidate genes. Beyond the findings reported here, our study provides a basis for further uncovering the biological roles of LOX genes in cotton development and adaptation to stress conditions.

Overcoming limitation of “recalcitrant areas” to phytoextraction process: The synergistic effects of exogenous cytokinins and nitrogen treatments

The aim of the present work was to test the efficiency of the phytoextraction process involving the use of exogenous phytohormone (cytokinins, CKs) and fertilizer (nitrogen, N) treatments in phytotechnologies to address risk management in “recalcitrant areas”. The CKs and N treatments, alone or combined (CKs + N) in a Modulated Application (MA), were tested on the crop plant Helianthus annuus, common to Mediterranean area, fast growing and with high biomass production. Plants were grown on boron (B) contaminated sediments (collected from a geothermal area located in Tuscany (Italy). Plant growth, B uptake, together with plant stress parameters were investigated. Boron is easily taken up and translocated by some crop plants, but the high phytotoxicity can dramatically impact the plant growth and consequently the applicability and efficiency of the phytoextraction process. As indicators of plant stress, oxidative balance and photosynthetic parameters were investigated to give a deeper insight of phytotoxic mechanisms. Results showed that while each treatment (CKs and N alone) had significantly positive effects on plant health, the MA treatment provided a synergistic effect on morphological parameters and biomass production as a whole. After MA treatment, plants showed antioxidant activity comparable to that of the control (unpolluted sediments) and showed an increase of net photosynthesis. Moreover, our data showed very high values of B uptake and translocation (about 800 mg kg−1 in shoots), without any alteration triggered by the treatments (CKs and N alone or combined in MA). B phytoextraction resulted increased about fivefold with the MA treatments, while each treatment alone increased only two or three folds when treated with either CKs or N. The MA treatment is not “contaminant specific”, so it could be applied in other “recalcitrant areas” where different types of contaminations occur, in order to overcome limitations of plant growth.

Overexpression of VaWRKY14 increases drought tolerance in Arabidopsis by modulating the expression of stress-related genes.

Overexpression of VaWRKY14 increases drought tolerance in Arabidopsis by modulating the expression of stress-related genes, including COR15A, COR15B, COR413, KIN2, and RD29A. The WRKY family is one of a largest transcription factors in plants, and it is a key component of multiple stress responses. In this study, the drought- and cold-induced WRKY family gene VaWRKY14 was isolated and characterized. Phylogenetic analysis indicated that VaWRKY14 belongs to the WRKY IIa subfamily, of which several members participate in biotic and abiotic stress responses in plants. Fluorescence observation from Arabidopsis mesophyll protoplasts transformed with the VaWRKY14::eGFP fusion vector suggested that VaWRKY14 was localized in the nucleus. The VaWRKY14 in yeast cells did not display any transcriptional activity. The expression of VaWRKY14 could be induced by exogenous phytohormones, including salicylic acid (SA) and abscisic acid (ABA). Overexpression of VaWRKY14 enhanced the drought tolerance of transgenic Arabidopsis. Compared with wild-type Arabidopsis, the VaWRKY14-OE lines exhibited higher water content and antioxidant enzyme activities in leaves after drought treatment. RNA sequencing analysis revealed that several stress-related genes, including COR15A, COR15B, COR413, KIN2, and RD29A, were upregulated in transgenic plants relative to their expression in wild-type Arabidopsis under normal conditions. Several genes (3 upregulated and 49 down-regulated) modulated by VaWRKY14 were also affected by drought stress in wild-type plants. These data suggest that VaWRKY14 responds to drought and cold stresses and that drought tolerance may be enhanced by regulating the expression of stress-related genes in Arabidopsis.

Combined effect of exogenous phytohormones on biomass and lipid production in Acutodesmus obliquus under nitrogen limitation

The use of phytohormones in microalgal biofuel production is gaining interest due to their substantial effect on biomass and lipid enrichment under standard and nitrogen-limited conditions. In the present study, the collaborative effect of combination of selected phytohormones viz. zeatin (Z), indole acetic acid (IAA), and gibberellic acid (GA) was studied to optimize biomass and lipid production in microalga Acutodesmus obliquus under nitrogen-limitation using response surface methodology (RSM). Significantly higher biomass and lipid productivity was obtained with the supplementation of combination of Z (0.5 mg L−1), IAA (1.0 mg L−1), and GA (5.0 mg L−1) under nitrogen-limitation with 49.07% and 77.20% increase respectively as compared to optimized nitrogen control (ON). Zeatin was found to be the most significantly influencing phytohormone followed by GA in RSM data analysis. Present study elucidated the synergistic effect of combination of exogenous phytohormones in enhancing biomass and lipid productivity under nitrogen-limitation for microalgal biofuel production.

Determination of Five Plant Growth Regulator Containing Carboxyl in Bean Sprouts Based on Chemical Derivatization by GC-MS

An efficient and sensitive analytical method for the simultaneous determination of five plant growth regulators (PGRs) has been successfully developed, including 3-Indoleacetic acid (IAA), 2-Naphthylacetic acid (2-NAA), Beta-indolebutyric acid (IBA), 2-(2,4-dichlorophenoxy), acetic acid (2.4-D), and 4-Chlorophenoxyacetic acid (4-CPA) in bean sprouts. Using 10% boron trifluoride of methanol as the derived reagent and the reaction was derivatized at 70 °C for 30 min, the derivatives of five PGRs have been completely separated within 19 min. It has a linear relationship in the concentration range of 0.01–0.20 mg/kg and the correlation coefficients (r2) in excess of 0.997. The average recoveries were ranged from 72.7–98.6% at three spiking different concentration levels of 0.05, 0.10, and 0.15 mg/kg, respectively. The relative standard deviations (RSDs) were ranged from 1.2 to 9.0%. The limits of detection and the limits of quantification were ranged from 0.00024 to 0.00172 mg/kg and 0.0008–0.0052 mg/kg, respectively. On the basis of these, the measurement has been successfully applied to the analysis of the exogenous phytohormones in the bean sprouts. Except for 4-CPA and IAA, the rest of the analytes were undetected in samples. In sum, the current method can be used for accurate determination and confirmation of PGRs in many other crops, such as bean sprouts.

Effects of Exogenous Phytohormones on Spore Germination and Morphogenesis of Polystichum aculeatum (L.) Roth Gametophyte in vitro Culture

The effects of exogenous phytohormones–gibberellic acid (GA3) and benzyl-aminopurine (BAP)–on the spore germination and morphogenesis of Polystichum aculeatum (L.) Roth gametophyte in vitro culture were studied. In the control, four stages of gametophyte morphogenesis were determined and their periods were established. Spore germination and protonema formation of P. aculeatum occurred according to the Vittaria-type and prothalium development according to the Aspidium-type. The spore germination percentage depended on the storage time duration. It was found that 80–95% of freshly collected spores germinated. Spore viability was within the range of 68–95% after 4–6-month storage under lab conditions and did not exceed 20% after 1.5 year of the storage period. High concentrations of exogenous GA3 (10–5 and 10–6 M) and BAP (10–5 M) significantly inhibited spore germination, whereas low concentrations (GA3 10–7–10–8 M) had an insignificant stimulating effect or did not affect germination at all (BAP 10–6, 10–7, 10–8 M). All concentrations of exogenous BAP were demonstrated to inhibit the development of P. aculeatum gametophyte at the protonema stage, which might be due to the removal of apical dominance. The inhibiting effect directly depended on BAP concentrations. The formation of abnormal thalli of the P. aculeatum gametophyte in the response to exogenous GA3 treatments occurred as a result of impairment of cell growth by elongation. A direct interrelationship between GA3 concentrations and level of morphological abnormalities and grade of thalli underdevelopment was demonstrated.

Genome-wide identification and expression analysis of the CaLAX and CaPIN gene families in pepper (Capsicum annuum L.) under various abiotic stresses and hormone treatments.

Auxin plays key roles in regulating plant growth and development as well as in response to environmental stresses. The intercellular transport of auxin is mediated by the following four gene families: ATP-binding cassette family B (ABCB), auxin resistant1/like aux1 (AUX/LAX), PIN-formed (PIN), and PIN-like (PILS). Here, the latest assembled pepper (Capsicum annuum L.) genome was used to characterise and analyse the CaLAX and CaPIN gene families. Genome-wide investigations into these families, including chromosomal distributions, phytogenic relationships, and intron/exon structures, were performed. In total, 4 CaLAX and 10 CaPIN genes were mapped to 10 chromosomes. Most of these genes exhibited varied tissue-specific expression patterns assessed by quantitative real-time PCR. The expression profiles of the CaLAX and CaPIN genes under various abiotic stresses (salt, drought, and cold), exogenous phytohormones (IAA, 6-BA, ABA, SA, and MeJA), and polar auxin transport inhibitor treatments were evaluated. Most CaLAX and CaPIN genes were altered by abiotic stress at the transcriptional level in both shoots and roots, and many CaLAX and CaPIN genes were regulated by exogenous phytohormones. Our study helps to identify candidate auxin transporter genes and to further analyse their biological functions in pepper development and in its adaptation to environmental stresses.

Comparative effects of two indole-producing Trichoderma strains and two exogenous phytohormones on the growth of Zea mays L., with or without tryptophan

Comparative effects of two indole-producing Trichoderma strains and two exogenous phytohormones on the growth of Zea mays L., with or without tryptophan

Role of PtrXTH1 and PnXTH1 Genes Encoding Xyloglucan Endo-Transglycosylases in Regulation of Growth and Adaptation of Plants to Stress Factors

The expression level of the gene PtrXTH1 encoding xyloglucan endo-transglycosylase in the leaves of Populus tremula L. of wild-type and in response to exogenous phytohormones treatment was analyzed. The highest level of transcripts of PtrXTH1 was detected in young, intensively growing leaves of aspen. In young aspen leaves, the expression of PtrXTH1 was induced by cytokinins, auxins, and brassinosteroids. The content of PtrXTH1 transcripts increased under the constitutive expression of the PnARGOS-LIKE gene. Bioinformatic analysis of PtXTH1 putative promoter region in P. trichocarpa Torr. and A. Gray ex. Hook showed the presence of cis-regulatory elements associated with the regulation of growth and stress resistance. To determine the role of the gene under study, we also created transgenic tobacco plants with constitutive expression of the PnXTH1 gene (the ortholog of PtrXTH1 from the black poplar P. nigra). Transgenic tobacco plants were characterized by an increase in leaf size and fresh and dry weight of the aboveground part under normal growth conditions. When grown under conditions of salinization and drought, transgenic plants were distinguished by increased stress resistance due to the maintenance of cell expansion in roots and stems at a higher level and the ability to more effectively retain water in leaves compared with wild-type plants.

Exogenous Phytohormones Induced Resistance in Citrus reticulata Blanco against Diaphorina citri Kuwayama

Effect of salicylic acid (SA), jasmonic acid (JA) and β-amino butyric acid (BABA) applied on Citrus reticulata Blanco against eggs, nymphs and adults of Asian citrus psylla, Diaphorina citri Kuwayama is reported. Mean number of eggs per budling and nymphs per budling was significantly less in case of SA treatment 1.5 mM (13.7 eggs per budling; 4.3 nymphs per budling) followed by 1.0 mM (28.0 eggs per budling; 9.3 nymphs per budling) in comparison to control (107.3 eggs per budling; 56.2 nymphs per budling). No adult was recorded in both the SA treatments. Mean number of eggs per budling in JA @ 0.10 mM was 61.0 eggs per budling and nymphs 22.3 per budling while on an average 4.0 adults emerged. Different SA and JA treatments resulted in 28.5–87.2, 41.0–92.4 and 51.4–98.3 per cent and 8.9–62.2, 26.2–65.6 and 43.3–89.5 per cent reduction in eggs, nymphs and adults per budling, respectively. Foliar application of BABA @ 400 mM recorded significantly less number of eggs per budling (51.6) which was at par with 300 mM (55.6 eggs per budling). However, the mean number of nymphs per budling was less in 400 mM (25.7) as compared to the other doses. The findings reveal a possibility of deployment of these phytohormones in significantly inhibiting development of D. citri.

Protective role of exogenous phytohormones on redox status in pea seedlings under copper stress

The present work aims to provide insight on the role of phytohormone application in developing efficient practical defense strategies to improve plants tolerance under heavy metal contamination. For this purpose, pea (Pisum sativum L.) seeds were germinated in an aqueous solution of 200μM CuCl2 up to the 3rd day and then continued to germinate in the presence of distilled water (stress cessation) or were subjected to following combinations: Cu+1μM IAA and Cu+1μM GA3 for 3 additional days. The results showed that copper excess induced oxidative stress in germinating seeds, which resulted in changes of the redox state of glutathione and cysteine, and proteomics revealed Cu-induced modifications of thiols (SH) and carbonyls (CO) (indicators of protein oxidation). However, application of IAA or GA3 in the germination medium after 3days of Cu exposure alleviated toxicity on seedlings, despite the persistence of Cu up to 6th day. This improving effect seems to be mediated by a cell Cu accumulation decrease and a protein reduced status recovery, since phytohormones modulate thioredoxin/ferredoxin systems in favor of protecting proteins against oxidation. In addition, an IAA and GA3 protective effect was evidenced by a cellular homeostasis amelioration resulting from the balance conservation between the regeneration and consumption processes of glutathione and cysteine reduced forms. The exogenous effectors also induced modifications of profiles of SH and CO, suggesting changes in the regulation and expression of proteins that could be involved in defense mechanism against Cu stress.

ВЛИЯНИЕ AZOTOBACTER НА АКТИВНОСТЬ ПЕРОКСИДАЗЫ И СОДЕРЖАНИЕ ПЕРЕКИСИ ВОДОРОДА В КОРНЯХ ПРОРОСТКОВ ГОРОХА, ИНОКУЛИРОВАННЫХ RHIZOBIUM

The influence of nodule bacteria, Azotobacter and exogenous phytohormones (IAA and cytokinins) on H 2 O 2 content and the activity of peroxidase in the roots of pea seedlings was studied. H 2 O 2 content, both in control samples and roots inoculated using Rh.lg, and additionally when combined with Azotobacter, was increased over 24 hours following exposure. H 2 O 2 content was lower in seedlings inoculated by Rh.lg than in control plants, and higher in those exposed to Azotobacter. In variants with exogenous phytohormones, the maximum content of H 2 O 2 was reached in 10 minutes; after 24 hours, it became lower than in the control plants. Exogenous phytohormones and Azotobacter during the inoculation of pea plants by Rh. lg. result in significant responses relevant for the regulation of the initial stages of symbiont interaction.

Phytohormones and Beneficial Microbes: Essential Components for Plants to Balance Stress and Fitness.

Plants are subjected to various abiotic stresses, such as drought, extreme temperature, salinity, and heavy metals. Abiotic stresses have negative impact on the physiology and morphology of plants through defects in the genetic regulation of cellular pathways. Plants employ several tolerance mechanisms and pathways to avert the effects of stresses that are triggered whenever alterations in metabolism are encountered. Phytohormones are among the most important growth regulators; they are known for having a prominent impact on plant metabolism, and additionally, they play a vital role in the stimulation of plant defense response mechanisms against stresses. Exogenous phytohormone supplementation has been adopted to improve growth and metabolism under stress conditions. Recent investigations have shown that phytohormones produced by root-associated microbes may prove to be important metabolic engineering targets for inducing host tolerance to abiotic stresses. Phytohormone biosynthetic pathways have been identified using several genetic and biochemical methods, and numerous reviews are currently available on this topic. Here, we review current knowledge on the function of phytohormones involved in the improvement of abiotic stress tolerance and defense response in plants exposed to different stressors. We focus on recent successes in identifying the roles of microbial phytohormones that induce stress tolerance, especially in crop plants. In doing so, this review highlights important plant morpho-physiological traits that can be exploited to identify the positive effects of phytohormones on stress tolerance. This review will therefore be helpful to plant physiologists and agricultural microbiologists in designing strategies and tools for the development of broad spectrum microbial inoculants supporting sustainable crop production under hostile environments.

Effects of heterologous expression of Populus euphratica brassinosteroids biosynthetic enzyme genes CPD (PeCPD) and DWF4 (PeDWF4) on tissue dedifferentiation and growth of Arabidopsis thaliana seedlings

To understand the functions of Populus euphratica CPD (PeCPD) and DWF4 (PeDWF4), the responses to exogenous phytohormone in Arabidopsis-PeCPD and -PeDWF4 transgenic lines (PeCPD-TL and PeDWF4-TL) and corresponding wild type (WT) seedlings were investigated. Results showed that all of PeCPD-TL, PeDWF4-TL and WT seedlings cultured on the mediums containing 2,4-dichlorophenoxyacetic acid (2,4-D) + 6-benzylaminopurin (6-BA) or 2,4-D + 6-BA + brassinolide (BL) could be dedifferentiated to callus with 100% frequency, but they displayed strong differences in callus formation sites, callus growth rates (CGRs) and tissue dedifferentiation degrees. On the medium containing 2,4-D alone, the seedlings of all the plants could formed callus, but callus formation times (CFTs) were delayed, and callus formation rates (CFRs) were differentially decreased. After adding lower concentrations of BL, their CFRs were all restored to 100%, but tissue dedifferentiation degrees were obviously lower than these on the mediums with 2,4-D + 6-BA or 2,4-D + 6-BA + BL. On the mediums containing 6-BA or 6-BA + BL, the seedlings of all the plants failed to produce callus. Semi-quantitative RT-PCR analysis also showed that the transcription levels of PeCPD, PeDWF4, AtCPD and AtDWF4 in PeCPD-TL, PeDWF4-TL and WT were evidently different. These results suggest that PeCPD and PeDWF4 play similar but not exactly the same roles in the regulation of callus morphogenesis of Arabidopsis seedlings, and that BL can partially replace the role of cytokinin to induce callus formation through interacting with auxin.

Tobacco alpha-expansin EXPA4 plays a role in Nicotiana benthamiana defence against Tobacco mosaic virus.

Tobacco EXPA4 plays a role in Nicotiana benthamiana defence against virus attack and affects antioxidative metabolism and phytohormone-mediated immunity responses in tobacco. Expansins are cell wall-loosening proteins known for their endogenous functions in cell wall extensibility during plant growth. The effects of expansins on plant growth, developmental processes and environment stress responses have been well studied. However, the exploration of expansins in plant virus resistance is rarely reported. In the present study, virus-induced gene silencing (VIGS) and Agrobacterium-mediated transient overexpression were conducted to investigate the role of Nicotiana tabacum alpha-expansin 4 (EXPA4) in modulating Tobacco mosaic virus (TMV-GFP) resistance in Nicotiana benthamiana. The results indicated that silencing of EXPA4 reduced the sensitivity of N. benthamiana to TMV-GFP, and EXPA4 overexpression accelerated virus reproduction on tobacco. In addition, our data suggested that the changes of virus accumulation in response to EXPA4 expression levels could further affect the antioxidative metabolism and phytohormone-related pathways in tobacco induced by virus inoculation. EXPA4-silenced plants with TMV-GFP have enhanced antioxidant enzymes activities, which were down-regulated in virus-inoculated 35S:EXPA4 plants. Salicylic acid accumulation and SA-mediated defence genes induced by TMV-GFP were up-regulated in EXPA4-silenced plants, but depressed in 35S:EXPA4 plants. Furthermore, a VIGS approach was used in combination with exogenous phytohormone treatments, suggesting that EXPA4 has different responses to different phytohormones. Taken together, these results suggested that EXPA4 plays a role in tobacco defence against viral pathogens.

ABA signalling manipulation suppresses senescence of a leafy vegetable stored at room temperature.

SummaryPostharvest senescence and associated stresses limit the shelf life and nutritional value of vegetables. Improved understanding of these processes creates options for better management. After harvest, controlled exposure to abiotic stresses and/or exogenous phytohormones can enhance nutraceutical, organoleptic and commercial longevity traits. With leaf senescence, abscisic acid (ABA) contents progressively rise, but the actual biological functions of this hormone through senescence still need to be clarified. Postharvest senescence of detached green cabbage leaves (Brassica oleracea var. capitata) was characterized under cold (4 °C) and room temperature (25 °C) storage conditions. Hormonal profiling of regions of the leaf blade (apical, medial, basal) revealed a decrease in cytokinins contents during the first days under both conditions, while ABA only increased at 25 °C. Treatments with ABA and a partial agonist of ABA (pyrabactin) for 8 days did not lead to significant effects on water and pigment contents, but increased cell integrity and altered 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and cytokinins contents. Transcriptome analysis showed transcriptional regulation of ABA, cytokinin and ethylene metabolism and signalling; proteasome components; senescence regulation; protection of chloroplast functionality and cell homeostasis; and suppression of defence responses (including glucosinolates and phenylpropanoids metabolism). It is concluded that increasing the concentration of ABA (or its partial agonist pyrabactin) from the start of postharvest suppresses senescence of stored leaves, changes the transcriptional regulation of glucosinolates metabolism and down‐regulates biotic stress defence mechanisms. These results suggest a potential for manipulating ABA signalling for improving postharvest quality of leafy vegetables stored at ambient temperature.

Novel Zinc Finger-Homeodomain Gene from Barley (HvZFHD1) is Differentially Regulated During Spike Development and under Hormonal Treatments and Abiotic Stresses

Plant zinc finger-homeodomains (ZFHDs) are transcriptional factors that play an important role in regulating plant growth and development. Several ZFHD genes were cloned and characterized in many plant species. In the present study, a full-length cDNA sequence of ZFHD gene was cloned from barley (termed as HvZFHD1) using reverse transcription polymerase chain reaction (RT-PCR). The sequence analysis showed that the HvZFHD1 was 1477 bp in length, and contained a complete open reading frame (ORF) of 1161 bp. The deduced protein is composed of 386 amino acids, with a predicted molecular weight of 40.46 kDa and a theoretical isoelectric point of 8.5. Multiple sequence alignment indicated that HvZFHD1 protein shared high identity with ZFHD proteins from wheat, maize, and rice. The predicted HvZFHD1 protein contained the characteristic putative zinc finger domain in the N-terminus and a DNA binding homeodomain in the C-terminus. The expression level of HvZFHD1 was investigated using qRT-PCR during spike development and in response to exogenous phytohormones and abiotic stresses. The results showed that the expression level of HvZFHD1 was fluctuated during spike development with higher expression during anthesis, medium milk, late milk, and early dough stages. The expression of barley ZFHD1 was strongly responsive to abscisic acid treatment and was up-regulated in seedlings treated with methyl jasmonate, salicylic acid, and ethephone. In addition, the expression levels of HvZFHD1 were increased by dehydration, salinity, and heat stress, but not affected by cold stress. The expression patterns of HvZFHD1 suggest that it might play a role in flowering and flower development and is involved in plant responses to abiotic stresses.

The role of expansin genes PtrEXPA3 and PnEXPA3 in the regulation of leaf growth in poplar

The genes of α-expansins of woody plants are of great interest for genetic engineering, since they can potentially be used to improve the tree growth parameters. In the flora of Russia, model woody plants for plant biotechnology are aspen (Populus tremula L.) and black poplar (Populus nigra L.). The objective of this study was to determine the role of α-expansin-encoding genes, aspen PtrEXPA3 and black poplar PnEXPA3, in the regulation and maintenance of woody plant growth. To achieve this goal, the PtrEXPA3 expression level were determined upon exogenous phytohormone treatment, the action of stress factors, and constitutive expression of the PnARGOS-LIKE gene. In addition, transgenic aspen plants with constitutive expression of the black poplar PnEXPA3 gene were generated, and their morphological analysis was carried out. The highest PtrEXPA3 mRNA level was detected in young intensely growing aspen leaves, and furthermore, expression of the gene was induced by exogenous cytokinins and auxins. In response to NaCl and constitutive expression of the PnARGOS-LIKE gene, the PtrEXPA3 mRNA level decreased. Transgenic aspen plants with constitutive PnEXPA3 expression were characterized by the decreased size of leaves, petioles, and internodes, as well as the increased size of leaf epidermal cells, while the stem size remained unchanged. Taken together, the data obtained enable the suggestion that the PtrEXPA3 and PnEXPA3 genes encode cytokinin- and auxin-regulated, leaf-specific expansins that are involved in the cell expansion.