The aim of this work was to assess the effect of different Cd2+concentrations on some antioxidant enzymes in Festuca arundinacea. Increased activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione S-transferase, and glutathione reductase were ascertained in response to low Cd²⁺ concentrations (0-20 μM), whereas the enzyme activities were less increased or decreased at a higher Cd²⁺ dosage (50 μM) and a longer exposure. The content of reduced glutathione (GSH) decreased significantly with increasing Cd²⁺ concentrations, whereas the content of oxidized glutathione (GSSG) increased proportionally to the amount of Cd²⁺ applied. Further experiments, performed by incubating the enzyme extracts with oxidized glutathione, evidenced that the addition of GSSG to the incubation mixtures caused significant decreases of some enzymatic activities. Finally, the effect of glutathione S-transferase, FaGST I, extracted from fescue seedlings and purified till homogeneity, on these enzyme activities was investigated. It was found that FaGST I enhanced the decreased enzymatic activities caused by GSSG.

Viral resistance can be effectively induced in transgenic plants through their silencing machinery. Thus, we designed nine short hairpin RNAs (shRNA) constructs to target nuclear inclusion protein b (NIb), helper component proteinase (HC-Pro), cylindrical inclusion protein (CI) and viral protein genome linked (VPg) genes of Potato virus Y (PVY^N) and Tobacco etch virus (TEV-SD1). The shRNAs were completely complementary to the genes of PVY^N, and contained 1-3 nt mismatches to the genes of TEV-SD1. To study the specificity of gene silencing in shRNA-mediated viral resistance, the constructs were introduced into tobacco plants. The results of viral resistance assay revealed that these nine kinds of transgenic tobacco plants can effectively induce viral resistance against both PVY^N and TEV-SD1, and the shRNA construct targeting the NIb gene showed higher silencing efficiency. Northern blot and short interfering RNA (siRNA) analyses demonstrated that the viral resistance can be attributed to the degradation of the target RNA through the RNA silencing system. Correlation analysis of siRNA sequence characteristics with its activity suggested that the secondary structure stability of the antisense strand did not influence siRNA activity; 1 to 3 nt 5' end of the sense strand caused a significant effect on siRNA activity where the first base such as U was favourable for silencing; the base mismatch between the siRNA and the target gene may be more tolerated in the 5' end.

In this work, the response of the halophytic shrub Prosopis strombulifera to lowering an osmotic potential (Ψ_o) to -1.0, -1.9, and -2.6 MPa generated by NaCl, Na₂SO₄, and the iso-osmotic combination of them was studied at 6, 12, and 24 h after reaching such values in the growing media. By analyzing the content of abscisic acid (ABA) and related metabolites and transpiration rates, we observed that ABA content varied depending on type of salt, salt concentration, organ analyzed, and age of a plant. ABA content in leaves was much higher than in roots, presumably because of rapid biosynthesis and transport from roots. Leaves of Na₂SO₄-treated plants had the highest ABA content at Ψ_o -2.6 MPa (24 h) associated with sulfate toxicity symptoms. Significant content of ABA-glucose ester (ABA-GE) was found in both the roots and leaves, whereas only low content of phaseic acid (PA) and dihydrophaseic acid (DPA). The roots showed high ABA-GE accumulation in all treatments. The highest content of free ABA was correlated with ABA-GE glucosidase activity. The results show that ABA-GE and free ABA work together to create a specific stress signal.

The present study examined the effect of salicylic acid (SA) pre-treatment on soybean seedlings exposed to cadmium and/or UV-B stress. Dry mass, pigment content, net photosynthetic rate (P_N), stomatal conductance (g_s), and transpiration rate (E) were decreased by the Cd and/or UV-B stress. SA alleviated the adverse effects of Cd and/or UV-B on growth, pigment content, PN, and gs, but did not mitigate the inhibitory effect of Cd/UV-B on E, or that of Cd on chlorophyll fluorescence parameters. Cd and/or UV-B induced oxidative stress and increased lipid peroxidation that was significantly decreased by SA pre-treatment. The Cd and/or UV-B increased superoxide dismutase (SOD) activity, decreased peroxidase (POD) activity, and catalase (CAT) activity was mostly unaltered. SA might act as one of the potential antioxidants as well as a stabilizer of membrane integrity to improve plant resistance to the Cd and/or UV-B stress.

Nitric oxide (NO), gibberellic acid (GA), and phosphorus (P) have been reported to regulate primary root (PR) growth, but interactions between them in the growth of Arabidopsis PR remain unknown. This work confirmed that low P availability significantly inhibited PR growth and that NO arrested PR growth in either high P or low P conditions. Moreover, NO counteracted the stimulatory effects of GA on PR growth under low P conditions. Finally, the dependence of low P and NO inhibition of PR growth on the DELLA-SLY pathway revealed that NO stabilized a major DELLA protein. We therefore conclude that antagonistic interactions between NO and GA regulate PR growth under both the high and low P conditions, and a DELLA-SLY module is the node where NO, GA, and P pathways converge and interact.

Globe artichoke (Cynara cardunculus L. var. scolymus) is rich in flavonoids which contribute to its health-promoting properties. With the aim of understanding the genetic control of flavonoid accumulation in artichoke, we isolated an artichoke full-length cDNA sequence encoding flavonoid 3'-hydroxylase (F3'H), a major enzyme of the flavonoid hydroxylation pattern. In silico studies confirmed that the deduced amino acid sequence of CcF3'H is highly similar to F3'Hs isolated from other Asteraceae. The Northern blot analysis demonstrated that CcF3'H was highly expressed in leaves and in specific parts of the heads. Its expression differed slightly among artichoke cultivars. The overexpression of CcF3'H in tobacco plants led to the accumulation of flavonoids and to an increase of flower colour intensity, thus identifying CcF3'H as promising candidate for genetic engineering. CcF3'H represents the first structural gene of the flavonoid biosynthesis isolated from C. cardunculus, and its characterization sheds light on the accumulation of flavonoids.

We have earlier reported that the endophyte infection can enhance photosynthetic capacity and antioxidant enzyme activities in rice exposed to salinity stress. Now, the changes in primary photochemistry of photosystem (PS) II induced by Na₂CO₃ stress in endophyte-infected (E+) and endophyte-uninfected (E-) rice seedlings were studied using chlorophyll a fluorescence (OJIP-test). Performance indices (PI_ABS and PI_Total) of E- and E+ rice seedlings revealed the inhibitory effects of Na₂CO₃ on PS II connectivity (occurrence of an L-band), oxygen evolving complex (occurrence of a K-band), and on the J step of the induction curves, associated with an inhibition of electron transport from plastoquinone A (Q_A) to plastoquinone B (Q_B). In E+ seedlings, Na₂CO₃ effects on L and K bands were much smaller, or even negligible, and also there was no pronounced effect on the J step. Furthermore, the OJIP parameters indicated that 20 mM Na₂CO₃ had a greater influence on the photosystem (PS) II electron transport chain than did the 10 mM Na₂CO₃, and that changes were greater in E- than in E+. Endophyte infection was therefore deemed to enhance the photosynthetic mechanism of Oryza sativa exposed to salinity stress.

Amino acids (AAs) play significant roles in metal binding, antioxidant defense, and signaling in plants during heavy metal stress. In the present study, the essential amino acids (EAAs), non-essential amino acids (NEAAs), as well as the enzymes of proline and cysteine biosynthetic pathways were studied in contrasting arsenic accumulating rice genotypes grown in hydroponic solutions with addition of arsenate (As^V) or arsenite (As^III). Under a mild As stress, the total AAs content significantly increased in both the rice genotypes with a greater increase in a low As accumulating rice genotype (LAARG; IET-19226) than in a high As accumulating rice genotype (HAARG; BRG-12). At the equimolar concentration (10 μM), As^III had a greater effect on EAAs than As^V. Conversely, As^V was more effective in inducing a proline accumulation than As^III. Among NEAAs, As significantly induced the accumulation of histidine, aspartic acid, and serine. In contrast, a higher As concentration (50 μM) reduced the content of most AAs, the effect being more prominent during As^III exposure. The inhibition of glutamate kinase activity was noticed in HAARG, conversely, serine acetyltransferase and cysteine synthase activities were increased which was positively correlated with the cysteine synthesis.

A gene (named BcFLC1) homologous to the AtFLC gene, which encodes a floral repressor, was isolated from the nonheading Chinese cabbage (Brassica campestris L. ssp. chinensis) cv. NJ074. The gene showed high similarity to AtFLC. For studying the gene function, we designed to introduce the BcFLC1 gene into Arabidopsis thaliana. The results showed that BcFLC1 had effects on flowering time similar to AtFLC. We also found that Arabidopsis cold-tolerance was enhanced by BcFLC1 overexpression. Under low temperature stress, the BcFLC1 transgenic plants exhibited stronger growth than wild-type plants. The elevated cold tolerance of the BcFLC1 over-expressing plants was also confirmed by the changes of electrolyte leakage and malonyldialdehyde and proline content.

In vitro flowering protocols were developed for a limited number of early flowering pea (Pisum sativum L.) cultivars. This work was undertaken to understand the mechanisms regulating in vitro flowering and seed-set across a range of pea genotypes. Its final goal is to accelerate the generation cycle for faster breeding novel genotypes. We studied the effects of in vivo and in vitro applications of the antigibberellin Flurprimidol together with radiation of different spectral compositions on intact plants, plants with the meristem removed, or excised shoot tip explants. Based on our results, we present a simple and reliable system to reduce generation time in vitro across a range of pea genotypes, including mid and late flowering types. With this protocol, more than five generations per year can be obtained with mid to late flowering genotypes and over six generations per year for early to mid flowering genotypes.

This study investigated the effects of exogenous hydrogen sulfide (H₂S) on the redox states of ascorbate (AsA) and glutathione (GSH) in maize leaves under NaCl (100 mM) stress. Salt stress increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), Γ-glutamylcysteine synthetase (Γ-ECS), and L-galactono-1,4-lactone dehydrogenase (GalLDH), malondialdehyde content and electrolyte leakage, and reduced the ratios of reduced and oxidised forms of AsA (AsA/DHA) and GSH (GSH/GSSG) compared with control. Pretreatment with NaHS (H₂S donor) further enhanced the activities of the above enzymes except MDHAR and ameliorated the decrease in the ratios of AsA/DHA and GSH/GSSG compared with the salt stress alone. Pretreatment with NaHS significantly reduced the malondialdehyde content and electrolyte leakage induced by the salt stress. Pretreatment with NaHS alone did not affect any of the above mentioned parameters compared with the control. Our results suggest that exogenous H2S could maintain the redox states of ascorbate and glutathione by up-regulating the ascorbate and glutathione metabolism and thus play an important role for acquisition of salt stress tolerance in maize.

Rice (Oryza sativa L.) is seriously impacted by global soil salinization. To determine the quantitative trait loci (QTLs) related to salt tolerance in rice roots, F_2:3 and BC₁F_2:3 populations derived from a cross between the cv. Dongnong 425 of high quality and yield and the salt-tolerant cv. Changbai 10, were studied at different development stages. Two genetic linkage maps of F_2:3 and BC1F_2:3 populations were constructed. A 66 mM NaCl solution was used to irrigate the field and to analyze the dynamic QTL of some rice root traits. Using unconditional and conditional QTL mapping methods, 30 unconditional QTLs and 16 conditional QTLs related to the 6 root traits were detected on the 9 rice chromosomes during different developmental stages. Fourteen pairs of unconditional and conditional QTLs were detected at the identical developmental stage in the identical population. A number of QTLs were detected at different developmental stages, however, many did not appear at the last stage. Remarkably, qRKC1 appeared continuously at multiple stages in both the populations suggesting its key role in regulating the salt tolerance of rice roots.

Cinnamate 4-hydroxylase (C4H) is the second enzyme in the phenylpropanoid pathway which participates in the synthesis of numerous phenylpropanoid compounds such as flavonoids, lignins, suberins and others. We identified a gene putatively coding for Class I C4H in apricot and plum and we analyzed the expression pattern of this gene under different apricot/plum graft combinations with different degree of compatibility. The full-length cDNA is 1 739 bp with a 1 515 bp open reading frame encoding a protein of 504 amino acids. Like other C4Hs, the predicted C4H polypeptides included conserved domains of cytochrome P₄₅₀. The genomic sequence of the apricot C4H gene was interrupted by two introns 335 bp and 904 bp long. Several regulatory motifs including P-, A-, L- and H-boxes, which were conserved across phenylpropanoid metabolism-related genes in higher plants, were found in a 1 300 bp upstream promoter region of the apricot C4H gene. A phylogenetic analysis showed that all Prunus sequences clustered together and were closely related to Malus and Rubus C4H genes. The transcription of Class I PruC4H was detected in all the examined graft combinations, which suggested its rather constitutive character.

Soil salinity is a major abiotic stress and salt overly sensitive (SOS) pathway plays an important role in imparting tolerance to salinity by reinstating cellular ionic equilibrium. Salt overly sensitive 1 (SOS1) gene of SOS pathway has been implicated in increasing salt tolerance in plants. In this study, a 734 bp fragment of SOS1 promoter (SbUSOS1) was isolated from a halophyte Salicornia brachiata Roxb. In silico analysis of SbUSOS1 predicted several cis-acting regulatory elements such as DOF motif, GT elements, ABRE-like sequence, and root specific motifs. Functional validation of SbUSOS1 into tobacco stems and leaves using the GUS reporter gene showed that this promoter is induced by salt stress (250 mM NaCl) but not by ABA (500 μM) and cold (4 °C) stresses. This study indicated that SbUSOS1 was functional with predicted cis-acting elements that could be responsible for its salt-inducible nature. It can be used for the development of salt stress tolerant transgenic plants.

Seasonal dimorphism (summer/winter) has been so far studied only in a few plants and has been focused on summer drought stress. However, Thymus sibthorpii in the study area appears to be affected by winter chilling stress and not by summer drought stress. Thus, the winter leaves were thicker and more compact compared to the summer leaves and they had more stomata and peltate hairs, more sclerenchymatous fibers, vacuoles with phenolics, and chloroplasts than the summer leaves. In addition, their chloroplasts possessed large grana and starch grains. In the summer leaves, cell vacuoles in mesophyll did not contain phenolics, and chloroplasts were devoid of starch grains and had large plastoglobuli. Physiological measurements revealed higher net photosynthetic rate and chlorophyll content in the winter leaves than in the summer leaves. Proline and soluble sugar content along with antioxidative enzyme (superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase) activities were increased in the winter leaves.

We studied the influence of inorganic nitrogen sources (NO₃ ^- or NH₄ ⁺) and potassium deficiency on expression and activity of plasma membrane (PM) H⁺-ATPase in sorghum roots. After 15 d of cultivation at 0.2 mM K⁺, the plants were transferred to solutions lacking K⁺ for 2 d. Then, K⁺ depletion assays were performed in the presence or absence of vanadate. Further, PMs from K⁺-starved roots were extracted and used for the kinetic characterization of ATP hydrolytic activity and the immunodetection of PM H⁺-ATPase. Two major genes coding PM H⁺-ATPase (SBA1 and SBA2) were analyzed by real-time PCR. PM H⁺-ATPase exhibited a higher V_max and K_m in NH₄ ⁺-fed roots compared with NO₃ ^- -fed roots. The optimum pH of the enzyme was slightly lower in NO₃ ^- -fed roots than in NH₄ ⁺-fed roots. The vanadate sensitivity was similar. The expressions of SBA1 and SBA2 increased in roots grown under NH₄ ⁺. Concomitantly, an increased content of the enzyme in PM was observed. The initial rate of K⁺ uptake did not differ between plants grown with NO₃ ^- or NH₄ ⁺, but it was significantly reduced by vanadate in NH₄ ⁺-grown plants.

In this study, we cloned flowering-related genes FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) from domesticated octaploid strawberries (Fragaria × ananassa) and analyzed their expression patterns in cultivars Tochiotome and Akihime. The floral meristem generation was induced under the short day and low temperature (SDLT), but not under the long day and high temperature (LDHT). We found that FaFT1, which is an orthologue of the Arabidopsis floral activator FT, was highly expressed in leaves under LDHT but not expressed in leaves under SDLT. On the other hand, the expression of FaTFL2, which belongs to the TFL1 family of flowering repressing genes, decreased in crowns (stem tissue including meristem) under SDLT. These results suggest that FaTFL2, as opposed to FvTFL1 in wild diploid strawberry Fragaria vesca, is related to flowering of the cultivated strawberry. Moreover, the FaTFL2 expression might be regulated by temperature rather than by photoperiod. We demonstrated that a reduction of the FaTFL2 expression is a key signal for flowering in domesticated strawberries.

Fluorophore tagged proteins are used in Arabidopsis thaliana to understand their functional role in plant development. This requires the analysis of their spatial localization in planta. However, the localization analysis is often perturbed by a significant overlap of the fluorophores used to label proteins of interest and the optical filtering methods available on the confocal microscope. This problem can be addressed by the use of spectral imaging with linear unmixing the image data. We applied this method to help us identify double transgenic A. thaliana lines which expressed two fluorescently tagged auxin transporter proteins: the auxin efflux protein PIN-FORMED-3 (PIN3), tagged with green fluorescent protein (GFP), and the auxin influx protein LIKE-AUX1-3 (LAX3), tagged with yellow fluorescent protein (YFP). This method allows the reliable separation of overlapping GFP and YFP fluorescence signals and subsequent localization analysis highlighting the potential benefit of this methodology in studies of lateral root development.

The performance of control and water-stressed 10-d-old wheat seedlings was compared. During short-term water stress (irrigation was withheld for 9 d), rates of photosynthesis and transpiration, stomatal conductance, and relative water content decreased whereas the proline content increased. Chloroplast proteins were extracted from the leaves, separated by iso-electric focusing through two-dimensional electrophoresis, and stained with CBB R-250. Differentially expressed proteins were detected and analyzed with MALDI-TOF/TOF mass spectrometry. Under water stress, 9 proteins were up-regulated whereas 11 proteins were not affected. The ribulose-1,5-bisphospate carboxylase/oxygenase (Rubisco) small and large subunits, chloride carrier/channel family, and H⁺-ATPase were up-regulated by water stress whereas membrane-bound ATP synthase subunit b and cytochrome b6-f complex were down-regulated.

Abscisic acid (ABA) regulates plant responses to various environmental stresses. Oxidative cleavage of cis-epoxycarotenoids catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED) is the critical step in the biosynthesis of ABA in higher plants. Using a homologous cloning approach, a NCED-like gene (designated as TaNCED1) was isolated from wheat (Triticum aestivum). It contained an open reading frame of 1 848 bp and encodes a peptide of 615 amino acids. Multiple sequence alignments showed that TaNCED1 shared high identity with NCEDs from other plants. Phylogenetic analysis revealed that TaNCED1 was most closely related to a barley HvNCED1 gene. The predicted 3D structure of TaNCED1 showed high similarity with other homologues. Southern blot analysis indicated that TaNCED1 was a single copy in the genome of wheat. TaNCED1 was differentially expressed in various organs and the expression was up-regulated by low temperature, drought, NaCl, and ABA. Heterologous expression of TaNCED1 in tobacco (Nicotiana tabacum) significantly improved its drought tolerance. Under drought treatment, TaNCED1-overexpressing transgenic tobacco plants exhibited higher germination rate, higher relative water content, content of soluble sugars and of ABA when compared with the wild type plants.

Content of malondialdehyde (MDA), proline, phenolics, and saccharides was analyzed during different developmental stages of in vitro root and shoot organogenesis in saffron. The highest content of MDA, proline, and phenolics was detected in nodular calli. Significant changes were also found in the content of polysaccharides, soluble saccharides, oligosaccharides, and reducing saccharides during developmental stages. Histological investigation of nodular calli showed meristematic zones with small and densely stained cells situated at peripheral zones of calli. The meristematic zones surrounded some vascular areas from which de novo organs originated. The parenchymatic cells of inner zones of calli converted to procambium cells that produced vascular tissues.

The present study was carried out to examine the effects of seed soaking in 1 mM ascorbic acid (AA) or 1 mM proline on the growth, content of photosynthetic pigments and proline, relative water content, electrolyte leakage, antioxidant enzymes and leaf anatomy of Hordeum vulgare L. Giza 124 seedlings grown in greenhouse under 100 or 200 mM NaCl. The plants exposed to the NaCl stress exhibited a significant reduction in growth, relative water content, leaf photosynthetic pigments, soluble sugars, as well as alterations in leaf anatomy. However, the treatment with AA or proline ameliorated the stress generated by NaCl and improved the above mentioned parameters. NaCl increased electrolyte leakage, proline content, and activities of antioxidant enzymes (SOD, CAT, and POX). The antioxidant enzymes and leaf anatomy exhibited considerable changes in response to AA or proline application in the absence or presence of NaCl.

In order to elucidate the role of lanthanum (La) in response of Vigna radiata to a salt stress, we investigated the effects of La on the ascorbate and glutathione metabolism. The results show that in comparison with a control, the salt stress increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), γ-glutamylcysteine synthetase (γ-ECS), and L-galactono-1,4-lactone dehydrogenase (GalLDH), and the content of ascorbic acid (AsA) and glutathione (GSH). It also increased the malondialdehyde content (MDA) and electrolyte leakage. The salt stress significantly decreased the ratios of AsA/dehydroascorbate (DHA) and GSH/glutathione disulphide (GSSG) compared with the control. The pretreatment with La not only significantly increased the activities of the above enzymes, the content of AsA, GSH, and the ratios of AsA/DHA and GSH/GSSG, but also significantly reduced the MDA content and electrolyte leakage compared with the salt stress alone. Our results suggest that La could up-regulate the ascorbate and glutathione metabolisms and could have an important role for acquisition of salt stress tolerance in Vigna radiata.

Purple acid phosphatases (PAPs), which are normally found in plant tissues, can hydrolyze a broad spectrum of phosphate esters. In this study, a mungbean [Vigna radiata (L.) Wilczek cv. KPS1] acid phosphatase gene (VrPAP1) was isolated from seedling cotyledons. The full-length of VrPAP1 cDNA contained an open reading frame of 1 644 bp encoding 547 amino acid residues with a predicted molecular mass of 62.07 kDa. Sequence analysis showed that VrPAP1 is purple acid phosphatase. RNA blot analyses indicated that the VrPAP1 accumulated during the first hour in cotyledons of germinating seeds and reached a maximum expression after 24 h and then decreased. The VrPAP1 mRNA was observed in cotyledons, hypocotyls and leaves but not in radicles or dry seeds. DNA blot analysis indicated that VrPAP1 is a single copy gene in the mungbean genome.

Homogeneous low phosphorus availability was reported to regulate root architecture in Arabidopsis via auxin, but the roles of auxin in root architecture plasticity to heterogeneous P availability remain unclear. In this study, we employed auxin biosynthesis-, transport- and signalling-related mutants. Firstly, we found that in contrast to low P (LP) content in the whole medium, primary root (PR) growth of Arabidopsis was partially rescued in the medium divided into two parts: upper with LP and lower with high P (HP) content or in the reverse arrangement. The down part LP was more effective to arrest PR growth as well as to decrease density of lateral roots (DLR) than the upper LP, and effects were dependent on polar auxin transport. Secondly, we verified that auxin receptor TIR1 was involved in the responses of PR growth and lateral root (LR) development to P supply and loss of function of TIR1 inhibited LR development. Thirdly, effects of heterogeneous P on LRD in the upper part of PR was dependent on PIN2 and PIN4, and in the down part on PIN3 and PIN4, whereas density of total LRs was dependent on auxin transporters PIN2 and PIN7. Finally, heterogeneous P availability altered the accumulation of auxin in PR tip and the expression of auxin biosynthesisrelated genes TAA1, YUC1, YUC2, and YUC4. Taken together, we provided evidences for the involvement of auxin in root architecture plasticity in response to heterogeneous phosphorus availability in Arabidopsis.

In the present study, we measured the markers of oxidative stress as well as activity of antioxidative enzymes and content of α-tocopherol in the acclimated and non-acclimated cucumber (Cucumis sativus L.) cell suspension cultures subjected to 150 and 200 mM NaCl. The content of carbonyl groups and lipid peroxidation were lower in the acclimated cultures than in the non-acclimated ones as well as their increases after NaCl treatments. Both NaCl concentrations enhanced activity of glutathione peroxidase in the examined cultures whereas activity of glutathione-S-transferase rose only in the acclimated ones. The increase in content of α-tocopherol induced by NaCl was more pronounced in the acclimated cultures. NaCl caused high decline in cell vigour in the non-acclimated cultures up to 80-90 % at the end of the experiment. The presented data suggest that the acclimated cultures coped with the salt stress better than the non-acclimated ones.

Interactions between indole-3-acetic acid (IAA), abscisic acid (ABA), and ethylene (ET) in the photoperiodic flower induction of a short-day (SD) plant Pharbitis nil were investigated. It was shown that both IAA and ABA applied just before and during the first half of the 16-h-long inductive night inhibited flower induction in P. nil. Ethylene is also thought to be a strong flowering inhibitor of SD plants but only when it is applied in the second half of the inductive night. The application of IAA just before the inductive night decreased the content of endogenous ABA in cotyledons only during the first half of the inductive night. Additionally, the application of 2-aminoethoxyvinylglycine (AVG) - an ethylene biosynthesis inhibitor - partially reversed the inhibitory effect of IAA and ABA on flowering. The results suggest that the mechanisms of P. nil flower inhibition by IAA and ABA might be independent. However, both the hormones influenced ethylene production which directly inhibited flowering. We also show that ABA applied on the cotyledons of P. nil seedlings just before the inductive night caused a clear increase in the expression of PnACS1 and PnACS2 genes (encoding enzymes involved in ethylene biosynthesis) from the first hours after its application. The transcripts of PnACO1 and PnACO3 genes were also increased but their maximal values were shifted in relation to the PnACS1 and PnACS2. The data presented here strongly support the idea that both IAA and ABA inhibit P. nil flowering through the modulation of ethylene biosynthesis.

Plant regeneration through indirect somatic embryogenesis was attempted from the immature cotyledon-derived explant of Cassia angustifolia Vahl. - a valuable leguminous shrub. The highest frequency (90.5 %) of somatic embryos was obtained on a Murashige and Skoog (MS) medium augmented with 10.0 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.0 μM benzyladenine (BA) with the production of a maximum of 22.8 embryos per explant, of which 35.3 % germinated on the same medium after 6 weeks of culture. A half strength MS medium without plant growth regulators facilitated better conversion of embryos into complete plantlets compared to a full strength MS medium. Regenerated plantlets were successfully acclimatized in sterile Soilrite and transferred to field conditions with a 70 % survival rate. Histological studies performed at different stages of embryogenesis revealed the mode of differentiation of embryos from the callus. The content of chlorophylls (a + b) and carotenoids, and the net photosynthetic rate (P_N) in the regenerated plantlets were tested during different periods of acclimatization.

The roles of ascorbic acid (AsA, 1 mM) under an osmotic stress [induced by 15 % (m/v) polyethylene glycol, PEG-6000] were investigated by examining morphological and physiological attributes in Brassica species. The osmotic stress reduced the fresh and dry masses, leaf relative water content (RWC), and chlorophyll (Chl) content, whereas increased the proline (Pro), malondialdehyde (MDA), and H₂O₂ content, and lipoxygenase (LOX) activity. The ascorbate content in B. napus, B. campestris, and B. juncea decreased, increased, and remained unaltered, respectively. The dehydroascorbate (DHA) content increased only in B. napus. The AsA/DHA ratio was reduced by the osmotic stress in all the species except B. juncea. The osmotic stress increased the glutathione (GSH) content only in B. juncea, but increased the glutathione disulfide (GSSG) content and decreased the GSH/GSSG ratio in all the species. The osmotic stress increased the activities of ascorbate peroxidase (APX) (except in B. napus), glutathione reductase (GR) (except in B. napus), glutathione S-transferase (GST) (except in B. juncea), and glutathione peroxidase (GPX), and decreased the activities of catalase (CAT) and monodehydroascorbate reductase (MDHAR) (only in B. campestris). The osmotic stress decreased the glyoxalase I (Gly I) and increased glyoxalase II (Gly II) activities. The application of AsA in combination with PEG improved the fresh mass, RWC, and Chl content, whereas decreased the Pro, MDA, and H₂O₂ content in comparison with PEG alone. The AsA addition improved AsA-GSH cycle components and improved the activities of all antioxidant and glyoxalase enzymes in most of the cases. So, exogenous AsA improved physiological adaptation and alleviated oxidative damage under the osmotic stress by improving the antioxidant and glyoxalase systems. According to measured parameters, B. juncea can be recognized as more drought tolerant than B. napus and B. campestris.

Biotechnological improvement of monocots is often hampered by the lack of efficient regeneration systems, requisite wound responses and low cell competence. Despite these limitations, the biolistic and Agrobacterium methods have been successfully used to produce several transgenic monocots by adjusting the parameters that govern efficient delivery and integration of transgene(s) into plant genome. It is now possible to transform even difficult monocots using tailor-made gene constructs and promoters, suitable A. tumefaciens strains and a proper understanding of the entire process. This success has been reviewed in the present article and a special emphasis was laid on the measures that were taken in overcoming the difficulties that arise due to the differential responses of monocots and dicots. This information is necessary for biotechnological improvement of still newer monocotyledonous plants that have been hitherto difficult to transform.