Calcium ion (Ca²⁺) is essential secondary messenger in plant signaling networks. In this study, the effect of Ca²⁺ on oxidative damage caused by a high irradiance (HI) was investigated in the leaves of two cultivars of tall fescue (Arid3 and Houndog5). Pretreatment of the tall fescue leaves with a CaCl₂ solution significantly increased Ca²⁺ content and intrinsic HI tolerance due to a decreased ion leakage and content of malondialdehyde, hydrogen peroxide, and superoxide radicals. Moreover, the activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase increased in both the cultivars in the presence of Ca²⁺ under the HI stress. In contrast, treatments with a Ca²⁺ chelator ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) or a plasma membrane Ca²⁺ channel blocker LaCl₃ reversed these effects. On the other hand, a pronounced increase in nitric oxide synthase-like activity and NO release by exogenous Ca²⁺ treatment was observed in the tolerant Arid3 plants after exposure to the HI, whereas only a small increase was observed in more sensitive Houndog5. Moreover, the inhibition of NO production by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide or N ^ω-nitro-L-arginine blocked the protective effect of exogenous Ca²⁺, whereas the inhibition of Ca²⁺ by EGTA or LaCl₃ had no influence on the protective effect of NO. The results indicate that NO might be involved in the Ca²⁺-induced activities of antioxidant enzymes further protecting against HI-induced oxidative damage. This protective mechanism was found to be more efficient in Arid3 than in Houndog5.

Alternative respiration pathway (AP) is an important pathway which can be induced by environment stresses in plants. In the present study, we show a new mechanism involving the AP in nitrogen deprivation-induced tolerance of Poa annua callus to salt stress. The AP capacity markedly increased under a 600 mM NaCl treatment or nitrogen deprivation pretreatment and reached a maximum under the nitrogen deprivation pretreatment combined with the NaCl treatment (-N+NaCl). Malondialdehyde (MDA) and H₂O₂ content and Na⁺/K⁺ ratio significantly increased under the 600 mM NaCl treatment but less under the-N+NaCl treatment. Moreover, both the nitrogen deprivation and the NaCl stress stimulated the plasma membrane (PM) H⁺-ATPase activity and increased pyruvate content. The maximal stimulating effect was found under the-N+NaCl treatment. When the AP capacity was reduced by salicylhydroxamic acid (SHAM, an inhibitor of AP), content of MDA and H₂O₂ and Na⁺/K⁺ ratio dramatically increased, whereas PM H⁺-ATPase activity decreased. Moreover, exogenous application of pyruvate produced a similar effect as the nitrogen deprivation pretreatment. The effects of SHAM on the Poa annua callus were counteracted by catalase (a H₂O₂ scavenger) and diphenylene iodonium (a plasma membrane NADPH oxidase inhibitor). Taken together, our results suggest that the nitrogen deprivation enhanced the capacity of AP by increasing pyruvate content, which in turn prevented the Poa annua callus from salt-induced oxidative damages and Na⁺ over-uptake.

Plants are subjected to several abiotic stresses that adversely affect growth, metabolism and yield. The dynamic research in plant genetics complemented by genome sequencing has opened up avenues to address multiple problems caused by abiotic stresses. Though many drought-induced genes have been phytoengineered in a wide range of plants, the drought signal transduction pathways, and the alteration of plant sensing and signaling systems to adverse environments still remain an intriguing subject for comprehensive investigation. To impart enhanced drought tolerance in plants, a thorough perception of physiological, biochemical and gene regulatory networks is essential. Recent functional genomics tools have facilitated the progress in our understanding of stress signaling and of the linked molecular regulatory networks. This has revealed several stress-inducible genes and various transcription and signaling factors that regulate the drought stress-inducible systems. Translational genomics of these drought specific genes using model plants have provided encouraging outcomes, but the in-depth knowledge of the specific roles of various metabolites in plant stress tolerance will lead to evolvement of strategies for the phytoengineering of drought tolerance in plants in future.

Histone deacetylases (HDACs) catalyze histone deacetylation and play an important role in suppression of gene transcription in multiple cellular processes. HDACs are widely distributed in eukaryotes, however, detailed characterrization of HDACs in woody plants is not available. In this study, the sequences of reduced potassium dependency 3/histone deacetylase 1 (RPD3/HDA1) family proteins in black cottonwood (Populus trichocarpa Torr. & A. Gray) were characterized and their expression patterns in response to cold and salt stresses were determined. The RPD3/HDA1 proteins had conserved HDAC domains and can be divided into three classes based on sequence similarity and phylogenetic analysis. The transcripts of the HDAC genes were detected in different amounts in leaves, stems, and roots. The expressions of HDAC genes HDA902, HDA903, HDA904, HDA909, and HDA912 were up-regulated in a cold stress. Interestingly, in a salt stress, most of the HDAC genes were down-regulated. These results indicate that the poplar HDAC genes were regulated by the cold and salt stresses, and the members of the RPD3/HDA1 family play a role in stress responses.

Dicer proteins belong to the RNase III family of proteins, which are key components in small RNA biogenesis. In Solanum lycopersicum, seven Dicer-like (DCL) genes have been identified and have been named SlDCL. In this study, we cloned the full-length sequence of the SlDCL genes including untranslated regions using RNA ligase-mediated rapid amplification of cDNA ends. Our analysis indicates that 7 SlDCLs were located on 5 tomato chromosomes (6, 7, 8, 10, and 11). The gene structure of the SlDCLs covered long genomic regions and contained more than 20 exons. Phylogenetic analysis divided the seven SlDCL members into four subgroups. In general, all seven SlDCLs were expressed in all organs but more in flowers and fruits than in the other parts. Moreover, the expressions of some genes changed slightly after treatment with ethylene or 1-methylcyclopropene suggesting their likely roles in plant responses to ethylene. Our findings provide essential information on SlDCL genes in tomato and will aid in the functional classification of DCL families in plants.

The life cycle of flowering plants is partially defined by environmental cues like day length and temperature. In the model plant Arabidopsis thaliana and temperate cereals, such as barley (Hordeum vulgare) and wheat (Triticum spp.), differences in life cycle control have been associated with a natural variation in FLOWERING LOCUS C (FLC) and VERNALIZATION 1-3 (VRN1-3). In sugar beet (Beta vulgaris L.), variation in vernalization requirement and life cycle is determined by a major gene at the B locus. This gene has recently been identified as a pseudo-response regulator (PRR) gene BOLTING TIME CONTROL 1 (BTC1). A second gene in beet with homology to BTC1 and ARABIDOPSIS PSEUDO RESPONSE REGULATOR 7 (APRR7) in Arabidopsis was identified and termed Beta vulgaris PSEUDO RESPONSE REGULATOR 7 (BvPRR7). We functionally characterized BvPRR7 by transgenic analysis in Arabidopsis and expression profiling during development in beet. We show that BvPRR7 was diurnally regulated and responded to cold. Constitutive expression of BvPRR7 distorted diurnal rhythms and caused late flowering in Arabidopsis suggesting a conserved function of BvPRR7 in clock regulation. Conceivably, the retention of a functional role of BvPRR7 in clock regulation may have facilitated the evolution of a distinct role as major floral regulator of the second PRR7 homolog in beet, BTC1.

Carbon monoxide (CO) is considered as a new emerging cell signal molecule which is involved in plant growth, development, and acquisition of stress tolerance. In recent years, hydrogen sulfide (H₂S) has been found to have similar functions, but crosstalk between CO and H₂S in the acquisition of heat tolerance in plants is not clear. In this study, pretreatment of tobacco (Nicotiana tabaccum L.) cells cultured in a suspension with a CO donor hematin significantly increased survival percentage of cells under a heat stress and regrowth ability after the heat stress, alleviated a decrease in cell vitality, and accumulation of malondialdehyde. In addition, treatment with hematin enhanced the activity of L-cysteine desulfhydrase, a key enzyme in H₂S biosynthesis, which in turn induced accumulation of endogenous H₂S in tobacco cells. Interestingly, hematin-induced heat tolerance was enhanced by addition of NaHS, a H₂S donor, but weakened by specific inhibitors of H₂S biosynthesis DL-propargylglycine or its scavenger hypotaurine. Furthermore, pretreatment with hemoglobin (a CO scavenger) and zinc protoporphyrin IX (a CO specific synthetic inhibitor) had no significant effect on NaHS-induced heat tolerance of tobacco cells. These results suggest that CO pretreatment could improve the heat tolerance of tobacco suspension cultured cells, and H₂S might exert its signal role downstream to CO-induced heat tolerance.

Water use efficiency (WUE) is an worth attempting trait to discover the genomic regions governing it, especially in view of the diminishing water resources for the crop plants in general and rice in particular. In order to address this, the present investigation was aimed at identification of genomic regions governing WUE employing a recombinant inbred line population derived from a cross between INRC10192, a high WUE landrace, and IR64, a high yielding cultivar. A total of 36 quantitative trait loci (QTLs) were detected under control as well as drought conditions on chromosomes 1, 2, 4, 8, 9, 10, and 11. Among all, the QTLs with the marker intervals RM486-RM6703, RM6703-RM11484, RM404-RM447, RM24879-RM171, and RM229-RM332 on chromosomes 1, 8, 10, and 11 were found to govern the water use efficiency related traits such as carbon isotope discrimination, specific leaf area, leaf width, and relative water content. Nine major QTL intervals were targeted for candidate gene identification using gene ontology (GO) and transcriptome-based analyses. Overrepresented GO terms in the targeted QTLs were found to be associated with the genes/pathways controlling stomatal regulatory mechanism, stress responsive genes or transcription factors, and saccharide biosynthesis pathways under stress situation. Hence, these genes or genomic regions are potential candidates for development of high WUE rice cultivars.

Two genes encoding CAX2-like proteins were isolated from a Zn/Cd hyperaccumulating ecotype (HE) and nonhyperaccumulating ecotype (NHE) of Sedum alfredii Hance, and they were named SaCAX2h and SaCAX2n, respectively. Both SaCAX2h:eGFP and SaCAX2n:eGFP proteins were localized to the vacuolar membrane of tobacco epidermal cells and yeast mutants. Heterologous expression of SaCAX2h or SaCAX2n in the Δzrc1 yeast mutant increased Cd content in yeast cells. Yeast complementary assay also revealed that both the transporters could suppress Ca and Mn hypersensitivity and enhance Ca and Mn accumulation in a K667 yeast mutant. The expression patterns of the two genes were different under the Cd treatment. Transcription of SaCAX2h was down-regulated in roots and up-regulated in shoots whereas transcription of SaCAX2n was down-regulated in shoots after the exposition to Cd. Furthermore, over-expression of SaCAX2h enhanced metal accumulation in the tobacco plants. The Cd content increased by 17-19 % in shoots and 31-36 % in roots; the Ca content of the transgenic plants increased by 31-32 % in shoots, and the Mn content increased by 60-79 % in shoots and 22-29 % in roots. These results indicate that SaCAX2h was responsible for Ca and Mn sequestration into vacuoles, and over-expression of SaCAX2h enhanced Cd accumulation in the transgenic tobacco.

Several studies have been performed to elucidate the role of brassinosteroids (BRs) in plant growth and development. However, information on the role of BR signaling in nutrient uptake is limited. This study explores the relationship between BRs and ammonium transporter 1 (AMT1) expression in Arabidopsis roots. We found that BR treatment reduced the expression of AMT1 genes and that a BR receptor BRI1 mutant bri1-5 reversed its BR-repressed expression. Furthermore, the BR signaling transcription factor, BES1, regulates AMT1 expression in roots. NH₄ ⁺-mediated repression of AMT1;1, AMT1;2, and AMT1;3 was suppressed in a gain-of-function BES1 mutant (bes1-D). This mutant was more sensitive to methyl-ammonium and contained a higher ammonium content compared to wild-type plants. However, BES1 failed to bind E-box elements present in the promoter region of the AMT1 genes. Furthermore, NH₄ ⁺-mediated glutamine synthetase (GS) and glutamine oxoglutarate aminotransferase (GOGAT) gene expressions were partially inhibited, and GS activity was slightly lower in the bes1-D mutant relative to that observed in wild-type En2 roots. NH₄ ⁺-mediated AMT1 suppressions are known to be caused by N-metabolites rather than NH₄ ⁺ itself, and glutamine application inhibited AMT1 expression in both En2 and bes1-D indicating that BES1 activation inhibited NH₄ ⁺-mediated GS/GOGAT induction, which might in turn inhibit AMT1 repression. In conclusion, the present study demonstrates that BR regulated nitrogen uptake and assimilation via the BR signaling pathway.

The role of peroxisomes in the oxidative injury induced by the auxin herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in leaves of pea (Pisum sativum L.) plants was studied. Applications of (2,4-D) on leaves or to root substrate increased the superoxide radical production in leaf peroxisomes. Foliar application also increased H₂O₂ contents in leaf peroxisomes. Reactive oxygen species (ROS) overproduction was accompanied by oxidative stress, as shown by the changes in lipid peroxidation, protein carbonyls, total and protein thiols, and by the up-regulation of the activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase, catalase, glucose 6-phosphate dehydrogenase and NADP⁺-dependent isocitrate dehydrogenase. Foliar or root 2,4-D applications also induced senescence symptoms in pea leaf peroxisomes, as shown by the decrease of protein content and glycolate oxidase and hydroxypyruvate reductase activities, and by the increase of endopeptidase, xanthine oxidase, isocitrate lyase and acyl-CoA oxidase activities as well as of 3-ketoacyl-CoA thiolase and thiol-protease protein contents. 2,4-D did not induce proliferation of pea leaf peroxisomes but induced senescence-like morphological changes in these organelles. Results suggest that peroxisomes might contribute to 2,4-D toxicity in pea leaves by overproducing cell-damaging ROS and by participating actively in 2,4-D-induced leaf senescence.

Ttranscription factors WRKY play vital roles in response to biotic and abiotic stresses, and previous studies have predominantly focused on model plants and fairly limited research has been performed with tomato. In the present study, a novel pathogen-induced WRKY gene named SpWRKY6 was isolated from the late blight resistant tomato (Solanum pimpinellifolium) cultivar L3708 using in silico cloning and reverse transcription polymerase chain reaction (RT-PCR) methods. Multiple sequence alignment with other plant WRKYs indicates that SpWRKY6 contains two WRKY domains and belongs to group I WRKY transcription factors. Furthermore, some cis-acting elements associated with responses to environmental stresses were observed in the promoter region of this gene. Gene expression patterns were determined by analyzing microarray data of SpWRKY6 in tomato and of an orthologous gene from Arabidopsis thaliana using the Genevestigator tool. The results reveal a very strong biotic and abiotic stress responsive behaviour of this gene. Moreover, bioinformatics results were confirmed by real time quantitative polymerase chain reaction and show that SpWRKY6 expression was rapidly induced after infection with Phytophthora infestans and Botrytis cinerea, respectively. Expression of SpWRKY6 was up-regulated by application of various phytohormones including salicylic acid, methyl jasmonate, and abscisic acid. Likewise, the SpWRKY6 expression was induced by NaCl, drought, heat, cold, and HgCl₂ treatments.

The effects of exogenous salicylic acid (SA), sodium nitropusside (SNP, a nitric oxide donor), or their combination on dwarf polish wheat (Triticum polonicum L.) seedlings under UV-B stress were studied. The UV-B stress significantly decreased plant height, shoot dry mass, pigment content, net photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, transpiration rate, and variable to maximum chlorophyll fluorescence ratio (F_v/F_m) in all plants, but less in the presence of SA, SNP, and their combination. On the other hand, there were considerable increases in malondialdehyde (MDA), proline, O₂ ^*-, and H₂O₂ content under the UV-B stress. When SA, SNP, and their combination were applied, content of MDA, proline, H₂O₂, and O₂ ^*- were less increased. Moreover, there were considerable increases in activities of superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione reductase under the UV-B stress and more in the presence of SA, SNP, and their combination. Therefore, it is considered that SA, SNP, and especially their combination could alleviate UV-B stress in dwarf polish wheat.

To investigate the antioxidative response of glutathione metabolism in Urtica dioica L. to a cadmium induced oxidative stress, activities of glutathione reductase (GR), glutathione-S-transferase (GST), and glutathione peroxidase (GSH-Px), content of reduced (GSH) and oxidized (GSSG) glutathione, lipid peroxidation (LPO), and also accumulation of Fe, Zn, Mn, Cu besides Cd were determined in the roots, stems, and leaves of plants exposed to 0 (control), 0.045, and 0.09 mM CdCl₂ for 58 h. Whereas the Cd content continuously increased in all organs, the Fe, Zn, Mn, and Cu content decreased in dependence on the applied Cd concentration and incubation time. The Cd treatment resulted in increased GR and GST activities in all organs, however, GSH-Px activity was dependent on Cd concentration and plant organ. The GSH/GSSG ratio maintained above the control level in the stems at both Cd concentrations. The LPO was generally close to the control values in the roots and stems but it increased in the leaves especially at 0.09 mM Cd.

Members of the Brassicaceae family disperse their seeds through a mechanism commonly referred to as fruit dehiscence or pod shatter. Pod shatter is influenced by variations in valve margin structure and by the molecular control pathways related to valve development. Anatomical patterns of the dehiscence zone from Brassica napus L., Brassica rapa L., Brassica carinata L., and Sinapis alba L., representing fruit types differing in pod shatter resistance, were compared using histological staining. The pod shatter-susceptible plant B. napus showed an increased lignin deposition at the vascular bundle of the replum as well as an increased separation of cell layers. In pod shatter-resistant plants S. alba, B. rapa, and B. carinata, we observed two layers of lignified valve margin cells. From these four species, we isolated and identified homologs of SHATTERPROOF (SHP1, SHP2), INDEHISCENT (IND), ALCATRAZ (ALC), FRUITFULL (FUL), AGAMOUS (AG), NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1), and SEEDSTICK (STK) genes involved in fruit development and pod shatter in Arabidopsis. Transcriptional analysis of these eight genes was performed by real-time polymerase chain reaction and the results demonstrate that differences in the expression patterns of the eight genes may be associated with dehiscence variation within these four species.

Ascorbate (AsA) is an important antioxidant that can scavenge reactive oxygen species to protect plant cells against oxidative stress. Guanosine 5'-diphosphate (GDP)-L-galactose phosphorylase (GGP) is a key enzyme in the AsA biosynthetic pathway. To investigate the functions of GGP in AsA synthesis and oxidative stress tolerance in tomato, antisense lines with a reduced expression of SlGGP were obtained. Photobleaching after treatment of leaf disks with methyl viologen was more severe in transgenic lines compared to wild type (WT) plants. Moreover, compared with the WT plants, the transgenic plants showed a higher content of hydrogen peroxide, superoxide anion, malondialdehyde, as well as ion leakage, but a lower content of AsA and chlorophylls, ascorbate peroxidase activity, net photosynthetic rate, and maximal photochemical efficiency of photosystem II. Results of real-time quantitative polymerase chain reaction show that suppression of the SlGGP gene in the transgenic plants reduced their oxidative stress tolerance.

Leaf anatomy and irradiance-dependent leaf transmittance changes serving as irradiance acclimation mechanisms in leaves were studied in two ecologically contrasting Tradescantia species, a shade plant T. fluminensis Vell. and a sun plant T. sillamontana Matuda, grown at different irradiances. A dramatic increase in leaf thickness (2 to 4-fold) under a high growth irradiance (800 μmol m^-2 s^-1) compared with a low growth irradiance (60 μmol m^-2 s^-1), achieved mainly by expansion of the epidermis, was recorded in both species. The effect took place on the background of modest changes in mesophyll thickness (1.8-fold in T. fluminensis and 1.15-fold in T. sillamontana) and chloroplast size (0.8-fold in T. fluminensis and an insignificant change in T. sillamontana). Mesophyll structure and growth irradiance response did not seem to facilitate significantly light-dependent chloroplast (avoidance) movement in these species. Nevertheless, an exceptionally large (2 to 4-fold) irradiance-induced increase in light transmittance attributable to chloroplast avoidance movement was revealed. This increase by far exceeded that in other higher plants according to available literature. The magnitude of the irradiance-dependent transmittance changes positively correlated both with the rate of photosystem II recovery and with the extent of xanthophyll deepoxidation in the leaves. This was opposite to a negative correlation observed between the same parameters in different plant species. We hypothesize that, at the evolutionary timescale, chloroplast avoidance movement might adjust independently from other photoprotective mechanisms, e.g., non-photochemical quenching, whereas, on the ontogenetic timescale, adjustment of these mechanisms inevitably follows the same trend.

In northern China, freezing injury is observed frequently in the rare species Magnolia wufengensis but not in the more common species Magnolia denudata. To investigate the role of the phytohormone abscisic acid (ABA) on frost tolerance in these two species, exogenous ABA was applied to the seedlings and then physiological and biochemical responses were measured during cold acclimation. Shoot growth cessation was stimulated by ABA in M. wufengensis but not in M. denudata. Abscisic acid inhibited shoot growth in M. wufengensis but not in M. denudata. Treatment with ABA stimulated leaf senescence in both species, and this effect was greater in M. denudata. For both species, ABA-treated plants exhibited bud dormancy sooner and had an increased tolerance to freezing, decreased water content and increased accumulation of proline, glucose, and fructose in shoots. These effects were generally greater for M. denudata. Freezing tolerance was significantly correlated with content of water, proline, glucose, and fructose for both species, but freezing tolerance was significantly correlated with raffinose content only in M. wufengensis. We conclude that exogenous ABA could increase cold acclimation and improve cold hardiness of both Magnolia species, although M. denudata was more responsive to ABA than M. wufengensis, which might result from a greater dehydration and accumulation of proline and certain soluble sugars.

PopW, a harpin protein identified from Ralstonia solanacearum, has multiple beneficial effects in plants, promoting plant growth and development, increasing crop yield, and inducing resistance to pathogens. Tobacco plants transformed with popW, the PopW-encoding gene, exhibited a promoted growth rate and enhanced resistance to Tobacco mosaic virus (TMV). Here, it is documented that the transgenic tobacco plants overexpressing popW exhibited a higher resistance to R. solanacearum YN10 infection compared with that of the wild-type plants. In the popW-expressing tobacco lines, an enhanced H2O2 accumulation and hypersensitive reaction (HR) were activated in the inoculated site. In addition, the resistance was accompanied with increased transcripts in numbers of genes related to defense (including HR), reactive oxygen species (ROS) scavenging, and salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) production. These results suggest that popW acted as positive regulator in tobacco resistance against R. solanacearum via modulation of SA-, JA-, and ET-mediated signaling pathways. We report for the first time that the expression of a harpin-encoding gene in vivo improved plant resistance to R. solanacearum.

The roles of ethylene (ET) or salicylic acid (SA) in plant response to low temperature (LT, 5 °C) have been implicated. However, the combined effect of ET- and SA-signaling on plant growth and metabolism under LT remains to be evaluated. In this study, we comparatively analyzed the response of Arabidopsis ethylene insensitive (ein) 2-1 (an ET insensitive mutant), nonexprressor of pathogenesis relative (npr)1-1 (an SA insensitive mutant) and double mutant ein2-1/npr1-1 plants to LT. The results show that a LT of 5 °C induced plant growth retardation to a less degree in ein2-1, an intermediate degree in npr1-1, but a much larger in ein2-1/npr1-1 compared to the wild-type (WT) plants. The LT susceptibility of the ein2-1/npr1-1 plants was correlated to a lower net photosynthetic rate and proline content, and a higher content of H₂O₂ and malondialdehyde and electrolyte leakage relative to the WT plants. Lower activities of superoxide dismutase, peroxidase, and catalase, as well as a lower glutathione content and a ratio of its reduced form to its oxidized form were also observed in the double mutant plants as compared with the WT plants. However, at normal conditions (23 °C), all the tested physiological and biochemical parameters were comparable between the ein2-1/npr1-1 and WT plants, and plant growth was even better in the double mutant than in the WT plants. On the contrary, most of the above-mentioned parameters were advantageous in the ein2-1 and npr1-1 plants over the WT plants under the LT conditions. These data suggest that a parallel function or physiological redundancy of nonexpressor of pathogenesis relative 1 and ethylene insensitive 2 existed in the Arabidopsis plant response to the LT. On the other hand, an interaction between ET- and SA-signaling occurred during this process.

The effects of NiSO₄, calcium, and L-histidine (His) on the components of ascorbate-glutathione cycle, antioxidant enzymes and lipid peroxidation in a tomato cultivar Early Urbana Y was investigated. The activities of enzymes including catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR), lipoxygenase (LOX), and phenylalanine ammonia lyase (PAL) were measured. In addition, the content of H₂O₂, ascorbate (ASC), dehydroascorbate (DHA), reduced glutathione (GSH), chlorophyll (Chl) a+b, carotenoids, proteins, malondialdehyde (MDA), membrane aldehydes, and electrolyte leakage (EL) were determined. Results suggest that the excess of Ni increased the content of H₂O₂, MDA, membrane aldehydes and proteins in roots as well as GPX, LOX, APX activities, and EL in leaves, whereas Ca and His ameliorated these effects. Moreover, decreasing leaf GSH and DHA content and GR activity were observed under the Ni stress, but these parameters were raised by Ca plus His treatment. However, no improvement in leaf protein, ASC, root GSH content, and activities of PAL and CAT were observed by using Ca or His under Ni stress.

Polygalacturonases are enzymes involved in plant cell wall growth and reorganization. Transgenic Arabidopsis thaliana plants with a Saccharomyces cerevisiae endopolygalacturonase gene (PGU1) were obtained. The yeast gene was properly expressed in the plants as it has been shown by RT-PCR as well as by the increase in the endopolygalacturonase activity. The transgenic plants showed conspicuous malformations in early stages of development probably due to a weak cell adhesion. On the other hand, adult plants exhibited almost no phenotypic differences as compared to the wild type plants, this suggesting the appearance of some mechanisms on the plant side to counteract the effect of the overexpressed polygalacturonase.

Sunflower plants were transformed via co-cultivation of previously bombarded hypocotyl explants with Agrobacterium tumefaciens harboring the plasmid pNGL that contains the human lysozyme gene. The transformed shoots were selected using kanamycin and regenerated plants were analyzed using histochemical β-glucuronidase assay. Southern, Western and Northern blot analyses indicated the transfer, expression and stable integration of the foreign DNA into the sunflower genome. Resistance against the phytopathogenic fungus Sclerotinia sclerotiorum, which causes white mold disease, was confirmed using a phytopathogenic test and microscopic observation of the infection process.

The present study evaluated the use of γ-radiation to physically remove selective marker genes previously introduced into the soybean genome. Homozygous seeds from a transgenic soybean line carrying the gus and ahas transgenes were irradiated with γ-rays. Six plants presenting a deleted gus gene were analyzed by Southern blot to confirm removal of both ahas and gus genes. Line 1A presented an absence of the gus gene cassette and presence of the ahas gene cassette.

The pattern and expression level of β-glucuronidase (gus) reporter gene regulated by six heterologous promoters were studied in transgenic Populus tremula × P. alba plants obtained by Agrobacterium-mediated transformation. Binary vector constructs used contained the following promoter sequences: the CaMV35S from cauliflower mosaic virus; its duplicated version fused to the enhancer sequence from alfalfa mosaic virus; CsVMV from cassava vein mosaic virus; ubiquitin 3 from Arabidopsis thaliana (UBQ3); S-adenosyl-L-methionine synthetase (Sam-s) from soybean; and the rolA from Agrobacterium rhizogenes. Histochemical staining of root, stem and leaf tissues showed phloem and xylem-specific gus expression under rolA promoter, and constitutive expression with the other putative constitutive promoters. Quantitative GUS expression of 10 - 15 independently transformed in vitro grown plants, containing each promoter, was determined by fluorimetric GUS assays. The UBQ3-gus fusion induced the highest average expression level, although an extensive variation in expression levels was observed between independent transgenic lines for all the constructs tested.

This review summarizes the recent progress made towards the development of transgenic plants with improved tolerance to water stress and salinity. Of the various strategies employed, emphasis has been given to the genes engineered for the biosynthesis of osmoprotectants and osmolytes. This review also briefly discusses the importance of the use of specific stress inducible promoters and the future prospects of transgenic plants with improved agronomic traits.

Three types of transgenic plants of Solanum tuberosum cvs. Kamyk and Oreb, and Nicotiana tabacum cvs. Maryland Mammoth and Trapezond were selected according to intensity of introduced ipt gene expression and resulting amount of synthesised cytokinins (CKs). In comparison with controls, original transgenic regenerants grown in vitro showed a massive increase of CK contents, in tobacco by 379 % and in potato by 159 % (MAS). Potato grown in soil from tubers of transgenic plants demonstrated a moderate increase (44 %) of CK contents (MOD). Transgenic tobacco grown from seeds in vitro did not show any significant change in CK contents (NOT). Initial (RuBPC_i and RuBPO_i) and total (RuBPC_t) activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), and the activity of phosphoenolpyruvate carboxylase (PEPC) were not significantly affected by the transformation in the NOT plants. In the MOD plants, the RuBPCO activities were stimulated by up to 34 % whereas the PEPC activity was decreased by 17 %. On the other hand, all the measured enzyme activities were 32 - 91 % lower in the MAS. Leaf area, fresh and dry masses, and chlorophyll and soluble protein contents also went down with increasing CK amounts in the transformants. Dependence of RuBPC_i/RuBPO_i and RuBPC_t/PEPC ratios on the relative CK amounts in transgenic plants revealed that the individual enzyme activities were not affected uniformly. Endogenous CK contents in the MAS thus apparently exceeded an optimum needed for positive effects on many physiological traits and became a stress factor for such plants.

Following drought stress at supraoptimal temperature the increase in proline (Pro) content in transgenic (T) soybean [Glycine max (L.) Merr. cv. Ibis] plants overexpressing the gene coding for the last enzyme of Pro biosynthesis, L-Δ¹-pyrroline-5-carboxylate reductase, was much greater than in wild type (W) plants (105-fold versus 19-fold after 7 d). Under control conditions arginine accounted for nearly 60 % of the total free amino acid content. After stress treatment the content of Pro was more than 50 % in both T and W genotypes, and at the end of recovery the γ-aminobutyrate content reached 27 and 53 % in the W and T plants, respectively. Without stress treatment there was only a 2-fold difference between T and W in the tyrosine content. However, during the stress period and the subsequent recovery a similar difference was found for many amino acids. The present results indicate that manipulating of the content of a single amino acid influences the whole free amino acid composition in soybean.

Using 2-D electrophoresis, we analyzed proteins from transgenic rice overexpressing gibberellin acid (GA) catabolic enzyme, GA2-oxidase. These results indicate eight specific proteins differentially expressed in the transformed rice stems of T₁ generation, but non in case of T₂ generation. Proteins isolated from different stages of leaves of T₁ generation showed no significant differences, except one-month-old leaf, where five differentially expressed proteins are visible.

In vitro cultures of Azadirachta indica A. Juss. were raised by first culturing the root segments on modified Murashige and Skoog (MS) medium supplemented with 8.88 μM 6-benzylaminopurine (BAP), 9.84 μM N⁶-(2-isopentenyl) adenine (2iP), 5.71 μM indole-3-acetic acid (IAA), 81.43 μM adenine hemisulphate and 2.27 μM putrescine for 2 d followed by their transfer to the same medium except containing one-tenth of the initially used concentrations of BAP, 2iP and IAA. The regenerated shoots sustained proliferation in the basal medium supplemented with 1.11 μM BAP, 1.43 μM IAA and 135.72 μM adenine hemisulphate. The isolated shoots were rooted to produce plantlets in the presence of 2.46 μM indole-3-butyric acid (IBA). The plantlets showed uniform luxuriant growth under field conditions. True-to-type nature of the field-grown root-regenerated plants was ascertained by random amplified polymorphic DNA (RAPD) analysis.