Molecular characterization and expression analysis of the <Emphasis Type="Italic">SPL</Emphasis> gene family with <Emphasis Type="Italic">BpSPL9</Emphasis> transgenic lines found to confer tolerance to abiotic stress in <Emphasis Type="Italic">Betula platyphylla</Emphasis> Suk.

Christolea crassifolia HARDY: gene (CcHRD) belongs to the AP2/ERF-like tanscritpion factor family, and overexpression of HRD gene has been proved to result in improved water use efficiency and enhanced drought resistance in multiple plant species. In the present study, we cloned the CcHRD gene from Christolea crassifolia, which shares 99.1% sequence similarity with the HRD gene from Arabidopsis thaliana. We generated transgenic tomato plants expressing CcHRD gene by agrobacterium-mediated genetic transformation. Our results revealed that the transgenic tomato plants showed a more developed root system and higher fruit yield than the wild-type plants. Furthermore, the leaf relative water content, chlorophyll content and Fv/Fm value in transgenic plants were significantly higher than the wild type, while the relative conductivity and MDA content of transgenic plant leaves were markedly lower than those of wild type under drought stress. We also observed that the major agronomic traits of transgenic tomato plants were improved under natural drought stress compared with those of the wild type. In summary, results in this transgenic study showed that the CcHRD gene could enhance the drought resistance in tomato, and also provided important information for the application of drought-responsive genes in improving crop plant resistance to abiotic stresses.     

Constitutive Expression of a Tomato Small Heat Shock Protein Gene <Emphasis Type="Italic">LeHSP21</Emphasis> Improves Tolerance to High-Temperature Stress by Enhancing Antioxidation Capacity in Tobacco

It is well established that small heat shock proteins (sHSPs) play an important role in thermotolerance in various organisms due to their abundance and diversity. In the present study, a chloroplast small heat shock protein gene (LeHSP21) from tomato (Lycopersicon esculentum cv PKM-1) was constitutively expressed in tobacco (Nicotiana tabacum L. cv Wisconsin 38) plants via Agrobacterium-mediated transformation. When compared to wild-type control plants, transgenic tobacco plants constitutively expressing LeHSP21, driven by the cauliflower mosaic virus 35S promoter, exhibited improved tolerance to both high temperature and oxidative stress. Furthermore, when the seedlings were subjected to high temperature treatment, the activities of anti-oxidative enzymes and the content of proline were significantly higher in transgenic plants than those in the wild-type plants. Our results presented here demonstrate the feasibility of improving high temperature and oxidative stress tolerance in plants through the expression of LeHSP21 gene.     

Overexpression of Tomato Homolog of Glycolate/Glycerate Transporter Gene <Emphasis Type="Italic">PLGG1/AtLrgB</Emphasis> Leads to Reduced Chlorophyll Biosynthesis

LrgA and LrgB genes have been identified as new components in regulation of programmed cell death (PCD) in bacteria. While in Arabidopsis, it has been documented that AtLrgB plays a crucial role in chloroplast development and photorespiration by acting as a glycolate/glycerate translocator (PLGG1) in the chloroplast inner membrane. However, little is known about LrgB homologs in other plant species, especially those with fleshy fruits. In this study, a homologous gene of AtLrgB, here designated SlLrgB, was identified in tomato. Similar to AtLrgB, structure analysis suggests that the LrgA and LrgB genes have evolved into two domains of the SlLrgB protein. Expression pattern analysis showed that SlLrgB accumulated mainly in green tissues and could be regulated by light, hormone, and abiotic stress treatments. Compared to wild-type plants, parts of SlLrgB overexpression plants displayed etiolated leaves and a growth retardation phenotype, with significantly reduced chlorophyll content both in leaves and fruits. The qPCR results revealed that the SGR gene, which was associated with chlorophyll degradation, was severely repressed. Two key genes in the chlorophyll biosynthesis pathway, CAO and POR, were also suppressed in the SlLrgB overexpression plants. Taken together, we suggest that SlLrgB may play important roles in the regulation of chlorophyll metabolism pathways in tomato.     

Morphological changes and increase of resistance to oxidative stress by overexpression of the <Emphasis Type="Italic">LebZIP2</Emphasis> gene in <Emphasis Type="Italic">Nicotiana benthamiana</Emphasis>

The tomato bZIP2-encoding gene was inserted into the Nicotiana benthamiana genome using Agrobacterium-mediated transformation to characterize resistance to oxidative stress and two herbicides, glyphosate and paraquat. We produced transgenic tobacco plants using the LebZIP2 gene, which were then utilized to examine salt stress and herbicide resistance through oxidative mechanisms. Transgenic LebZIP2-overexpressing plants were examined using specific primers for selection marker genes (PCR using genomic DNA) and target genes (RT-PCR). Based on microscopic examination, we observed an increase in leaf thickness and cell number in transgenic plants. The electrolyte leakage of leaves suggested that LebZIP2-overexpressing lines were weak tolerant to NaCl stress and resistant to methyl viologen. During our analysis, transgenic lines were exposed to different herbicides. Transgenic plants showed an increased tolerance based on visual injury, as well as an increased biomass. Based on these results, the LebZIP2 gene may be involved in oxidative stress tolerance and cell development in plants.     

Persistence and spread of mycoplasma in axenic callus tissue cultures of tobacco (Nicotiana glauca Grah.) in the presence of kinetin and IAA in nutrient medium

A technique is described for the establishment of infectious axenic callus cultures originated from stems of tobacco plants suffering from a mycoplasma disease, potato witches' broom. When stem pieces from a diseased tobacco plant (Nicotiana glauca Grah.) are culture on a modified nutrient medium according toMurashige andSkoog (1962) with added kinetin (0.64 mg or 2.56 mg 1 000 ml^?1) and IAA (2 mg or 4 mg 1 000 ml^?1), the pathogen persists and spreads in the newly formed callus tissue. The presence of the pathogen was proved by implantation of callus slices into stems of tomato plants which indicate the disease very reliably. Reconstituted tobacco plants too recovered the infectious agent of potato witches' broom; 27 plants from the 35 reconstituted plants were diseased. Similar results were obtained with Crimean yellows. Calli were cultured and subcultured from 1 to 18 monthsin vitro and some infectious cultures are maintained and their investigation goes on. We suppose that kinetin plays a very important role for infectivity preservation in callus cultures.     

Comparative proteomic analysis of leaf tissue from tomato plants colonized with <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis>

A comparative proteomic approach was performed to analyze the differential accumulation of leaf proteins in response to the symbiosis between Solanum lycopersicum and the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis. Protein profiling was examined in leaves from tomato plants colonized with AMF (M), as well as non-colonized plants fertilized with low phosphate (20 μM P; NM-LP) and non-colonized plants fertilized with regular phosphate Hoagland’s solution (200 μM P; NM-RP). Comparisons were made between these groups, and 2D-SDS-PAGE revealed that 27 spots were differentially accumulated in M vs. NM-LP. Twenty-three out of the 27 spots were successfully identified by mass spectrometry. Two of these proteins, 2-methylene-furan-3-one reductase and auxin-binding protein ABP19a, were up-accumulated in M plants. The down-accumulated proteins in M plants were associated mainly with photosynthesis, redox, and other molecular functions. Superoxide dismutase, harpin binding protein, and thioredoxin peroxidase were down-accumulated in leaves of M tomato plants when compared to NM-LP and NM-RP, indicating that these proteins are responsive to AMF colonization independently of the phosphate regime under which they were grown. 14-3-3 protein was up-accumulated in NM-RP vs. NM-LP plants, whereas it was down-accumulated in M vs. NM-LP and M vs. NM-RP, regardless of their phosphate nutrition. This suggests a possible regulation by P nutrition and AMF colonization. Our results demonstrate AMF-induced systemic changes in the expression of tomato leaf proteins, including the down-accumulation of proteins related to photosynthesis and redox function.     

Root nematode infection enhances leaf defense against whitefly in tomato

The foliar response to different herbivores sharing the same hosts is an important topic for the study of plant-insect interactions. Plants evolve local and systemic resistant strategies to cope with herbivores. Many researchers have characterized the mechanisms of leaf responses to insect infestation; however, the fact that roots serve as systemic resistance modulators to leaf herbivores has been widely ignored. Here, we report that tomato (Solanum lycopersicum) plants infected with southern root-knot nematodes (Meloidogyne incognita)—which feed on the roots to form nodules—enhanced leaf defenses against aboveground attackers, specifically, the whitefly (Bemisia tabaci). Our results show that nematode infection reduced the whitefly population abundance because of conferring a stronger SA-dependent defense pathway against whitefly than in tomato plants without nematode infection. Meanwhile, nematode-infected tomato plant also activated the foliar JA-dependent defense pathway at 4 h after whitefly infestation. However, the foliar JA-dependent defense under whitefly infestation alone was suppressed, with the JA content being nearly 30 % lower than that in tomato plants co-infected with nematodes and whiteflies. Furthermore, nematode infection significantly decreased the plant nitrogen concentration in leaves and roots. As a result, nematode infection reduced the number of whiteflies by enhancing foliar SA-dependent defense, activating JA-dependent defense and decreasing nitrogen nutrition. Our results suggest that underground nematode infection significantly enhances the defense ability of tomato plants against whitefly.     

Salt stress induced soybean <Emphasis Type="Italic">GmIFS1</Emphasis> expression and isoflavone accumulation and salt tolerance in transgenic soybean cotyledon hairy roots and tobacco

Effects of isoflavones on plant salt tolerance were investigated in soybean (Glycine max L. Merr. cultivar N23674) and tobacco (Nicotiana tabacum L.). Leaf area, fresh weight, net photosynthetic rate (Pn), and transpiration rate (Tr) of soybean N23674 plants treated with 80 mM NaCl were significantly reduced, while a gene (GmIFS1) encoding for 2-hydroxyisoflavone synthase was highly induced, and isoflavone contents significantly increased in leaves and seeds. To test the impact of isoflavones to salt tolerance, transgenic soybean cotyledon hairy roots expressing GmIFS1 (hrGmIFS1) were produced. Salt stress slightly increased isoflavone content in hairy roots of the transgenic control harboring the empty vector but substantially reduced the maximum root length, root fresh weight, and relative water content (RWC). The isoflavone content in hrGmIFS1 roots, however, was significantly higher, and the above-mentioned root growth parameters decreased much less. The GmIFS1 gene was also transformed into tobacco plants; plant height and leaf fresh weight of transgenic GmIFS1 tobacco plants were much greater than control plants after being treated with 85 mM NaCl. Leaf antioxidant capacity of transgenic tobacco was significantly higher than the control plants. Our results suggest that salt stress-induced GmIFS1 expression increased isoflavone accumulation in soybean and improved salt tolerance in transgenic soybean hairy roots and tobacco plants.     

Phylogenetic,toxigenic and virulence profiles of <Emphasis Type="Italic">Alternaria</Emphasis> species causing leaf blight of tomato in Egypt

Species of Alternaria are serious plant pathogens, causing major losses on a wide range of crops. Leaf blight symptoms were observed on tomato leaves, and samples were collected from various regions. Isolation was done from symptomatic tomato leaves, and 15 representatives were selected from a collection of 65 isolates of Alternaria species. The virulence of Alternaria isolates was investigated on detached leaves (DL) and whole plants of tomato cv. Super strain B. A phylogenetic analysis was performed based on three partial gene regions, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), the RNA polymerase second largest subunit (RPB2) and the Alternaria major allergen gene (Alt a 1). The potentiality of Alternaria isolates to produce toxins was also investigated on the basis of thin-layer chromatography (TLC). Our investigations revealed that Alternaria isolates showed different levels of virulence either on tomato plants or DL. Based on the phylogeny of three genes, Alternaria isolates encompassed two species of small-spored morphospecies: A. alternata (14 isolates) and A. arborescens (single isolate). The produced toxins varied among Alternaria isolates with tenuazonic acid (TeA) being the most abundant mycotoxin produced by most isolates. This study highlighted on other Alternaria species in Egypt that might represent a serious concern for tomato producers as causal agents of leaf blight over other species, i.e. A. solani.     

The poplar ARGOS-LIKE gene promotes leaf initiation and cell expansion,and controls organ size

We identified a Populus nigra auxin-regulated gene involved in organ size (PnARGOS)-LIKE, encoding one organ size related protein in black poplar. It is homologous to AtARGOS and AtARGOS-LIKE genes of Arabidopsis thaliana. ABRE-like, G-box, GATA and I-box motifs were discovered in the promoter region of the poplar ARGOS-LIKE gene. In wild type aspen (Populus tremula) plants, an ortholog of the PnARGOS-LIKE gene (PtrARGOS-LIKE) was noticeably expressed in actively dividing and expanding young leaves and calli, whereas its mRNA content increased in response to exogenous 6-benzylaminopurine, 1-naphthaleneacetic acid, and 24-epibrassinolide. Expression of the PtrARGOS-LIKE gene was reduced under a salinity treatment. In addition, we generated transgenic tobacco and aspen plants with an up-regulated expression of the PnARGOS-LIKE gene. A constitutive expression of the gene contributed to an increase in size of stems and leaves of the transgenic tobacco plants. In the transgenic aspen, a constitutive expression of the PnARGOS-LIKE gene promoted an increase in the frequency of leaf initiations and in leaf length and area. The size of transgenic tobacco and aspen leaves increased due to the enlargement of individual cells. The results show the significance of the PnARGOS-LIKE gene for control of leaf initiation and organ growth by cell expansion in poplar.     

Contrasting hydraulic strategies in <Emphasis Type="Italic">Salix psammophila</Emphasis> and <Emphasis Type="Italic">Caragana korshinskii</Emphasis> in the southern Mu Us Desert,China

Salix psammophila and Caragana korshinskii are two common shrubs in the southern Mu Us Desert, China. Their hydraulic strategies for adapting to this harsh, dry desert environment are not yet clear. This study examined the hydraulic transport efficiency, vulnerability to cavitation, and daily embolism refilling in the leaves and stems of these two shrubs during the dry season. In order to gain insight into water use strategies of whole plants, other related traits were also considered, including daily changes in stomatal conductance, leaf mass per area, leaf pressure–volume parameters, wood density and the Huber value. The leaves and stems of S. psammophila had greater hydraulic efficiency, but were more vulnerable to drought-induced hydraulic dysfunction than C. korshinskii. The difference between leaf and stem water potential at 50 % loss of conductivity was 0.12 MPa for S. psammophila and 0.81 MPa for C. korshinskii. Midday stomatal conductance decreased by 74 % compared to that at 8:30 in S. psammophila, whereas no change occurred in C. korshinskii. Daily embolism and refilling occurred in the stems of S. psammophila and leaves of C. korshinskii. These results suggest that a stricter stomatal regulation, daily embolism repair in stems, and a higher stem water capacitance could be partially compensating for the greater susceptibility to xylem embolism in S. psammophila, whereas higher leaf elastic modulus, greater embolism resistance in stems, larger difference between leaf and stem hydraulic safety, and drought-induced leaf shedding in C. korshinskii were largely responsible for its more extensive distribution in arid and desert steppes.     

Differences in physiological traits and resistances of <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> after herbivory by generalists and specialists

Many researchers have surveyed damages caused by natural enemies of invasive plants in both native and introduced ranges to test the enemy release hypothesis. In this study, we report our findings on the physiological and morphological impacts of a co-evolved specialist insect (Agasicles hygrophila) and two generalist insects (Atractomorpha sinensis and Hymenia recurvalis) in introduced ranges on an invasive plant, Alternanthera philoxeroides, in both field trials and controlled environments. The resistance of A. philoxeroides against the generalists and the specialist was also studied. We obtained consistent results in both the field trials and the controlled treatments: both the generalists and the specialist decreased leaf biomass, photosynthesis, leaf nitrogen content, and total leaf non-structural carbohydrate content in A. philoxeroides. However, the specialist decreased leaf mass, photosynthesis, and leaf nitrogen content more acutely than the generalists. Moreover, A. philoxeroides increased both leaf lignin and cellulose concentrations upon the generalists’ attack but only increased cellulose concentration in response to the specialist. Our results showed that even under the same population density, the co-evolved specialists from original ranges caused more severe morphological and physiological damage to A. philoxeroides than the generalists in introduced ranges. This revealed that invasive plants released some herbivory stress before their co-evolved specialists were introduced, which may contribute to the superior performance of invasive plants in introduced regions.     

Host preferences and biotic potential of <Emphasis Type="Italic">Trialeurodes vaporariorum</Emphasis> and <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Hemiptera: Aleyrodidae) in tomato and pepper

Whiteflies Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) are important pests in pepper (Capsicum annuum L.) and tomato (Solanum lycopersicum L.) crops in many countries. Contrary to what is observed for all other countries, in Uruguay, B. tabaci is mainly found on pepper and rarely on tomato, while T. vaporariorum is exclusively found on tomato. This study tested the oviposition preferences and biotic potential of these two whiteflies reared on both host plants. The developmental time, survival rates, longevity, fecundity and main population parameters were characterized. Both whitefly species showed different preference patterns regarding their host plants. T. vaporariorum preferred tomato instead of pepper to oviposit. Their developmental time is longer on pepper. B. tabaci preferred pepper, but the difference from tomato was not very strong. Pepper affects the biotic expression of T. vaporariorum negatively, while B. tabaci is able to develop equally on both host plants. These results show that the distribution differences of both whiteflies observed on both host plants could have a biological basis.     

Induction of salt tolerance in salicylate-deficient <Emphasis Type="Italic">NahG</Emphasis> Arabidopsis transformants using the nitric oxide donor

The effects of treatment with nitric oxide donor sodium nitroprusside (SNP, 0.5 mM) on salt tolerance of wild type (Col–0) Arabidopsis thaliana plants and Arabidopsis thaliana plants transformed with the bacterial salicylate hydroxylase gene (NahG) were compared. Basic salt tolerance level (200 mM NaCl) was higher in NahG transformants. Under salt stress conditions, these plants showed higher activity levels for antioxidant enzymes as well as higher content of sugars and anthocyanins. The treatment with NO donor induced salt tolerance in the plants of both genotypes, which could be observed as less strong growth inhibition, reduced oxidative damage, and preservation of chlorophyll pool in leaves. After the exposure to salt stress, the activity of both superoxide dismutase and guaiacol peroxidase was higher in SNP-treated wild type plants and NahG transformants than in the nontreated plants. After the imposition of salt stress, proline content in leaves of the wild type plants treated with the nitric oxide donor was lower than in the leaves of the nontreated plants. In contrast, SNP treatment of NahG transformants led to a significant increase in the proline content in leaves under the salt stress conditions. Conclusions have been made that wild type Col-0 plants and NahG transformants differ in how their systems of protection against salt stress are activated and that nitric oxideinduced mobilization of protection systems in A. thaliana may not require the presence of salicylate.     

<Emphasis Type="Italic">Piriformospora indica</Emphasis> Alleviates Salinity by Boosting Redox Poise and Antioxidative Potential of Tomato

More than 20% of irrigated land has been influenced by salt stress, decreasing crop production. In this research, we investigated the effect of different levels of salinity (0, 50, 100 and 150 mM NaCl) and the efficiency of Piriformospora indica on growth, biochemical traits, antioxidative defense system in tomato (Solanum lycopersicum L.). NaCl stress reduced chlorophyll content, height and biomass of plants. Higher level of salinity (150 mM) declined the plant height by 22.65%, total dry weight by 56.44% and total chlorophyll by 44.34%, however, P. indica inoculation raised plant height by 43.47%, dry weight by 69.23% and total chlorophyll content by 48.09%. Salinity stress increased H₂O₂, malondialdehyde (MDA), superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH) level in leaves and roots tomato seedlings. However, P. indica inoculation reduced H₂O₂, MDA and superoxide anion and enhanced DPPH compared to non-inoculated plants at all NaCl levels. The total phenol and flavonoids increased with NaCl treatment. On the other hand, the total phenolic and flavonoid increased more in P. indica inoculated plants compared to non-inoculated ones. Moreover, inoculation of P. indica implicated noteworthy improvement of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) activity in tomato upon salinity. Notably, colonization with P. indica significantly improved the content of reduced ascorbic acid (AsA), glutathione (GSH) and redox ratio in the tomato plants under salinity resulting in reduced redox state. Our findings confirmed that salinity had negative effect on tomato seedling; however, P. indica inoculation increased tolerance to salinity by improving the content of phenolic compounds, non-enzymatic antioxidants, and increasing the activity of antioxidant enzymes.     

Assessment of the preventive effect of vermicompost on salinity resistance in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> cv. Ailsa Craig)

To determine the effects of vermicompost leachate (VCL) on resistance to salt stress in plants, young tomato seedlings (Solanum lycopersicum, cv. Ailsa Craig) were exposed to salinity (150 mM NaCl addition to nutrient solution) for 7 days after or during 6 mL L^??1 VCL application. Salt stress significantly decreased leaf fresh and dry weights, reduced leaf water content, significantly increased root and leaf Na⁺ concentrations, and decreased K⁺ concentrations. Salt stress decreased stomatal conductance (g_s), net photosynthesis (A), instantaneous transpiration (E), maximal efficiency of PSII photochemistry in the dark-adapted state (F_v/F_m), photochemical quenching (qP), and actual PSII photochemical efficiency (ΦPSII). VCL applied during salt stress increased leaf fresh weight and g_s, but did not reduce leaf osmotic potential, despite increased proline content in salt-treated plants. VCL reduced Na⁺ concentrations in leaves (by 21.4%), but increased them in roots (by 16.9%). VCL pre-treatment followed by salt stress was more efficient than VCL concomitant to salt stress, since VCL pre-treatment provided the greatest osmotic adjustment recorded, with maintenance of net photosynthesis and K⁺/Na⁺ ratios following salt stress. VCL pre-treatment also led to the highest proline content in leaves (50 µmol g^??1 FW) and the highest sugar content in roots (9.2 µmol g^??1 FW). Fluorescence-related parameters confirmed that VCL pre-treatment of salt-stressed plants showed higher PSII stability and efficiency compared to plants under concomitant VCL and salt stress. Therefore, VCL represents an efficient protective agent for improvement of salt-stress resistance in tomato.