Leafy Tissues Research Articles

Nickel and Soil Fertility: Review of Benefits to Environment and Food Security

Nickel (Ni) is an essential micronutrient for plants, responsible for metabolizing urea nitrogen (urea-N) by urease and mitigating abiotic and oxidative stresses through the glyoxalase (Gly) and glutathione (GSH) cycles. However, excess Ni is toxic to flora at >100 mg kg−1, except for hyperaccumulators that tolerate >1000 mg kg−1 Ni. This review discusses the benefits of Ni nutrient management for soil fertility, improving food security, and minimizing adverse environmental impacts from urea overapplication. Many farming soils are Ni deficient, suggesting that applying 0.05–5 kg ha−1 of Ni improves yield and urea-N use efficiency. Applied foliar and soil Ni fertilizers decrease biotic stresses primarily by control of fungal diseases. The bioavailability of Ni is the limiting factor for urease synthesis in plants, animal guts, and the soil microbiome. Improved urease activity in plants and subsequently through feed in livestock guts reduces the release of nitrous oxide and nitrite pollutants. Fertilizer Ni applied to crops is dispersed in vegetative tissue since Ni is highly mobile in plants and is not accumulated in fruit or leafy tissues to cause health concerns for consumers. New methods for micronutrient delivery, including rhizophagy, recycled struvite, and nanoparticle fertilizers, can improve Ni bioavailability in farming systems.

Response of glutathione pools to cadmium stress and the strategy to translocate cadmium from roots to leaves (Daucus carota L.)

Carrots are one of the most highly consumed vegetables in the world. Due to the large area of cadmium (Cd) contaminated farmland, to abate the impact of Cd contamination on carrot quality and safety, a novel strategy is required to drive Cd translocation from the soil to the overground leafy tissues of carrots to protect the edible roots and thus ensure food security. To this end, this article presents an experimental study with mathematical models to assess the tolerance and accumulation capacity of Cd in inedible carrot leaves, as well as the regulatory factors affecting Cd distribution in carrots. The glutathione (GSH) pools were examined in carrot leaves in response to the oxidation stress induced by Cd exposures, and it was found that under low Cd stress (1 and 3 mg/L) the changes of GSH pools were dominated by the variation of GSH, showing higher GSH content and low levels of oxidized GSH content (GSSG). In contrast, both of these two indicator variables as well as the GSH/GSSG ratio all decreased under high Cd stress (5 and 9 mg/L). Combining this information with Cd concentrations in leaves, a model was established to predict the Cd accumulation capacity of leaves. The data showed that the potential Cd accumulation in carrot leaves could be as high as 514 μg/kg dry weight. Furthermore, the factors and primary physiological indicators affecting and regulating GSH pools by multiple stepwise regression were analyzed. The results showed that increasing chlorophyll a/b ratio and γ-glutamylcyclotransferase activity while inhibiting phytochelatin synthase activity could expand the tolerance of carrot leaves to Cd. These findings suggest a possible strategy for regulating the distribution of toxic metals in plants through a molecular-based approach and provide some important information that could be conducive to achieving food safety and phytoremediation of contaminated soils.

Cadmium mobility, uptake, and accumulation in spinach, kale, and amaranths vegetables as influenced by silicon fertilization

Using silicon (Si) can reduce heavy metal stress in plants, which have been grown in soil contaminated with cadmium (Cd). This study aimed at evaluating the influence of Si on Cd uptake, mobility, and compartmentation in leafy vegetables: spinach, kale, and amaranths. The study was conducted in both greenhouse and field experiments, which included four treatments: Cd, Cd + Si, Si, and control. Data were collected on root, stem, and leaves Cd concentration, transfer index (TI), translocation factor (TF), and Cd uptake by leafy vegetables. The Cd concentration was higher in roots than in stems and leaves in all the treatments whereas its TI and TF were less than one with spinach having the highest TF. Generally, Cd transfer was highest in roots and least in leaves in all treatments and it increased with age of the vegetables. Spiking the soils with Cd in the greenhouse resulted in higher Cd concentration in leafy vegetable tissues than in the field experiment. With application of Si, there was a significant reduction in the concentration of Cd in plant tissues of between 20 and 40%, which further resulted in strong and positive relationships between the Cd concentration in the soil and plant tissues. Therefore, the study recommends against the production of leafy vegetables in Cd contaminated soils for human consumption. Nonetheless, under unavoidable circumstances, we recommend application of Si to alleviate the transfer of Cd to edible tissues of leafy vegetables.

The influence of posttranscription silensing protein-suppressor P19 on the transient gfp gene expression level in aztec tobacco plants (Nicotiana rustica L.)

Aim. Genetic constructs creation for studying the influence effect of the viral posttranscriptional silencing protein suppressor p19 on transient reporter green fluorescent protein (GFP) expression and accumulation. Methods. The Golden Gate molecular cloning method was used to create the genetic constructs; the leafy tissues of the Aztec tobacco plants (Nicotiana rustica L.) were infiltrated with a suspension of Agrobacterium tumefaciens L.; the gfp gene expression level was determined by spectrofluorometric and quantitative protein (Bradford method) assays. Results. As a result of the work, the pSPV2324 genetic construct was created, which contained the reporter gene for the green fluorescent protein gfp and the gene for the synthesis of the viral posttranscriptional silencing protein suppressor p19 and its effect on the accumulation of the recombinant GFP protein was determined. A comparative analysis of the gfp gene expression level without and with the suppressor protein synthesis gene in the genetic vector showed that the fluorescence level of GFP protein in Aztec tobacco tissues was 1.3 times higher during spectrofluorimetric analysis using the p19 suppressor gene construct. Conclusions. The positive effect of the viral suppressor silencing P19 gene on the accumulation of recombinant GFP protein in tissues plants of N. rustica L. was shown for the first time. The increase in GFP protein fluorescence when using the p19 suppressor protein construct in spectrofluorimetric analysis coincides with an increase in the total concentration of total water-soluble proteins and the level fluorescence of GFP protein in their native electrophoretic separation.
 Keywords: cloning, genetic constructs, transient expression, silencing protein suppressor p19, green fluorescent protein (GFP).

Synergistic Effect of Zinc Oxide Nanoparticles and Heat Stress on the Alleviation of Transcriptional Gene Silencing in Arabidopsis thaliana.

Phytotoxicity is an inevitable consideration in evaluating the potential ecological effects of nanoparticles (NPs). Natural ecosystems are complex and accompanied by many other environmental factors. Thus understanding the impact of NPs on plant response to other environmental stresses is crucial to assess the comprehensive toxicity of NPs in ecosystem. In the present study, Arabidopsis thaliana seedlings were cultured in medium containing zinc oxide NPs (ZnO-NPs) then subjected to heat stress at 37°C. Alleviation of transcriptional gene silencing (TGS) in aerial leafy tissues was assessed as an epi-genotoxic endpoint. Results showed that 1 µg/mL ZnO-NPs alone can not alleviate GUS gene (β-glucuronidase) which silenced by TGS (TGS-GUS), but it significantly enhanced heat stress-induced alleviation of TGS-GUS, suggesting an synergistic effect of ZnO-NPs and heat stress on genomic instability. Further study showed that the initiation of synergistic effect could be regulated by plant developmental stage, heat duration and temperature, and heat shock related genes might be involved in.

Alkaloid synthesis is coupled to shoot morphogenesis in Argemone mexicana L. (Papaveraceae) in vitro cultures

During the induction process of an in vitro callus culture of Argemone mexicana L. (Papaveraceae), the levels of two benzylisoquinoline alkaloids known as berberine and sanguinarine displayed opposing trends. While the berberine levels steadily decreased from the initial explant stage up to the early proliferation of unorganized parenchymatous cell masses, the sanguinarine content increased. Once the callus culture was established, sanguinarine was the primary alkaloid present and berberine could no longer be detected. However, upon shoot regeneration, the berberine accumulation recovered, but sanguinarine was found in the newly formed leafy tissue. After root formation, sanguinarine was relocated to this organ, whereas berberine was evenly distributed between both tissues. Explants from stem internodes did not form callus, and berberine—plus sanguinarine—containing axillary shoots emerged from lateral buds in the induction medium. In contrast to callus-derived shoots, no root formation was observed. Therefore, alkaloid synthesis in A. mexicana in vitro cultures is related to the level of tissue organization in different ways, and while berberine accumulation seems to require the presence of differentiated organs, this is not the case for sanguinarine. Moreover, leafy parts of rootless shoots acquired the capacity to accumulate sanguinarine, which is usually absent in aerial tissues of mature plants. However, when these shoots were rooted, sanguinarine was mainly located in the newly formed roots, while berberine was detected in the shoots at similar levels found in the roots.

Heterologous expression of HpBHY and CrBKT increases heat tolerance in Physcomitrella patens

Heat stress can restrict plant growth, development, and crop yield. As essential plant antioxidants, carotenoids play significant roles in plant stress resistance. β-carotene hydroxylase (BHY) and β-carotene ketolase (BKT), which catalyze the conversions of β-carotene to zeaxanthin and β-carotene to canthaxanthin, respectively, are key enzymes in the carotenoid biosynthetic pathway, but little is known about their potential functions in stress resistance. Here, we investigated the roles of β-carotene hydroxylase and β-carotene ketolase during heat stress in Physcomitrella patens through expressing a β-carotene ketolase gene from Chlamydomonas reinhardtii (CrBKT) and a β-carotene hydroxylase gene from Haematococcus pluvialis (HpBHY) in the moss P. patens. In transgenic moss expressing these genes, carotenoids content increased (especially lutein content), and heat stress tolerance increased, with reduced leafy tissue necrosis. To investigate the mechanism of this heat stress resistance, we measured various physiological indicators and found a lower malondialdehyde level, higher peroxidase and superoxide dismutase activities, and higher endogenous abscisic acid and salicylate content in the transgenic plants in response to high-temperature stress. These results demonstrate that CrBKT and HpBHY increase plant heat stress resistance through the antioxidant and damage repair metabolism, which is related to abscisic acid and salicylate signaling.

A potential involvement of plant systemic response in initiating genotoxicity of Ag-nanoparticles in Arabidopsis thaliana

The extensive availability of engineered nanomaterials in global markets has led to the release of substantial amounts of nanoparticles (NP) into atmosphere, water body and soil, yielding both beneficial and harmful effects in plant systems. The NP are mainly aggregated onto the surface of plant roots and leaves exposed and only slightly transported into other tissues with a low rate of internalization. This raises a question of whether plant systemic response is involved in the induction of biological effects of NP. To address this, model plant Arabidopsis thaliana were root exposed to low concentrations of Ag-NP of two particle sizes (10-nm and 60-nm), and expressions of homologous recombination (HR)-related genes and the alleviation of transcriptional gene silencing (TGS) in aerial leafy tissues were examined as genotoxic endpoints. Results showed that exposure of roots to two sizes of Ag-NP up-regulated expressions of HR genes, and reactivated TGS-silenced repetitive elements in aerial tissues. These effects were blocked by the impairment in the salicylic acid signal pathway, indicating a potential involvement of plant systemic response in the induction of Ag-NP genotoxicity. This is further supported by ICP-MS analysis, in which the Ag content in aerial tissues was not significantly changed by root exposure to 10-nm Ag-NP. Although a significant increase in the Ag content in aerial tissues was observed after root exposure to 60-nm Ag-NP, its genotoxic effects had no obvious difference from that by 10-nm Ag-NP exposure, also suggesting that the genotoxicity might be mainly induced via plant systemic response, at least in the experiments of root exposure to Ag-NP.

Rice tocopherol deficiency 1 encodes a homogentisate phytyltransferase essential for tocopherol biosynthesis and plant development in rice.

RTD1 encodes a homogentisate phytyltransferase catalyzing a key step in rice tocopherol biosynthesis, confers cold tolerance and regulates rice development by affecting the accumulation of DELLA protein SLENDER RICE1. Tocopherols are one of the most important lipid-soluble antioxidants having indispensable roles in living organisms. The physiological functions of tocopherols have been comprehensively characterized in animals and artificial membranes. However, genetic and molecular functions of tocopherols in plants are less understood. This study aimed to isolate a tocopherol-deficient mutant rtd1 in rice. The rtd1 mutant showed overall growth retardation throughout the growth period. Most of the agronomic traits were impaired in rtd1. Map-based cloning revealed that the RTD1 gene encoded a homogentisate phytyltransferase, a key enzyme catalyzing the committed step in tocopherol biosynthesis. RTD1 was preferentially expressed in green leafy tissues, and the protein was located in chloroplasts. Cold tolerance was found to be reduced in rtd1. The cold-related C-repeat-binding factor (CBF)/dehydration-responsive element-binding protein 1 (DREB1) genes were significantly upregulated in rtd1 under natural growth conditions. Moreover, rtd1 exhibited a reduced response to gibberellin (GA).The transcript and protein levels of DELLA protein-coding gene SLENDER RICE 1 (SLR1) in rice was increased in rtd1. However, the GA content was not changed, suggesting a transcriptional, not posttranslational, regulation of SLR1. These findings implied that tocopherols play important roles in regulating rice growth and development.

Simultaneous use of irradiated sodium alginate and nitrogen and phosphorus fertilizers enhance growth, biomass and artemisinin biosynthesis in Artemisia annua L.

Marine polysaccharides (sodium alginate, carrageenan, chitosan, etc.) have proved as growth promoting substances in their depolymerized form for a number of medicinal and agricultural plants. Antimalarial drug, artemisinin, extracted from the leafy tissue of Artemisia annua L., is an effective and safe alternative remedy against malaria; it has proved effective against the highly adaptable malaria parasite. In order to increase plant growth and artemisinin content, field experiment was conducted for two consecutive years, using foliar application of an aqueous solution of gamma-ray irradiated sodium alginate along with split application of nitrogen and phosphorus fertilizers. Crop performance was assessed at pre-flowering and flowering stage in terms of growth, physiological and biochemical parameters and production of artemisinin in A. annua. Foliar application of 80mgL−1 of irradiated sodium alginate (ISA) along with split application of nitrogen (40+40kgNha−1) and phosphorus (20+20kg Pha−1) (i.e. ISA80+N40+40+P20+20) proved the best integrated treatment that gave maximal values for the attributes studied at flowering stage. As compared with the control, effect of this treatment (ISA80+N40+40+P20+20) was positive on dry leaf yield, leaf artemisinin concentration and artemisinin yield. The combined treatment enhanced the content and yield of artemisinin by 43.3 and 87.9%, respectively.

Effect of irradiated sodium alginate and phosphorus on biomass and artemisinin production in Artemisia annua

It is now being realized that irradiation products of natural bioactive agents can also be beneficially utilized to impart value addition in agriculture by converting these bioactive agents into more useful form. Polysaccharides, such as sodium alginate, have proven to be wonderful growth promoting substances in their depolymerized form for various plants. Artemisinin has been increasingly popular as an effective and safe alternative therapy against malaria; also proved effective against the highly adaptable malaria parasite, which has already become resistant to many other drugs. The drug artemisinin can be extracted from the leafy tissues of Artemisia annua. Therefore, experiments were conducted with an aim to evaluate artemisinin production and overall plant development though depolymerized sodium alginate application and nutrient supply. In the present study, sodium alginate, irradiated by Co-60 gamma rays together with various phosphorus doses, was used to study their effect on growth, physiological and biochemical processes and production of artemisinin in A. annua. Among various applied doses of phosphorus fertilizer, P40 (40kg Pha−1) together with ISA80 (80mgL−1) significantly improved all the parameters studied. Increase in plant height as well as weight was noted at this treatment. Dry leaf yield, artemisinin concentration in leaves and artemisinin yield was also significantly enhanced by the treatment.

Cumulative role of irradiated sodium alginate and nitrogen fertilizer on growth, biochemical processes and artemisinin production in Artemisia annua

Being the world's most severe parasitic infection, malaria causes more than a million deaths annually. Artemisinin and its derivatives are effective against malaria without any reputed cases of resistance. The drug artemisinin can be extracted from the leafy tissues of Artemisia annua L. Application of ionizing radiation to degrade natural bioactive agents, such as sodium alginate and then using them as growth promoting substances is a novel emerging technology to exploit full genetic potential of crops in terms of growth, yield, and quality. In the present study, sodium alginate, irradiated by Co-60 gamma rays together with various nitrogen doses, was used to study their effect on growth attributes, physiological and biochemical processes and production of artemisinin in A. annua. Of the various applied doses of nitrogen, N80 (80kgNha−1) together with ISA80 (80mgL−1) proved superior in positively regulating almost all the parameters studied. Most importantly, an increase of 38.1 and 80.5% in artemisinin content and yield respectively, was noticed at this treatment.

Composition and tissue specificity of endophytic fungi associated withNothapodytes nimmoniana(J. Graham) Mabberly from the Western Ghats of India

Western Ghats in India is one of the global biodiversity hot spots of the world. The objective of this study was to isolate, recognize the composition and tissue specificity of endophytic mycobiota in healthy disease free parts of an important anticancer medicinal plant, Nothapodytes nimmoniana (J. Graham) Mabberly from the forest in Amboli. Different plant parts (fresh disease free stem, leaves, leaf petiole, flowers and pedicel) were subjected to ‘3-step surface sterilization’ technique which resulted in the recovery of 192 isolates of fungi from 280 segments comprising 80 stem tissues, 120 leafy tissues, 40 leaf petiole tissues, 20 flower tissues and 20 pedicel issues segments, with infection rates of 56.25, 62.5, 50, 180 and 80 percent, respectively. The most frequent fungi were Cladosporium oxysporum, Corynespora sp., Fusarium monoliforme, one unidentified pycnidial fungus and two non sporulating mycelia (NSM 1 and 2). The composition and abundance of the endophytes varied according to the host tissues tested and was found to be dependent on the tissue type. Some fungi were specific to the various parts/tissues of the plant. They were segregated on the basis of their occurrence viz; leaf (midrib, margin, laminar), stem (outer bark, middle cortical and innermost core region), petiole, flower and pedicel.

ARABIDILLO gene homologues in basal land plants: species-specific gene duplication and likely functional redundancy

ARABIDILLO proteins regulate multicellular root development in Arabidopsis thaliana. Conserved ARABIDILLO homologues are present throughout land plants, even in early-evolving plants that do not possess complex root architecture, suggesting that ARABIDILLO genes have additional functions. Here, we have cloned and characterised ARABIDILLO gene homologues from two early-evolving land plants, the bryophyte Physcomitrella patens and the lycophyte Selaginella moellendorffii. We show that two of the PHYSCODILLO genes (PHYSCODILLO1A and -1B) exist as a tail-to-tail tandem array of two almost identical 12kb sequences, while a third related gene (PHYSCODILLO2) is located elsewhere in the Physcomitrella genome. Physcomitrella possesses a very low percentage of tandemly arrayed genes compared with the later-evolving plants whose genomes have been sequenced to date. Thus, PHYSCODILLO1A and -1B genes represent a relatively unusual gene arrangement. PHYSCODILLO promoters are active largely in the haploid gametophyte, with additional activity at the foot of the sporophyte. The pattern of promoter activity is uniform in filamentous and leafy tissues, suggesting pleiotropic gene functions and likely functional redundancy: the latter possibility is confirmed by the lack of discernible phenotype in a physcodillo2 deletion mutant. Interestingly, the pattern of PHYSCODILLO promoter activity in female reproductive organs is strikingly similar to that of an Arabidopsis homologue, suggesting co-option of some PHYSCODILLO functions or regulation into both the sporophyte and gametophyte. In conclusion, our work identifies and characterises some of the earliest-evolving land plant ARABIDILLO homologues. We confirm that all land plant ARABIDILLO genes arose from a single common ancestor and suggest that PHYSCODILLO proteins have novel and pleiotropic functions, some of which may be conserved in later-evolving plants.

The ability of land plants to synthesize glucuronoxylans predates the evolution of tracheophytes

Glucuronoxylans with a backbone of 1,4-linked β-D-xylosyl residues are ubiquitous in the secondary walls of gymnosperms and angiosperms. Xylans have been reported to be present in hornwort cell walls, but their structures have not been determined. In contrast, the presence of xylans in the cell walls of mosses and liverworts remains a subject of debate. Here we present data that unequivocally establishes that the cell walls of leafy tissue and axillary hair cells of the moss Physcomitrella patens contain a glucuronoxylan that is structurally similar to glucuronoxylans in the secondary cell walls of vascular plants. Some of the 1,4-linked β-D-xylopyranosyl residues in the backbone of this glucuronoxylan bear an α-D-glucosyluronic acid (GlcpA) sidechain at O-2. In contrast, the lycopodiophyte Selaginella kraussiana synthesizes a glucuronoxylan substituted with 4-O-Me-α-D-GlcpA sidechains, as do many hardwood species. The monilophyte Equisetum hyemale produces a glucuronoxylan with both 4-O-Me-α-D-GlcpA and α-D-GlcpA sidechains, as does Arabidopsis. The seedless plant glucuronoxylans contain no discernible amounts of the reducing-end sequence that is characteristic of gymnosperm and eudicot xylans. Phylogenetic studies showed that the P. patens genome contains genes with high sequence similarity to Arabidopsis CAZy family GT8, GT43 and GT47 glycosyltransferases that are likely involved in xylan synthesis. We conclude that mosses synthesize glucuronoxylan that is structurally similar to the glucuronoxylans present in the secondary cell walls of lycopodiophytes, monilophytes, and many seed-bearing plants, and that several of the glycosyltransferases required for glucuronoxylan synthesis evolved before the evolution of tracheophytes.

USING TISSUE AMMONIA AND FERMENTATIVE VOLATILE CONCENTRATIONS AS INDICATORS OF BENEFICIAL AND STRESSFUL MODIFIED ATMOSPHERES FOR LEAFY AND FLORAL VEGETABLES

Ammonia, a product of protein catabolism associated with senescence of leafy green vegetables, is toxic to plant cells if not efficiently re-incorporated by glutamate synthetase. In experiments on various intact and fresh-cut leafy and floral vegetables (broccoli, cauliflower, romaine lettuce, spinach and sugar snap peas) at 5-7.5°C, tissue ammonia concentrations were measured as a possible indicator of stressful modified atmospheres and compared with the time course of changes in concentrations of the fermentative volatiles ethanol and acetaldehyde. In spinach, increases in ammonia were observed with high CO 2 atmospheres and were associated with darkening of leaf tissues. In cauliflower florets, increases in ammonia and tissue discoloration were associated with the increases in fermentative volatiles in 15% CO 2 atmospheres, but minimal changes in ammonia and the fermentative volatiles occurred in air or non-damaging low O 2 atmospheres with 7.5% CO 2 . Increases in ammonia concentrations in sugar snap peas were also associated with increases in fermentative volatiles in 12 and 18% CO 2 atmospheres with 3% 0 2 ; these conditions resulted in browning discoloration. The same CA conditions resulted in no damage and only small increases in ammonia and fermentative volatiles in broccoli florets. In cut romaine lettuce, atmospheres with 9% but not 6% CO 2 resulted in notable increases in ammonia, but ammonia was not much affected by differences in O 2 concentrations (0.2, 1.0, or 21%). Increases in fermentative volatiles only occurred in cut lettuce stored in 0.2% O 2 alone or in combination with high CO 2 . These results indicate that ammonia may be a useful indicator of stress in modified atmosphere storage of leafy tissues. In cauliflower and spinach, atmosphere conditions that resulted in increases in ammonia also resulted in increases in fermentative volatiles. In romaine lettuce, ammonia concentrations indicated stressful atmospheres that were not associated with increases in fermentative volatiles. In other vegetables (sugar snap peas), increases in ammonia and fermentative volatiles had different time courses.

Characterisation of spatial variability and patterns in tree and soil δ13C at forested sites in eastern Canada

Wholistic isotopic studies provide a necessary foundation on which to build conceptual understanding of ecosystem development processes and provide the basis for further isotopic studies at a site or within an ecophysiological region. This study seeks to broadly characterise δ13C spatial variability and spatial patterns within soils and canopy tissues at five forest research sites in eastern Canada. We observe consistent and predictable patterns of leaf δ13C variation within trees and a consistent offset between woody and leafy tree tissues. Patterns are similar for both hardwoods and softwoods, but overall hardwoods had canopies that were more depleted in 13C. Soil carbon δ13C enrichment occurred with depth and appeared to vary according to site soil texture. Upper soil δ13C was intermediate between leaves and woody tissues, whereas deeper soil values suggested important contributions from more enriched tree tissues, such as persistent woody debris and possibly roots. The relationship between aboveground and belowground signatures suggests functional or developmental differences between study sites.

Biogas slurry added amino acids decreased nitrate concentrations of lettuce in sand culture

Human health worldwide is being threatened by excessive nitrate intake through the dietary pathway, i.e. vegetables and drinking water, and the former is the primary source (about 80%) for large quantitative ingestion and the biological characteristics of nitrate accumulation, especially for leafy vegetables. In this paper, four kinds of organic nutrient solutions (biogas slurry dilution or biogas slurry dilution with added glycine) were developed to culture lettuce in order to lower the nitrate concentrations in leafy tissue. The results showed that all organic nutrient solutions significantly decreased nitrate concentrations of lettuce shoot, and simultaneously had an increased or unbiased yield compared with inorganic nutrient solution (containing NO3 −-N solely) in sand culture with high-level nitrogen supply (8.69–15 mmol/L). In addition, glycine addition only slightly decreased nitrate concentrations in lettuce shoot both at 1:4 and 1:5 dilution rates of biogas slurry. Leafy SPAD values indicated that there were differences in lettuce N nutrition of new and old leaves responding to various N-form supplies, and no correlations between nitrate concentration and SPAD values were found. It was concluded that application of organic nutrient solutions formulated from biogas slurry dilution and amino acid in soilless cultivation is an effective means for reduction nitrate concentrations in leafy vegetables.

Screening for differential gene expression in Atropa belladonna leafy gall induced following Rhodococcus fascians infection

To better characterise at the molecular level the nature of plant responses to infection by Rhodococcus fascians PCR-based differential display patterns of Atropa belladonna leafy gall (LG) and non-infected plant tissues were compared. Six differentially expressed genes were identified and their altered expression was confirmed by RT-PCR. Three of them corresponded to up-regulated genes which encode proteins involved in plant defence. The three remaining cDNA fragments which correspond to down-regulated genes in LG, encoded proteins with similarity to a multicystatin, a miraculin and a methallothionein-like protein, respectively. Upon elimination of the bacteria from infected plant tissue, the expression of up-regulated genes was maintained, whereas expression of down-regulated genes resumed suggesting a potential role of these up-regulated genes in plant growth and development.

Relation between microbiological quality, metabolite production and sensory quality of equilibrium modified atmosphere packaged fresh-cut produce

The quality of four types of fresh-cut produce, packaged in consumer-sized packages under an equilibrium modified atmosphere and stored at 7 °C, was assessed by establishing the relation between the microbial outgrowth and the corresponding production of nonvolatile compounds and related sensory disorders. In vitro experiments, performed on a lettuce-juice-agar, demonstrated the production of nonvolatile compounds by spoilage causing lactic acid bacteria and Enterobacteriaceae. Pseudomonas fluorescens and yeasts, however, were not able to produce detectable amounts of nonvolatile metabolites. The type of spoilage and quality deterioration in vivo depended on the type of vegetable. Mixed lettuce and chicory endives, leafy tissues, containing naturally low concentrations of sugars, showed a spoilage dominated by Gram-negative microorganisms, which are not producing nonvolatile compounds. Sensory problems were associated with visual properties and the metabolic activity of the plant tissue. Mixed bell peppers and grated celeriac, on the other hand, demonstrated a fast and intense growth of spoilage microorganisms, dominated by lactic acid bacteria and yeasts. This proliferation resulted in detectable levels of organic acids and the rejection by the trained sensory panel was based on the negative perception of the organoleptical properties (off-flavour, odour and taste). The applied microbiological criteria corresponded well with detectable changes in sensory properties and measurable concentrations of nonvolatile compounds, surely in the cases where lactic acid bacteria and yeasts were provoking spoilage. Consequently, the freshness of minimally processed vegetables, sensitive for outgrowth of lactic acid bacteria and yeasts (e.g., carrots, celeriac, bell peppers, mixtures with non-leafy vegetables) can be evaluated via analysis of the produced nonvolatile compounds.