Leaf Interveinal Chlorosis Research Articles

Effects of Chromium Toxicity on Physiological Performance and Nutrient Uptake in Two Grapevine Cultivars (Vitis vinifera L.) Growing on Own Roots or Grafted onto Different Rootstocks

Chromium toxicity is considered within the most severe and dangerous nutritional disorders, and it can often be observed in crops grown in industrial areas. The present study aims to determine the effects of Cr(VI) toxicity on the growth, nutrition, and physiological performance of grapevines. In a pot hydroponic experiment, own-rooted Merlot and Cabernet Franc grapevine cultivars or cultivars grafted onto 1103P and 101-14 Mgt rootstocks were exposed to 120 μM Cr(VI). Leaf interveinal chlorosis appeared after forty-five days of treatment. Overall leaf chlorosis and brown root coloration after sixty days was reported. A significant effect on the majority of the measured parameters due to the Cr(VI) treatment was observed. Chromium stress increased the total Cr concentrations in all parts of the vines, i.e., leaves, shoots, roots, and trunks. When comparing between the studied plant sections, the roots presented the highest Cr concentrations, ranging from 396 to 868 mg kg−1 d. w., and then, in descending order, the Cr concentrations ranged from 41 to 102 mg kg−1 d. w. in the trunks, from 2.0 to 3.3 mg kg−1 d. w. in the leaves, and from 1.9 to 3.0 mg kg−1 d. w. in the shoots. Between the assessed rootstocks, 1103P was identified to be a better excluder of Cr concentration in the roots and other aerial parts of the vines. Additionally, chromium toxicity negatively affected the concentrations and compartmentalization of the most important nutrients. Leaf chlorophyll (Chl) concentration decreased down to approximately 53% after sixty days of Cr stress. Chromium toxicity significantly reduced the stem water potential (SWP), net CO2 assimilation rate (A), stomatal conductance (gs), and PSII maximum quantum yield in all the cases of grafted or own-rooted vines. At this stage, chromium stress increased the leaf total phenolic content from 46.14% in Merlot vines to 75.91% in Cabernet Franc vines.

Potential Role of Domains Rearranged Methyltransferase7 in Starch and Chlorophyll Metabolism to Regulate Leaf Senescence in Tomato.

Deoxyribonucleic acid (DNA) methylation is an important epigenetic mark involved in diverse biological processes. Here, we report the critical function of tomato (Solanum lycopersicum) Domains Rearranged Methyltransferase7 (SlDRM7) in plant growth and development, especially in leaf interveinal chlorosis and senescence. Using a hairpin RNA-mediated RNA interference (RNAi), we generated SlDRM7-RNAi lines and observed pleiotropic developmental defects including small and interveinal chlorosis leaves. Combined analyses of whole genome bisulfite sequence (WGBS) and RNA-seq revealed that silencing of SlDRM7 caused alterations in both methylation levels and transcript levels of 289 genes, which are involved in chlorophyll synthesis, photosynthesis, and starch degradation. Furthermore, the photosynthetic capacity decreased in SlDRM7-RNAi lines, consistent with the reduced chlorophyll content and repression of genes involved in chlorophyll biosynthesis, photosystem, and photosynthesis. In contrast, starch granules were highly accumulated in chloroplasts of SlDRM7-RNAi lines and associated with lowered expression of genes in the starch degradation pathway. In addition, SlDRM7 was activated by aging- and dark-induced senescence. Collectively, these results demonstrate that SlDRM7 acts as an epi-regulator to modulate the expression of genes related to starch and chlorophyll metabolism, thereby affecting leaf chlorosis and senescence in tomatoes.

First Report of Cucurbit chlorotic yellows virus infecting Cucumber Plants in Spain.

During the winter 2018, symptoms of leaf chlorotic spots (Figure 1) followed by symptoms of leaf interveinal chlorosis (Figure 2) and severe chlorosis in basal leaves were observed in cucumber cv Laredo (Cucumis sativus) plants in three separated greenhouses, sited in distinct locations in southern Spain. In all cases, Bemisia tabaci populations were observed on infected plants. The symptomology observed was similar to that caused by whitefly transmitted Cucurbit yellow stunting disorder virus (CYSDV, genus Crinivirus, family Closteroviridae), which is usually found infecting cucumber plants in this geographical area (1). Samples from four different cucumber plants of distinct greenhouses were collected and tested for the presence of CYSDV. Total RNA was extracted from the samples using the NucleoSpin RNA Plant kit (Macherey-Nagel, Germany). Molecular detection of CYSDV was performed using the multiplex and degenerate primer RT-PCR method (2), specific to the region of the highly conserved RNA-dependent RNA polymerase (RdRp) gene of criniviruses, which also detects other criniviruses such as Lettuce infectious yellows virus (LIYV) and Beet pseudo-yellows virus (BPYV). Results indicated that the viral species CYSDV, LIYV and BPYV were not detected in the four cucurbit plant samples. In 2004, an emergent crinivirus (Cucurbit chlorotic yellows virus, CCYV), inducing symptoms similar to those caused by CYSDV, was described infecting cucurbits in Japan (3). Recently, CCYV was detected in 2011 in Greece (4) and in 2014 in Egypt (5) and Saudi Arabia (6). Therefore, the four RNA samples were tested for the presence of the CCYV by a RT-PCR method previously described (7). Specific primers were designed to amplify 336 nt of the capsid protein (CP) gene and 680 nt of the RdRp gene, located on CCYV genomic RNA 1 and RNA 2, respectively. In all cases, clear cDNA bands of both expected sizes were detected for each cucumber sample that were then purified and sequenced via Sanger technology. BLAST analysis of those sequences showed 99% identity with the nucleotide sequence of the CP and RpRd genes from the CCYV isolates from Greece (LT992911, LT992910), China (KY400633.1, KX118632) and Taiwan (JF502222). To our knowledge, this is the first report of CCYV infecting cucurbits in Spain. Probably CCYV has been spread throughout the Mediterranean basin, remaining undetected due to the yellowing symptom similarities between CYSDV and CCYV. Detection of the emergent virus CCYV in Spain represents a new threat for the horticultural area of southern Europe.

Fomitiporia punicata and Phaeoacremonium minimum associated with Esca complex of grapevine in China

The Esca disease complex includes some of the most important trunk diseases of grapevines (Vitis spp.) and causes serious yield losses in grape production worldwide. However, there has been no detailed study on its presence and associated pathogens in China. During 2017–2019, a preliminary field survey was conducted in eight vineyards in Hebei and Ningxia provinces, China when unusual foliar symptoms were observed. Symptoms were distinct tiger striped leaves, which are typical of grapevine leaf stripe disease (GLSD), one of the most common diseases in the Esca complex. Tiger-stripe leaf symptoms were found in four vineyards, and incidence was cultivar dependent varying with vineyard and year. A total of 266 fungal isolates were obtained from wood tissues of grapevines with typical foliar symptoms of GLSD. Based on morphological characters and multigene-combined phylogenetic analyses, the Ascomycete Phaeoacremonium minimum, one of the pathogens associated with Esca complex was identified. The basidiomycete Fomitiporia punicata, which has never been reported infecting grapevine, was also identified and found to be associated with wood rot in grapevine. The remaining isolates included some known wood pathogens, such as Neofusicoccum species and Diaporthe species. Koch’s postulates were performed in the greenhouse, confirming that both F. punicata and P. minimum caused leaf interveinal chlorosis and necrosis that resembled the GLSD symptoms of the Esca complex observed in the field. The present study provides the first detailed report of the Esca complex in China. In addition, this is the first record of F. punicata associated with Esca complex of grapevine worldwide. The results of this study provide new insights into the knowledge of the Esca complex.

Molecular Characterization of the Alfalfa mosaic virus Infecting Solanum melongena in Egypt and the Control of Its Deleterious Effects with Melatonin and Salicylic Acid.

During the spring of 2019, distinct virus-like symptoms were observed in the Kafr El-Sheikh Governorate in Egypt in naturally infected eggplants. Leaves of affected plants showed interveinal leaf chlorosis, net yellow, chlorotic sectors, mottling, blisters, vein enation, necrotic intervention, and narrowing symptoms. The Alfalfa mosaic virus (AMV) was suspected of to be involved in this disease. Forty plant samples from symptomatic eggplants and 10 leaf samples with no symptoms were collected. The samples were tested by double antibody sandwich ELISA (DAS-ELISA) using AMV-IgG. Six of the 40 symptomatic leaf samples tested positive for AMV, while, DAS-ELISA found no AMV in the 10 leaf samples without symptoms. The AMV Egyptian isolate (AMV-Eggplant-EG) was biologically isolated from the six positive samples tested by DAS-ELISA and from the similar local lesions induced on Chenopodium amaranticolor and then re-inoculated in healthy Solanum melongena as a source of AMV-Eggplant-EG and confirmed by DAS-ELISA. Reverse transcription polymerase chain reaction (RT-PCR) assay with a pair of primers specific for coat protein (CP) encoding RNA 3 of AMV yielded an amplicon of 666 bp from infected plants of Solanum melongena with AMV-Eggplant-EG. The amplified PCR product was cloned and sequenced. Analysis of the AMV-Eggplant-EG sequence revealed 666 nucleotides (nt) of the complete CP gene (translating 221 amino acid (aa) residues). Analysis of phylogeny for nt and deduced aa sequences of the CP gene using the maximum parsimony method clustered AMV-Eggplant-EG in the lineage of Egyptian isolates (shark-EG, mans-EG, CP2-EG, and FRE-EG) with a high bootstrap value of 88% and 92%, respectively. In addition to molecular studies, melatonin (MTL) and salicylic acid (SA) (100 μM) were used to increase the resistance of eggplant to AMV- infection. Foliar spray with MLT and SA caused a significant increase in the morphological criteria (shoot, root length, number of leaves, leaf area, and leaf biomass), chlorophyll and carotenoid content, antioxidant enzymes, and gene expression of some enzymes compared to the infected plants. On the other hand, treatment with MLT and SA reduced the oxidative damage caused by AMV through the reduction of hydrogen peroxide, superoxide anions, hydroxyl radicals, and malondialdehyde. In conclusion, MLT and SA are eco-friendly compounds and can be used as antiviral compounds.

Hydrogen sulphide alleviates iron deficiency by promoting iron availability and plant hormone levels in Glycine max seedlings

BackgroundHydrogen sulphide (H2S) is involved in regulating physiological processes in plants. We investigated how H2S ameliorates iron (Fe) deficiency in soybean (Glycine max L.) seedlings. Multidisciplinary approaches including physiological, biochemical and molecular, and transcriptome methods were used to investigate the H2S role in regulating Fe availability in soybean seedlings.ResultsOur results showed that H2S completely prevented leaf interveinal chlorosis and caused an increase in soybean seedling biomass under Fe deficiency conditions. Moreover, H2S decreased the amount of root-bound apoplastic Fe and increased the Fe content in leaves and roots by regulating the ferric-chelate reductase (FCR) activities and Fe homeostasis- and sulphur metabolism-related gene expression levels, thereby promoting photosynthesis in soybean seedlings. In addition, H2S changed the plant hormone concentrations by modulating plant hormone-related gene expression abundances in soybean seedlings grown in Fe-deficient solution. Furthermore, organic acid biosynthesis and related genes expression also played a vital role in modulating the H2S-mediated alleviation of Fe deficiency in soybean seedlings.ConclusionOur results indicated that Fe deficiency was alleviated by H2S through enhancement of Fe acquisition and assimilation, thereby regulating plant hormones and organic acid synthesis in plants.

Prevalence, epidemiology and molecular studies of Tomato chlorosis virus (ToCV) in South Africa.

Criniviruses accumulate in the phloem tissue and damage crops by reducing chlorophyll which is essential for plant growth and development. Tomato chlorosis crinivirus (ToCV) is vectored by several whitefly species that damage tomato crops throughout the world. In South Africa, ToCV is a poorly studied pathogen of global economic importance. Therefore, a national survey was initiated to investigate the occurrence and distribution of criniviruses infecting tomato crops in South Africa. Whitefly infested tomato crops exhibiting interveinal leaf chlorosis and chlorotic flecking symptoms were assayed for crinivirus infections using a multiplex reverse transcription polymerase reaction (RT-PCR) approach to assess for the presence of crinivirus species that are known to infect solanaceous hosts. Next-generation sequencing (NGS) was used to generate the complete genome of ToCV from South Africa. Results from the survey indicated that ToCV is presently the only crinivirus species infecting tomatoes in South Africa. Blast analysis showed that the RNA-1 segment of ToCV from South Africa (ToCR1-186) matched 99% to Spanish isolates. On the other hand, the RNA-2 (ToCR2-186) segment matched 98% to a South Korean isolate and three Spanish isolates. Although recombination events were not detected, phylogenetic studies showed inconsistencies in the grouping of RNA-1 and RNA-2 segments for some of the ToCV isolates analyzed in this study. Therefore, we suggest the possibility of intraspecific reassortment. This is the first comprehensive study and full genome sequence of ToCV from South Africa. The information generated from this study is intended to raise awareness of ToCV infections on tomato crops in South Africa.

The mechanism of hydrogen sulfide mitigation of iron deficiency-induced chlorosis in strawberry (Fragaria × ananassa) plants.

A study was carried out to assess the mitigation mechanism of exogenously applied sodium hydrosulfide (NaHS) as a donor of H2S on strawberry seedlings under iron deficiency. The ameliorative effects of NaHS on oxidative damage, ion hemostasis and uptake, and availability of Fe were investigated by spraying solution of 0.2mM NaHS or 0.2mM NaHS plus 0.2mM hypotaurine (HT), a scavenger of H2S to plant leaves. Iron deficiency was created using 0.1mM FeSO4 instead of 0.1mM EDTA-Fe in Hoagland's nutrient solution. After a 28-day treatment, strawberry plants exhibited leaf interveinal chlorosis under Fe deficiency, but these apparent symptoms of iron deficiency were overcome by foliar application of NaHS. Exogenously applied NaHS enhanced chlorophyll contents and available iron and Fe accumulation in young leaves, but application of H2S scavenger hypotaurine with NaHS did not change those parameters under Fe deficiency. This clearly shows that NaHS improved iron availability in the strawberry plants. Furthermore, exogenously applied NaHS increased endogenous H2S and iron levels in the roots and leaves. Moreover, NaHS enhanced the levels of zinc (Zn2+), calcium (Ca2+), and magnesium (Mg2+) in both leaves and roots of the strawberry plants grown at Fe deficiency, except for Zn in roots which decreased significantly. This also suggests that NaHS maintains the levels of inorganic ions restricted by Fe deficiency. Fe deficiency increased electrolyte leakage (EL) and the levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in plant leaves. Exogenous NaHS reduced the accumulation of H2O2, MDA, and EL and upregulated the activities of key antioxidant enzymes. Overall, NaHS improved Fe uptake and activation by improving endogenous H2S, maintained balance of mineral nutrients and activities of the antioxidant enzymes, and reduced the generation of MDA and H2O2 as well as electrolyte leakage caused by Fe deficiency. So NaHS proved to be effective in ameliorating iron chlorosis caused by iron deficiency.

A new species of Scopulariopsis and its synergistic effect on pathogenicity of Verticillium dahliae on cotton plants

A new species, Scopulariopsis gossypii, was found to be present in the vascular bundles of cotton plants (Gossypium hirsutum) infected by Verticillium dahliae which is an economically important pathogen in Hangzhou, China. The fungus was only present in the diseased plants, but it never became isolated from the healthy plants. Scanning electron microscopy showed that the fungus was present in parenchyma cells enclosing vessels in dark brown vascular tissues of stems, and produced asexual conidia within the tissues. Phylogenetic analysis of combined nuclear ribosomal D1/D2 region of the 28S rDNA as well as translation elongation factor 1-alpha (TEF1) and beta-tubulin (TUB) gene showed that S. gossypii represents an undescribed species of Scopulariopsis, Microascaceae. In this study, characteristics of sexual and asexual stages of the fungus were described, illustrated and compared with similar taxa. In addition, the molecular and morphological analyses indicated that S. gossypii was a distinct species of Scopulariopsis. The pathogenicity tests proved by inoculation of wounded roots confirmed that S. gossypii was an opportunistic pathogen causing leaf interveinal chlorosis and vascular browning of cotton plants. However S. gossypii did not infect host with undamaged roots. Moreover, coinoculation with S. gossypii and V. dahliae significantly increased disease severity.

Quantitative trait loci underlying host responses of soybean to Fusarium virguliforme toxins that cause foliar sudden death syndrome.

Soybean deploys multiple genetic mechanisms to confer tolerance to Fusarium virguliforme toxins. This study revealed that F. virguliforme culture filtrates could be used in mapping QTL underlying foliar SDS resistance. Sudden death syndrome (SDS) is a major soybean disease throughout most of the soybean growing regions in the world including the United States. The disease is caused by the fungal pathogen, Fusarium virguliforme (Fv). The fungus produces several toxins that are responsible for development of interveinal leaf chlorosis and necrosis, which are typical foliar SDS symptoms. Growing of resistant cultivars has been the most effective method in controlling the disease. The objective of the present study was to identify quantitative trait loci (QTL) underlying host responses of soybean to Fv toxins present in culture filtrates. To accomplish this objective, two recombinant inbred line (RIL) populations, AX19286 (A95-684043 × LS94-3207) and AX19287 (A95-684043 × LS98-0582), segregating for SDS resistance were evaluated for foliar symptom development by applying two screening protocols, the stem cutting and the root feeding assays. The AX19286 population revealed two major and seven minor QTL for SDS resistance. In the AX19287 population, we identified five major QTL and three minor QTL. The two QTL mapped to Chromosome 7 [molecular linkage group (MLG) M] and Chromosome 20 (MLG I) are most likely novel, and were detected through screening of the AX19287 population with stem cutting and root feeding assays, respectively. This study established that Fv culture filtrates could be employed in mapping QTL underlying foliar SDS resistance. The outcomes of the research also suggest that multiple genetic mechanisms might be used by soybean to overcome the toxic effects of the toxins secreted by the pathogen into culture filtrates.

Hydrogen sulphide improves adaptation of Zea mays seedlings to iron deficiency.

Hydrogen sulphide (H2S) is emerging as a potential molecule involved in physiological regulation in plants. However, whether H2S regulates iron-shortage responses in plants is largely unknown. Here, the role of H2S in modulating iron availability in maize (Zea mays L. cv Canner) seedlings grown in iron-deficient culture solution is reported. The main results are as follows: Firstly, NaHS, a donor of H2S, completely prevented leaf interveinal chlorosis in maize seedlings grown in iron-deficient culture solution. Secondly, electron micrographs of mesophyll cells from iron-deficient maize seedlings revealed plastids with few photosynthetic lamellae and rudimentary grana. On the contrary, mesophyll chloroplasts appeared completely developed in H2S-treated maize seedlings. Thirdly, H2S treatment increased iron accumulation in maize seedlings by changing the expression levels of iron homeostasis- and sulphur metabolism-related genes. Fourthly, phytosiderophore (PS) accumulation and secretion were enhanced by H2S treatment in seedlings grown in iron-deficient solution. Indeed, the gene expression of ferric-phytosiderophore transporter (ZmYS1) was specifically induced by iron deficiency in maize leaves and roots, whereas their abundance was decreased by NaHS treatment. Lastly, H2S significantly enhanced photosynthesis through promoting the protein expression of ribulose-1,5-bisphosphate carboxylase large subunit (RuBISCO LSU) and phosphoenolpyruvate carboxylase (PEPC) and the expression of genes encoding RuBISCO large subunit (RBCL), small subunit (RBCS), D1 protein (psbA), and PEPC in maize seedlings grown in iron-deficient solution. These results indicate that H2S is closely related to iron uptake, transport, and accumulation, and consequently increases chlorophyll biosynthesis, chloroplast development, and photosynthesis in plants.

Effects of Nitric Oxide on Iron-Deficiency Stress Alleviation of Peanut

The aim of this research was to study the role of nitric oxide (NO) in alleviating iron deficiency induced chlorosis of peanut (Arachis hypogaea L.). For this study, sodium nitroprusside (SNP) was used to supply NO for hydroponic peanut plants. After 18 days, the peanut seedlings growing without iron exhibited significant leaf interveinal chlorosis, and this iron-deficiency induced symptom was completely prevented by NO. An increased content of chlorophyll and active iron was observed in NO-treated young leaves, suggesting an improvement of iron availability in plants. In addition, the improved rhizosphere acidification and increased secretion of organic acids by root in NO-treated plants suggesting that NO is effective in modulating iron uptake and transport inside the peanut plants. Furthermore, NO treatment alleviated the increased accumulation of superoxide anion (O2•−) and malondialdehyde (MDA), and modulated the antioxidant enzymes. However, the SNP with a prior sunlight treatment that does not release NO had no significant effect on the chlorophyll levels in iron-deficient plants. Therefore, these results support a physiological action of NO on the availability, uptake and transport of iron in the plant.

Effects of foliar application of salicylic acid and nitric oxide in alleviating iron deficiency induced chlorosis of Arachis hypogaea L.

BackgroundThe aim of this experiment was to analyze the alleviation mechanism of exogenous salicylic acid (SA) and sodium nitroprusside (SNP, a nitric oxide donor) on peanut seedlings under Fe deficiency. The effects of SA and SNP on iron uptake and availability, ions balance and oxidant damage were studied with foliar application of exogenous 1.0 mM SA (SA) or 2.5 mM SNP (SNP) or 0.5 mM SA+1.25 mM SNP [1/2(SA+SNP)] or 1.0 mM SA+2.5 mM SNP (SA+SNP).ResultsThe results showed that after 21 days treatment, the peanut seedlings growing under iron deficiency conditions exhibited leaf interveinal chlorosis, and this iron-deficiency induced symptom was prevented by foliar application of SA, SNP, 1/2 (SA+SNP), especially SA+SNP. The increased contents of chlorophyll and active iron, and increased Fe accumulation in cell organelles were observed in SA+SNP treated young leaves, suggesting that an improvement of iron availability in plants. Moreover, the improved nutrient solution pH, increased H+-ATPase activity and increased iron concentration in roots in SA+SNP treated plants, suggesting that SA+SNP is effective in modulating iron uptake. Furthermore, the increased calcium (Ca), magnesium (Mg) and zinc (Zn) concentrations and decreased manganese (Mn) and copper (Cu) concentrations in the leaves and roots of peanut indicated that SA+SNP stimulated the maintenance of ions disturbed by Fe deficiency. In addition, SA+SNP alleviated the increased accumulation of superoxide anion (O2•-) generation rate and malondialdehyde (MDA), and modulated the antioxidant enzymes.ConclusionsThese results indicated that the interaction of SA and SNP promoted Fe uptake, translocation and activation; modulated the balance of mineral elements; and protected Fe deficiency induced oxidative stress. Therefore, SA and SNP had synergistic effects in alleviating chlorosis induced by Fe deficiency.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-55-9) contains supplementary material, which is available to authorized users.

Molecular characterisation and pathogenicity of Phaeoacremonium spp. associated with esca disease of grapevine in Northern Iran

Esca is a very important and destructive disease of grapevine in many grapevine producing countries. Several groups of fungi have been reported from grapevines with esca disease symptoms; however, Phaeoacremonium species are the main hyphomycete fungi involved in this disease. In recent years, esca disease symptoms with consequent decline disease have frequently been observed in vineyards of north-western Iran. Nevertheless, the involvement of Phaeoacremonium spp. with esca disease symptoms in this region remains unknown. During 2008–2010 growing seasons, wood samples were collected from vines showing typical esca disease symptoms such as interveinal leaf chlorosis with subsequent necrosis and various types of internal wood deterioration in north-western parts of Iran. A total of 44 Phaeoacremonium-like hyphomycetes were recovered from sampled materials. Fungal isolates were subjected to tentative morphological identification and were further characterised by using sequenced data from ITS-rDNA and β-tublin gene. Phylogeny inferred using sequence data from ITS-rDNA region and β-tublin gene revealed that Phaeoacremonium aleophilum and P. mortoniae together with Sarocladium strictum (syn. Acremonium strictum) are associated with esca disease symptoms in this region. The pathogenicity of Phaeoacremonium spp. and Sarocladium strictum were verified by the inoculation of cutting root and stems under greenhouse conditions. Isolates of P. aleophilum and P. mortoniae were the most virulent based on the length of vascular necrosis on woody stems that followed by Sarocladium strictum. This is first study on the pathogenicity of Sarocladium strictum on grapevine worldwide and the first report on the occurrence of P. mortoniae on grapevines in north-western Iran.

Exogenous nitric oxide alleviates iron-deficiency chlorosis in peanut growing on calcareous soil

Sodium nitroprusside (SNP), a nitric oxide (NO) donor, was added into controlled release fertilizer (CRF) or sprayed on leaves to supply NO on iron deficiency stress in peanut (Arachis hypogaea Linn) plants growing on calcareous soils. Iron deficiency reduced plant growth and chlorophyll content. NO improved plant growth and alleviated leaf interveinal chlorosis, and increased the activity of root Fe<sup>III</sup> reductase and the concentration of available iron in cultured soil, suggesting that NO action could be related to iron availability to the plant. The actual photochemical efficiency (ΦPSII) and photochemical maximum efficiency of PSII (Fv/Fm) were increased, and minimum fluorescence yield (Fo) was decreased under NO-treated condition, which supported the protective effect of NO on photosystem II (PSII) in peanut leaves. NO increased the activities of antioxidant enzymes, and reduced malondialdehyde (MDA) accumulation. These results suggest that exogenous NO could alleviate iron deficiency induced chlorosis of peanut plants growing on calcareous soil.  

Manganese and Oxidative Damage in Cucumber

ABSTRACT Micronutrients in low or high concentration can affect growth, respiration, photosynthesis, and reproduction in plants. Cucumber (Cucumis sativus, L.) is grown in India in areas low or high in manganese concentration in soils. A study was conducted to investigate the effects of manganese concentration on some metabolic activities affecting developmental responses in cucumber. Seed of cucumber, cv. Sonali, were grown in refined sand and provided manganese at rates of: 0.1, 1.0, 2.0, 10, 100, or 200 μM on 6 of 7 days in a week for up to 102 days. At 20 days after planting, symptoms of leaf interveinal chlorosis, which intensified later and developed into irregular brown spots, developed with daily application rates of <10 μM Mn. When daily application of >10 μM of Mn was used interveinal chlorosis on old leaves was followed by necrosis and death of the leaf lamina. Plant growth was retarded. Plants treated with Mn above or below 10 μM had lower fruit yield and lower biomass, concentrations of chlorophylls (a and b), Hill reaction activity, and catalase activity than those grown with 10 μM. There was increased activity of peroxidase, superoxide dismutase, and ascorbate peroxidase in plants treated with Mn above or below 10 μM. The Mn concentration in tissues increased as levels of Mn increased from 0.1 to 200 μM. Detrimental effects due to manganese <10 and >10 μM was related to the Mn concentration in the leaves.

First report of a 16SrII group phytoplasma associated with die‐back diseases of papaya and citrus in Ethiopia

Citrus orange (Citrus aurantifolia) and papaya (Carica papaya) are amongst the most common fruits grown in Ethiopia and the area devoted to their cultivation has increased considerably in the last six decades (Seifu, 2003). Recently decline disorders of both citrus and papaya have been reported as causing significant yield losses amongst the major farms growing these crops in the country. Symptoms in citrus include leaf interveinal chlorosis, mosaic or mottling, a reduction in the size and curling of leaves. In severe cases, premature fruit fall, twig drying and die-back, and death of the tree. In papaya, the first symptom is a bright yellowing of the upper young leaves; later, symptoms of mosaic, crinkling and leaf tip necrosis develop, followed by a drying of the upper leaves, which progresses to death of the whole plant. Leaf samples showing symptoms from 12 papaya and 6 orange plants were collected from farms in the Melkassa area of east Shewa, during September 2005. Citrus tristeza virus (CTV) has been previously reported in Ethiopia (Khassaye et al., 1977), so citrus samples were tested for CTV by DAS-ELISA, yielding 4/6 positives. DNA was extracted from all plants and indexed in both a nested PCR with phytoplasma generic primers P1/P7 and R16F2n/R16R2, and a simple PCR for papaya bunchy top (PBT) rickettsia using primers PBTF1/PBTR1 (Davis et al., 1998). Nested PCR amplicons were obtained for 11/12 papaya and six citrus samples. Following RFLP analysis, all exhibited identical HaeIII, RsaI and AluI profiles, which were typical of a 16SrII phytoplasma. None of the papaya and citrus samples evaluated was positive for the PBT rickettsia. Sequencing was done by The Sequencing Service (Univ. Dundee, Scotland; http://www.dnaseq.co.uk) using Applied Biosystems Big-Dye Ver 3·1 chemistry, on an Applied Biosystems model 3730 sequencer. The 16S rDNA phytoplasma sequences of a representative sample of papaya (GenBank Acc. No. DQ285659) and citrus (GenBank Acc. No. DQ286576) were identical and their highest similarity (98%) was with papaya yellow crinkle in Australia (GenBank Acc. No. Y10097), a member of the 16SrII group (Candidatus Phytoplasma aurantifolia). This is the first record of phytoplasmas associated with die-back diseases of papaya and citrus in Ethiopia. The finding of a mixed infection of phytoplasma and CTV in some citrus samples will require further studies before any recommendations for disease management can be made. Work in the UK was done under Defra plant health license No. PHF 174D/5185(08/2005). Rothamsted Research receives grant aid from the Biotechnology and Biological Sciences Research Council of the UK.

A novel major facilitator superfamily protein at the tonoplast influences zinc tolerance and accumulation in Arabidopsis.

Zinc (Zn) is an essential micronutrient required by all cells but is toxic in excess. We have identified three allelic Zn-sensitive mutants of Arabidopsis (Arabidopsis thaliana). The gene, designated ZINC-INDUCED FACILITATOR1 (ZIF1), encodes a member of the major facilitator superfamily of membrane proteins, which are found in all organisms and transport a wide range of small, organic molecules. Shoots of zif1 mutants showed increased accumulation of Zn but not other metal ions. In combination with mutations affecting shoot-to-root Zn translocation, zif1 hma2 hma4 triple mutants accumulated less Zn than the wild type but remained Zn sensitive, suggesting that the zif1 Zn-sensitive phenotype is due to altered Zn distribution. zif1 mutants were also more sensitive to cadmium but less sensitive to nickel. ZIF1 promoter-beta-glucuronidase fusions were expressed throughout the plant, with strongest expression in young tissues, and predominantly in the vasculature in older tissues. ZIF1 expression was highly induced by Zn and, to a lesser extent, by manganese. A ZIF1-green fluorescent protein fusion protein localized to the tonoplast in transgenic plants. MTP1 has been identified as a tonoplast Zn transporter and a zif1-1 mtp1-1 double mutant was more sensitive to Zn than either of the single mutants, suggesting ZIF1 influences a distinct mechanism of Zn homeostasis. Overexpression of ZIF1 conferred increased Zn tolerance and interveinal leaf chlorosis in some transgenic lines in which ZIF1 expression was high. We propose that ZIF1 is involved in a novel mechanism of Zn sequestration, possibly by transport of a Zn ligand or a Zn ligand complex into vacuoles.

First Report of Xylella fastidiosa Infecting Citrus in Costa Rica.

Citrus variegated chlorosis (CVC) is an important disease mainly of sweet orange (Citrus sinensis (L.) Osbeck) cultivars. It was first described in Brazil in the state of Sā Paulo in 1987 (4). The disease has spread to all Brazilian states that grow citrus and is affecting more than one-third of the orange trees grown in Brazil. CVC is caused by Xylella fastidiousa, a xylem-limited, gram-negative bacterium. During the last 4 years, symptoms including leaf interveinal chlorosis, stunting, canopy dieback, and hard and undersized fruits, similar to those caused by CVC (3), appeared in sweet orange trees used as shade plants for coffee plantations and as fence posts in Costa Rica. Necrotic lesions on the abaxial side of the leaves as reported in Brazil were rarely observed. Leaf petiole samples from 25 symptomatic sweet orange trees reacted positively with a X fastidiosa-specific antiserum (AGDIA Inc., Elkart, IN) in a double-sandwich antibody enzyme-linked immunosorbent assay (DAS-ELISA). A fastidious, gram-negative bacterium identified as X. fastidiosa using DAS-ELISA was isolated on perwinkle wilt (PW) medium plates (1) from citrus stems showing CVC symptoms, but not from asymptomatic trees. The isolated colonies were circular and opalescent with diameters of 2 to 3 mm and were clearly visible within 6 to 7 days after streaking. Petiole sections from symptomatic plants observed with scanning electron microscopy showed rod-shaped bacteria with rippled cell walls tightly packed in xylem vessels, as described for X. fastidiosa previously (2), and with transmission electron microscopy, the bacteria were morphologically similar to those reported previously for CVC (2). To our knowledge, this is the first report of X. fastidiosa associated with citrus in Costa Rica.

Fitotoxidez de cádmio para Eucalyptus maculata e E. urophylla em solução nutritiva

Estudaram-se os efeitos de doses crescentes de Cd em solução nutritiva no crescimento e absorção mineral de mudas de Eucalyptus maculata e E. urophylla e respectivos sintomas de fitotoxidez em casa de vegetação. Mudas foram mantidas por cinco semanas em vasos contendo 2 L de solução nutritiva de Clark, adicionando-se 0, 45, 90, 135 e 180 miM de Cd fornecido como CdSO4. Após uma semana de exposição aos tratamentos, E. maculata exibiu pontuações avermelhadas nas nervuras, clorose internerval, necrose, murchamento das folhas e escurecimento das raízes. Além desses sintomas, E. urophylla apresentou morte das gemas apicais e acentuada queda de folhas. A dose crítica de Cd para reduzir em 10% a matéria seca da parte aérea foi baixa; 2,4 miM e 1,5 miM de Cd para E. maculata e E. urophylla, respectivamente. Os níveis críticos de toxidez na parte aérea foram de 14,5 mg kg-1 em E. maculata e 10,8 mg kg-1 de Cd em E. urophylla. Esses resultados indicaram que E. maculata é provavelmente menos sensível ao Cd do que E. urophylla. Foi também observado que o Cd reduziu a translocação de Cu em até 24 e 43% em E. maculata e E. urophylla, respectivamente. A translocação de Fe caiu de 36% em média, nas duas espécies no controle para apenas 12% com 180 miM Cd. A elevação nas doses de Cd reduziu os teores de Ca e Mg na parte aérea das espécies, atingindo-se teores de Mg abaixo da faixa considerada adequada em E. urophylla. Ficaram evidenciadas a fitotoxidez de Cd no Eucalyptus e a relação desta com a diminuição da translocação de Cu e Fe e com a diminuição dos teores foliares de Mg.