Shoot Cortex Research Articles

Anatomical limitations in adventitious root formation revealed by magnetic resonance imaging, infrared spectroscopy, and histology of rose genotypes with contrasting rooting phenotypes.

Adventitious root (AR) formation is one of the most important developmental processes in vegetative propagation. Although genotypic differences in rose rooting ability are well known, the causal factors are not well understood. The rooting of two contrasting genotypes, 'Herzogin Friederike' and 'Mariatheresia', was compared following a multiscale approach. Using magnetic resonance imaging, we non-invasively monitored the inner structure of stem cuttings during initiation and progression of AR formation for the first time. Spatially resolved Fourier-transform infrared spectroscopy characterized the chemical composition of the tissues involved in AR formation. The results were validated through light microscopy and complemented by immunolabelling. The outcome demonstrated similarity of both genotypes in root primordia formation, which did not result in root protrusion through the shoot cortex in the difficult-to-root genotype 'Mariatheresia'. The biochemical composition of the contrasting genotypes highlighted main differences in cell wall-associated components. Further spectroscopic analysis of 15 contrasting rose genotypes confirmed the biochemical differences between easy- and difficult-to-root groups. Collectively, our data indicate that it is not the lack of root primordia limiting AR formation in these rose genotypes, but the firmness of the outer stem tissue and/or cell wall modifications that pose a mechanical barrier and prevent root extension and protrusion.

Translocation and transformation of selenium in hyperaccumulator plant Cardamine enshiensis from Enshi, Hubei, China

Cardamine enshiensis (C. enshiensis) is a selenium (Se) hyperaccumulator plant found in Enshi, a typical seleniferous area in southwestern Hubei Province, central China. The aim of this work was to investigate the translocation and transformation of Se in C. enshiensis, which may help to elucidate the mechanism on the tolerance and hyperaccumulation of Se in C. enshiensis. The contents of Se in roots, shoots and leaves of C. enshiensis were measured by ICP-MS. The spatial distribution and chemical forms of Se in roots, shoots and leaves of C. enshiensis were studied using synchrotron radiation microfocused X-ray fluorescence analysis (μ-SRXRF) and in situ Se K-edge X-ray Absorption Near Edge Spectroscopy (μ-XANES). The Se species in roots, shoots and leaves were further studied by RP-HPLC-ICPMS. Roots, shoots and leaves of C. enshiensis contained an average of 2985, 3329 and 2491 mg/kg Se DW, respectively. μ-SRXRF found that Se was primarily located in the cortex, endodermis, and vascular cylinder in roots, while it was in the epidermis, cortex and vascular bundle of shoots and concentrated in the leaf veins and the peripheral parts. In situ μ-XANES analysis showed that the root vascular tissue contained 16% SeO42−, 19% C-Se− (using selenocystine, SeCys as model compound) and 65% C-Se-C (using methylselenocystine, MeSeCys as model compound), and shoot vascular bundle contained 10% SeO42−, 28% C-Se− and 62% C-Se-C while leaves had 84% C-Se− and 16% SeO32−. RP-HPLC-ICPMS confirmed that the major Se species were MeSeCys and SeCys. C. enshiensis is a hyperaccumulator plant with the majority of Se in it as organic Se species like MeSeCys and SeCys. Se was translocated from roots via shoots to leaves through vascular tissues, and was deposited in the cortex and endodermis of roots, epidermis and cortex of shoots and periphery of leaves. The high concentration of organic Se species like MeSeCys suggests that C. enshiensis may be used for health promotion in people suffered from cancer and other diseases. Besides, the hyperaccumulation of Se in C. enshiensis may also identify itself to be applied for phytoremediation in Se-contaminated areas.

Genome-wide analysis of the WRKY gene family in physic nut (Jatropha curcas L.)

The WRKY proteins, which contain highly conserved WRKYGQK amino acid sequences and zinc-finger-like motifs, constitute a large family of transcription factors in plants. They participate in diverse physiological and developmental processes. WRKY genes have been identified and characterized in a number of plant species. We identified a total of 58 WRKY genes (JcWRKY) in the genome of the physic nut (Jatropha curcas L.). On the basis of their conserved WRKY domain sequences, all of the JcWRKY proteins could be assigned to one of the previously defined groups, I–III. Phylogenetic analysis of JcWRKY genes with Arabidopsis and rice WRKY genes, and separately with castor bean WRKY genes, revealed no evidence of recent gene duplication in JcWRKY gene family. Analysis of transcript abundance of JcWRKY gene products were tested in different tissues under normal growth condition. In addition, 47 WRKY genes responded to at least one abiotic stress (drought, salinity, phosphate starvation and nitrogen starvation) in individual tissues (leaf, root and/or shoot cortex). Our study provides a useful reference data set as the basis for cloning and functional analysis of physic nut WRKY genes.

First Report of Avocado sunblotch viroid in Avocado from Michoacán, México

The State of Michoacán, México cultivates approximately 100,000 ha of avocados (Persea americana M.) (4). During a survey from 2006 to 2007 in cv. Hass avocado groves in Tingambato County, in the State of Michoacán, deep yellow spots and streaks, which sometimes became necrotic or reddish, were observed on the skin of fruits and the pulp of the fruit also showed big yellow spots. Some young shoots developed fine, yellow streaks, and leaves of symptomatic trees sometimes showed irregular, white-to-yellow spots. These symptoms were similar to those recorded for Avocado sunblotch viroid (ASBVd) (3). To determine if ABSVd was associated with these symptoms, total RNA extracted (1) from the skin and pulp of symptomatic and asymptomatic fruits and also from leaves and bark of shoots from five trees collected in a commercial plot in Tingambato County was tested by a one-step reverse transcription (RT)-PCR protocol using one primer pair to amplify specifically the complete ASBVd genome sequence (3). All 30 samples of skin and pulp of fruits, leaves, and cortex of shoots from symptomatic trees yielded two PCR fragments with estimated sizes of 250 and 500 base pairs (bp) corresponding to the putative monomeric and dimeric forms of ASBVd, respectively. The 500-bp RT-PCR fragments obtained from the different samples were purified from an agarose gel and cloned. The 249-bp nucleotide sequence of the ASBVd genomic monomer was determined using the clones from the fruit skin from sample Arb No. 3 (GenBank Accession No. EU888588), pulp from sample Arb No. 5 (GenBank Accession No. EU888590), leaves from samples Arb No. 15 (GenBank Accession No. EU888589) and Arb No. 8 (GenBank Accession Nos. EU888591 and EU888592), and cortex of shoots from sample Arb No. 16 (GenBank Accession Nos. EU888593, EU888594, EU888595, EU888596, and EU888597). BLAST analysis of the ASBVd sequences showed a range of 98 to 100% nucleotide identity to ASBVd sequences (GenBank Accession Nos. AF404064, AF404051, or AF229821). A clone of the Michoacán ASBVd (GenBank Accession No. EU888593) was used to synthesize a Dig-High Prime-UTP-T7 (Roche, Mannheim, Germany) fluorescent riboprobe complementary to the ASBVd plus strand to perform a dot-blot analysis as described previously (2). All ASBVd samples positive by RT-PCR gave a strong signal in the dot-blot analysis. This riboprobe will be used to index the ASBVd in other commercial avocado groves in Michoacán. To our knowledge, this is the first report of ASBVd in Michoacán, México.

Storage and mobilization of nonstructural carbohydrates and biomass development of beech seedlings (Fagus sylvatica L .) under different light regimes

Beech seedlings were grown under 8%, 13%, 23% and 100% relative light intensity for 2 years after germination. Starch, sucrose and monosaccharides from the bark and wood parenchyma of shoots and roots were analyzed during the course of the second year. The annual allocation pattern of starch revealed five successive phases: starch disintegration in November (1) was paralleled by high monosaccharide concentrations in the shoot cortex (≤ 33.4 mg/g DW). Seedlings of all light variants reached maximum sucrose concentrations (≤ 82.8 mg/g DW) during starch disintegration in January (2) that coincided with decreased monosaccharide contents. Up to mid-April, resynthesis of starch (3) occurred in most shaded and unshaded seedlings. In May, starch was converted into monosaccharides in all storage tissues (4). Seedlings grown under 13% light intensity showed de novo synthesis of starch (5) 4 weeks after bud burst. These seedlings reached 98% maximum starch storage capacity of the shoot and 89% of the root in July. In mid-October, the maximum starch concentration of the roots increased with light intensity, and this corresponded with an increase of lateral root growth. The variation of shoot and root dry weight was closely related to the content of nonstructural carbohydrates during the second year. The shift of shoot growth to the first half of the growing season and the suppression of lateral root growth during the second half is assumed to be a strategy of young beech to survive under light limiting conditions.

Interactions between hosts and non‐hosts of Pinus spp. and Matsucoccus josephi: anatomical responses of stem to infestation

SUMMARYArtificial infestation of seven pine species revealed that Matsucoccus josephi (Homoptera: Margarodidae) completes its development on Pinus brutia, P. eldarica and P. halepersis, whereas only a small number of the scale larvae infesting P. cunariensis and P. pined reached the second instar and none developed to the adult stage. M. josephi crawlers died while trying to feed on P. radiata and P. pinaster. Histological examination of the infested plant sections indicated that necrosis in shoot and stem barks of P. eldarica and P. halepensis occurs just before or after the scale completes its development. Injury reached the cambium, and traumatic resin ducts; parenchyma cells instead of tracheids and curved tracheids were formed. In P. brutia wound periderm was observed in the stem section but not in the shoot cortex following scale development. Wound periderm was also formed in the stem cortex of P. canariensis and P. pinena whereas no pathological changes were detected in the infested cortex of P. pinaster and P. radiata.Mechanical lesions caused by needle punctures resulted in the production of parenchyma cells instead of tracheids in all four pine species investigated. The response of the pine cortex was non‐specific; however several similarities in the response to scale infestation, such as the formation of resin ducts, were observed. We hypothesize that the response of the pine tissue to the scale saliva is a hypersensitive reaction. It is suggested that the development of Matsucoccus species on particular pine species is related to the scale's inability to trigger the defence system of the host while the larvae are feeding.