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Micromorphology and phytochemistry of the foliar secretory structures of Stachys natalensis Hochst. and development of an in vitro propagation protocol.
No full textM. Sc. University of KwaZulu-Natal, Durban 2014.Many members of the genus Stachys have been used as ornamental plants, or as edible foods and, in a number of cultures, as traditional medicine. One such species, Stachys natalensis Hochst., is a perennial, straggling shrub with aromatic leaves that are covered with hairs. Despite its widespread use for a number of reasons, little information has been available on this plant thus far, its foliar secretory apparatus, or the nature and potential therapeutic value of these secretions. Hence, the aims and objectives of the present study were to elucidate key micromorphological features of the leaf secretory structures of S. natalensis, using both light and electron microscopy and to determine the location and chemical composition of the exudates using various histochemical and phytochemical techniques. An additional aim was to establish an in vitro micropropagation protocol for the sustained and high-yielding production of this elusive and often difficult to cultivate species. Furthermore, the foliar micromorphological fidelity between field and in vitro propagated material was compared.
Electron micrographs indicated the presence of glandular and non-glandular trichomes on both abaxial and adaxial foliar surfaces of field grown plants. Greater trichome density was observed on the abaxial surface with trichome distribution decreasing as the leaf developed (p<0.05). Uniseriate, unbranched and striated non-glandular trichomes, present on the foliar surfaces of S. natalensis are known to play a role in physical plant defence mechanisms against herbivory. The presence of an elevated cellular pedestal and striated micro-ornamentation on the stalk served as characteristic features of the non-glandular trichomes. Peltate and capitate glandular trichomes were also identified on the foliar surfaces across all developmental stages. Peltate glands consisted of a short stalk and a multicellular head containing two to eight secretory cells. Two types of capitate trichomes were observed. Type I capitate trichomes consisted of a striated stalk, cutinized neck cell and bulbous head which may be uni- or bi-cellular;Type II capitate trichomes were comprised of a wide base, long and tapering, septate stalk, neck cell and a multicellular secretory head cell. The process of secretion differed between the peltate and capitate glandular trichomes. The peltate and Type II capitate trichomes included a porose cuticle which facilitated the release of secretion to the exterior. Cuticular rupture at weak points of the equatorial plane of the secretory head was observed in Type I capitate trichomes. Qualitative histochemical staining of leaf sections and preliminary phytochemical tests revealed the presence of alkaloids, lipid components, terpenoids and complex polysaccharides concentrated in the glandular trichome head cells and leaf crude extracts, respectively. The perceived therapeutic benefits of this plant are likely to lie within this suite of secondary metabolites. Stachys natalensis plant extracts also contained considerable levels of total phenolic compounds (3.43 ± 0.01 mg GAE/g dry material) and flavonoids (3.04 ± 0.01 mg QE/g dry material). The methanolic extracts demonstrated significant free radical scavenging ability (49.49 ± 3.87 ug/ml) which indicates the potential for its use as a natural antioxidant.
In vitro propagation protocol using axillary bud explants was developed for this species. A multi-step decontamination treatment involving explant immersion in 1% and 3% NaClO, followed by 0.1% HgCl₂ was the most efficient method for explant decontamination, resulting in overall explant survival of 48%. All media preparations resulted in > 70% bud break within three weeks with cultures initiated on Medium C ( MS supplemented with 0.5 mg/l BAP and 0.5 mg/l IBA) showing the highest percentage of bud break. Growth medium B (0.5 mg/l kinetin and 0.5 mg/l IAA) showed the greatest total shoot multiplication, number of shoots/explant (9.1 ± 3.6) and height/explant (50.2 ± 5.0 mm) compared to other PGR combinations after 12 weeks. The addition of exogenous auxin (2 mg/l IAA) to MS medium allowed for 64% of plantlets to produce adventitious roots in five weeks, after which rooted plants were acclimatized. Acclimatized plantlets (92 ± 4.2 %) did not show any gross morphological abnormalities compared to field-grown plants, apart from the presence of visibly longer non-glandular trichomes. The peltate and both subtypes of capitate glandular trichomes of acclimatized plants were morphologically similar to their field-grown counterparts. Trichome density on acclimatized plants was greater on the abaxial surface of emergent leaves and this density decreased with leaf maturity, as was observed with field-grown plants. This study appears to be the first investigation of the micromorphology of the foliar structures of S. natalensis. Future studies on morphological aspects of secretory structures should include cytochemical investigations to determine the exact mechanism and origin of glandular secretions. Further analyses regarding the composition of the glandular essential oils and its potential pharmacological efficacy are required. With an effective in vitro propagation protocol being presently established, further optimisation with respect to the type and concentration of exogenous PGRs, explant type or even various routes of organogenesis can be investigated. This may provide a means of enhancing plantlet production, maintaining superior-selected genotypes, and thus potentially maximising the yield of putative pharmacologically-important secondary metabolites
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The actions of, and interactions between, auxins and cytokinins and their effect on in vitro rooting of selected Eucalyptus clones.
Full text linkThesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.Clonal propagation of Eucalyptus spp. and its hybrids allows for competitiveness in the
commercial forestry industry through the propagation and preservation of superior/elite
genotypes. Vegetative propagation through rooted cuttings is the industry‟s standard
and the choice of clones selected for plantations are determined by their rooting ability.
However, as many potentially valuable genotypes are recalcitrant to adventitious
rooting, micropropagation is the only effective means of propagating them.
Micropropagation results in high plantlet yields, achieved primarily through the
empirical use of the key plant growth regulators (PGRs) cytokinins and auxins, for
shoot and root production, respectively. Their selection for use in vitro is driven by their
effects on percent rooting rather than root quality. Little is known regarding the quality
of the roots of the plantlets ex vitro, but there is some evidence that they are different
from those of seedlings and cuttings. It was therefore hypothesized that the properties of
exogenous PGRs and their interaction with other exogenous and endogenous PGRs,
influenced root development and subsequent root quality. This was tested in vitro using
a good-rooting E. grandis (TAG31) and two poor-rooting E. grandis x nitens hybrid
clones (GN155 and NH58). In the former, the auxins supplied during the pre-rooting
culture stages (multiplication and elongation) were sufficient for 100% rooting in an
auxin-free rooting medium. Different combinations of PGRs in the two pre-rooting
stages, followed by rooting without auxins, revealed a direct relationship between the
stability of the supplied auxin and the rooting ability of TAG31. Gas chromatographymass
spectrometry (GC-MS) analyses indicated that endogenous shoot levels of indole-
3-acetic acid (IAA) influenced graviperception. Also, low IAA content was associated
with atypical starch grain accumulation or its absence from root tips (53.1 nmol IAA gˉ¹
DW compared with 325.7 nmol IAA g-¹ DW in gravisensing roots). The specific roles
of the natural auxins IAA and IBA on root morphogenesis were then investigated using
2,3,5-triiodobenzoic acid (TIBA; inhibits IAA transport), ρ-chlorophenoxyisobutyric
acid (PCIB; inhibits auxin signal transduction), and the auxin antagonist kinetin in the
rooting medium, following root induction. After 3 weeks, the mean root diameter was
significantly reduced from 552.8μm (control) to 129.2μm (with PCIB) and 278.6μm
(with kinetin). TIBA increased root diameter to 833.4μm, decreased Δ root length,
increased root vasculature and resulted in agravitropism. Hence, whereas rooting could
be induced by IBA, IAA was necessary for the maintenance of vascular integrity and
graviperception. This critical role of IAA in root development is of importance as IBA,
owing to its higher stability, has been traditionally relied upon for root induction in the
majority of micropropagation protocols.
The potential of incorporating IAA into the media formulations of in vitro protocols for
poor-rooters that do not respond well to IAA was then investigated, using GN155 and
NH58. While PCIB in the rooting medium of GN155 completely inhibited rooting, the
addition of dihydroxyacetophenone (DHAP), an inhibitor of auxin conjugation, to the
rooting medium, did not significantly increase % rooting in the presence of 0.1 mg 1ˉ¹
IBA (i.e. 50% rooting with 2mM DHAP and IBA, compared with 45% with IBA alone).
The results suggested that the inability of some eucalypts to induce roots easily in vitro
was not due to a deficiency in auxin signal transduction or to auxin conjugation.
Instead, rooting was inhibited by an accumulation of kinetin within shoots during the
pre-rooting culture stages. The endogenous levels of PGRs in shoots of GN155 and
NH58 showed a strong relationship (R² = 0.943) between the shoot kinetin:auxin and
shoot rootability. Substituting kinetin with the relatively less stable natural cytokinin
trans-zeatin in the elongation stage resulted in a significant increase in % rooting in
both clones, from 19% to 45% (GN155) and from 31% to 52% (NH58), with 0.1 mg 1ˉ¹
IAA in the rooting medium. However, omitting all cytokinins from the elongation
medium, resulted in over 95% and 75% rooting of shoots of GN155 and NH58,
respectively, with 0.1 mg 1ˉ¹ IAA.
These results suggest that IAA is a requirement for root development and cannot be
substituted by its analogues in certain root developmental events. Hence, IAA should be
the preferred auxin for eucalypt micropropagation. As fundamental research, the
approach taken in this study circumvents the empirical method used in improving
micropropagation protocols. The importance of the properties and the interactions
between endogenous and exogenous PGRs in regulating root morphogenesis, and the
practical implications of these findings is emphasised
Development of a fluidised-bed bioreactor system for the treatment of acid mine drainage, using sulphate reducing bacteria
No full textDissimilatory sulphate reduction, brought about by the action of sulphate reducing bacteria (SRB) was used in the treatment of acid mine drainage (AMD) in a fluidised bed bioreactor. Biologically produced hydrogen sulphide and bicarbonate ions, by SRB, facilitated the precipitation of heavy metals and the generation of alkalinity in the synthetic acid mine water, respectively. The SRB that had been selected were able to utilize acetate as the sole carbon source and were capable of growing in the bioreactors at low pHs, facilitating an increase in the influent pH from 2.75-7.0 to 5.4-7.8, after a 24-hour hydraulic retention time (HRT). The precipitation efficiencies for Fe, Mn, Zn, Cu, Cr and Al after a HRT of 24 h as metal sulphides ranged between 84- 99% for influent pH values of between 4 and 7, and above 54% for influent pH values between 2.75 and 4. Microbial metabolic activity decreased with decreasing influent pH. This was inferred from the decreasing differences in chemical oxygen demand (COD) depletion rate over a 24 h HRT, as influent acidity levels approached pH 2.75. Molecular studies, using PCR-DGGE analysis on the microbial consortium in the bioreactor, revealed the presence of at least 8 different bacterial species in the consortium. Attempts at sequencing these bands yielded inconclusive results, with the bands showing sequence homology to a large number of previously uncultured and undescribed bacteria. Scanning electron microscopy confirmed the presence of bacteria of different morphology, as well as the presence of biofilms, which account for the heavy metal and low pH tolerances that the bacteria sustained
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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