Browsing by Author "Farrant, J M"

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    Cell wall characteristics and structure of hydrated and dry leaves of the resurrection plant Craterostigma wilmsii, a microscopical study.
    (Elsevier, 1999) Vicré, M; Sherwin, H W; Driouich, A; Jaffer, M A; Farrant, J M
    The cell wall architecture of leaf tissues of the resurrection plant Craterostigma wilmsii at various stages of dehydration and rehydration was studied using electron microscopy and immunocytochemistry with antibodies to a hemicellulose (xyloglucan) and pectins. Upon dehydration, the cell walls were shown to fold extensively. It is thought that this folding may prevent excessive mechanical stress developing between the cell wall and the plasmalemma. Our immunocytochemical results show a significant increase in labelling of xyloglucan and unesterified pectins in the cell wall during drying, with levels declining again during rehydration. These components are known to play an important structural role within the cell wall, giving it more tensile strength. It is hypothesised that this increase in tensile strength allows the cell wall to contract and then fold as the plant dries and ultimately prevents the total inward collapse of the cell walls in dry tissue. The increased tensile strength may also be necessary to prevent the cell wall from unfolding and expanding too rapidly upon rehydration, thus allowing plasmalemma-cell wall connections to be reestablished.
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    Seed development, morphology and quality testing in selected species of the nut-fruited Restionaceae
    (Elsevier, 2002) Newton, R J; Bond, W J; Farrant, J M
    Seed germination is poor in species of the nut-fruited Restionaceae. Investigations of seed morphology and development, seed collection and sorting, and seed viability were conducted in species of Cannomois Desv., Hypodiscus Nees and Willdenowia Thunb. to supplement existing knowledge, and to determine whether poor seed quality resulted in the poor seed germination identified in previous studies. Suitability of collection methods and the effectiveness of sorting techniques were evaluated using x-radiography. Shaking and ground collection methods yielded consistently higher proportions of full seed than extracting seed from cut shoots. However in species with bony bracts and few seeds per plant, the cutting method was more suitable. Floating was a better seed sorting technique than weighing for separating full from incompletely filled seeds. Seed viability in seed collections that had been sorted to contain only fully developed seeds was assessed using tetrazolium salts. Viability was generally high (mostly >80%), suggesting that poor germination in studies with well-sorted seeds is likely to be due to seed dormancy.
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    The effect of smoke teatment on the germination on four species of Mesembryanthemum: some preliminary observations
    (1995) Janse van Rensburg, Sue; Farrant, J M
    The effect of plant derived smoke on germination, extent of eosine dye penetration and amount of abscisic acid (ABA) in the seeds of two Karoo non-fire-prone species: Ruschia caroli and Drosanthemum speciosum, and two fynbos fire-prone species: R. macowanii and D. stokoei, of Mesembryanthemum were investigated. The seed coat characteristics of each species were also investigated. Pierce et al. (1995) found that smoke promotes seed germination in the Karoo species R. caroli (scarified) and D. speciosum, whereas smoke has no effect on the germination of R. macowanii and D. stokoei (fynboss species). Results presented in this investigation support those of Pierce et al. (1995). The extent of dye penetration in smoke treated seeds if D. speciosum was significantly greater then that in untreated seeds of this species. This was due to the breakdown of some barrier, apparently in the membrane between the endosperm and the seed coat, by smoke. Seed ABA levels were reduced by smoke treatment in all four species, however this reduction was more pronounced in the smoke responsive species. Seeds coat studies revealed that the least responsive species was the only one to be covered by a waxy cuticle. Seed dormancy was a feature of the species in which seed was improved by germination, whereas the seeds of the unresponsive species, R. macowanii and D. stokoei were non-dormant. Hence, smoke appears to act as a dormancy release cue, having no, or little effect, on the seed germination of non-dormant species. Results from this study indicate that the mechanism of smoke triggered dormancy release involves the chemical alteration of the membrane bounding the endosperm and the reduction in the ABA concentration in the species investigated.
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    An ultrastructural investigation of the surface microbiota present on the leaves and reproductive structures of the resurrection plant Myrothamnus flabellifolia
    (Elsevier, 2011) Moore, J P; Waldron, M; Lindsey, G G; Farrant, J M; Brandt, W F
    The leaves, flower and stems of the southern African angiosperm resurrection plant Myrothamnus flabellifolia were investigated at the ultrastructural level to determine the source of previously reported fungal contamination. Fungal mycelia and hyphae of the genera Aspergillus and Penicillium were found localized to the hydathodes of the leaves and stigmatic surfaces of the female flowers in both desiccated and hydrated specimens. A waxy bacterium of the genus Bacillus was found to colonise the waxy epidermal surfaces of the leaves and flowers which was also where fungal cells were found to be absent. It is suggested that the wax like deposits within the leaves and stems as well as over the epidermal surface prevent the growth of the fungal organisms. These fungi opportunistically invade moist surfaces, such as the floral stigmas, during periods of moisture availability and may thus negatively impact plant development.
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    An ultrastructural investigation of the surface microbiota present on the leaves and reproductive structures of the resurrection plant Myrothamnus flabellifolia
    (Elsevier, 2011) Moore, J P; Waldron, M; Lindsey, G G; Farrant, J M; Brandt, W F
    The leaves, flower and stems of the southern African angiosperm resurrection plant Myrothamnus flabellifolia were investigated at the ultrastructural level to determine the source of previously reported fungal contamination. Fungal mycelia and hyphae of the genera Aspergillus and Penicillium were found localized to the hydathodes of the leaves and stigmatic surfaces of the female flowers in both desiccated and hydrated specimens. A waxy bacterium of the genus Bacillus was found to colonise the waxy epidermal surfaces of the leaves and flowers which was also where fungal cells were found to be absent. It is suggested that the wax like deposits within the leaves and stems as well as over the epidermal surface prevent the growth of the fungal organisms. These fungi opportunistically invade moist surfaces, such as the floral stigmas, during periods of moisture availability and may thus negatively impact plant development.