C.H. Bornman

The potential of smoke in seed technology

Smoke is an important factor involved in fire and postfire germination cues. The role of smoke in stimulating germination was first highlighted in South Africa in a study on Audouinia capitata , a threatened fynbos species. Further studies on South African fynbos, Californian chaparral and Australian species have illustrated the widespread ability of smoke to promote germination of many species from fire-prone areas. However, smoke-stimulated germination is not limited to species from fire-prone habitats, and a variety of species from fire-free habitats also respond positively. Smoke and aqueous smoke extracts can potentially be used for a variety of applications related to seed technology. These include uses in horticulture, agriculture, ecological management and rehabilitation of disturbed areas.

Biotechnology of southern African bulbs

The greatest diversity of bulbs, including petaloid monocotyledons with corms, rhizomes and tubers, can be found in the Cape Floral Kingdom in southern Africa. Biotechnological approaches are used to meet the growing demand for bulbs and to conserve those over-exploited by the herbal medicine trade. This review outlines the principles and practices of micropropagation, flower bulb improvement, in vitro conservation, molecular marker applications and secondary metabolite production for southern African bulbs and discusses the future role of bulbs and biotechnology in the development of the region.

Somatic embryos can be induced from the vegetative shoot apex of mature Pinus patula trees

Embryogenic cultures were initiated and established and somatic embryos produced in Pinus patula using thin sections from the dome of the vegetative shoot apex. Factors affecting initiation, basal medium and plant growth regulators were investigated. We report for the first time the initiation of embryogenic tissue and embryos from shoot apical domes (zones) of 15-year-old Pinus patula trees. The growth of embryogenic lines were comparable to those obtained from zygotic embryos. Plantlets were regenerated.

GRAZING PREFERENCES OF IMPALA: A QUANTITATIVE FAECAL ANALYTICAL AND ANATOMICAL EVALUATION

Summary Quantitative microscopic analysis of impala (Aepyceros m. melampus) faeces showed that epidermi of grass leaves persist undigested in fairly large fragments, and that interspecific anatomical variation provides diagnostic criteria for identification of these grasses. Relative abundance of these species growing in the impala habitat was determined and a comparison between relative abundance and relative amount eaten showed significant selection for or against different species. Selection was attributed to palatability. In those species where selection was not significant, it is suggested that the relative amounts eaten were probably determined by their abundance.

Flower abscission: environmental control, internal regulation and physiological responses of plants

Many aspects of the abscission process have been reviewed in the past and it has been some time since a review on flower abscission has been published. Recent advances in this field thus permit a consolidation of the current research. The flowering syndrome in plants is an intricate and complex process that ensures survival of the species. As such, it is a strictly controlled and tightly regulated series of developmental events, the success of which is a major priority. Abscission of flowers and floral organs is an important part of the reproductive cycle, that is similarly under exact direction. Flowers may be shed in response to an internal or genetic timing mechanism as well as external factors such as environmental stimuli, pathogen attack and pollination. These cues are processed and converted into physiological responses that include alteration in hormone production, induction and repression of specific signal transduction pathways, activation of existing enzymes and transcription of new proteins. While much progress has been made in identifying components of abscission using mutants and molecular biological approaches, many gaps remain in our understanding, especially in terms of considering abscission and its related events in the light of energy (carbohydrate) supply and demand.

Nicotiana tabacum Callus Studies I. Assessment of Growth and Differentiation

Summary Nicotiana pith expiants containing bundles of internal phloem attain the same plateau of growth in terms of mass and volume after 14 days as do expiants devoid of internal phloem after 21 days. The lag appears to be related to the time required for the dedifferentiation of the quiescent pith parenchyma. Tracheary element differentiation occurred in controls as well as in all treatments with only indoleacetic acid (IAA), 0.3 mgl −1 being significantly effective. Expiants treated only with kinetin (K) developed small numbers of tracheary elements at all concentrations. Sieve elements were not induced in response to media including K but without IAA or with a high level of IAA (3 mgl −1 ) in the absence of K. At low and intermediate levels of IAA phloic tissue differentiated at all levels of sucrose (2, 4 and 6%) with the exception of 0.03 mgl −1 IAA, 1 mgl −1 K and 2% sucrose. There was a lack of consistency in the extent of sieve element differentiation. However, when comparing individual combinations of IAA and K among various sucrose levels, more phloem was initiated at 4 than at 2 or 6%.

Watsonias as container plants: Using paclobutrazol for flowering and height control

South African watsonias were evaluated for their potential as flowering pot plants, following chemical dwarfing. Corms were treated with paclobutrazol as a 5mg, 10mg or 20mg active ingredient (a.i.) per pot post-emergent soil drench, or vacuum-infiltrated pre-planting with 0.5mg, 1mg or 2mg a.i. per corm. Both treatments significantly reduced perpendicular leaf height, although infiltration of all but the most under-developed corms caused inflorescence abortion. Flowering plants shorter than 36cm were considered to be attractive, commercially viable pot plants — provided that flowering percentage, flower number and the onset of flowering were not adversely affected by treatment and that flowers were displayed clear of the foliage. The highest concentration of paclobutrazol applied as a drench resulted in obscured inflorescences, indicating an enhanced dwarfing effect on the inflorescence rather than leaf heights. Marketable dwarfs were obtained following a single drench treatment of 10mg a.i. per pot or after a single infiltration episode with 1mg a.i. per corm, allowing the successful adaptation of watsonias to container cultivation.

Inhibition and promotion by abscisic acid of growth in Spirodela

SummaryThe effect of different concentrations of abscisic acid on the growth of Spirodela oligorrhiza has been studied. Abscisic acid effectively permanently arrests growth at concentrations down to 10-1 mg/l (one part per 10 million). Normal growth tends to be resumed at concentrations of 10-2 and 10-3 mg/l between 9 and 12 days after treatment. A concentration of 10-8 mg/l, however, results in a significant increase in dry weight at both 9 and 12 days after introduction to the culture medium. It is suggested that the resumption of growth 12 days after treatment at those concentrations which inhibit growth up to 9 days, is due to a possible progressive inactivation of abscisic acid resulting in a lowering of its concentration to a level that is promotive. Sterile plants must be used since abscisic acid has shown no effect whatsoever in controlling growth of Saprolegnia, a water-mould of the Phycomycetes to which Spirodela apparently is the host.

Welwitschia mirabilis: Morphology of the Seedling

Seedlings of Welwitschia mirabilis Hooker were grown from seeds collected on the Welwitschia Fläche at the confluence of the Khan and Swakop Rivers in South-West Africa. Germination is epigeous. Two lanceolate cotyledons constitute the first photosynthetic organs. They reach maximum size in about 9 1/2 weeks, but apparently remain photosynthetically functional for approximately 1 1/2 years. The only pair of foliage leaves are opposite and decussately arranged with respect to the cotyledons. The strap-shaped foliage leaves grow indefinitely from a basal meristem and increase in width by intercalary growth. Another pair of foliar structures is produced by the shoot apex before it becomes meristematically inactive, but they do not develop into foliage leaves. At first narrow and triangular in shape, these primordial leaves gradually thicken and extend laterally, burying the shoot tip. The bases of the foliage leaves become ensheathed in deep grooves which are formed during the development of meristematically active ridges on both sides of the leaves Strobili of adult plants are usually borne on the inner ridge. The seedling root system is not extensive and appears to serve mainly for anchorage. As Welwitschia tends to be confined to a narrow fog belt, it seems feasible that fog condensate, absorbed through the stomata, constitutes its main water supply.

Artificial seed from Pinus patula somatic embryos

Somatic and zygotic embryos of Pinus patula Scheide et Deppe. were encapsulated in 2.2% sodium alginate to examine the potential of producing artificial seeds. The alginate beads were supplemented with sucrose, maltose and activated charcoal. Somatic embryos encapsulated in alginate beads supplemented with both sucrose and charcoal germinated from the alginate beads after 14 days, and could be stored for 20 days with a 30% decrease in the percentage germination.