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The main objective of this study was to examine the contribution of arbuscular mycorrhizal (AM) colonization on nickel (Ni) uptake and Ni tolerance in sunflower (Helianthus annuus L.) at a vegetative or reproductive stage of development. The combined effect of AM colonization, Ni input, and nitrogen (N) fertilization on N-assimilation in sunflower plants was also investigated. Furthermore, concerns over the transfer of heavy metals (HMs) to higher trophic levels led us to investigate whether the AM colonization and accumulation of Ni within plant tissues would induce synthesis of secondary defense compounds. It was hypothesized that AM colonization increases Ni content and plant Ni tolerance, the activities of N-assimilating enzymes (nitrate reductase, NR; glutamine synthetase, GS; and glutamine dehydrogenase, GDH), and induces the accumulation of sesquiterpene lactones (STLs), in sunflower grown under soil Ni conditions. It was also hypothesized that N-type fertilization affects ammonium assimilation as the activities of GS and GDH would be enhanced in plants supplied with an NH+4 as compared to a NO-3 fertilizer. To verify these hypotheses, three greenhouse experiments were performed with sunflower cv. "Lemon Queen", with or without the AM fungus, Glomus intraradices Schenck & Smith, and treated with (1) 0 or 100 mg Ni kg-1 dry soil (DS) at the reproductive stage, and supplied with NO-3 or NH+4 fertilizer; (2) 0, 100, 200 or 400 mg Ni kg-1, at the reproductive stage and supplied with a complete NH4NO 3 fertilization; and (3) 0, 200 or 400 mg Ni kg-1, at the vegetative stage and supplied with a complete NH4NO 3 fertilizer. The overall results indicated that AM colonization significantly enhances Ni content in sunflower plants, exposed to a moderate soil Ni level of 100 mg Ni kg-1, at the reproductive stage. Furthermore, at 100 mg Ni kg-1, the AM plants had a significantly higher shoot Ni extracted %, suggesting that the AM symbiosis contributed to Ni uptake and its translocation from roots to shoots. The AM contribution to plant Ni content and Ni extracted % were significantly higher in plants supplied with NO-3 than with NH+4 . Moreover, the plant biomass and shoot height were significantly higher in plants supplied with NO-3 than with NH+4 . In late Ni exposed sunflower, the AM colonization significantly increased the Ni extracted % at 400 mg Ni kg-1, yet also resulted in a biomass reduction of 45% as compared to only 14% at 100 mg Ni kg -1. Furthermore, a soil [Ni] of 400 mg Ni kg-1 was toxic to sunflower directly seeded in Ni treated soils, as all seedlings died within four weeks after sowing. The mineral concentrations were enhanced in AM plants, especially at lower soil Ni treatments. It is therefore concluded that the AM contribution to Ni uptake was optimal at 100 mg Ni kg-1 . The AM colonization also contributed to enhance the activities of N-assimilating enzymes, especially under NH+4 fertilization. Moreover, our results showed that the effects of HM stress and N fertilization were linked, as the activities of NR, GS, and GDH were significantly enhanced in plants under NH+4 and at 100 mg Ni kg-1. These results suggest that the combined treatments of soil Ni input and NH+4 nutrition enhance N assimilation via concurrent activities of the GS/GOGAT and GDH pathways. We also observed that both soil Ni input and AM colonization lead to an accumulation of STLs in sunflower leaves. In addition, the combination of AM colonization and soil Ni input would result in a synergistic effect to maximize defense properties while minimizing energy expenditure. These findings support the hypothesis that the AM symbiosis contributes to enhanced Ni uptake and Ni plant tolerance. It is therefore concluded that sunflower, especially in association with AM fungi, shows promise as a "candidate" species in phytoremediation strategies.

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Two methods of vegetative propagation, stem cuttings under mist and air layering, were examined for the 'Desert Museum' hybrid palo verde and species of Cercidium, Parkinsonia, and Prosopis. Basal cuttings of 'Desert Museum' gave higher rates of rooting than apical cuttings and showed better rooting in April than September. Two-node cuttings produced more rooted cuttings for an equal stem length than three- or four-node cuttings. Cuttings of six other species and hybrids of Cercidium and Parkinsonia, as well as six species and hybrids of Prosopis, were also successfully rooted. Indolebutyric acid (IBA) in the range of 2,500 to 5,000 ppm generally improved rooting compared with no IBA treatment. Bottom heat of 30 to 35°C was required for high rooting rates for all species. Air layers of Prosopis chilensis averaged 94% rooting using stem diameters of 8 to 10 mm. IBA at 5,000 ppm improved rooting by 70% over 0 ppm. Air layers of Cercidium, Parkinsonia, and other species of Prosopis were also rooted.

Each year the horticultural industry is demanding increasing amount of high quality soilless media. To meet the need this study evaluated coconut coir as an organic component in substrates. Asian and different Mexican coir-based media were compared to sphagnum peat to characterize coir suitability in tobacco transplant growth. These organic components were combined in different proportions with inorganic constituents to create three water holding capacity levels. The organic components, standardized in their capability to hold water, were evaluated by four growth parameters: leaf area, transplant height, dry weight, and total nitrogen concentration. Uncompressed, aged, and leached coir-based media produced transplants equivalent to those produced in peat-based media and were superior to those of either compressed or unleached coirs. Both extreme compression and high chloride concentration appear to affect coir suitability in growing transplants. Two Mexican leached coir and sand combinations produced the highest transplant quality under the conditions of this study.

A molecular and cytogenetic characterization of asymmetric somatic hybrids of Nicotiana was performed to study the use of somatic hybridization as a tool for gene transfer between plant species. The asymmetric somatic hybrids had been previously formed by protoplast fusion between wild-type Nicotiana tabacum and a plant line of N. plumbaginifolia carrying a stably integrated kanamycin-resistance gene. These plants were examined with respect to their morphology, fertility, organellar and nuclear genomic organization, and inheritance of the selectable marker. To determine the extent of genomic asymmetry in the hybrids, a species-specific repetitive DNA sequence was cloned from N. plumbaginifolia and used as a probe for both dot blot and in situ hybridization studies. Dot-blot hybridization data indicated two groups of hybrid plants: Asymmetric hybrids containing 15-25% N. plumbaginifolia DNA and extremely asymmetric hybrids with 1-4% N. plumbaginifolia DNA. Using in situ hybridization it was possible to visualize individual N. plumbaginifolia chromosomes in the hybrids. The asymmetric hybrids retain 8-12 chromosomes and chromosome fragments from N. plumbaginifolia, whereas the extremely asymmetric hybrids contain only a single N. plumbaginifolia chromosome. In several of the hybrids it was possible to show the presence of intergenomic translocations between the chromosomes of N. tabacum and N. plumbaginifolia. RFLP analysis, using a cloned 5S-gene repeat sequence, provided evidence for chromosomal linkage of the kanamycin-resistance gene and a 5S-gene cluster from N. plumbaginifolia. Absence of this linkage was correlated with intergenomic translocations in two of the hybrids. Analysis of organellar DNAs was performed to detect any extra-nuclear genomic recombination in the hybrids. The results of these analyses were correlated with morphological and / fertility data in an attempt to understand the molecular basis of male sterility and partial female fertility exhibited in the asymmetric hybrids. / Source: Dissertation Abstracts International, Volume: 52-02, Section: B, page: 0663. / Major Professor: George W. Bates. / Thesis (Ph.D.)--The Florida State University, 1990.