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Hazel Y. Wetzstein

Commercial pesticide formulations of triphenyltin hydroxide, benomyl plus triphenyltin hydroxide, and phosalone completely inhibited pollen germination of pecan [Carya illinoensis Wangenh C. Koch] when incorporated in in vitro germination media at one-fourth to one times the recommended rates. Scanning electron microscopic evaluations of spray effects on receptive stigmatic surfaces showed varying degrees of injury, ranging from minor surface wrinkling with triphenyltin hydroxide to severe collapse and degeneration of stigma papillae with phosalone treatments. Controlled pollinations 1 hour after pesticide sprays resulted in an inhibition of pollen germination and tube growth. Water sprays followed by pollination resulted in normal pollen adherence, hydration, and germination. Chemical names used: methyl[1-[(butylamino)carbonyl]-1H-benzimidazol-2-yl]carbamate (benomyl); S-[(6-chloro-2-oxo-3-(2H)-benzoxazolyl)methyl] 0,0-diethyl phosphorodithioate (phosalone).

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Hazel Y. Wetzstein and Amnon Levi.

Embryogenesis in higher plants follows a standard developmental program with sequential stages of histodifferentiation, maturation (reserve deposition), and postabscission (desiccation and rapid decline in metabolic activity). In this study, morphological, physiological and anatomical characteristics were integrated to demarcate the developmental stages of pecan embryos. Fruit were collected, morphological characteristics were recorded, fresh and dry weights, and water content of embryos were determined, and embryos were prepared for microscopic study. The procedures used here can be a useful guide for characterizing embryo development in pecan and related species.

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Tehryung Kim and Hazel Y. Wetzstein

It has been shown that perennial woody plants exhibit marked seasonal changes in nutrient content, carbon metabolism, and organ development. A knowledge of seasonal nutrient allocation and temporal accumulation patterns can be useful in the development of fertilization regimes that reflect the biology of a tree crop. Maintenance of optimum leaf nutrient status is an important priority in pecan cultural practice. However, a systematic evaluation of nutrient resorption is lacking in pecan. In this work, seasonal changes in nutrients and carbohydrates were evaluated in pecan trees grown under orchard conditions. In addition, resorption efficiencies of eight pecan cultivars were evaluated. Significant levels of resorption were observed in all essential elements, but cultivar differences were not significant. Seasonal patterns of nutrient and carbohydrate content in leaf, stem, and shoot tissue, will be presented as well as a structural evaluation of abscission zone formation.

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Ni Lee and Hazel Y. Wetzstein

Plantlets were recovered from axillary bud cultures of muscadine grape (Vitis rotundifolia, `Summit'). Nodal segments 0.5 to 1.0 cm long were cultured in Murashige and Skoog (MS) basal medium supplemented with 5, 10, 20, or 40 μm BA. Best total shoot production was obtained with 10 μm BA; with higher BA levels, shoots were unexpanded and exhibited high mortalities. MS medium supplemented with IBA enhanced rooting by increasing rooting percentage and number per plantlet. Shoots previously proliferated on medium with 5 μm BA rooted significantly better than those multiplied on 10 μM BA. Shoot vigor during rooting was greater in shoots proliferated on 5 vs. 10 μm BA. Root development was not significantly affected by liquid vs. agar-solidifted medium or shoot length. Chemical names used: N-(phenylmethyl) -1H-purin-6-amine (BA), 1H-indole-3-butyric acid (IBA).

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Tehryung Kim and Hazel Y. Wetzstein

Zinc deficiency is a widespread nutritional disorder in plants and occurs in both temperate and tropical climates. In spite of its physiological importance, cytological and ultrastructural changes associated with zinc deficiency are lacking, in part because zinc deficiency is difficult to induce. A method was developed to induce zinc deficiency in pecan (Carya illinoinensis (Wangenh.) C. Koch) using hydroponic culture. Zinc deficiency was evaluated in leaves using light and electron microscopy. Zinc deficiency symptoms varied with severity ranging from interveinal mottling, overall chlorosis, necrosis, and marginal curving. Zinc deficient leaves were thinner, and palisade cells were shorter, wider, and had more intercellular spaces than zinc sufficient leaves. Cells in zinc deficient leaves had limited cytoplasmic content and accumulated phenolic compounds in vacuoles. Extensive starch accumulation was observed in chloroplasts. This work represents the first detailed microscopic evaluations of zinc deficiency in leaves, and provides insight on how zinc deficiency affects leaf structure and function.

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Weiguang Yi and Hazel Y. Wetzstein

Herbs have been long known to provide health-promoting benefits and are demonstrated to have antioxidant, anti-inflammatory, antibacterial, analgesic, and antitumor activities. This study evaluated the effects of drying conditions and extraction protocols on the biochemical activity of three culinary and medicinal herbs: rosemary (Rosmarinus officinalis), motherwort (Leonurus cardiaca), and peppermint (Mentha piperita). Leaf tissues were dried by sun, oven-dried at 40 °C, or oven-dried at 70 °C and extracted using 80% methanol or 80% ethanol. Total polyphenol (TPP) using the Folin-Ciocalteu reagent method and antioxidant capacity using the Trolox-equivalent antioxidant capacity (TEAC) assay were determined. Both drying and extraction conditions significantly impacted TPP content and TEAC in the three herb species. Sun-dried or 40 °C oven-dried herbs exhibited significantly higher TPP content and TEAC capacity than fresh samples, suggesting low-temperature drying may be a good postharvest means to store medicinal/culinary herbs. Exposure to 70 °C oven-drying caused significant antioxidant loss. In addition, the current study showed that with fresh tissue, 80% ethanol extraction had significantly higher TPP and TEAC than 80% methanol extraction for all three herbs, yet for dried herbs, the efficacy of ethanol/methanol extraction varied with different drying treatments.

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Seong Min Woo and Hazel Y. Wetzstein

Georgia plume, Elliottia racemosa Muhlenb. ex. Elliott, is an extremely rare small tree or shrub endemic to Georgia, which is being severely affected by habitat loss and lack of sexual recruitment. In vitro plant regeneration of Georgia plume has not been previously reported and may be a method for the conservation and propagation of this threatened species. Studies evaluated the effects of sterilization methods, explant types, medium composition, and light environment on plant regeneration. An efficient plant regeneration system was developed in which adventitious shoot buds were induced using young, expanding leaf explants placed on an induction medium supplemented with 10 μm thidiazuron and 5 μm indole-3-acetic acid with Gamborg's B5 salts. Shoot elongation was promoted on a medium with 25 μm (2-isopentenyl) adenine incorporated into Woody Plant Medium. In vitro rooting studies evaluated continuous and pulse auxin treatments and ex vitro rooting trials after KIBA (indole-3-butric acid, potassium salt) dips. A 5-day pulse treatment on 100 or 150 μm indole-3-butyric acid produced ≈90% rooting of shoots with greater shoot and root dry weight than other pulse times. High rooting frequencies were obtained under in vitro and ex vitro conditions with over 85% survival of plantlets transferred to greenhouse conditions. The culture protocol was found to be effective with material collected from mature specimens in the wild from divergent populations. Tissue culture appears to be a promising approach for the propagation and conservation of this rare and threatened plant.

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Hazel Y. Wetzstein and S. Edward Law

Stigma characteristics and morphology can be useful in taxonomic and phylogenetic studies, indicate relationships in stigma function and receptivity, and be valuable in evaluating pollen–stigma interactions. Problematic is that in some taxa, copious stigmatic exudate can obscure the fine structural details of the stigmatic surface. Such is the case for Citrus, which has a wet stigma type on which abundant exudate inundates surface papillae. The components of stigmatic surface compounds are highly heterogeneous and include carbohydrates, proteins, lipids, glycoproteins, and phenolic compounds. This study evaluated the efficacy of several pre-fixation wash treatments on removing surface exudate to visualize the underlying stigmatic surface. Wash treatments included various buffer solutions, surfactants, dilute acids/bases, and solvents. Stigmas prepared using conventional fixation methods in glutaraldehyde had considerable accumulations of reticulate surface deposits with stigmatic cells obscured. Pre-fixation washes containing solvents such as methanol, chloroform, and ethanol left accumulations of incompletely removed exudate and crystalline deposits. Alkaline water washes produced a crust-like deposit on stigma surfaces. Buffer washes left residues of plaque-like deposits with perforated areas. In contrast, excellent removal of stigmatic exudate was obtained with a pre-fixation wash composed of 0.2 M Tris buffer, pH 7.2, containing 0.2% Triton X-100 surfactant and allowed clear imaging of the stigma and surface papillae morphology. A central sinus and radially arranged openings on the stigmatic surface were clearly visible and shown for the first time using scanning electron microscopy (SEM).

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Hazel Y. Wetzstein and Choong-Suk Kim

Although somatic embryogenesis in vitro has been carried out successfully in a number of plants, a limiting factor in many somatic embryogenic systems is that plantlet regeneration is not obtainable or restricted to low frequencies. We have developed a repetitive, high frequency somatic embryogenic system in pecan (Carya illinoensis) and have identified effective treatments for improved somatic embryo conversion. A 6 to 10 week cold treatment followed by a 5 day desiccation, promoted enhanced root germination and extension, and epicotyl elongation. Light and transmission electron microscopic evaluations of somatic embryo cotyledon development will be presented and related to conversion enhancing treatments and their possible roles in embryo maturation.

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Hazel Y. Wetzstein and Choong-Suk Kim

Although somatic embryogenesis in vitro has been carried out successfully in a number of plants, a limiting factor in many somatic embryogenic systems is that plantlet regeneration is not obtainable or restricted to low frequencies. We have developed a repetitive, high frequency somatic embryogenic system in pecan (Carya illinoensis) and have identified effective treatments for improved somatic embryo conversion. A 6 to 10 week cold treatment followed by a 5 day desiccation, promoted enhanced root germination and extension, and epicotyl elongation. Light and transmission electron microscopic evaluations of somatic embryo cotyledon development will be presented and related to conversion enhancing treatments and their possible roles in embryo maturation.