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- Author or Editor: Hazel Y. Wetzstein x
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.
Abstract
Actively expanding apical meristems of geranium (Pelargonium × hortorum Bailey) growing in ambient light or in 60% shade were viewed with a scanning electron microscope at weekly intervals. Floral initiation was 37 days earlier in plants receiving ambient light and differentiation time was reduced by 7 days compared with shadegrown plants. Leaves of shade-grown plants emerged more slowly and were smaller when plants were young compared with ambient light-grown plants. Flowers of shadegrown plants were smaller and fewer in number compared with ambient-grown plants, both during differentiation and at anthesis. Shade-grown plants had 22–24 nodes at flower initiation compared with 16–18 nodes in ambient-grown plants.
Abstract
The acclimatization or hardening-off of in vitro-cultured sweetgum (Liquidambar styraciflua L.) plantlets was studied using scanning electron microscopy. Comparisons were made among leaves of plantlets differentiated in culture, plantlets acclimatized after transfer from in vitro conditions, greenhouse seedlings, and mature trees. Leaves of plantlets directly from tissue culture had superficial, circular stomata and epidermal cells with irregular, sinuous undulations in the anticlinal walls. Leaves from acclimatized plantlets had ellipsoid, depressed stomata and irregularly shaped epidermal cells. Seedling and field-grown leaves had depressed, ellipsoid stomata and well-defined isodiametric epidermal cells. Stomata in all cases were confined to the abaxial surface, with densities significantly greater in leaves of in vitro plantlets than in acclimatized plantlets or greenhouse-grown plants. Epicuticular wax was generally smooth and absent of waxy outgrowths in all conditions.
Abstract
Internal porosity, availability of internally adsorbed water, and root growth within a pine bark particle were studied. Internal pore spaces comprised about 43% to 44% of the volume of a pine bark particle. Scanning electron microscopy (SEM) of Coleus blumei Benth. and Vaccinium ashei Reade showed roots anchored on the exterior surface and developing within the bark particle. Seedling development (Raphanus sativus L.) in water-saturated pieces indicated that internally adsorbed water was available provided that roots developed within the bark particle. The quantity of available water remains to be determined.
Abstract
The occurrence and structure of abnormal outgrowths developed on leaves of sweet potato [Ipomoea batatas (L.) Lam] on sterile meristem plantlets maintained in culture tubes were described using light and scanning electron microscopy. The outgrowths or intumescences generally were wart-like, hemispherical forms or irregular, perpendicularly elevated protuberances that formed on both abaxial and adaxial surfaces. Their development resulted from a hypertrophy and hyperplasia of epidermal and mesophyll cells, which resulted in greatly enlarged, roughly isodiametric cells. Swelling and enlargement of stomata were evident; rupture of the epidermal surface did not occur.
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).
Georgia plume (Elliottia racemosa Muhlenb. ex. Elliott) is a rare deciduous shrub or small tree. It has sustained severe loss of habitat and its range is now restricted to a limited number of sites in the state of Georgia. Tissue culture protocols have been developed as a means to propagate and conserve this threatened species using leaf explants induced on medium supplemented with 10 μm thidiazuron (TDZ) and 5 μm indole-3-acetic acid (IAA). Bud-like clusters, elongated embryo-like protrusions, and shoot-like structures were produced from the leaf explants. Morphological and histological evaluations of cultures during induction and development were conducted using light microscopy of sectioned material and scanning electron micrography. Histology of explant tissues indicates that plant regeneration of Georgia plume occurs through a shoot organogenesis pathway that involves the formation of actively dividing meristematic regions originating in subepidermal cell layers that proliferate to form protuberances on the explant surface. Numerous well-formed shoot apical meristems with leaf primordia are produced, as well as fused shoot-like structures. Elongated, embryo-like structures had various degrees of shoot apex development. Evaluations of serial sections found that they lacked a defined root apex, and that basal portions were composed of parenchymatous files of cells with a broad point of attachment to the parent tissue. The lack of bipolarity and a root pole signifies that true somatic embryogenesis does not occur.
Pomegranate fruit is valued for its juice-containing arils and is consumed and marketed as whole fresh fruit, extracted arils, juice, syrup (grenadine), wine, teas, seed oil, and other products. Recent consumption has rapidly increased attributable in part to reported health benefits that include efficacy against coronary heart disease, atherosclerosis, cancer, hypertension, and infectious diseases. Within commercial orchards, the size of fruits produced can be quite variable even with trees of the same genotype grown under similar cultivation practices. Although pomegranates have been cultivated since antiquity, fruit attributes, particularly those related to size, are poorly defined. In this study, compositional changes in pomegranate fruits of the Wonderful cultivar, including volume and weight, aril weight and number, pericarp weight, seed weight, and juice/pulp content, were evaluated in fruits of variable sizes. Correlations between fruit characteristics were determined, and factor analysis established fruit and aril indices. Results indicated that because fruit volume, fruit weight, and total aril weight are closely correlated, any of these characteristics can be used as an indicator of fruit size. The number of arils per fruit was highly correlated with fruit size with larger fruit containing greater numbers of arils. This is in contrast to individual average aril weight, which showed no significant relationship to fruit size. Crop production strategies aimed at increasing aril numbers may be a means for obtaining larger fruit in pomegranate.
The coordinate expression of mRNA classes in pecan (Carya illinoensis) zygotic and somatic embryos has been studied. MRNA was isolated from zygotic embryos at early and late maturation stages (12 to 22 weeks post-pollination) and during germination. Additionally, mRNA was isolated from somatic embryos derived from a repetitive embryogenic system prior and after cold (6 weeks at 4°C) and desiccation treatments (5 days). These treatments have been determined to enhance somatic embryo conversion. The abundance of embryogenic mRNA classes was determined using various cloned cotton mRNA probes (Hughes and Galau, 1989). This study is a part of our efforts to elucidate the developmental and physiological differences between zygotic and somatic embryo systems in pecan.
Repetitive somatic embryogenic lines of pecan (Carya illinoensis) were obtained and subcultured on basal WPM, following a one week induction of zygotic embryo tissue on modified WPM with 6 mg/L NAA. Gene expression of somatic embryos has been studied and compared with that occurring in zygotic embryos. Somatic embryos simultaneously expressed mRNA classes that are specific to each of the zygotic embryo cotyledon (Cot), maturation (Mat), and post abscission stages (Late embryogenesis, Lea). Somatic embryos exhibiting such multiple, nonregulated gene expression patterns have a low germination rate. Treatments found to enhance embryo germination (cold and desiccation) may be effective in part, by modifying gene expression patterns. Some of the Cot and Mat mRNA classes decreased following such treatments, while Lea mRNAs were not effected. Cold and desiccation treatments appear to coordinate gene expression in pecan somatic embryos, which might be associated with embryo germination.