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  • Author or Editor: Hazel Wetzstein x
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Abstract

Early pollen-stigma responses were observed microscopically in controlled pollinations of pecan [Carya illinoensis (Wangenh) C. Koch]. Receptive stigmatic surfaces have rounded, basally attached projecting papillae with an irregularly patterned, noncopious exudate. Polarly flattened pollen, characteristic of grains at anthesis, becomes rounded and hydrated by 1 hr after pollination. Pollen tube emergence is visible within 3 hr of pollination, and extensive pollen tube growth on the stigma is apparent after 8 to 12 hr. Tube growth generally occurs along the stigmatic surface and between adjacent cells. Stigmatic cells collapse after pollen hydration and germination, with collapse extensive 24 hr after pollination. By 48 hr after pollination, stigmatic cells are flattened, and pollen grains and emerged pollen tubes have contents discharged with a similar collapse.

Open Access

Abstract

Inflorescence and staminate flower development in pecan [Carya illinoinensis (Wang.) K. Koch] were examined using scanning electron microscopy. Organogenesis was described from inception to pollen dehiscence. The order of organ initiation was: a single bract, rounded floral apex, 2 lateral bracteoles, and 3-7 stamens. The initiation and time when stages of floral differentiation occur were determined for 1 protandrous and 2 protogynous cultivars. The time of early inflorescence development and the initiation of floral primordia and bracts were similar in both cultivar types, occurring about 12 months prior to staminate maturity. However, the initiation time of later floral development stages was divergent. The floral stages in the protandrous cultivar up to anther lobing occurred during the previous growing season. In the protogynous cultivars, initiation of bracteoles, the floral apex, stamen primordia and anther lobing took place in the spring of their anthesis.

Open Access

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.

Open Access

Tomato (Lycopersicon esculentum Mill.) transplants can be affected by an intermittent physiological problem manifested by loss of apical meristem function and retarded growth rates, referred to herein as apical meristem decline (AMD). Production losses associated with this condition can be substantial. Similar abnormal and arrested development of the shoot apex has been observed in a number of other species, and referred to as blindness, budlessness, toplessness, blindwood, and bud abortion. A developmental study using scanning electron microscopy was conducted in `Agriset' tomato during an occurrence of AMD to evaluate and compare normal and afflicted plants. The AMD condition was associated with cessation of leaf primordia development and lack of flower initiation. The shoot apex of plants with AMD remained vegetative compared to normal plants which at the same age had well-differentiated flower primordia. No evidence of abortion, die back, or necrosis of the shoot apex was observed. The effects of mineral nutrient additions on symptom development varied with year. In year 1, N fertilization reduced the incidence of both AMD and retarded bud growth (i.e., the percentage of normal plants increased from 29% to 97% with N applications). Preplant applications of P, alone or in conjunction with CaCO3 and trace elements, also ameliorated AMD. In year 2, AMD was observed only at very low levels, i.e., 4% or less, and mineral nutrition had no apparent effect on AMD or normal plant number.

Free access

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.

Free access

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.

Open Access

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.

Open Access

Ozone is a highly oxidizing phytotoxic air pollutant, whose effects are documented to adversely affect crop growth and productivity. In contrast to the large body of published work investigating the effects of atmospheric ozone on outdoor agronomic and forestry crops, relatively few studies have addressed the effects of ozone exposure on greenhouse-grown crops. Outdoor concentrations of ozone can commonly attain concentrations in the 50–150 ppb range, which are known to detrimentally impact plant growth. The objective of this study was to characterize ozone exposure in commercial greenhouses as a prelude to the determination of dose–response effects on specific greenhouse crops and the development of ozone abatement methods, if appropriate. This study documented the levels and diurnal fluctuations in atmospheric ozone concentrations over two annual June–October “ozone seasons.” Measurements were taken every 10 min. for both indoor and outdoor ozone concentration, solar radiation, and temperature. Unexpectedly, indoor ozone concentrations often exhibited elevated levels that were 25% to 35% higher than outdoor concentrations, even in well-ventilated houses. These findings suggest that additional ozone production may occur within the greenhouse environment. Evaluations of causative factors and ozone effects on commercial crop production are warranted.

Free access

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.

Free access

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.

Free access