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  • Author or Editor: Hazel Y. Wetzstein x
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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

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

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.

Open Access

Abstract

Floral initiation and development in the hybrid geranium, Pelargonium X hortorum Bailey, were examined using scanning electron microscopy. Inflorescence initiation was marked by a raising of the apex followed by the formation of convex flower primordia. In floral development, 5 sepal primordia were delimited, closely followed by 5 petal primordia. Imbricate sepals enclosed the floral apex during later developmental stages. Five antesepalous, then 5 antepetalous stamen primordia were initiated. Five gynoecial primordia arose, forming a pentagonal ridge, carpellary lobes, and eventually an elongate style with stigma. Three of the antepetalous stamen primordia developed into filaform starninodia.

Open Access

Abstract

Structural differences in leaves of pecan [Carya illinoensis (Wang) K. Koch] of cultivars resistant and susceptible to the scab pathogen, Cladosporium caryigenum (Ell. et Lang) Gottwald com. nov (formerly designated Fusicladium effusum Wint.), were examined using scanning and transmission electron microscopy. In immature leaf tissue, cultivar resistance was correlated with fewer peltate glandular trichomes, a greater frequency of collapsed trichomes, and abundant phenolic compounds in the palisade parenchyma and bundle sheath cells compared to susceptible cultivars. In mature, scab-resistant leaves of all cultivars, trichomes were collapsed and less numerous, phenolics were abundant, and cuticular and epidermal cell wall development was greater compared to that of immature leaves.

Open Access

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).

Free access

Somatic embryogenic cultures of pecan (Carya illinoinensis) were induced on medium with either naphthaleneacetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D). Percent embryogenesis, embryo development, and subsequent performance were assessed. Cultures induced on medium with NAA were more zygotic-like, with a higher frequency of embryos that had well-defined shoot apices. In contrast, cultures induced with 2,4-D exhibited more extensive callusing and more fused and/or abnormal embryos. Adjustment of the auxin used during induction may be a means of obtaining higher quality embryos, that have higher rates of conversion into plants.

Free access

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.

Free access

Zinc deficiency is a nutrient disorder that is observed in pecan production areas. In the field it is characterized by a rosette shoot habit and interveinal leaf chlorosis. Up to now, the induction of zinc deficiency has not been accomplishable in the field or greenhouse. Thus any critical evaluations of effects of zinc nutrition on tree growth and development have been lacking. A hydroponic culture system was developed where zinc deficiency was induced. Seedstocks collected from `Stuart', `Curtis', and `Wichita' trees were grown with and without zinc supply. Biomass, leaf area, node number, and visual symptoms were assessed. Foliar deficiency symptoms were rated 4 and structural evaluations were conducted using light and electron microscopy. Significant differences in visual symptoms were observed between treatments and among cultivars. Leaf area significantly decreased in `Stuart' and `Curtis' under zinc deficient conditions. Zinc had no significant effect on biomass and internodal length. Foliar nutrient contents were compared between cultivars. Our data suggest that genotypic differences in sensitivity to zinc deficiency exists and improving pecan production through genetic selection for zinc efficiency appears promising.

Free access

As a plant nutrient, nitrogen is the element in highest demand in terms of quantity and makes up about 2% to 3% of plant dry matter. In this study, we evaluated the effect of nitrogen source on plant growth and nutrient uptake in pecan (Carya illinoensis). Seedlings were hydroponically grown under three nitrogen nutrient regimes where the ratio of nitrate: ammonium was varied, i.e., 3:1, 1:1, and 1:3. High ammonium nutrition had an inhibiting effect on seedling growth. Plants grown under 1:3 (nitrate: ammonium) exhibited significantly lower biomass, decreased root/shoot ratio, and lower specific leaf weight than other treatments. Total nitrogen uptake on a dry weight basis was highest in the high ammonium treatment. In the equal molar treatment (1:1 nitrate: ammonium), plants exhibited preferential uptake of ammonium-form nitrogen. Ammonium-form nitrogen is generally used in pecan orchard practice. Our data suggest that further studies evaluating the effects of nitrogen source are warranted to determine if similar detrimental effects on pecan growth occur in the field. Such studies would be useful for optimizing current fertilization practices.

Free access