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Dennis P. Stimart, John C. Mather, and Kenneth R. Schroeder

Expanding shoot tips of Pulmonaria `Roy Davidson' and Pulmonaria saccharata `Margery Fish' were cultured in vitro on a modified Murashige and Skoog medium containing BA to establish proliferating cultures for use in comparing BA concentrations on shoot proliferation and rooting. The optimum level for shoot proliferation was 8.8 μm BA. Greatest rooting was on medium without BA. Genotype and time in culture influenced shoot and root counts. Chemical names used: N6-benzyladenine (BA)

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James S. Busse, Monica Figueroa-Cabanas, and Dennis P. Stimart*

Adventitious shoot formation in vitro from Antirrhinum majus L. hypocotyls was investigated using two inbred lines, the most and least regenerative lines selected from screening. Time course analysis indicated cell division in the most regenerative line occurred first in one or a small number of epidermal cells with periclinal and anticlinal divisions. Subsequently, cortical then vascular cells were recruited beneath the dividing epidermal cells. Once shoots formed, their vascular system was continuous with the original hypocotyl explant. The least regenerative line had no cell division directed toward organogenesis. Shoot formation on hypocotyls of A. majus was adventitious in origin, by direct organogenesis and genotype dependent.

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Kenneth R. Schroeder, Dennis P. Stimart, and Erik V. Nordheim

Nicotiana alata Link and Otto (Jasmine tobacco) was transformed with an autoregulated senescence-inhibition gene construct PSAG12-IPT encoding isopentenyl transferase via Agrobacterium-mediated transformation. Transformation was confirmed by polymerase chain reaction. Transgenic plants exhibited up to 2- to 4-fold fewer senesced leaves, 29% longer in situ flower life, 26% more shoot dry weight, and a 32% to 50% reduction in flowers per branch. Additionally, transgenics were 28% shorter and had up to 174% more branches, indicative of cytokinin overproduction and a lack of tight autoregulation of PSAG12-IPT. Variation among independent transgenics suggests selection for enhanced PSAG12-IPT is feasible. Our observations of increased branching and in situ flower longevity, as well as reduced plant height and flowers per branch provide new information on PSAG12-IPT and its potential value for biological study and horticultural application.

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Rozlaily Zainol, Dennis P. Stimart, and Ray F. Evert

Anatomical analysis was performed using a double-flowered mutant of Nicotiana alata Link & Otto. Flower doubleness resulted from petaloid modification of the androecium. Vascularized petal-like outgrowths arose from the anther, connective, and filament of the stamen. The vasculature in petaloid outgrowths from the anther and upper part of the filament originated from and was continuous with the vascular bundle of the filament. In contrast, the vascular bundles formed in the outgrowths from the lower part of the filament developed independently of the vascular bundle of the filament and were not connected to it at any time. Emergences consisting of epidermal and ground parenchyma tissue and lacking vascularization arose from the filament.

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James F. Harbage, Dennis P. Stimart, and Carol Auer

The influence of root initiation medium pH on root formation was investigated in relation to uptake and metabolism of applied IBA in microcuttings of Malus ×domestica Borkh. `Gala' and `Triple Red Delicious'. Root formation and uptake of H 3-IBA were related inversely to root initiation medium pH. Maximum root count (10.3 roots) and IBA uptake were observed at pH 4.0. Regardless of pH, overall root count of `Gala' was higher (13.5 roots) than `Triple Red Delicious' (4 roots). Uptake of IBA was highest at pH 4.0 for `Gala' (1.7% uptake) and at pH 4 and 5 for `Triple Red Delicious' (0.75% uptake). Metabolism of IBA was the same regardless of root initiation medium pH or cultivar examined. One-half of the IBA taken up was converted to a compound that coeluted with IBAsp during high-performance liquid chromatography. Apparently, pH regulates root formation by affecting IBA uptake but not metabolism. The level of auxin in tissue appeared unrelated to root formation between genotypes. Chemical names used: 1H-indole-3-butyric acid (IBA); 5-H 3-indole-3-butyric acid (H 3-IBA); indole-3-butrylaspartic acid (IBAsp).

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Nicholas P. Howard, Dennis Stimart, Natalia de Leon, Michael J. Havey, and William Martin

Impatiens (Impatiens walleriana) are currently among the most valuable and widely cultivated floriculture crops in the world. Attractive floral display is a primary goal for breeders of impatiens. Although breeders have selected for this trait, little consideration has been given to floral longevity as a means to increase the floral display of bedding crops. In this study, 259 commercial inbred lines of impatiens were grown in a greenhouse and evaluated for floral longevity as defined by the time between when a flower was completely open to when all of the petals abscised from the pedicle. Mean floral longevity of inbreds ranged from 3.3 ± 0.4 to 15.8 ± 2.5 days. Twelve inbreds (six with long floral longevity and six with short floral longevity) were chosen and crossed in a half diallel to create 66 hybrids that were analyzed for floral longevity in three greenhouse environments. Mean floral longevity of hybrids across greenhouse environments ranged from 2.8 ± 0.4 to 14.1 ± 2.8 days. Significant general (GCA) and specific (SCA) combining abilities for floral longevity were detected. GCA mean squares were 37 times larger than SCA mean squares, revealing that additive genetic effects play a more important role in the inheritance of floral longevity in impatiens. This information, coupled with the significant amount of variation for floral longevity among inbreds, indicates that there is good potential for breeding for floral longevity in impatiens to improve the floral display of hybrids.