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  • Author or Editor: Robert Griesbach x
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Abstract

Somatic cell genetics is a relatively new discipline which relies upon various plant tissue culture techniques. This discipline may be defined broadly as any genetic or physiological investigation involving cultured cells, and includes such areas as gene transfer, gene regulation, cell selection for genetic variants, control of development, and regulation of metabolism.

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Differences in structural gene expression are responsible for a wide range of responses from human cancer to patterned flowers. Gene silencing is one of the ways in which gene expression is controlled. We have developed a model system to study gene silencing using a gene silencing mutation in Petunia ×hybrida (Star mutation) and the ability of certain viruses to reverse the silencing mutation. This model system was used to characterize how the Star flower color pattern was controlled.

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Flower color results from the interaction of a pigment (anthocyanin) with a co-pigment (usually a flavonone or flavonol) at a specific pH. At more alkaline pHs (pH 5 to 6), an anthocyanin/co-pigment complex is blue; while at more acidic pHs (pH 3-4), the same anthocyanin/copigment complex is red. In Phalaenopsis pulcherrima, a mutation in pH resulted in a bluer flower color. The difference in pH between the normal-colored magenta flowers (pH 5.8) and mutant violet flowers (pH 5.5) was due to a single co-dominantly inherited gene.

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The genetic distance for three Petunia species was determined based upon an intron in the chalcone synthase gene. The sequence of the intron was obtained for P. integriflolia ssp. integriflolia var. depauperata, P. integriflolia ssp. integriflolia Torres ecotype, P. altiplana and P. littoralis. These species are very closely related and believed by some taxonomists to be part of a large single species complex. In all the taxa, the intron contained multiple repeated and inverted sequences. The P. integriflolia ssp. integriflolia Torres ecotype intron differed from the P. integriflolia subsp. integriflolia var. depauperata intron in 3 of 930 nucleotides. While, the P. littoralis intron differed from the P. integrifolia subsp. integrifolia var. depauperata intron in 15 of 930 nucleotides. As compared to the P. integrifolia subsp. integriflolia var. depauperata intron, the intron in P. altiplana intron was longer (1125 bp), had a section of 338 nucleotides with a completely different sequence, and differed by 27 of 787 nucleotides in the common sequence.

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Many studies have examined anthocyanin gene expression in colorless tissues by introducing anthocyanin regulatory genes of the MYC/R and MYB/C1 families. Expression of the two regulatory genes under the control of a strong promoter generally results in high anthocyanin accumulation. However, such approaches usually have a negative effect on growth and development of the recovered plants. In this study the author used two promoters of different strengths—a weak (Solanum tuberosum L. polyubiquitin Ubi3) and a strong (double 35S) promoter—and generated two sets of expression constructs with the Zea mays L. anthocyanin regulatory genes MycLc and MybC1 . A transient expression system was developed using biolistic bombardment of white Phalaenopsis amabilis (L.) Blume flowers, which the authors confirmed to be anthocyanin regulatory gene mutants. Transient expression of different combinations of the four constructs would generate three different MycLc -to-MybC1 ratios (>1, 1, <1). The enhanced green florescent protein gene (EGFP) was cotransformed as an internal control with the two anthocyanin regulatory gene constructs. These results demonstrate that the ratio of the two transcription factors had a significant influence on the amount of anthocyanin produced. Anthocyanin accumulation occurred only when MybC1 was under the control of the 35S promoter, regardless of whether MycLC was driven by the 35S or Ubi3 promoter.

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Considerable diversity exists in Capsicum L. germplasm for fruit and leaf shape, size and color, as well as plant habit. This morphological diversity, together with diverse ripe fruit color and varying hues of green to purple and variegated foliar pigmentation, affords myriad opportunities to develop unique cultivars for ornamental applications. The Agricultural Research Service of the United States Department of Agriculture announces the release of a new pepper [Capsicumannuum (L.)] cultivar named `Black Pearl'. `Black Pearl' is intended for ornamental applications and affords growers a new crop to add to their bedding and landscape plant assortment. `Black Pearl' combines black foliage with erect clusters of small round red-pigmented fruit. The vibrant fruit and foliage colors of this new cultivar add interest to the summer and fall garden. Black Pearl' has been trialed extensively for use as a bedding plant where its compact growth habit, black foliage, and brightly colored fruit provide an attractive ornamental display. Limited evaluations suggest that this cultivar is equally well suited for pot culture under high light conditions. `Black Pearl' was designated a 2006 All America Selection award winner after completion of national trials in 2004. `Black Pearl' is a release made available from a cooperative research and development agreement with Pan American Seed Company. Seed of `Black Pearl' is available from Pan American Seed Company, 622 Town Road, West Chicago, IL 60185. Plant Variety Protection for `Black Pearl' is pending.

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