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  • Author or Editor: William R. Woodson x
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Abstract

The opening of Freesia hybrida Bailey flowers cut in the tight bud stage was promoted by treatment with sucrose and 200 mg·liter−1 8-hydroxyquinoline citrate. A pulse treatment for 24 to 48 hr with 20% sucrose resulted in complete inflorescence development and prolonged vase life. Reduced sucrose concentrations or increased pulse durations were not as effective. Pulse-treating flowers with 20% sucrose for 24 hr prior to 3 days of simulated shipping improved subsequent flower opening and vase life.

Open Access

The senescence of carnation (Dianthus caryophylus) flower petals is regulated by the phytohormone ethylene and is associated with the expression of a number of senescence-related genes. These genes encode enzymes in the ethylene biosynthetic pathway, including both ACC synthase and ACC oxidase. Members of these gene families are differentially regulated in floral organs, with specific members responsible for the increase in ethylene biosynthesis that leads to petal senescence. Pollination often serves as the external signal to initiate the senescence cascade. Following pollination, a rapid increase in ethylene production by the pistal occurs, which is subsequently followed by increased ethylene in the petal. This response is mediated by pollen–pistil interaction(s) that occurs only in compatible pollinations. Recent data indicate that the signal transduction cascade following this cell-cell communication involves protein phosphorylation, as pollination-induced ethylene is sensitive to protein kinase and phosphatase inhibitors. To date, our lab has cloned and characterized a number of senescence-related genes that are believed to play a role in the process of senescence. These include genes that encode enzymes involved in cell wall dissolution (b-galactosidase), protein degradation (cysteine proteinase) and detoxification of breakdown products (glutathione s-transferase). Many of these senescence-related genes are under the transcriptional regulation of ethylene, which has been characterized at the molecular level. A number of biotechnology approaches to controlling the senescence of flowers have been explored. These include the down-regulation of ethylene biosynthetic genes, the expression of a dominant-negative mutation of the ethylene receptor gene, and the expression of genes that lead to increased cytokinin levels in tissues. These will be discussed in relation to the potential for delaying senescence through genetic engineering.

Free access

The target of many genetic engineering experiments is to inhibit the expression of an endogenous gene. For example, research in my laboratory attempts to suppress the expression of ethylene biosynthetic pathway genes to inhibit the production of ethylene and delay flower senescence. The silencing of endogenous genes is generally accomplished by engineering plants to express either antisense or sense RNAs homologous to the target sequence. The mechanism by which gene silencing occurs is not clearly understood. Genetic and molecular analyses of transgene-induced silencing has revealed both meiotically reversible and fully stable phenotypes resulting from the expression of the transgene. In several cases, the mechanisms potentially involved in the silencing of the transgene and concomitant reversion of phenotype have been studied. These include transgene copy number, configuration of the integrated DNA, level of transgene RNA, and environmental factors. In many cases the silencing of transgenes was correlated with DNA methylation. These phenomena and the implications for engineering horticultural crops to express transgenes will be discussed in this workshop.

Free access

Transgenic tomatoes (Lycopersicon esculentum Mill. `Ohio 8245') expressing an antisense catalase gene (ASTOMCAT1) were used to test the hypothesis that modification of the reactive oxygen species scavenging mechanism in plants can lead to changes in oxidative stress tolerance. A 2- to 8-fold reduction in total catalase activity was detected in the leaf extracts of transformants. A 2-fold increase in levels of H2O2 was observed in the transgenic plants with reduced catalase activity. Electrophoretic characterization of multiple catalase isoforms revealed the specific suppression of CAT1 in transgenic plants. Homozygous plants carrying the antisense catalase transgene were used to study the effect of alteration in the expression of catalase on stress tolerance. Transgenic plants treated with 3% H2O2 showed visible damage within 24 hours and subsequently died. In contrast, wild-type and azygous control plants recovered from the treatment. Transgenic plants did not survive 4 °C chilling stress compared to control wild-type and azygous lines. Physiological analysis of these plants indicated that suppression of catalase activity in transgenic tomato led to enhanced sensitivity to oxidative stress. Our data support a role for catalase in oxidative stress defense system in tomato.

Free access

Following a compatible pollination in carnation (Dianthus caryophyllus L. `White Sim'), a signal that coordinates postpollination events is translocated from the style to the ovary and petals. In this paper the roles of ethylene and its direct precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in this signaling were investigated. Following pollination, ethylene and ACC increased sequentially in styles, ovaries, and petals. Ethylene and ACC were highest initially in the stigmatic region of the style but by 24 hours after pollination were highest in the base. Activity of ACC synthase correlated well with ethylene production in styles and petals. In ovaries, ACC synthase activity decreased after pollination despite elevated ethylene production. Lack of ACC synthase activity in pollinated ovaries, coupled with high ACC content, suggests that ACC is translocated within the gynoecium. Further, detection of propylene from petals following application to the ovary provided evidence for movement of ethylene within the flower. Experiments that removed styles and petals at various times after pollination suggest there is a transmissible pollination signal in carnations that has reached the ovary by 12 hours and the petals by 14 to 16 hours.

Free access

Treatment of cut carnation (Dianthus caryophyllus L. `White Sim') flowers with the synthetic cytokinin benzyladenine (BA) at concentrations >1.0 μm induced premature petal senescence. Flowers treated with 100 μm BA exhibited elevated ethylene production in styles and petals before untreated flowers. The gynoecia of BA-treated flowers accumulated 1-aminocyclopropane-l-carboxyllc acid (ACC) and enlarged before untreated flowers. Removal of the gynoecium (ovary and styles) or styles prevented BA-induced petal senescence and resulted in a substantial delay in petal senescence. In contrast, removal of the gynoecium had no effect on timing of petal senescence in flowers held in water. These results indicate BA stimulates petal senescence by inducing premature ACC accumulation and ethylene production in the gynoecium.

Free access