To find out whether change of HPV-infected skin cells is also associated with changes of the methylation of distinctive CpG dinucleotides

The ultimate goal of defoliants is to facilitate mechanical harvest, reduce trash and protect fiber and seed quality from weathering and staining by allowing earlier harvest. Another benefit is the reduced moisture content in the raw fibers and seed which is essential for storage of seedcotton. Selection of appropriate abscission chemicals is one of the critical decisions in cotton production. Herbicidal or hormonal defoliants, such as dimethipin and thidiazuron, are widely used in many cotton producing areas. Dimethipin is a plant growth regulator used as a harvest aid on a variety of crops. It causes leaf cells to slowly lose water and generates ethylene within plants. Dimethipin is considered a contact-type defoliant, whereas thidiazuron has growth-regulator properties and moves through the plant. Thidiazuron increases the concentration of ethylene relative to auxin in leaf petioles and results in the activation of the leaf abscission layer. However, these types of defoliants induce drastic leaf abscission which inhibits timely transport of nutrients from leaves to cotton bolls. Also, these defoliants do not directly influence boll ripening and must be applied in combination with ethephon, a boll opener, to provide satisfactory defoliation and boll opening. An abscission chemical with improved defoliation and boll opening properties is needed for cotton harvest practices. Coronatine is a chlorosis-inducing non-host-specific phytotoxin produced by several members in the Pseudomonas syringae group of pathovars. It induces inhibition of root elongation, senescence, production of defense-related protease inhibitors, and resistance to abiotic stresses. COR also induces growth regulator-like effects such as hypertrophy and stimulation of ethylene production and tendril coiling. In addition, COR has been reported to be a structural and functional analog of jasmonic acid and methyl jasmonate, which are important plant growth substances in octadecanoid TPCA-1 pointing out from the lively site groove in a similar direction signaling. Components of the octadecanoid pathway have been shown to affect the regulation of wounding, fruit ripening, and abscission. External application of methyl jasmonate and COR likely induced abscission by stimulating levels of ethylene when applied to the entire citrus tree canopy. However, the ability of COR to cause leaf abscission in cotton is unclear. Abscission is the main process that involves structural, biochemical, and molecular changes resulting in the detachment of plant organs, including leaves, flowers and fruits. Abscission occurs at predetermined sites referred to as abscission zones, which consist of a few layers of small, densely packed cells that respond in different ways from neighbouring cells to the same hormonal or environmental cues. Knowledge of mechanisms involved in abscission of leaves or other organs is essential to develop strategies to control them and improve harvesting practices or unwanted crop loss in fruit crops. Once abscission is initiated, cells in the abscission zone begin to enlarge, followed by increased expression of genes and the activities of cell wall-degrading enzymes such as b-1, 4-glucanase or cellulase and polygalacturonase. As a result, the middle lamellae of abscission zone cells dissolve and, ultimately, the organ abscises. Ethylene plays a primary role in accelerating leaf abscission and fruit ripening. The conversions of S-AdoMet to 1- aminocyclopropane-1-carboxylic acid is the rate-limiting step in ethylene biosynthesis, and is catalysed by ACC synthese. The observations that expression of the ACS genes is highly regulated by a variety of signals and that active ACC synthase is labile and present at low levels suggest that ethylene biosynthesis is tightly controlled. Both positive and negative feedback regulation of ethylene biosynthesis have been reported in different plant species. Most studies addressing ACS regulation have focused on ACS gene expression in response to various endogenous cues and environmental stimuli. In an attempt to understand how responses to COR operate, some physiological- and transcriptional- level responses of cotton to the application of COR need further study. The purpose of this study was first to investigate the possible roles of COR during cotton leaf abscission compared with using TDZ or water. In the present work, the phenotypic and anatomical changes in leaves, leaf detachment force, activity of abscission-related enzymes, and expression of genes encoding the enzymes in different cotton tissues were determined under greenhouse and/or field conditions. We also estimated the transcript levels of two hydrolytic enzyme genes and one ethylene biosynthesis enzyme gene in leaf, petiole and leaf abscission zone as well as during leaf abscission. Finally, we determined boll opening, seedcotton yield and seed quality to elucidate whether and how COR affects cotton boll ripening and seed development. Appropriate and safe abscission chemicals will improve timing and facilitate harvest of cotton. In this study, we demonstrated that the phytotoxin, coronatine induced leaf abscission during cotton defoliation. Abscission occurs in an anatomically distinct cell layer known as the abscission zone.

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