Auxin: regulation, action, and interaction.

Jasmonates: biosynthesis, perception, signal transduction and action in plant stress response, growth and development. An update to the 2007 review in Annals of Botany

Epigenetic phenomena in animals and plants are mediated by DNA methylation and stable chromatin modifications. There has been considerable interest in whether environmental factors modulate the establishment and maintenance of epigenetic modifications, and could thereby influence gene expression and phenotype. Chemical pollutants, dietary components, temperature changes and other external stresses can indeed have long-lasting effects on development, metabolism and health, sometimes even in subsequent generations. Although the underlying mechanisms remain largely unknown, particularly in humans, mechanistic insights are emerging from experimental model systems. These have implications for structuring future research and understanding disease and development.

Epigenetics and the environment: emerging patterns and implications.

EVidenceModeler (EVM) is presented as an automated eukaryotic gene structure annotation tool that reports eukaryotic gene structures as a weighted consensus of all available evidence. EVM, when combined with the Program to Assemble Spliced Alignments (PASA), yields a comprehensive, configurable annotation system that predicts protein-coding genes and alternatively spliced isoforms. Our experiments on both rice and human genome sequences demonstrate that EVM produces automated gene structure annotation approaching the quality of manual curation.

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Automated Eukaryotic Gene Structure Annotation Using EVidenceModeler and the Program to Assemble Spliced Alignments

■ Abstract Cytokinins are structurally diverse and biologically versatile. The chemistry and physiology of cytokinin have been studied extensively, but the regulation of cytokinin biosynthesis, metabolism, and signal transduction is still largely undefined. Recent advances in cloning metabolic genes and identifying putative receptors portend more rapid progress based on molecular techniques. This review centers on cytokinin metabolism with connecting discussions on biosynthesis and signal transduction. Important findings are summarized with emphasis on metabolic enzymes and genes. Based on the information generated to date, implications and future research directions are presented.

Cytokinin metabolism and action

Minitubers often exhibit a more protracted dormant period relative to their field-grown counterparts and this can have a detrimental impact on plant establishment. Treatment of dormant Russet Burbank minitubers with the synthetic cytokinins N-(2-chloro-4-pyridyl)-N′-phenylurea (CP) or 1-(α-ethylbenzyl)-3-nitroguanidine (NG) resulted in the premature termination of tuber dormancy. In contrast, treatment with the thidiazoyl-urea cytokinin TZ did not stimulate sprouting. Both CP and NG were more effective than the naturally occurring cytokinin zeatin and, unlike zeatin, both stimulated sprouting in minitubers during early storage. Unlike treatment with gibberellic acid (GA) which often induced excessive sprout growth, sprouts developing from minitubers treated with either cytokinin were short, thick, and robust. Upon transfer to room temperature, the endogenous content of ABA in apical bud periderm discs isolated from control minitubers declined more than 60% over a 15 day period. Treatment with either CP or NG had no appreciable effect on this decline while treatment with GA diminished the decrease in ABA content. Treatment with either synthetic cytokinin resulted in a large and sustained increase in endogenous ethylene production that was detectable immediately prior to visible sprout growth. In contrast, GA treatment resulted in a much smaller increase that was observed after sprout growth commenced. These results indicate that either CP or NG treatment can be effectively used to prematurely terminate tuber dormancy and induce sprout growth.

Effects of Synthetic Phenylurea and Nitroguanidine Cytokinins on Dormancy Break and Sprout Growth in Russet Burbank Minitubers

The effect of the defoliant thidiazuron (N-phenyl-N′1,2,3-thiadiazol-5-ylurea) on ethylene evolution from etiolated mung bean hypocotyl segments was examined. Treatment of hypocotyl segments with concentrations of thidiazuron equal to or greater than 30 nanomolar stimulated ethylene evolution. Increased rates of ethylene evolution from thidiazuron-treated tissues could be detected within 90 minutes of treatment and persisted up to 30 hours after treatment. Radioactive methionine was readily taken up by thidiazuron-treated tissues and was converted to ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) and an acidic conjugate of ACC. Aminoethoxyvinylglycine, aminooxyacetic acid, cobalt chloride, and α-aminoisobutyric acid reduced ethylene evolution from treated tissues. An increase in the endogenous content of free ACC coincided with the increase in ethylene evolution following thidiazuron treatment. Uptake and conversion of exogenous ACC to ethylene were not affected by thidiazuron treatment. No increases in the extractable activities of ACC synthase were detected following thidiazuron treatment.

Effect of the Defoliant Thidiazuron on Ethylene Evolution from Mung Bean Hypocotyl Segments

The involvement of ethylene in the dormancy breaking actions of cytokinins, GA, and BE was investigated using Russet Burbank minitubers. Injection of 10 µg tuber−1 BA, CP, GA, NG, or ZEA or 24 hour exposure to BE effectively broke dormancy and stimulated sprout growth over a two-week period. Although ethylene production was slightly enhanced by all treatments, a significant increase in ethylene production was observed in minitubers treated with BE, CP, or NG. Pretreatment with the ethylene antagonists STS or MCP did not affect the dormancy breaking actions of any of the agents tested. Application of the ethylene synthesis inhibitor AVG to NG-treated minitubers, completely suppressed ethylene production but had no effect on dormancy break. Application of exogenous ethylene or stimulation of endogenous ethylene production by ACC treatment did not break minituber dormancy or stimulate sprout growth. Collectively, these results indicate that endogenous ethylene does not play a role in the dormancy breaking actions of cytokinins, GA, or BE.

Ethylene Is Not Involved in Hormone- and Bromoethane-Induced Dormancy Break in Russet Burbank Minitubers

The speed of ethylene-induced leaf abscission in cotton (Gossypium hirsutum L. cv LG-102) seedlings is dependent on leaf position (i.e. physiological age). Fumigation of intact seedlings for 18 hours with 10 microliters per liter of ethylene resulted in 40% abscission of the still-expanding third true (3 degrees ) leaves but had no effect on the fully expanded first true (1 degrees ) leaves. After 42 hours of fumigation with 50 microliters per liter of ethylene, total abscission of the 3 degrees leaves occurred while <50% abscission of the 1 degrees leaves was observed. On a leaf basis, endogenous levels of free IAA in 1 degrees leaves were approximately twice those of 3 degrees leaves. Free IAA levels were reduced equally (approximately 55%) in both leaf types after 18 hours of ethylene (10 microliters per liter) treatment. Ethylene treatment of intact seedlings inhibited the basipetal movement of [(14)C]IAA in petiole segments isolated from both leaf types in a dose-dependent manner. The auxin transport inhibitor N-1-naphthylphthalamic acid increased the rate and extent of ethylene-induced leaf abscission at both leaf positions but did not alter the relative pattern of abscission. Abscission-zone explants prepared from 3 degrees leaves abscised faster than 1 degrees leaf explants when exposed to ethylene. Ethyleneinduced abscission of 3 degrees explants was not appreciably inhibited by exogenous IAA while 1 degrees explants exhibited a pronounced and protracted inhibition. The synthetic auxins 2,4-D and 1-naphthaleneacetic acid completely inhibited ethylene-induced abscission of both 1 degrees and 3 degrees explants for 40 hours. It is proposed that the differential abscission response of cotton seedling leaves is primarily a result of the limited abscission-inhibiting effects of IAA in the abscission zone of the younger leaves.

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Ethylene-Induced Leaf Abscission in Cotton Seedlings The Physiological Bases for Age-Dependent Differences in Sensitivity

https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=53728&content=PDF

Jeffrey C. Suttle

Papers

Effects of Synthetic Phenylurea and Nitroguanidine Cytokinins on Dormancy Break and Sprout Growth in Russet Burbank Minitubers

Effect of the Defoliant Thidiazuron on Ethylene Evolution from Mung Bean Hypocotyl Segments

Ethylene Is Not Involved in Hormone- and Bromoethane-Induced Dormancy Break in Russet Burbank Minitubers

Ethylene-Induced Leaf Abscission in Cotton Seedlings The Physiological Bases for Age-Dependent Differences in Sensitivity

Coordinate expression of AOS genes and JA accumulation: JA is not required for initiation of closing layer in wound healing tubers.