Continuous and ubiquitous expression of foreign genes sometimes results in harmful effects on the growth, development and metabolic activities of plants. Tissue-specific promoters help to overcome this disadvantage, but do not allow one to precisely control transgene expression over time. Thus, inducible transgene expression systems have obvious benefits. In plants, transcriptional regulation is usually driven by chemical agents under the control of chemically-inducible promoters. These systems are diverse, but usually contain two elements, the chimeric transcription factor and the reporter gene. The commonly used chemically-induced expression systems are tetracycline-, steroid-, insecticide-, copper-, and ethanol-regulated. Unlike chemical-inducible systems, optogenetic tools enable spatiotemporal, quantitative and reversible control over transgene expression with light, overcoming limitations of chemically-inducible systems. This review updates and summarizes optogenetic and chemical induction methods of transgene expression used in basic plant research and discusses their potential in field applications.
Tissue specificity of the effect of glucocorticoids on the density of ~-adrenoreceptors is shown. The hormone increases the number of receptors in the lungs, but has no effect on their density in the cerebral cortex either in the norm or after down-regulation. Key Words: ~-adrenoreceptors; glucocorticoids; adrenalectomy; desipramine; cerebral cortex13-Adrenoreceptors (13-AR) of the brain and peripheral tissues are involved in the regulation of various functions of the organism. The adrenoreactivity of tissue and the efficacy of adrenomimetic therapy largely depend on the density of the receptors.However, long-term treatment with adrenomimetics reduces the density of [3-AR. In clinical practice adrenoreactivity of the lungs may be successfully restored with glucocorticoids [3]. Treatment with these steroid hormones increases the number of 13-AR in the lungs, heart, and cells of the vas deferens [3,6], while their effect on the brain remains unclear. The hormones are shown to prevent adrenornimetic-induced reduction of the capacity for adenylate cyclase activation [12]. At the same time, corticosterone admini.~tration during prenatal development results in a reduced number of [3-AR in the cerebral cortex of one-week-old animals [1]. This effect of glucocortieoids may be due to an elevated concentration of norepinephrine in the cerebral cortex sue specificity of glucocorticoid regulation of the density of 13-AR. Our study was aimed at investigating this assumption by comparing the effect of a disturbed balance of glucocorticoids on the density of 13-AR in the lungs and cerebral cortex of rats. MATERIALS AND METHODSThe experiments were performed on mature male Wistar rats, which were caged individually under natural illumination, at 22-24~ and with free access to food and water. In some animals the organs producing endogenous glucocorticoids, the adrenal glands, were excised under nembutal narcosis, or a sham operation was performed. The experiments were started one week after the operation. A suspension of corticosterone (Calbiochem) in 0.2% Tween-80 in 0.2 ml distilled water was injected intraperitoneally in a dose of 5 rag/100 g body weight during 7 days. An inhibitor of reuptake of catecholamines, desipramine, was injected in a dose of 1 rag/100 g body weight via the same route. Control animals received either the same volume of solvent, or nothing. The animals were decapitated and samples from the lungs and frontal cortex were isolated. [~-AR were studied using 3H-dehydroalprenolol (3H-DHA, 75 Ci/mM, 0007-4888/95/0003-0320512.50 9Plenum Pubhshing Corporation
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