Modification of plant hormone levels and signaling as a tool in plant biotechnology

Plant hormones are signal molecules, present in trace quantities, that act as major regulators of plant growth and development. They are involved in a wide range of processes such as elongation, flowering, root formation and vascular differentiation. For many years, agriculturists have applied hormones to their crops to either increase the yield, or improve the quality of the commercial product. Nowadays, the knowledge of hormone biosynthesis, degradation and signaling pathways has allowed the utilization of biotechnological tools to further improve the main agricultural crops. Natural or artificial mutants, with impaired functioning of the corresponding genes, have been adopted because of their superior phenotype in specific agricultural traits. In addition, transgenic plants have been generated to regulate internal hormone levels, or their signaling pathways, resulting in some crops that have revolutionized agriculture.     

Hormone-mediated maternal effects in birds: mechanisms matter but what do we know of them?

Over the past decade, birds have proven to be excellent models to study hormone-mediated maternal effects in an evolutionary framework. Almost all these studies focus on the function of maternal steroid hormones for offspring development, but lack of knowledge about the underlying mechanisms hampers further progress. We discuss several hypotheses concerning these mechanisms, point out their relevance for ecological and evolutionary interpretations, and review the relevant data. We first examine whether maternal hormones can accumulate in the egg independently of changes in hormone concentrations in the maternal circulation. This is important for Darwinian selection and female physiological trade-offs, and possible mechanisms for hormone accumulation in the egg, which may differ among hormones, are reviewed. Although independent regulation of plasma and yolk concentrations of hormones is conceivable, the data are as yet inconclusive for ovarian hormones. Next, we discuss embryonic utilization of maternal steroids, since enzyme and receptor systems in the embryo may have coevolved with maternal effect mechanisms in the mother. We consider dose-response relationships and action pathways of androgens and argue that these considerations may help to explain the apparent lack of interference of maternal steroids with sexual differentiation. Finally, we discuss mechanisms underlying the pleiotropic actions of maternal steroids, since linked effects may influence the coevolution of parent and offspring traits, owing to their role in the mediation of physiological trade-offs. Possible mechanisms here are interactions with other hormonal systems in the embryo. We urge endocrinologists to embark on suggested mechanistic studies and behavioural ecologists to adjust their interpretations to accommodate the current knowledge of mechanisms.     

Development of oligodendrocytes. Studies of rat glial cells cultured in chemically-defined medium

Oligodendrocytes are macroglial cells that synthesize and maintain myelin in the central nervous system. Oligodendrocytes in rodent brain are formed postnatally from glial progenitor cells. These progenitors cells are bipotential and differentiate in a later stage of development into type-2 astrocytes. Recent studies with cultured cells indicate that growth factors such as platelet-derived growth factor and ciliary neurotrophic factor are instrumental in the control of these events. This paper discusses various methods for the isolation of oligodendrocytes and for their maintenance in culture. We use cerebra or spinal cords from one-week old rat pups to prepare glial cultures that are enriched in oligodendrocytes (60-80% or greater than or equal to 90%, respectively). After one day in serum-containing medium the cells are kept in chemically-defined medium, supplemented with the hormones insulin, T3 and hydrocortisone. The activities of astrocyte-and oligodendrocyte-specific marker enzymes were measured to evaluate the influence of these hormones on the differentiation of the oligodendrocytes. Finally, glial energy metabolism and the utilization of ketone bodies and of fatty acids are discussed briefly.     

Cyclic AMP mediated modification of cholesterol traffic in Leydig tumor cells

The level of nonesterified cholesterol within MA-10 Leydig Tumor cells is regulated acutely by trophic hormones (Freeman, D. A., and Ascoli, M. (1982) J. Biol. Chem. 257, 14231-14238). In the present studies, we localize the site of this steroidogenic cholesterol to the plasma membrane and characterize the means by which this membrane becomes cholesterol-depleted. It is possible to detect the translocation of both newly synthesized cholesterol and cholesterol derived from lipoproteins from the cell interior to the plasma membrane. Stimulated MA-10 cells that are actively producing steroid hormones divert cholesterol from the normal intracellular or plasma membrane acceptor sites into the steroid biosynthetic pathway. Another important effect of steroidogenic stimulation is to cause internalization of plasma membrane cholesterol. Changes in cholesterol traffic in stimulated cells can be blocked by preventing the utilization of cholesterol for steroidogenesis. This later finding indicates that the changes in cholesterol transport induced by trophic hormones are consequences rather than primary causes of steroidogenic stimulation.     

Hormonal regulation of anabolic processes and of protein utilization efficiency in the early postnatal period

The levels of thyroid, pituitary and steroid hormones-thyroxine, triiodothyronine and 11-hydroxycorticosteroids in the blood serum, somatotropin in the pituitary, and processes of protein assimilation were studied in rats in the early postnatal period. The highest endogenous production of thyroxine, triiodothyronine and somatotropin was detected in 15-day-old rats. The highest level of protein utilization was detected in 7 to 15-day-old rats, followed by the lowering of the utilization on changing over to definitive nutrition. Endogenous production of the anabolic hormones thyroxine, triiodothyronine and somatotropin was found to correlate with a high level of protein utilization in rats within the first days of life after birth.     

Further studies on the effects of central administration of neuropeptide Y on neuroendocrine function in the male rat: relationship to hypothalamic catecholamines

Following intraventricular (i.v.t.) administration of increasing doses of neuropeptide Y (NPY; 7.5-750 pmol/rat) the catecholamine levels and turnover were quantitatively measured in discrete hypothalamic regions by means of histofluorometry. In the same rats the adenohypophyseal hormones as well as vasopressin, aldosterone (ALDO) and corticosterone (CORTICO) levels in serum were determined. Neuropeptide Y seems to induce a biphasic change in amine utilization in the tuberoinfundibular dopamine (DA) neurons and in the noradrenergic (NA) utilization in various hypothalamic areas. Thus, the lowest doses seem to inhibit the catecholamine utilization while higher doses seem to enhance it. NPY (250-750 pmol) reduced the serum levels of thyreotropine (TSH), prolactin (PRL) and growth hormone (GH) but increased CORTICO, adrenocorticotropin (ACTH) and ALDO serum levels. In conclusion, it is suggested that the NPY induced changes in DA utilization in the tuberoinfundibular DA neurons may contribute to the NPY induced changes in PRL and TSH secretion. The increases in paraventricular NA utilization may contribute to the increases in ACTH, ALDO and CORTICO secretion induced by NPY. These data give further support for NPY as an important neuroendocrine modulator.     

Biotransformations of steroids

Different types of microbiological transformation of steroids are reviewed, with special attention given to bioconversions applied in the manufacturing of steroid hormones, i.e., 11 alpha- 11 beta-, 16 alpha-, 17 alpha-hydroxylations and 1-dehydrogenation. Availability and utilization of raw materials for industrial production of steroids of the estrane, androstane, and pregnane series are discussed. Among the current trends in steroid research of a practical nature, immobilization of enzymes and living cells and the spore process are emphasized as alternative techniques of steroid transformation of possible future importance. Efforts to recognize, in cell-free preparations, the components of steroid-transforming enzyme systems as well as the cellular mechanisms of control of their biosynthesis and activity are described in order to illustrate the main subjects of current basic investigation in steroid bioconversion.     

Effects of insulin and histamine in themselves and in combination on the glucose metabolism of Tetrahymena

The glucose metabolism and the related intracellular processes of Tetrahymena pyriformis GL cells are measurably influenced by several hormones of higher organisms, among others by the endocytosis stimulating hormone histamine, and the glucose metabolism regulating hormone insulin. Histamine does not interfere with the glucose metabolizing action of insulin, but markedly enhances the utilization of glucose, to judge from a significant decrease in the PAS-positive (hexose) component of histamine-exposed Tetrahymena pyriformis GL cells.     

Effect of adrenalectomy on in vivo glucose metabolism in insulin resistant Zucker obese rats

Lean (Fa/?) and obese (fa/fa) Zucker rats were adrenalectomized (ADX) in order to assess the contribution of adrenal hormones to insulin resistance of the obese Zucker rat. Glucose utilization was measured using an insulin suppression test. Sham-operated obese rats gained almost twice as much weight as sham-operated lean littermates. However, body weight gain of ADX animals was comparable in both genotypes. It was significantly less than that of the respective sham-operated controls. Body weight differences can be accounted for almost entirely by a marked loss of adipose tissue. Although insulin resistance may be attributable to obesity in part, steroid hormones are thought to be directly antagonistic to insulin for glucose metabolism. Adrenalectomy resulted in a decrease in serum glucose concentrations for both lean and obese Zucker rats compared with their respective sham-operated groups. Serum insulin concentration of lean ADX rats was 23% of sham-operated controls; in obese ADX rats, it was 9% of controls. Elevated levels of steady state serum glucose (SSSG) levels in sham-operated obese rats demonstrate a marked resistance to insulin induced glucose uptake compared with sham-operated lean animals. Adrenalectomy caused a marked improvement in insulin sensitivity of obese rats. The hyperglycemic SSSG levels of the obese rats were reduced 2.5 times by ADX. These results indicate that insulin resistance of Zucker obese rats can be ameliorated by ADX, suggesting adrenal hormones contribute to insulin resistance in these animals.     

树木菌根真菌美味红菇内源激素的提取及鉴定

本文报道从树木外生菌根真菌美味红菇 Russulu delica 的菌丝体和发酵滤液中分离提取内源激素的方法和步骤,并用高效液相色谱分析,从提取液中检测出玉米素(Z)、异戊烯嘌呤(IPA)、吲哚-3-乙酸(IAA)、脱落酸(ABA)、赤霉酸(GA3)、激动素(KT)六种植物内源激素。进一步明确了外生菌根真菌对树木生长发育起调控作用可能的物质基础。同时,也为更有效地开发和利用菌根真菌资源提供了依据。     

Glucose and lactate utilization by the amygdala of male and female rats

Gonadal hormones appear to modulate brain energy metabolism, and morphological and functional sexual differences are found in the amygdaloid complex (AC) of rats. Our aim was to study the CO₂ production and lipid synthesis, measured by the rate of L-[U-¹⁴C]lactate or D-[U-¹⁴C]glucose utilization (in pmol.hr^–1.mg^–1), by AC slices in vitro of male and female rats. Lactate was more used than glucose as energy substrate (p < 0.01) but no sex-related difference was observed in glucose or lactate oxidation to CO₂ (p > 0.05) or on lipid synthesis obtained from both substrates (p > 0.05). In addition, there was no effect of the estrous cycle on lactate oxidation to CO₂ by the AC of females (p > 0.05). Based on the present data, it appears that the endogenous normal levels of gonadal hormones are not able to promote sex-related differences in the in vitro glucose or lactate utilization by the AC of rats.     

Biologically active oxylipins from seaweeds

Our previous research has shown that many red algae metabolize polyunsaturated fatty acids to oxidized products resembling the eicosanoid hormones from mammals. We have extended these studies to members of the Phaeophyceae and Chlorophyta and find they also possess similar biosynthetic pathways. From several we have identified novel prostaglandin-like substances. Studies of the molecular mechanisms by which some of these marine oxylipins are formed have revealed that novel oxidative reactions are utilized. Understanding of these biosynthetic pathways in detail has allowed their utilization to produce research biochemicals of high value, such as 12S-hydroperoxyeicosatetraenoic acid (12S-HPETE). Because of their biological properties, seaweed-derived oxylipins have potential utility as pharmaceuticals and research biochemicals.     

The connection of adrenal function to nutritional factors and milk productivity in ruminant animals

In this paper the literature and experimental data about ruminant's adrenal function in the connect with feeding level, ration structure and lactation are generalized and systematized. It is shown, that the adrenal secretion and either glucocorticoid, or katecholamine metabolism can be changed in the dependence on the alimentary factors. When the animals feeding is not adequate physiologically, increased cortisol secretion is necessary for supporting of glucose level in the normal value, what leads to increased loading to the adrenal cortex and is accompanied by redistribution of this hormone between plasma and erythrocytes. The hypothesis explaining the received results is advanced. The ability of the endocrine indexes utilization for the estimation of physiological adequately of rations is discussed. The role of adrenal hormones in the regulation of the mammary gland supplying with the milk precursors, and the mechanisms of these hormones action (either positive, or negative) to the organism lactation function are studying.     

Metabolism of glucose and glutamine in lymphocytes from graves' hyperthyroid patients: influence of methimazole treatment

Several studies have shown that thyroid hormones are able to influence selected immune responses such as cell mediated immunity, differentiation of B lymphocytes and the activity of NK cells. These hormones can also regulate the metabolism of glucose and glutamine in rat macrophages and their effects seem to occur mainly through the Krebs cycle. Alterations in the hexokinase, citrate synthase, glucose-6-phosphate dehydrogenase and glutaminase activities in lymphocytes from patients with Graves' disease, either untreated or on methimazole (MMI) therapy were investigated. Experiments were also done in vitro to determine the activities of these enzymes in normal lymphocytes cultured for 24 h in the presence of MMI, T₃ and T₄ using concentrations close to the physiological. Changes in the conversion of [U-¹⁴C]-glucose and [U-¹⁴C]-glutamine to ¹⁴CO₂ as caused by the addition of MMI, T₃ or T₄ to the culture medium were also evaluated. The results indicate that high levels of thyroid hormones might stimulate the metabolism of glucose and glutamine for a short period of time but, if the stimulus is maintained, the utilization of glutamine by lymphocytes is then suppressed. Moreover, MMI does affect lymphocyte metabolism but the significance of this finding for its immunosuppressive effect remains to be examined.     

The hormonal system of the unicellular Tetrahymena: a review with evolutionary aspects

The unicellular ciliate, Tetrahymena has receptors for hormones of the higher ranked animals, these hormones (e.g. insulin, triiodothyronine, ACTH, histamine, etc.) are also produced by it and it has signal pathways and second messengers for signal transmission. These components are chemically and functionally very similar to that of mammalian ones. The exogenously given hormones regulate different functions, as movement, phagocytosis, chemotaxis, cell growth, secretion, excretion and the cells' own hormone production. The receptors are extremely sensitive, certain hormones are sensed (and response is provoked) at 10-21 M concentration, which makes likely that the function could work by the effect of hormones produced by the Tetrahymena itself. The signal reception is selective, it can differentiate between closely related hormones. The review is listing the hormones produced by the Tetrahymena, the receptors which can receive signals and the signal pathways and second messengers as well, as the known effects of mammalian hormones to the life functions of Tetrahymena. The possible and justified role of hormonal system in the Tetrahymena as a single cell and inside the Tetrahymena population, as a community is discussed. The unicellular hormonal system and mammalian endocrine system are compared and evolutionary conclusions are drawn.     

Trehalose 6-phosphate

Trehalose 6-phosphate (T6P) is a sugar signal of emerging significance. It is an essential component of the mechanisms that coordinate metabolism with plant growth adaptation and development. Its significance began to dawn when genetic modification of the trehalose pathway produced dramatic phenotypes, before the genetic proliferation of the trehalose pathway in plants was fully realised. T6P regulates sugar utilization and starch metabolism and interacts with other signalling pathways, including those mediated by plant hormones. Trehalose phosphate synthases (TPSs) and trehalose phosphate phosphatases are regulated at the gene level by sugars, nitrate, cytokinin and abscisic acid. TPSs are also regulated post-translationally. Mechanistic details of how T6P signals are emerging, but still sparse. Nevertheless, even at this stage, targeting central regulators such as T6P offers promise in crop improvement.