Hormone interactions during lateral root formation

Lateral root (LR) formation, the production of new roots from parent roots, is a hormone- and environmentally-regulated developmental process in higher plants. Physiological and genetic studies using Arabidopsis thaliana and other plant species have revealed the roles of several plant hormones in LR formation, particularly the role of auxin in LR initiation and primordium development, resulting in much progress toward understanding the mechanisms of auxin-mediated LR formation. However, hormone interactions during LR formation have been relatively underexamined. Recent studies have shown that the plant hormones, cytokinin and abscisic acid negatively regulate LR formation whereas brassinosteroids positively regulate LR formation. On the other hand, ethylene has positive and negative roles during LR formation. This review summarizes recent findings on hormone-regulated LR formation in higher plants, focusing on auxin as a trigger and on the other hormones in LR formation, and discusses the possible interactions among plant hormones in this developmental process.     

利用植物激素调控嫁接形成的初步研究

利用黄瓜（Ｃｕｃｕｍ ｉｓｓａｔｉｖｕｓ）试管苗进行离体茎段自体嫁接,研究ＩＢＡ 和６－ＢＡ 对嫁接形成的影响时发现：进行离体茎段嫁接时,用试管苗茎段可简化嫁接过程,减少污染。嫁接茎段的颜色变化、不定根发生和愈伤组织形成与激素浓度有关。植物激素通过影响砧木和接穗间维管束桥形成的时间和数目调控嫁接组合的发育。在作者的实验中,最佳的激素条件是：在接穗培养基中加ＩＢＡ １．２ ｍ ｇ／Ｌ,在接穗和砧木培养基中加６－ＢＡ ０．３ ｍ ｇ／Ｌ。     

Preliminary Studies on Controlling Graft Union Through Plant Hormones

The influences of IBA and 6-BA on the formation of grafting were studied by using explanted internode autografting of cucumber (Cucumis sativus) cultured in vitro, which was a simpler procedure for grafting with lower chance of contamination than the ordinary explanted internode grafting. Colour changes, root initiation and callus formation of the explanted internode graf related to the concentration of plant hormones added to the medium. Plant hormones controlled the formation of graft unions through influencing the time and the number of vascular bridges formation between the stock and the scion. In authors experiments, the optimal condition of plant hormone control was achieved when IBA 1.2 mg/L was added in the scion medium and 6-BA 0.3 mg/L was added to scion and stock medium.     

"Florigen ": an intriguing concept of plant biology.

"Florigen" is the name that Mikhail Chailakhyan coined in 1937 for the putative hormone regulating flowering. At this concept, plant physiologists arrived following early research concerning the effects of temperature and day length on the transition from vegetative to reproductive stages of plants. The existence of florigen was postulated on the experimental backgrounds involving i) the response of plants to inductive conditions; ii) transmission of a flowering stimulus by grafting; iii) extraction of this stimulus from induced plants. This experimental results showed the existence of florigen at least as concept because they always failed to offer the experimental evidence of its chemical existence. The myth of florigen persisted as long as the end of the Seventies, when physiologists began to consider flowering as a complex process in which various classes of hormones might variously interplay.     

激素对水生植物生理生态的影响及其应用

激素代谢是植物传导信号和调节生长发育的重要途径.陆地植物五大类激素在水生植物中也有分布,尽管近年来环境污染导致水生植物衰退的问题日益得到重视,但水生植物激素的研究和应用却远滞后于陆生植物.在总结了近年来激素类物质在水生植物中的研究成果,分别从激素的种类、激素的生理生态作用、激素生物合成的途径及作用的部位和机制、激素之间的相互作用.激素类物质在实验和实践上的应用等进行了全面阐述,指出了水生植物激素生理生态学研究的发展方向,从利用激素类物质诱导水生植物抗性的表达,提高抗逆性,恢复水生植被,以及研究和开发适于水生植物生产和管理的生长调节剂等方面,就水生植物激素的进一步研究和应用进行了探讨.     

果树成花转变途径与调控研究进展

植物成花转变是营养生长向生殖生长转变的过程,木本果树过长的童期严重制约了育种的进程。相对于模式植物,目前对果树成花转变与调控的研究相对较少。因此,了解并掌握果树成花转变的途径及调控方法,对于缩短果树童期、调控开花,加速果树育种具有重要意义。基于近年来国内外相关研究,本文系统总结了果树的成花途径,阐述了果树栽培措施、植物生长调节剂等成花调控方法,以及果树中成花调控的相关基因及网络机制。最后,本文还对以修饰组学为主的多组学以及嫁接和植物生长调节剂在果树成花调控中的研究前景进行了展望。     

Substances of plant flowering

The investigation of the hormonal nature of plant flowering in connection with their photoperiodic reaction has shown that flowering depends on a bicomponental system of hormones, gibberellins regulating stem formation and growth and substances of the anthesin type regulating flower formation. In agreement with the division of the photoperiodic reaction into a leaf and a stem phase the study of the internal factors acting on plant flowering was carried out by means of leaf and stem (apex, bud and callus) models. The results obtained from work with leaf models proved the presence of two groups of hormones of flowering in plants. The data obtained from the application of stem models pointed to the localization of the action of gibberellin and anthesin in different zones of the shoot apices and characterized the potential capacity for flower formation of isolated callus tissue of neutral and photoperiodically sensitive species.     

Gibberellin biosynthesis and the regulation of plant development

Gibberellins (GAs) form a large family of plant growth substances with distinct functions during the whole life cycle of higher plants. The rate of GA biosynthesis and catabolism determines how the GA hormone pool occurs in plants in a tissue and developmentally regulated manner. With the availability of genes coding for GA biosynthetic enzymes, our understanding has improved dramatically of how GA plant hormones regulate and integrate a wide range of growth and developmental processes. This review focuses on two plant systems, pumpkin and Arabidopsis, which have added significantly to our understanding of GA biosynthesis and its regulation. In addition, we present models for regulation of GA biosynthesis in transgenic plants, and discuss their suitability for altering plant growth and development.     

Hormone modulation of legume‐rhizobial symbiosis

Leguminous plants can establish symbiotic associations with diazotropic rhizobia to form nitrogenfixating nodules, which are classified as determinate or indeterminate based on the persistence of nodule meristem. The formation of nitrogen-fixing nodules requires coordinating rhizobial infection and root nodule organogenesis. The formation of an infection thread and the extent of nodule formation are largely under plant control, but vary with environmental conditions and the physiological state of the host plants. Many achievements in these two areas have been made in recent decades.Phytohormone signaling pathways have gradually emerged as important regulators of root nodule symbiosis. Cytokinin, strigolactones(SLs) and local accumulation of auxin can promote nodule development. Ethylene,jasmonic acid(JA), abscisic acid(ABA) and gibberellic acid(GA) all negatively regulate infection thread formation and nodule development. However, salicylic acid(SA) and brassinosteroids(BRs) have different effects on the formation of these two nodule types. Some peptide hormones are also involved in nodulation. This review summarizes recent findings on the roles of these plant hormones in legume-rhizobial symbiosis, and we propose that DELLA proteins may function as a node to integrate plant hormones to regulate nodulation.     

Responses to environmental stresses in woody plants: key to survive and longevity

Environmental stresses have adverse effects on plant growth and productivity, and are predicted to become more severe and widespread in decades to come. Especially, prolonged and repeated severe stresses affecting growth and development would bring down long-lasting effects in woody plants as a result of its long-term growth period. To counteract these effects, trees have evolved specific mechanisms for acclimation and tolerance to environmental stresses. Plant growth and development are regulated by the integration of many environmental and endogenous signals including plant hormones. Acclimation of land plants to environmental stresses is controlled by molecular cascades, also involving cross-talk with other stresses and plant hormone signaling mechanisms. This review focuses on recent studies on molecular mechanisms of abiotic stress responses in woody plants, functions of plant hormones in wood formation, and the interconnection of cell wall biosynthesis and the mechanisms shown above. Understanding of these mechanisms in depth should shed light on the factors for improvement of woody plants to overcome severe environmental stress conditions.     

Ligand–receptor interactions in plant hormone signaling

Small-molecule plant hormones principally control plant growth, development, differentiation, and environmental responses. Nine types of plant hormones are ubiquitous in angiosperms, and the molecular mechanisms of their hormone actions have been elucidated during the last two decades by genomic decoding of model plants with genetic mutants. In particular, the discovery of hormone receptors has greatly contributed to the understanding of signal transduction systems. The three-dimensional structure of the ligand–receptor complex has been determined for eight of the nine hormones by X-ray crystal structure analysis, and ligand perception mechanisms have been revealed at the atomic level. Collective research has revealed the molecular function of plant hormones that act as either molecular glue or an allosteric regulator for activation of receptors. In this review, we present an overview of the respective hormone signal transduction and describe the structural bases of ligand–receptor interactions.     

Genetic control of totipotency of plant cells in vitro

The main approaches have been considered to studying the genetic control of plant cell totipotency in an in vitro culture. The capacity of cultured plants for callusogenesis, organ formation, and somatic embryogenesis depends on the activity of genes that determine and maintain the meristematic state of cells, level of hormones in the cells, and sensitivity to hormones, as well as on the activity other genes that control different stages of plant morphogenesis.     

Hormone balance and abiotic stress tolerance in crop plants

Plant hormones play central roles in the ability of plants to adapt to changing environments, by mediating growth, development, nutrient allocation, and source/sink transitions. Although ABA is the most studied stress-responsive hormone, the role of cytokinins, brassinosteroids, and auxins during environmental stress is emerging. Recent evidence indicated that plant hormones are involved in multiple processes. Cross-talk between the different plant hormones results in synergetic or antagonic interactions that play crucial roles in response of plants to abiotic stress. The characterization of the molecular mechanisms regulating hormone synthesis, signaling, and action are facilitating the modification of hormone biosynthetic pathways for the generation of transgenic crop plants with enhanced abiotic stress tolerance.     

StGA2ox1 is induced prior to stolon swelling and controls GA levels during potato tuber development

The formation and growth of a potato ( Solanum tuberosum ) tuber is a complex process regulated by different environmental signals and plant hormones. In particular, the action of gibberellins (GAs) has been implicated in different aspects of potato tuber formation. Here we report on the isolation and functional analysis of a potato GA 2-oxidase gene ( StGA2ox1 ) and its role in tuber formation. StGA2ox1 is upregulated during the early stages of potato tuber development prior to visible swelling and is predominantly expressed in the subapical region of the stolon and growing tuber. 35S-over-expression transformants exhibit a dwarf phenotype, reduced stolon growth and earlier in vitro tuberization. Transgenic plants with reduced expression levels of StGA2ox1 showed normal plant growth, an altered stolon swelling phenotype and delayed in vitro tuberization. Tubers of the StGA2ox1 suppression clones contain increased levels of GA₂₀, indicating altered GA metabolism. We propose a role for StGA2ox1 in early tuber initiation by modifying GA levels in the subapical stolon region at the onset of tuberization, thereby facilitating normal tuber development and growth.     

Genetic Control of Totipotency of Plant Cells in an in vitro Culture

The main approaches have been considered to studying the genetic control of plant cell totipotency in an in vitro culture. The capacity of cultured plants for callusogenesis, organ formation, and somatic embryogenesis depends on the activity of genes that determine and maintain the meristematic state of cells, level of hormones in the cells, and sensitivity to hormones, as well as on the activity other genes that control different stages of plant morphogenesis.     

Effect of simulated microgravity on auxin polar transport in inflorescence axis of Arabidopsis thaliana.

The morphology, growth and development of higher plants are strongly influenced by environmental stimuli on the earth, which affect the changes in the dynamics of plant hormones in plants. Qualitative and quantitative changes in plant hormones are the most important internal factor to regulate plant growth and development. Among them, auxin (IAA) is of most significant. There are numerous reports concerning the physiological roles of auxin in plant growth and development (Matthysse and Scott 1984). One of the characteristics of auxin is to have the ability of polar transport along the vector of gravity on the earth (Schneider and Wightman 1978), suggesting that the activity of auxin polar transport is also important for the growth and development of plants. It has recently been reported that the normal activity of auxin polar transport in inflorescence axis of Arabidopsis thaliana was required for flower formation (Okada et al. 1991, Ueda et al. 1992). Considering the above evidence together with the fact that gravity affects the morphology, growth and development of higher plants, gravity might affect the qualitative and quantitative changes in plant hormones including the activity of auxin polar transport. In this paper, we report the effect of microgravity condition simulated by a three-dimensional (3-D) or a horizontal clinostat on the activity of auxin polar transport in inflorescence axis of Arabidopsis thaliana.     

真菌激素研究进展

真菌种类繁多,与人类健康、工农业生产和生态系统物质循环的关系非常密切。真菌合成多种性激素、植物激素和动物激素,这些内源激素以及来自动植物产生的外源激素能够被真菌感知,并影响真菌的生长发育、子实体形成、代谢、致病性和共生性等。然而,对真菌激素的合成和信号转导途径,及其起源和进化还知之不多。建立真菌激素学将极大地促进对真菌激素的研究和应用。     

Graft union formation in tomato plants: peroxidase and catalase involvement

BACKGROUND AND AIMS: The use of grafted plants in vegetable crop production is now being expanded greatly. However, few data are available on the formation of graft unions in vegetables. In this work, the structural development of the graft union formation in tomato plants is studied, together with the possible relationship with activities of peroxidases and catalases. METHODS: Tomato (Lycopersicon esculentum Mill.) seedlings of cultivar Fanny were grafted on the rootstock of cultivar AR-9704 using the 'tongue approach grafting' method, and were grown in a crop chamber. A study of the structural development of the graft union and the involvement of peroxidases and catalases in the process of graft formation was carried out during the first stages of the graft union (4, 8 and 15 d after grafting). KEY RESULTS: Observation of the structure of the graft union showed formation of xylem and phloem vessels through the graft union 8 d after grafting. In addition, root hydraulic conductance, L0, indicate that the graft union is fully functional 8 d after grafting, which coincided with an increase of peroxidase and catalase activities. CONCLUSIONS: These results suggest that increased peroxidase and catalase activities might be implicated in graft development in tomato plants.     

Axillary meristem development in Arabidopsis thaliana

Axillary shoot apical meristems initiate post-embryonically in the axils of leaves. Their developmental fate is a main determinant of the final plant body plan. In Arabidopsis, usually a single axillary meristem initiates in the leaf axil even though there is developmental potential for formation of multiple branches. While the wild-type plants rarely form multiple branches in the leaf axil, tfl1-2 plants regularly develop two or more branches in the axils of the rosette leaves. Axillary meristem formation in Arabidopsis occurs in two waves: an acropetal wave forms during plant vegetative development, and a basipetal wave forms during plant reproductive development. We report here the morphological and anatomical changes, and the STM expression pattern associated with the formation of axillary and accessory meristems during Arabidopsis vegetative development.     

Interactions between nitric oxide and plant hormones in aluminum tolerance

Nitric oxide (NO) is involved, together with plant hormones, in the adaptation to Al stress in plants. However, the mechanism by which NO and plant hormones interplay to improve Al tolerance are still unclear. We have recently shown that patterns of plant hormones alteration differ between rye and wheat under Al stress. NO may enhance Al tolerance by regulating hormonal equilibrium in plants, as a regulator of plant hormones signaling. In this paper, some unsolved issues are discussed based on recent studies and the complex network of NO and plant hormones in inducing Al tolerance of plants are proposed.