Biological Sciences
Plant Hormones
Plant hormones are chemical messengers produced by plants to regulate growth, development, and responses to environmental stimuli. They play a crucial role in controlling processes such as seed germination, root and shoot growth, flowering, and fruit ripening. The main classes of plant hormones include auxins, gibberellins, cytokinins, abscisic acid, and ethylene.
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11 Key excerpts on "Plant Hormones"
eBook - ePubProtective Chemical Agents in the Amelioration of Plant Abiotic Stress
Biochemical and Molecular Perspectives
- Aryadeep Roychoudhury, Durgesh K. Tripathi, Aryadeep Roychoudhury, Durgesh Kumar Tripathi, Aryadeep Roychoudhury, Durgesh Kumar Tripathi(Authors)
- 2020(Publication Date)
- Wiley-Blackwell(Publisher)
2005 ).The major advancement achieved in the area of phytohormones and their respective response is the identification of precise receptor for majorly known hormones. These chemical messengers are translocated to several organelles where they bind to their target site via receptor‐mediated recognition and further transduce the signal downstream by themselves getting degraded. Thus, ordered degradation of protein also plays a pivotal role in hormone signaling, which is regulated mainly by ubiquitin‐mediated degradation (Santner et al. 2009 ). Several synergistic or antagonistic actions take place simultaneously, which are primarily key to regulation of defense mechanism in plants against variety of stresses, and termed as signaling cross talk. In the recent research, efforts have been laid down to reveal the complex physiological and molecular responses of stress tolerance, however the molecular intricacy still remains ambiguous. The major problem lies in the complex nature of plant response for different situations, as both biotic as well as abiotic stresses are known to express extreme yet similar suites of genes. A common factor for both types of stress is said to be the generation of small molecules, which, if not regulated, are known to be highly toxic at higher concentration and are termed as active or reactive oxygen species (ROS ). The generation and simultaneous scavenging of ROS holds a key step involved in response to biotic and abiotic stresses (Apel and Hirt 2004 ). Using large scale transcriptome and microarray analysis, it is evident that similar cross talk exists between these signaling networks (Seki et al. 2002 ; Cheong et al. 2002 ; Davletova et al. 2005 ). The evidence that ROS may act as a common downstream messenger for transducing multiple stress signals was established in plants challenged either with heavy metal or with necrotrophic pathogen where a similar increase in ROS levels was monitored. The study demonstrated a similar yet overlapping set of responses in all plants challenged with either type of stress. Apart from their role in growth enhancement, an improved plant growth and yield was observed through exogenous application of phytohormones. In a study, Li et al. (2012 ) reported an increased photosynthetic activity, enhanced nitrogen metabolism, and improved generation of amino acid through application of brassinosteroid hormones in Camellia sinensis. The authors further reported an improved hormone metabolism as well as better antioxidant system in maize seedlings primed with exogenous salicylic acid and H2 O2 , thus helping maize seed to mitigate deleterious effects of chilling stress. Recent study conducted by Singh et al. (2017
eBook - ePub- Jiayang Li, Chuanyou Li, Steven M Smith(Authors)
- 2017(Publication Date)
- Academic Press(Publisher)
1.1.1. Hormones and signals
Since the discovery of the auxin indole-3-acetic acid in the 1930s, many endogenous signaling and regulatory molecules have been discovered, and more are yet to be discovered. There is great diversity among this array of signaling molecules, which includes small organic compounds, gases and volatiles, inorganic ions, oligosaccharides, peptides, and RNAs. Some of these substances are produced and act within individual cells, others pass between cells, others are transported between tissues and organs to regulate processes at the whole-plant level and yet others may be released into the environment to influence neighboring plants and other organisms.These observations raise the important question of how we define Plant Hormones. It is not easy to define them, and there is no absolute definition. The hormone concept in plants was borrowed from that of animals. A classical and simple definition of a hormone in animals is an organic chemical produced in one organ and transported at very low concentrations to other sites in the animal to regulate specific processes in target tissues. Examples include adrenaline, thyroxine, growth hormone (somatotropin) and the steroidal sex hormones, testosterone and estrogen. There are several aspects of such a definition that do not fit so well for plants. Firstly it is more difficult to identify discrete source organs and specific target tissues. Many such chemical signals are produced throughout the plant and can act locally, as well as distally. Some signaling substances have multiple functions, such as sugars which serve as a source of carbon and energy in addition to signaling, or calcium ions which serve signaling, enzymatic, and structural roles. Some signals such as reactive oxygen species (ROS) and nitric oxide (NO) are probably produced in all cells as an inevitable consequence of conducting metabolic activities in an oxygen-containing environment. Sugars and some other metabolic signals operate at high (mM) concentrations while others such as calcium ions operate at low (μM) concentrations, while hormones typically function at very low levels (nM to pM).
eBook - PDF- William V Dashek, Marcia Harrison(Authors)
- 2010(Publication Date)
- CRC Press(Publisher)
PLANT CELL BIOLOCY around the infection site (Taiz and Zeiger, 2002). Although this response results in a small zone of dead cells, it prevents further infection by the pathogen. Plant-produced Chemical Signals Plant Hormones coordinate most of the growth and development events in plants (see Chapter 5 to review plant hormone structures and actions) (Table 14.2). The five classical Plant Hormones—absdsic acid (ABA), auxin, cytokinin, emylene, and gib- berellic acid (GA)—and their responses were studied extensively throughout the tweitieth century, beginning in the 1920s with characterization of auxin as a plant growth regulator by Went and others (Arteca, 19% includes an historical over- view of auxin and the discovery of other Plant Hormones). The role of plant growth regulators seemed to be analogous to animal hormones, defined by Bayliss and Starling (1904) as substances produced in one part of an organism and transported to another part to induce a response there. However, the concept that plant growth- regulating substances function in the same manner as animal hormones was not experi- mentally demonstrated despite numerous studies on their biosynthesis and the biochemical changes that occur in response to changing levels of these hormones. Understanding the hormonal mechanisms of action of plant growth-regulating sub- stances began with genetic and molecular studies later in the twentieth century. It is now known that Plant Hormones are comparable to animal hormones in that they bind to proteins called receptors, and induce a series of interconnected biochemical steps that direct and amplify the response, causing a change in cellular physiology. These steps are collectively known as a "signal transduction cascade".
eBook - ePub- Hans-Walter Heldt, Birgit Piechulla(Authors)
- 2010(Publication Date)
- Academic Press(Publisher)
19 Multiple signals regulate the growth and development of plant organs and enable their adaptation to environmental conditionsIn complex multicellular organisms such as higher plants and animals, metabolism, growth, and development of the various organs are coordinated by the emission of signal compounds. In animals these signals can be hormones, which are secreted by glandular cells. Hormones are classified in paracrine hormones, which function as signals to neighboring cells, and endocrine hormones, which are emitted to distant cells (e.g., via the blood circulation). Also in plants, signal compounds are released from certain organs, often signaling to neighboring cells, but also to distant cells via the xylem or the phloem. All these plant signal compounds are termed phytohormones . Some of the phytohormones (e.g., brassinosteroids) resemble animal hormones in their structure, whereas others are structurally completely different. Like animal hormones, phytohormones also have many different signal functions. They control the adjustment of plant metabolism to environmental conditions, such as water supply, temperature, and day length, and regulate plant development. Light sensors including phytochromes , which recognize red and far-red light, and cryptochromes and phototropin monitoring blue light, control the growth and the differentiation of plants depending on the intensity and quality of light.The signal transduction chain between the binding of a certain hormone to the corresponding receptor and its effect on specific cellular targets, such as the transcription of genes or the activity of enzymes, is now known for many animal hormones. In contrast, signal transduction chains have not been fully resolved for any of the phytohormones or light sensors. However, partial results indicate that certain components of the signal transduction chain in plants may be similar to those in animals. The phytohormone receptors and light sensors apparently act as a multicomponent system , in which the signal transduction chains are interwoven to a network
eBook - ePubPlant Receptor-Like Kinases
Role in Development and Stress
- Santosh Kumar Upadhyay, Shumayla(Authors)
- 2022(Publication Date)
- Academic Press(Publisher)
Despite animals in which hormones are produced in specialized glands and regulated by the central nervous system, phytohormones are typically synthesized throughout the plants and regulated in a decentralized manner. Phytohormones are categorized into five common classes auxin, cytokinin, gibberellins (GA), abscisic acid (ABA), and ethylene as well as some newly identified Plant Hormones such as brassinosteroid (BR), jasmonic acid (JA), salicylic acid (SA), and even this list has been extended to some small proteins and biologically active peptides such as systemin, plant natriuretic peptides (PNPs), phytosulfokines (PSK), strigolactone (SL), CLAVATA3 (CLV3), S-locus cysteine-rich proteins (SCPs), and ENOD40 (Bahyrycz & Konopińska, 2007 ; Stacey et al., 2002 ; Wang & Irving, 2011 ; Wang et al., 2020 ; Wheeler & Irving, 2010). While auxin, cytokinin, gibberellins (GA), and brassinosteroid (BR) are considered leading developmental regulators, others such as jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA), strigolactones (SL) and ethylene are known as significant factors in stress responses (Gray, 2004 ; Peleg & Blumwald, 2011 ; Wolters & Jürgens, 2009). It’s worth reminding that the biological activity and biological phenomenon of the plant sometimes are manipulated by the combined interplay of different hormones that work synergistically or antagonistically with each other through complex interaction mechanisms (Fig. 15.1)
eBook - ePubOilseed Crops
Yield and Adaptations under Environmental Stress
- Parvaiz Ahmad(Author)
- 2017(Publication Date)
- Wiley-Blackwell(Publisher)
Several phytohormones produced within the plants, mainly auxins (IAA), abscisic acid (ABA), gibberellins (GA), ethylene, cytokinins (CKs), and salicylic acid (SA), have been recognized as coordinating various biochemical and physiological processes within the plants. Of all the aforementioned phytohormones, SA and ABA are well‐known hormones for their contribution in plant responses to biotic factors, such as various pathogenic micro‐organisms, herbivores, and abiotics, including UV irradiation, exposure to ozone, osmotic stress, and wounding (Hirsch et al., 1997; Madhaiyan et al., 2013; Pramanik & Bera, 2013; Kumar et al., 2014; Fahad et al., 2015). 9.3 Characteristics of phytohormones The main characteristics of phytohormones are as follows. Phytohormones are naturally synthesized within the plants and influence cellular division, the expression of genes, the transcription levels and growth. Furthermore, phytohormones are not only the nutrients for plants but also initiate several processes such as cell differentiation, development, and growth of the plants. The effective translocation of phytohormones through vascular tissues within the plants’ tissues is achieved by using movements, such as cytoplasmic movements in cells, diffusion of ions, localized movement, and using molecules within the cells (Iqbal, 2014; Iqbal et al., 2014; Kumar et al., 2014; Fahad et al., 2015). 9.4 Biosynthesis of phytohormones The phytohormones play an important role in several development and growth processes of various crops, including oilseed crops and their effects might be initiated during the plant’s biosynthesis. In this chapter we describe the biosynthesis of phytohormones and its role in improving the yields of oilseed crops. 9.4.1 Biosynthesis of auxin The biosynthesis of auxin is mainly divided into two types: (1) tryptophan dependent; and (2) tryptophan independent (Figure 9.1)
eBook - PDF- Pandey, Narendra Shankar(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Chapter 6 : Plant hormone Plants also produce signaling molecules as organic substances, called hormones , that have profound effects on development at vanishingly low concentrations. Until quite recently, plant development was thought to be regulated by only fve types of hormones: auxins, gibberellins, cytokinins, ethylene, and abscisic acid. However, there is now compelling evidence for the existence of plant steroid hormones, the brassinosteroids, that hav- e a wide range of morphological effects on plant development. 6.1 Auxin The auxin is indole-3- acetic acid (IAA). Several other auxins in higher plants were discovered later, but IAA is by far the most abundant and physiologically relevant. Because the structure of IAA is relatively simple. Types of Auxin 1. Natural Auxin Example- IAA, 4-chloro IAA etc. (Figure 6.1). 2. Synthetic Auxin They are not treated as phytohormones, but they considered ‘plant growth regulators’. Example - IPA, NAA, 2,4-D, 2,4,5-T, MCPA, 2-methoxy-3,6-dichlorobenzoic acid (Dicamba) etc. A bioassay is a measurement of the effect of a known or suspected biologically active substance on living material. Went used Avena sativa (oat) coleoptiles in a technique called the Avena coleoptile curvature test.The coleoptiles curved because the increase in auxin on one side stimulated cell elongation, and the decrease in auxin on the other side (due to the absence of the coleoptile tip) caused a decrease in the growth rate–a phenomenon called differential growth. Went found that he could estimate the amount of auxin in a sample by measuring the resulting coleoptile curvature. Auxin bioassays are- still used today to detect the presence of auxin activity in a sample. This ebook is exclusively for this university only. Cannot be resold/distributed. Figure 6.1: Structure of Three Natural Auxin. Figure 6.2: Diagrammatic Summary of Went’s Experiment in the Discovery of Auxin.
eBook - ePubPlant Ionomics
Sensing, Signaling and Regulation
- Vijay Pratap Singh, Manzer H. Siddiqui(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
Table 11.1 .Molecular structure of phytohormones.Figure 11.1Phytohormone: pathway, site of biosynthesis and its effect.Table 11.1S. No. Phytohormone Biosynthetic precursor Site of biosynthesis Effects 1. Cytokinins Purine derivatives Root and shoot meristem and embryo. Long‐distance transport through the xylem. RNA and protein synthesis, delay senescence, cell division, and expansion, suppress auxin‐regulated apical dominance 2. Auxin Indole derivatives of tryptophan The apical meristem, young leaves. Basipetal transport: cell to cell, long‐distance in the proximity of phloem. Apical dominance, tropism, cell growth, and division, adventitious root development 3. Abscisic Acid Carotenoids neoxanthin and violaxanthin. Root and shoot tissues Regulate dormancy of seeds and buds, induces stomatal closure, inhibits cell extension, induce abscission of fruits and leaves 4. Ethylene (ET) Methionine Numerous plant organs Formation of root hairs, arenchymya, flowering snd epinastic curvature of leaves, defense responses to pests and pathogens, and promotes seed germination, ripening, and senescence. 5. Gibberellins (GA) Gibbane C skeleton by terpenoid pathway Developing tissues and seeds Delay fruit and leaf senescence induce cell expansion, promote enzymatic activities (e.g. hydrolases), break seed and bud dormancy, stimulate shoot elongation, promote flowering 
eBook - PDFSurvey of Biological Progress
Volume 2
- George S. Avery, E. C. Auchter, G. W. Beadle, George S. Avery, E. C. Auchter, G. W. Beadle(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
The Control of Plant Growth by the Use of Special Chemi- cals, with Particular Emphasis on Plant Hormones BY LOUIS G. NICKELL Brooklyn Botanic Garden, Brooklyn, New York* I. INTRODUCTION The practical application of Plant Hormones in the field of horticulture and agriculture generally during the past decade emphasizes the importance of these and other physiologically active chemical compounds in the control of plant growth. The many practical applications growing out of theoretical research have been gratifying to investigators in this field. Probably the best known application of synthetic Plant Hormones is as "weed-killers." Their widespread utilization for this purpose often overshadows the many other aspects of plant growth that are influenced by this group of chemical compounds. Two books have been published in the past few years that treat the subject of Plant Hormones and their use in horticultural practice in a manner understandable to non-specialists (Avery et al., 1947; Mitchell and Marth, 1947). Between these two books there is a comprehensive coverage of the information available through 1946. Since that time several reviews have appeared on this subject written chiefly for specialists (Akamine, 1948b; Zimmerman and Hitchcock, 1948; Weintraub and Norman, 1949; Mitchell and Marth, 1950; Norman et al., 1950; Blackman et al., 1951; Larsen, 1951). The present survey concerns itself primarily with research findings published from 1947 through middle 1951. Earlier references are included only when necessary for background or by way of introduction. II. CONTROL OF VEGETATIVE PLANT GROWTH 1. Elimination of Undesirable Plants (Weed-Killers) Probably the most widespread use of growth regulating chemicals is in killing weeds through selective action. The research objective is to discover compounds that will destroy certain forms of vegetation but that will not at the same time injure economically useful crop plants.
- Peter Hedden, Stephen G. Thomas, Peter Hedden, Stephen G. Thomas(Authors)
- 2008(Publication Date)
- Wiley-Blackwell(Publisher)
Another common feature is the presence of feedback regulation, in which transduction of the hormone signal results in modifica-tion, usually repression, of biosynthesis at the transcript level, providing a mechanism for hormone homoeostasis. Moreover, it is also clear that there are complex inter-actions between the hormone pathways, acting on biosynthesis or signal transduction, that allow homeostasis at a higher level. Most developmental processes respond to several hormones, which mediate and integrate the different intrinsic and extrinsic cues that act on these processes. This volume includes chapters that consider the hor-monal regulation of reproductive development (Chapter 10) and of seed development and germination (Chapter 11). A complete understanding of the hormonal control of development will need to take account of their interactions, the complexity of which may ultimately be fully understood only with the help of computer modelling. This volume also includes a chapter on hormone distribution (Chapter 9), focus-ing on IAA, GAs and brassinosteroids, which differ considerably in their mobility. Among the hormones, only IAA is known to be actively transported, while other hormones may move by diffusion between cells or over longer distances in the vas-cular system. Some hormones undoubtedly act in some cases within the cell in which they are produced. Thus, as in animals, examples of autocrine, paracrine and even endocrine signaling can be found in plants. The debate about whether plant hor-mones can legitimately be called such on the basis of the original definition, which recognised only endocrine signals, has long since been abandoned as irrelevant. Plants have developed their own chemical signaling system, the importance of which for survival, development and response to the environment is becoming ever more apparent with increased understanding.
eBook - PDFThe Hormones
Physiology, Chemistry, and Applications
- Gregory Pincus, Kenneth V. Thimann, E. B. Astwood, Gregory Pincus, Kenneth V. Thimann, E. B. Astwood(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
It serves, along with other factors perhaps, to promote some processes and restrict others. In short, it ap-pears to be a regulating influence rather than a specific control. Only in a few instances—such as the growth of etiolated oat coleoptile—does its influence become so great that it may be called a control. (c) The systemic patterns of auxin effects in the plant, representing of course the correlation effects on growth and differentiation, are the final dimension which makes auxin the plant hormone par excellence. It is this quality of a chemical messenger which makes auxin a dominant influence in the ontogeny of many of the patterns of plant develop-ment. A system of chemical messengers is a principal ingredient for the creation of an organism out of what would otherwise be only a multi-cellular colony, and auxin is the outstanding participant in such a con-trol system. This review has attempted to emphasize the fundamental role of the hormone transport system in making such systemic effects possible and meaningful, though the magnificent polarity of this trans- I. Plant Hormones 51 port is only dimly understood. The plant hormone combines the ability to alter numerous physiological events with the ability to carry these influences in a functional pattern through the plant. Returning, then, to Huxley's definition of a hormone, we can see that there are numerous chemical substances produced in the organism exerting specific physiological functions (including the gibberellins, kinins, and others), but in our state of knowledge, auxin stands in the unique position of a known chemical entity providing functional correla-tive influences in the sense of acting as a mobile carrier of physiological signals through the organism—and in this sense as a plant hormone. REFERENCES 1. Addicott, F. T., and Lynch, R. S., Acceleration and retardation of abscission by indoleacetic acid. Science 114, 688-689 (1951). 2. Addicott, F. T., Lynch, R.
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