11777 results in Plant sciences
Acknowledgements
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9 - Trees in the Economy Of Nature
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Summary
Parallels between trees, humans and other animals reinforced Darwin’s progressive Enlightenment belief that improvements in science and medicine would ensure much longer and more comfortable lives virtually free from disease. As a doctor fascinated by similarities between bestial and vegetable bodies, Darwin took a strong interest in tree lifecycles as the most anthropomorphic of plants, inspired by the potential for new remedies and opportunities to apply medical approaches to their study. At the same time, as his pleasure in ‘unchastised nature’ demonstrates, he was also encouraged by – and helped to foster – the new romantic aesthetic of tree representations in art which celebrated individuality and even character and quirkiness, rather than seeing trees merely as undifferentiated ranks in plantations.
Framing other features such as rivers and bold rocky outcrops, trees were often represented within depictions of sublime scenes on increasingly popular tourist itineraries such as the Derwent valley gorge at Matlock, Derbyshire, or the Manifold valley, in the Peak (District). On touring Derbyshire in 1772, William Gilpin (1724–1804) was impressed by the beauty of the dales, particularly the Dove and Derwent valleys, and he described the former as ‘a most romantic and delightful scene, in which the ideas of sublimity and beauty are blended in a high degree’. The striking qualities of Matlock High Tor were enhanced by its silvan decoration and the rich, varied colours and surfaces of the rock. Encouraged by authors such as Gilpin and Uvedale Price, the Picturesque movement celebrated striking and unusual features, including trees of venerable antiquity with gnarled and twisted trunks, which increasingly became objects of fascination in their own right. Artists such as Paul Sandby (1731–1809) and Joseph Wright (1734–1797) made strenuous efforts to move away from stylistic representation and to draw and paint trees in a more naturalistic manner, which shaped Darwin’s depictions of trees in his poetry and natural philosophy. While they removed or moved some trees, landscape gardeners such as Lancelot Brown, William Emes and Humphry Repton brought veteran specimens and old coppice and plantations into their designs and appreciated the differences between tree kinds, positioning outliers and examples seen as special or ‘exotic’ at key points in parks and garden.
4 - Vegetable Physiology, Technology and Agriculture
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Summary
As well as supporting agricultural improvement, Darwin believed that there were specific ways in which the sciences could be applied to increase productivity in farming. This belief was founded upon practical observations of midlands agriculture and industry, gardening and horticultural experiments and the reading of major studies on these and related subjects, such as vegetable physiology. Phytologia, Darwin’s study of agriculture and gardening, was divided into three parts which dealt firstly with the physiology of vegetation, secondly with the economy of vegetation and lastly with agriculture and horticulture, while an appendix contained details for an ‘improved construction of the drill plough’ he had made with a new design for a seed-box by Thomas Swanwick (1755–1814). The first part, on vegetable physiology, examined what Darwin referred to as the buds, absorbent and umbilical vessels, pulmonary arteries and veins, aortal arteries and veins, glands and secretions, organs of reproduction and muscles, nerves and brain of vegetables. The language utilised underscored his repeatedly asserted belief in analogies between animal and vegetable bodies, and therefore the relevance of his medical knowledge and experience for the study of agriculture and horticulture. In the introduction Darwin made this relationship explicit, declaring that his book was a ‘supplement’ to Zoonomia (which had itself been partly modelled on the Linnaean system) because it was ‘properly a continuation of the subject’. Some of the material had already appeared in the latter, while the production of Phytologia aided him in preparing the much expanded third edition of Zoonomia (1801).
The second part of Phytologia, on the ‘economy of vegetation’, developed from observations made in The Economy of Vegetation (1791) that hinged upon what Maureen McNeil has called Darwin’s notion of ‘interrelated’ or ‘interlocking’ economies of vegetable, human and natural worlds, which was similar to the emphasis upon the ‘interconnectivity of life systems’ advocated by his friend Joseph Priestley (1733–1804) in his experiments on airs. He noted how vegetables replenished air and water and supported animal life; and, like animals, plants were distinctive organic entities with their own laws of motion which needed to be understood holistically in relation to their ‘total operations’ rather than in isolation.
Conclusion
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Summary
Beginning and ending in two botanic gardens at Lichfield and Kew, as Erasmus Darwin did in The Economy of Vegetation, we will conclude by highlighting some of the main themes that have emerged in our analysis of his approaches to gardening, botany, horticulture, tree cultures and farming, especially as expressed in Phytologia. These include the role of critical personal observations, medical practice and family members, patients and friends in nurturing his ideas and the usage he made of his body as an experimental tool to investigate potential novel foodstuffs. Secondly, we will examine some of the short-term and longer-term impacts that his contributions to these endeavours had, including the stimulus his arguments concerning agriculture and the agency of animals and plants provided to writers and scientists such as his grandson Charles Darwin and the chemist Humphry Davy. Finally, we will take a stroll with Darwin through the royal botanic gardens beside the Thames, encountering George III and Queen Charlotte, exploring some of the international dimensions of his medico-botany and presenting an offering to Hygeia, Greek goddess of health, in her sacred grove.
Darwin’s The Loves of the Plants (1789) and The Economy of Vegetation (1791) captured the imagination of late Georgian society partly because of the combination of poetry and illuminating scientific notes. Of these, the long essays on botany attracted much attention. As his grandson Charles Darwin remarked, their author’s success ‘was great and immediate’; his grandfather made much money from the publication and there were various British and foreign editions. Contemporaries such as Horace Walpole hailed Darwin’s ‘most beautifully and enchantingly imagined’ creation, while Richard Lovell Edgeworth claimed that sections ‘seized hold of his imagination’ to such a degree that his ‘blood thrilled back through his veins’. The young poets Samuel Taylor Coleridge, William Wordsworth and Percy Bysshe Shelley were initially excited and inspired, even if they later turned against Darwin’s style, while the older generation of poets, including William Cowper and William Hayley, were equally enthused.
The presentation of gardening, botany and horticulture in the epic poems and Phytologia had a major impact on how these endeavours were portrayed in literature and also helped to make picturesque botanical gardens more fashionable.
List of Figures
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Introduction
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Summary
The physician Dr Erasmus Darwin (1731–1802) (Figure 1) is still most well known as Charles Darwin’s grandfather, a major evolutionary thinker and a natural philosopher whose ideas partly prefigured those of his grandson. A genuine larger-than-life character of robust physical size and generous but sometimes sarcastic humour, whose medical practice took him travelling around the midland counties for decades, Erasmus Darwin obtained fame in his own lifetime as the author of The Botanic Garden (1791), an epic poem with lengthy philosophical notes published in two parts, The Loves of the Plants (1789), which amused Georgian society with its poetic portrayal of vegetable amours, and the longer Economy of Vegetation (1791). Darwin also published Zoonomia (1794/96), a major study of human physiology and medicine, The Temple of Nature (1803), a grand epic poetical celebration of the wonders of life with philosophical notes, and Phytologia (1800), on the philosophy of agriculture and gardening. He came from Nottinghamshire but spent most of his life in Lichfield, Staffordshire and Derby.
Darwin grew up on the low-lying family estate in Elston in east Nottinghamshire, close to the river Trent and its tributaries (Figure 2). The family were gentry who also owned land in other parts of the county and in Lincolnshire, some of which Darwin inherited on his marriage to his first wife Mary Howard (1740–1770) in 1757. His father Robert (1682–1754), a lawyer, and his mother Elizabeth (Hill) (1702–97) had six other children: Elizabeth (1725–1800), Anne (1727–1813), Susannah (1729–1789), William Alvey (1726–1783), John (1730–1805), rector of Elston, and Robert Waring (1724–1816), a lawyer and botanist who inherited Elston Hall (Figure 3). Darwin attended Chesterfield school, Derbyshire, when it had a strong reputation under William Burrow (1683–1758), which conjured up memories of ‘a thousand pleasing circumstances’ and where his classmates included the antiquarian Rev. Samuel Pegge (1733–1800) and Lord George Cavendish (1728–94), second son of William Cavendish, 3rd duke of Devonshire.
After receiving a medical education at St John’s College, Cambridge, and Edinburgh University during the 1750s and unsuccessfully trying to practise at Nottingham in 1756, Darwin quickly built up a reputation and income as a physician at Lichfield and Derby, travelling around the midland counties tending to patients and thriving in the highly competitive, burgeoning medical marketplace of Georgian England (Figure 4).
Select Bibliography
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Contents
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1 - Lichfield and Derby Gardens
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Summary
Erasmus Darwin loved seeing, touching, smelling, using, studying and celebrating plants and wanted others to share in his enjoyment, from members of his family to his patients, who utilised their virtues or powers as drugs to combat their illnesses and improve their lives. In Phytologia, his treatise upon agriculture and gardening, he exclaimed that ‘the beautiful colours of the petals of flowers with their polished surfaces’ were ‘scarcely rivalled’ by those of shells, feathers or ‘precious stones’. Many of these ‘transient beauties’ that gave such ‘brilliancy to our gardens’ delighted ‘the sense of smell with their odours’ and were employed extensively ‘as articles either of diet, medicine, or the arts’. Knowledge of plants was always important for Darwin, given that vegetable products were the basis of so much of the materia medica (substances prescribed as treatments), and botany was taught in the medical schools in order that practitioners could distinguish useful from useless or even dangerous plants.
During the 1770s and 1780s, however, botany and gardening assumed greater significance in Darwin’s life, encouraged by a community of plant enthusiasts and what Sylvia Bowerbank has described as literary ‘defenders’ of ‘environmental stewardship’ who were centred upon Lichfield and invested it with ‘deep feeling and value’ as a multilayered ‘storied place’. Among them were the poet Anna Seward, Rev. John Saville (1736–1803), Darwin’s future wife Elizabeth Pole and the members of the botanical society that Darwin formed, as noted above, with Brooke Boothby and William Jackson (1743/5–1798), who were engaged upon a project to translate some of the works of Carl Linnaeus (1707–1778) from Latin into English. Encouraged by his medical and scientific botanical concerns, his growing love of gardening and his experience of the countryside around Lichfield and the local coterie of plant lovers, Darwin developed a botanic garden in a small well-watered valley near the city, which inspired the two parts of his epic poem The Botanic Garden (1791). The formation of the Lichfield botanical garden was a crucial moment in both Darwin and Seward’s poetical careers. Through the success of the Botanic Garden, which, as the poet Samuel Taylor Coleridge (1772–1834) remarked, was ‘for some years greatly extolled, not only by the reading public in general’ but by poets of his generation, Darwin’s Lichfield creation became one of the most influential British botanical gardens.
3 - Agricultural Improvement: Enclosure and the Application of Science and Technology
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Summary
Erasmus Darwin’s most important contribution to the science of farming was the publication Phytologia, a major treatise on agriculture and gardening that attracted some contemporary praise. More recently, Robert Schofield was puzzled that an ‘elderly, established doctor’ with ‘little public indication of an interest in agriculture’ should have published a treatise on the subject. And while Maureen McNeil argued that Darwin’s inspiration lay primarily in Scottish writings concerning agricultural improvement, the Agricultural Revolution and the ‘scarcity crisis of the 1790s’, along with some aspects of Linnaean botany and the creation of the Lichfield botanic garden, she still found it hard to explain how these provided ‘sufficient stimulus for a six-hundred page treatise on agriculture’. While some interest in the technologies of agricultural improvement and plant physiology were already evident in Darwin’s commonplace book from the 1770s, for McNeil ‘explanations of Darwin’s agrarian interest’ founded only upon his ‘personal situation’ are ‘inadequate’ and she saw ‘no necessary transition’ from prose and poetical ‘nature studies’ to agriculture. His medical interests did not provide a full explanation either, given the small part of agriculture that was devoted to generating ‘tools of medicine’. However, this underestimates the extent to which he mixed with farmers and landowners throughout his career, the extent of his experiences combating animal and plant diseases and the impact of his medical ideas and experiences upon his analyses of agriculture and horticulture.
Darwin was a strong supporter of the Georgian ideology of improvement, which, as Raymond Williams argued, like the notion of ‘cultivation’, contained meanings that were ‘historically linked but in practice so often contradictory’: ‘working agriculture’ existed alongside the costly ‘improvement of houses, parks, artificial landscapes’, interweaving the desire for increased wealth and productivity with landscape aesthetics reinforced by moral judgement. This chapter argues that Darwin’s belief that the sciences and medicine could be used to better harness nature and help realise a more productive countryside is evident in Phytologia, his medical treatise Zoonomia and the references to agriculture and gardening in his poetry and correspondence. McNeil has argued that, as such, his emphasis was on the ‘intellectual, rather than on the manual aspect’ of farming and that he was ‘eager to celebrate’ both agricultural as much as industrial ‘capitalists’ as ‘social heroes’ as well as those who helped encourage farmers to better organise their ‘space, capital and time’.
Chapter 13 - Phloem Transport
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Attempts to demarcate the two processes of transportation: of inorganic, as well as organic nutrients in plants, dates back to the 17th century. A plant anatomist, Malpighi conducted a experiment in which he separated a ring of bark (phloem) from the wood (xylem) of young stems by detaching the two in the region of vascular cambium - ‘girdling’ or ‘ringing’ (Figure 13.1). Since the xylem remained intact, water and inorganic solutes kept on rising all the way upto the foliar region and the plant remained alive for a few days. However, girdled plants showed swelling of the bark in the area just above the girdle due to accumulation of photo-assimilates flowing downward. The downward stream also consisted of nitrogenous compounds and hormones, which caused cell enlargement above the girdle. Ultimately, the root system was subjected to starvation because of lack of nutrients and the girdled plants died away.
Evidences in Support of Phloem Transport
1. An analysis of phloem exudate obtained by making an incision into the phloem tissue provides evidence, supporting the fact that photoassimilates are translocated through the phloem.
2. Aphid technique: Aphids, constituting groups of small insects, feed on herbaceous plants by inserting a long mouth part (proboscis) deep into individual sieve-tube elements of the phloem. While aphids are feeding, they are anaesthetized with a gentle stream of CO2 and the proboscis is carefully removed with a sharp blade. Meanwhile, the uncontaminated phloem liquid continues to ooze out from the cut proboscis for a long period (Figure 13.2). This demonstrates that phloem sap is under pressure. The aphid technique has proved to be of great use in understanding the mechanism of phloem transport.
3. Radioactive tracers: Evidence is also garnered by employing radioactive elements, specifically 14C on the leaves of herbaceous and woody plants. The radioautographs that follow, reveal that radioactive photoassimilates being transported out from the leaves, are confined to only the phloem tissue.
Composition of the Photoassimilates Translocated in the Phloem
The major component of phloem sap in most of the plants is sucrose. But, a small number of plant families translocate oligosaccharides of the raffinose groups (raffinose, stachyose and verbascose) and sugar alcohols (mannitol and sorbitol).
Chapter 6 - Enzymes
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Summary
Historical Background
The use of enzymes by mankind dates back to the Greek civilization, that first used enzymes in the process of fermentation to produce wine. After the discovery of the catalytic process in the early nineteenth century, a Swedish chemist, Brazelius (1836) suggested that the numerous chemical reactions in living organisms might depend upon the presence of catalysts within the tissues. In 1857, Louis Pasteur, a French scientist demonstrated the involvement of ‘living, intact’ yeast cells in the process of alcoholic fermentation and proposed the term ‘ferments’ for these biocatalysts. The term ‘enzyme’ was later coined by Kuhne (1878) for soluble ferment of yeast or bacteria. However, a significant breakthrough in the study of enzymes was made when the Buchner brothers (1897) in Germany accidentally discovered that the ‘squeezed out’ juice from non-living yeast extract when mixed with sugar could bring about fermentation. Yeast juice is now known to be a mixture of at least twelve different catalysts. The name ‘enzyme’ was coined for the postulated catalyst in juice.
The chemical nature of enzyme remained uncertain until Sumner (1926) purified and crystallized first, the enzyme ‘urease’ from Jackbean (Canavalia ensiformis) and further discovered that it was proteinaceous in nature. Thereafter, hundreds of enzymes have been separated in a pure or semi-pure state and all have proved to be proteins except for ribozymes.
Characteristics of Enzyme-catalyzed Reactions
• High rates of reaction: Enzyme-catalyzed reactions have typically 106–1012 times higher rates as compared to uncatalyzed reactions. Most of enzymes have the capability to convert thousands of substrate into product molecules every second.
• High specificity: Enzymes have the capablility to recognize extremely minute and specific differences in substrate as well as product molecules and can even distinguish between mirror images of any molecule (stereoisomers or enantiomers) e.g., D-Galactose and L-Galactose.
• Mild reaction conditions: Enzymatic reactions usually take place at atmospheric pressure, relatively low temperatures and within a narrow range of pH (approximately 7.0) except for certain protein-degrading enzymes in vacuoles which function at pHs near 4.0, or enzymes present in thermophilic bacteria that can survive in hot sulphur springs (at 100 °C).
Chapter 18 - Abiotic and Biotic Stress
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Summary
Under both natural and agricultural situations, plants are often subjected to environmental stresses. Stress plays an important role in determining how soil and climate restrict the distribution of plant species. Stress is usually defined as a disadvantageous impact on the physiology of a plant, induced upon a sudden shift from optimal environmental condition where homeostasis is maintained to suboptimal level which disturbs the initial homeostatic state. In most cases, stress is measured in terms of plant survival, crop productivity or the primary assimilation processes, which are all co-related to overall growth.
Plant stress can be divided into two categories: Abiotic and Biotic.
Abiotic Stress
Plants grow and reproduce in hostile environments containing large numbers of abiotic chemical and physical variables, which differ both with time and geographical location. The primary abiotic environmental parameters that affect plant growth are light, water, carbon dioxide, oxygen, soil nutrient content and availability, temperature, salts, and heavy metals. Fluctuations of these abiotic factors generally have negative biochemical and physiological impact on plants. Being fixed, plants are unable to avoid abiotic stress by simply moving to a more suitable environment. Instead, plants have evolved the ability to compensate for stressful conditions by switching over physiological and developmental processes to maintain growth and reproduction.
Responses to abiotic stress depend on the extremity and time duration of the stress, developmental stage, tissue type and interactions between multiple stresses (Figure 18.1). Experiencing stress typically promotes alterations in gene expression and metabolism, and reactions are frequently centred on altered patterns of secondary metabolites. Plants are complex biological systems comprising of thousands of different genes, proteins, regulatory molecules, signalling agents, and chemical compounds that form hundreds of interlinked pathways and networks. Under normal growing conditions, the different biochemical pathways and signalling networks must act in a coordinated manner to balance environmental inputs with the plant's genetic imperative to grow and reproduce. When exposed to unfavourable environmental conditions, this complex interactive system adjusts homeostatically to minimize the negative impacts of stress and maintain metabolic equilibrium.
Chapter 2 - Absorption and Translocation of Water
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Summary
Absorption of Water
Water is the essential medium of life. Thus, Plants that are land-based (as opposed to aquatic ones) are faced with potentially lethal desiccation through water loss to the atmosphere. This problem is aggravated by the large surface area of leaves, that are exposed to high levels of radiant energy (sunlight) and their need to have an open pathway for CO2 uptake. Thus, there is a conflict between the need for water conservation and the need for CO2 assimilation.
The need to resolve this vital conflict determines much of the structure of plants that grow on land, namely: (i) the development of an extensive root system to absorb water from the soil; (ii) a low-resistance pathway through the tracheary elements to bring water to the leaves; (iii) hydrophobic cuticle lining the surfaces of the plant to reduce evaporation; (iv) microscopic stomata on the leaf surface to allow gaseous exchange; (v) guard cells to regulate the diameter and diffusional resistance of the stomatal opening.
Algae and simple land plants like mosses and lichens may absorb water through their entire surface but in the vascular plants, the absorption of water takes place mostly through the roots. The source of water supply, with few exceptions, is the soil. The principal source of soil water is rain.
Different types of water
• Run-away water (not available to the plant): After a heavy rainfall or irrigation, some of the water drains away along the slopes. This is called run-away water.
• Gravitational Water (also not available to the plant): Some of the water percolates downwards through the larger pore spaces between the soil particles under the influence of gravitational pull until it reaches the water table.
• Hygroscopic Water (again not available to the plant): Water gets adsorbed on the surface of soil colloids and held tightly by them.
• Chemically combined Water (again not available to the plant): A small amount of water is bound to the molecules of some soil minerals by strong chemical bonds.
• Capillary Water (the form that is available to the plant): The remainder of the water that fills the spaces between the non-colloidal smaller soil particles.
Capillary water plays a major role as it is readily adsorbed by the roots. The total amount of water held in the soil is called ‘holard’.
Colour Plates
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Acknowledgments
- Sanjay Singh
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Acknowledgements
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Unit VII - Some Experimental Exercises
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Preface to the First Edition
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Summary
Our earlier book, Comprehensive Practical Plant Physiology, was first published in 2012 and was very warmly received by students and teachers alike. In a large measure, the book succeeded in generating a lot of interest amongst students and scholars alike, in the field of Botany and Agricultural Sciences. However, the readers have urged us to restructure the text and update the information so that the book becomes self-contained in itself, matching other leading titles in the field of plant physiology.
During the course of reorganisation, we were greatly influenced by the feedback reviews we received from the many experts based within the country and in Southeast Asia, as well as the suggestions offered to us by the editorial staff at Cambridge University Press, India. We are much pleased to present to our readers an altogether new book, in which we have ensured a continuous flow of information so that the readers can assimilate the knowledge without too much effort. The material is presented in a concise and lucid manner, so that the readers can comprehend the conceptual complexities, come to know about the recent achievements in the field, and share the joy that we feel for this subject.
Salient features of this edition are as follows:
In addition to the generalized and well-informed textual content in each chapter, we have attempted to highlight the important information through models and flow charts; such as the information in the chapter on ‘growth and development’ regarding various topic like, mode of action, physiological role, biosynthesis and inactivation of auxins, gibberellins, ethylene, and abscisic acid. The role of the recently discovered hormones such as jasmonates, polyamines, salicylic acid and nitric oxide, etc., has also been emphasised upon appropriately. The mode of action of phytochrome-mediated responses based on their requirements such as LFRs, VLFRs and HIRs, also finds a special mention. Included also in the discussion is the work on Arabidopsis thaliana as an experimental tool and model system for research in genetics and molecular biology, enumerating its advantages over other plant materials. We have also included a discussion on Reactive Oxygen Species (ROS) and Asada-Halliwell or Ascorbate-Glutathione Pathway in the chapter ‘Stress Physiology and Secondary Metabolites’.
Chapter 12 - Sulphur, Phosphorus and Iron Assimilation in Plants
- S. L. Kochhar, University of Delhi, Sukhbir Kaur Gujral, University of Delhi
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Sulphur Metabolism
Sulphur is an essential macronutrient for all living organisms, and it occurs in nature in different states of oxidation as a component of inorganic and organic compounds. The chief inorganic form of sulphur, sulphate, is obtained predominantly from the weathering of parent rock material. Natural organic sulphur compounds include gases such as hydrogen sulphide, dimethylsulphide and sulphur dioxide, which are discharged into the air both by geochemical processes and by activity of the biosphere. In the gaseous phase, sulphur dioxide (SO2) reacts with a hydroxyl radical and oxygen to form sulphur trioxide (SO3) which upon dissolving in water produces a strong sulphuric acid (H2SO4), the major source of acid rain. A high concentration of sulphate is also found in the oceans (approximately 26mM or 2.8 g L-1). Plants have a capacity to metabolize sulphur dioxide absorbed in the gaseous phase through their stomata. A prolonged exposure of nearly more than eight hours to high atmospheric concentrations of SO2 (i.e. more than 0.3 ppm) tends to damage plant tissues extensively due to formation of sulphuric acid.
Sulphate uptake and transport
Sulphate enters a plant from the soil solution, primarily through the roots by an active proton cotransport. Sulphate uptake is generally inhibited by the presence of anions such as selenate, molybdate, and chromate anions, which can compete with sulphate for binding to the transporters. Sulphate uptake systems can be classified as either sulphate permeases or facilitated transport systems. Plant sulphate permeases are similar to fungal and mammalian co-transporters. They consist of a single polypeptide chain with 12 transmembrane domains, characteristic of cation/solute transporters. A second mechanism, ATP-dependent transport, is exemplified by a system in cyanobacteria that includes a multiprotein complex of three cytoplasmic membrane components and a sulphate-binding protein in the periplasmic space.
Roots take up sulphate from the soil via electrogenic- symporters (SULTRs). Two high-affinity transporters are expressed in root epidermis and cortex. Although sulphate assimilation occurs in roots, most of the sulphate is transported to the shoots. In photosynthetic cells, sulphate can be translocated either into chloroplasts for assimilation, or into the vacuoles for storage. It has been found that leaves are usually more active in assimilation of sulphur as compared to roots, perhaps because photosynthesis supplies reduced ferredoxin, and photorespiration produces an amino acid serine, which might activate the synthesis of O-acetylserine.