Introduction to Plant Physiology, 4th Edition by William G. Hopkins the book is updated to MATLAB (Release Tal Gilat (Marquette pdf. Library of Congress Cataloging-in-Publication Data: Hopkins, William G. Introduction to plant physiology / William G. Hopkins and Norman P. A. Hüner. – 4th ed. Introduction to Plant Physiology This page intentionally left blank Introduction to Plant Physiology Fourth Edition William G. Hopkins and Norman P. A. Huner.
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Introduction To Plant Physiology
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This book is printed on acid-free paper. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections or of the United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc.
Library of Congress Cataloging-in-Publication Data: Hopkins, William G. Includes index. Plant physiology. Huner, Norman P. H67 The book should provide a broad framework for those interested in pursuing advanced study in plant physiology, but it should also provide the general understanding of plant function necessary for students of ecology or agriculture. The text should be interesting and readable. It should include some history so the student appreciates how we arrived at our current understanding.
Consequently, the text must be selective and focused on those topics that form the core of the discipline. Those changes include: With the help of the publisher, we have also introduced color into the illustrations. We have removed the traditional introductory chapter on Cells, Tissues, and Organs and distributed some of this information in chapters to which it pertains directly. The list of references at the end of each chapter has been updated throughout the new edition. All life depends on energy and water.
Unlike previous editions, the fourth edition begins with four chapters that focus on the properties of water, osmosis, water potential, and plant—water relations, followed by a series of eight chapters dealing with bioenergetics, primary plant metabolism, and plant productivity.
A major change in this edition is the presence of three new chapters 13, 14, and Using the basic information and concepts developed in chapters 1 to 12, these chapters focus on the inherent plasticity of plants to respond to environmental change on various time scales.
The coverage of each hormone concludes with a general description of the current status of receptors and signal transduction pathways. A Glossary has been created for the new edition. William G. Huner London, Ontario April v 6. It is about the questions that plant physiologists ask and how they go about seeking answers to those questions. Most of all, this book is about how plants do the things they do in their everyday life. The well-known conservationist John Muir once wrote: Muir might well have been referring to the writing of a plant physiology textbook.
The scope of plant physiology as a science is very broad, ranging from biophysics and molecular genetics to environmental physiology and agronomy. Photosynthetic metabolism not only provides carbon and energy for the growing plant, but also determines the capacity of the plant to withstand environmental stress. To get the most out of this book, we suggest you be aware of these limitations as you read and think about how various mechanisms are integrated to form a functional plant.
Many models and explanations contained in this book may have been revised by the time the book appears on the market. You can learn what has happened since this book was written by seeking out reviews and opinions published in the more recent editions of those same journals. We hope that, through this book, we are able to share with you some of our own fascination with the excitement, mystery, and challenge of learning about plant physiology.
Huner 7. Energy and Information 93 6. CO2 Assimilation 8. Harvesting Sunlight 7. Unlocking the Energy Stored in Photoassimilates A Complex Pattern of Exchange Light Harvesting and Photoprotection An Overview Auxins Gibberellins Abscisic Acid, Ethylene, and Brassinosteroids Responding to Light Responding to Red and Far-Red Light Orienting Plants in Space Reaching for the Sun Controlling Development by Photoperiod and Endogenous Clocks Plant Development and Distribution A Natural Products Terpenes Glycosides Lipids, Proteins, and Carbohydrates I.
Water is the most abundant constituent of most organisms. The actual water content will vary according to tissue and cell type and it is dependent to some extent on environmental and physiological conditions, but water typically accounts for more than 70 percent by weight of non-woody plant parts.
The thermal properties of water ensure that it is in the liquid state over the range of temperatures at which most biological reactions occur. This is important because most of these reactions can occur only in an aqueous medium. The thermal properties of water also contribute to temperature regulation, helping to ensure that plants do not cool down or heat up too rapidly.
Water also has excellent solvent properties, making it a suit- able medium for the uptake and distribution of mineral nutrients and other solutes required for growth. Many of the biochemical reactions that characterize life, such as oxidation, reduction, condensation, and hydrolysis, occur in water and water is itself either a reactant or a product in a large number of those reactions.
The transparency of water to visible light enables sunlight to penetrate the aqueous medium of cells where it can be used to power photosynthesis or control development. Water in land plants is part of a very dynamic system. Plants that are actively carrying out photosynthesis experience substantial water loss, largely through evaporation from the leaf surfaces.
For example, it is estimated that the turnover of water in plants due to photosynthesis and transpiration is about tonnes per year. The uptake of water by cells generates a pressure known as turgor; in the absence of any skeletal system, plants must maintain cell turgor in order to remain erect.
As will be shown in later chapters, the uptake of water by cells is also the driving force for cell enlargement. Few plants can survive desiccation.
There is no doubt that the water relations of plants and 1 This chapter is concerned with the water relations of cells.
Topics to be addressed include the following: H O O These concepts provide the basis for understanding water movement within the plant and between the plant and its environment, to be discussed in Chapter 2.
Water consists of an oxygen atom covalently bonded to two hydrogen atoms Figure 1. The oxygen atom is strongly electronegative, which means that it has a tendency to attract electrons. One consequence of this strong electronegativity is that, in the water molecule, the oxygen tends to draw electrons away from the hydrogen. The shared electrons that make up the O—H bond are, on the average, closer to the oxygen nucleus than to hydrogen.
As a consequence, the oxygen atom carries a partial negative charge, and a corresponding partial positive charge is shared between the two hydrogen atoms. B The hydrogen bond dashed line results from the electrostatic attraction between the partial positive charge on one molecule and the partial negative charge on the next.
Overall, water remains a neutral molecule, but the separation of partial negative and positive charges generates a strong mutual electrical attraction between adjacent water TABLE 1.
This attraction is called hydrogen bonding Figure 1. Hydrogen bonding is largely responsible for the many unique properties of water, compared with other molecules of similar molecular size Table 1.
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In addition to interactions between water molecules, hydrogen bonding also accounts for attractions between water and other molecules or surfaces. Hydrogen bonding, for example, is the basis for hydration shells that form around biologically important macromolecules such as proteins, nucleic acids, and carbohydrates.
These layers of tightly bound and highly oriented water molecules are often referred to as bound water. It has been estimated that bound water may account for as much as 30 percent by weight of hydrated protein molecules. Fortuitously, a second product of the so-called Weizmann process was acetone. Acetone was another commercially impor- tant chemical as an ingredient in the manufacture of explo- sives.
In addition, acetone and butanol together could be used to make isobutyl acetate, the best solvent known for the new plastic nitrocellulose. Interestingly, nitrocellulose was the film on which the early stars of Hollywood were immortalized. Nitrocellulose was also the source of gun cotton, a component of high explosives. Yes, the early films produced by Hollywood were highly flammable! And what about all that glycerol being produced by fermenta- tion in Germany at the same time?
When glycerol is chemically reacted with nitric acid, the product is nitroglycerin. Nitroglyc- erin, which is extremely unstable and highly explosive, was the explosive of choice for early miners. In , Swedish inventor Alfred Nobel discovered that the explosive power of nitroglycerin could be stabilized by absorbing the liquid on an inert non-reac- tive powder, thus producing dynamite.
Dynamite made Nobel a very rich man and, on his death, he endowed the international prizes that bear his name. Rubber and explosivesit is not dif- ficult to draw connections between the direction taken by bio- The Early Days of Biotechnology 17 technology in the years prior to and the developing political climate of the time, which culminated in World War I.
The Weizmann process proved to be significant in many ways, not just for its economic impact. Most industrial fermentations up to then were carried out in oak caskscontinuing in the brew- ing tradition, of courseand did not require aseptic sterile conditions. The Weizmann process, on the other hand, required that laboratory standards for sterility be maintained on an indus- trial scale and production was carried out in modern aluminum fermentation vessels.
Weizmanns process sealed a partnership between microbiology, chemical engineering, and modern mate- rials that was to dominate biotechnology until the s, when recombinant DNA came on the scene. What is Fermentation? One of the more interesting things about nature is its extreme conservatism.
In spite of their striking differences, organisms as diverse as fungi, oak trees, earthworms, and elephants all share many of the same genes and do things, in a metabolic sense at least, in much the same way. For example, when organisms break down sugars, fats, and proteins to retrieve energy, the pathway used is virtually identical in all living organisms.
The end result, however, is different depending on whether or not oxygen is available. When oxygen is present, this pathway is called cellular respiration. When oxygen is absent, the same pathway is called fermentation. The initial steps of respiration and fermentation, a process called glycolysis, are the same. In preparation for respiration or fermentation, complex storage molecules such as starch plants or glycogen animals must first be broken down into their com- ponent glucose molecules.
Glucose, a simple sugar made up of six carbon atoms, is further broken down through glycolysis Figure 2. The net result of glycolysis is that one six-carbon mol- ecule glucose is converted to two three-carbon molecules called 18 Plant Biotechnology Figure 2.
The pyruvic acid molecules are broken down further via two different pathways depending on the presence or absence of oxygen. A small amount of energy is released, and the carbon atoms in the glucose have been slightly rearranged, but otherwise not a lot has happened up to this point.
The Early Days of Biotechnology 19 The difference between respiration and fermentation lies in the fate of pyruvic acid. When oxygen is present, the pyruvic acid enters a metabolic pathway called the citric acid cycle or Krebs cycle , where it is completely broken down into carbon dioxide and most of the energy is retrieved for use by the cell.
This is what normally happens in your own cells to provide the energy the cells need to function. In the absence of oxygen, however, the citric acid cycle shuts down and the pyruvate undergoes more limited changes. This is what we call fermentation. Depending on the organism and the conditions of fermentation, a variety of end products are possible. Lactic acid: The fermentation product in human muscle when exercising under oxygen debt.
Lactic acid is responsible for muscle soreness, and it is also the fermentation product of certain fungi and bacteria.
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Lactic acid can be converted to iso- prene, which can be used in the manufacture of synthetic butyl rubber. Ethyl alcohol ethanol : The fermentation product of several fungi, especially Saccharomyces cerevisiae. Glycerol: Under alkaline conditions, S. Acetic acid vinegar : The fermentation product of the bacte- rium Acetobacter.
Contamination of wine with Acetobacter can be a problem for wine producers because the acetic acid sours the wine. Acetic acid is widely used as a raw material in the manufacture of fibers, plastics, and other industrial products.
Processing Food and Drink In modern systems of classification, fungi are no longer considered plants, but since the beginnings of biotechnology are so intimately associated with the fungi, we will consider them as close cousins to the plants and include them in our discussions. In addition to beer, wine, and bread, fungi are used in the processing of many different 20 Plant Biotechnology foods, especially in Asia.
As with beer and wine, the fungi are used to improve the texture, flavor, and nutritional value of foods as well as to delay spoilage. In Japan, China, and other Asian countries, a large variety of foods are prepared from soybeans Glycine max. These include tempeh, a solid food prepared by processing soybeans with the fungus Rhizopus species; sufu, a Chinese cheese prepared from soybeans with the help of the fungus Actinomucor elegans; and soy sauce, a condiment prepared by fermenting soybeans and wheat with Aspergillus oryzae.
In addition to fungi, bacteria have also proven useful in tradi- tional biotechnology. As noted earlier, bacteria produce acetic acid, which is used in preserving and flavoring foods and as an impor- tant industrial feedstock. In Europe and North America, lactic acid produced by the bacterium Lactobacillus has long been used to preserve cabbage sauerkraut and naturally fermented pickles. Industrial Production of Fungal Metabolites We have seen how fungi have been used to process foods, chang- ing both the flavor and the composition of foodstuffs.
Fungi also produce a wide range of metabolites, or chemical products of metabolism, that have commercial use on their own.
These products include organic acids, alcohols, antibiotics, vitamins, and enzymes Table 2. When water deficit develops slowly enough to allow changes in developmental processes, it has several effects on growth, one of which is a limitation of leaf expansion.
Because leaf expansion depends mostly on cell expansion, the principles that underlie the two processes are similar. Inhibition of cell expansion results in a slowing of leaf expansion early in the development of water deficits.
The resulting smaller leaf area transpires less water, effectively conserving a limited water supply in the soil over a longer period. Altering leaf shape is another way that plants can reduce leaf area. Under conditions of water, heat, or salinity extremes, leaves may be narrower or may develop deeper lobes during development Figure 3.
The result is a reduced leaf surface area and therefore, reduced water loss and heat load defined as amount of heat loss [cooling] required to maintain a leaf temperature close to air temperature. For protection against overheating during water deficit, the leaves of some plants may orient themselves away from the sun. Leaf orientation may also change in response to low oxygen availability. Stomatal opening and closing is modulated by uptake and loss of water in guard cells, which changes their turgor pressure.
Although guard cells can lose turgor as a result of a direct loss of water by evaporation to the atmosphere, stomatal closure in response to dehydration is almost always an active, energy-dependent process rather than a passive one. Abscisic acid ABA mediates the solute loss from guard cells that is triggered by a decrease in the water content of the leaf.
Plants constantly modulate the concentration and cellular localization of ABA, and this allows them to respond quickly to environmental changes, such as fluctuations in water availability. The adjustment involves a net increase in solute content per cell that is independent of the volume changes that result from loss of water. There are two main ways by which osmotic adjustment can take place.
A plant may take up ions from the soil, or transport ions from other plant organs to the root, so that the solute concentration of the root cells increases. This is a common event in saline areas, where ions such as potassium and calcium are readily available to the plant. The accumulation of ions during osmotic adjustment is predominantly restricted to the vacuoles, where the ions are kept out of contact with cytosolic enzymes or organelles. When ions are compartmentalized in the vacuole, other solutes must accumulate in the cytoplasm to maintain water potential equilibrium within the cell.
These solutes are called compatible solutes or compatible osmolytes. Compatible solutes are organic compounds that are osmotically active in the cell, but do not destabilize the membrane or interfere with enzyme function, as high concentrations of ions can.
Plant cells can hold large concentrations of these compounds without detrimental effects on metabolism.
Introduction to Plant Physiology, 4th Edition
Common compatible solutes include amino acids such as proline, sugar alcohols such as mannitol, and quaternary ammonium compounds such as glycine betaine. Phytochelatins chelate certain ions, reducing their reactivity and toxicity Chelation is the binding of an ion with at least two ligating atoms within a chelating molecule.
Chelating molecules can have different atoms available for ligation, such as sulfur S , nitrogen N , or oxygen O , and these different atoms have different affinities for the ions they chelate. By wrapping itself around the ion it binds to form a complex, the chelating molecule renders the ion less chemically active, thereby reducing its potential toxicity. The complex is then usually translocated to other parts of the plant, or stored away from the cytoplasm typically in the vacuole.
The thiol groups act as ligands for ions of trace elements such as Cd and As. Once formed, the phytochelatin-metal complex is transported into the vacuole for storage. Many plants have the capacity to acclimate to cold temperature The ability to tolerate freezing temperatures under natural conditions varies greatly among tissues. Hydrated, vegetative cells can also retain viability at freezing temperatures, provided that ice crystal formation can be restricted to the intercellular spaces and cellular dehydration is not too extreme.
Temperate plants have the capacity for cold acclimation — a process whereby exposure to low but nonlethal temperatures typically above freezing increases the capacity for low temperature survival. Cold acclimation in nature is induced in the early autumn by exposure to short days and nonfreezing, chilling temperatures, which combine to stop growth. A diffusible factor that promotes acclimation, most likely ABA, moves from leaves via the phloem to overwintering stems.
ABA accumulates during cold acclimation and is necessary for this process. Plants survive freezing temperatures by limiting ice formation During rapid freezing, the protoplast, including the vacuole, may supercool; that is, the cellular water remains liquid because of its solute content, even at temperatures several degrees below its theoretical freezing point.
Supercooling is common to many species of the hardwood forests. Spontaneous ice formation sets the low-temperature limit at which many alpine and subarctic species that undergo deep supercooling can survive. Several specialized plant proteins, termed antifreeze proteins, limit the growth of ice crystals through a mechanism independent of lowering of the freezing point of water.
Synthesis of these antifreeze proteins is induced by cold temperatures. The proteins bind to the surfaces of ice crystals to prevent or slow further crystal growth.
Cold-resistant plants tend to have membranes with more unsaturated fatty acids As temperatures drop, membranes may go through a phase transition from a flexible liquid-crystalline structure to a solid gel structure.
Chilling-resistant plants tend to have membranes with more unsaturated fatty acids. Prolonged exposure to extreme temperatures may result in an altered composition of membrane lipids, a form of acclimation. Certain transmembrane enzymes can alter lipid saturation, by introducing one or more double bonds into fatty acids.
This modification lowers the temperature at which the membrane lipids begin a gradual phase change from fluid to semicrystalline form and allows membranes to remain fluid at lower temperatures, thus protecting the plant against damage from chilling. A large variety of heat shock proteins can be induced by different environmental conditions Under environmental extremes, protein structure is sensitive to disruption. Plants have several mechanisms to limit or avoid such problems, including osmotic adjustment for maintenance of hydration and chaperone proteins that physically interact with other proteins to facilitate protein folding, reduce misfolding and aggregation, and stabilize protein tertiary structure.
Cells that have been induced to synthesize HSPs show improved thermal tolerance and can tolerate subsequent exposure to temperatures that otherwise would be lethal. Heat shock proteins are also induced by widely different environmental conditions, including water deficit, ABA treatment, wounding, low temperature, and salinity.
Thus, cells that have previously experienced one condition may gain cross-protection against another. During mild or short-term water shortage, photosynthesis is strongly inhibited, but phloem translocation is unaffected until the shortage becomes severe Changes in the environment may stimulate shifts in metabolic pathways. Production of lactate lactic acid lowers the intracellular pH, inhibiting lactate dehydrogenase and activating pyruvate decarboxylase.
These changes in enzyme activity quickly lead to a switch from lactate to ethanol production.
The net yield of ATP in fermentation is only 2 moles of ATP per mole of hexose sugar catabolized compared with 36 moles of ATP per mole of hexose respired in aerobic respiration. Thus, injury to root metabolism by O2 deficiency originates in part from a lack of ATP to drive essential metabolic processes such as root absorption of essential nutrients.
Water shortage decreases both photosynthesis and the consumption of assimilates in the expanding leaves. As a consequence, water shortage indirectly decreases the amount of photosynthate exported from leaves. Because phloem transport depends on pressure gradients, decreased water potential in the phloem during water deficit may inhibit the movement of assimilates. The ability to continue translocating assimilates is a key factor in almost all aspects of plant resistance to drought.The thiol groups act as ligands for ions of trace elements such as Cd and As.
The uptake of water by cells generates a pressure known as turgor; in the absence of any skeletal system, plants must maintain cell turgor in order to remain erect. Are you sure you want to Yes No. Such responses are often referred to as phenotypic plasticity, and represent nonpermanent changes in the physiology or morphology of the individual that can be reversed if the prevailing environmental conditions change.
About William G. You just clipped your first slide! Amylase is a natural component of human saliva. The plant protoplast is, in turn, surrounded by a cell wall.