Herbicide Mode of Action
Practical Applications of Herbicide Physiology
This lesson will focus on the impact of herbicide and plant characteristics important in determining herbicide performance. Visual images will be used to illustrate several principles including herbicide site of uptake, translocation, site of action sensitivity, and environmental effects on herbicide performance. This information provides a basis for maximizing herbicide performance.
Aplicaciones prácticas de la fisiología de los herbicidas en las plantas
Esta lección se focaliza en el impacto de las características de la planta y el herbicida, importantes para determinar el desempeño del herbicida. Se usarán imágenes visuales para ilustrar varios principios, incluyendo el sitio de absorción del herbicida en la planta, transporte, el sitio de acción sensible, y efectos del ambiente sobre el desempeño del herbicida. Esta información provee la base para maximizar la utilidad del uso de los herbicidas.
Auxin and Auxinic Herbicide Mechanism(s) of Action - Part 1 - Introduction
The selective control of broadleaf weeds in cereal grain crops by auxinic herbicides has made this group one of the most widespread and important herbicide families in use. These herbicides were the first organic herbicides developed that were selective or able to kill one group of plants, but not another (i.e. kill broadleaf, but not grass plants). This lesson will introduce the major features of these herbicides, discuss their major uses and describe the symptoms of the injury they cause as well as introduce how they kill sensitive plants.
Mecanismo(s) de Acción de las Auxinas y los Herbicidas Auxínicos - Parte 1- Introducción
Descripción: El control selectivo de malezas de hoja ancha en cultivos de cereales utilizando herbicidas auxínicos ha hecho de éstos una de las familias de herbicidas actualmente en uso más ampliamente distribuidas e importantes. Estos herbicidas fueron los primeros herbicidas orgánicos desarrollados que presentaron selectividad; es decir, capaces de matar un cierto grupo de plantas sin afectar a otros grupos (por ejemplo: matar plantas de hoja ancha pero no las de hoja angosta; en este documento se utilizará el término "gramíneas" para referirse a las plantas de hoja angosta o cereales). En esta lección se presentarán las principales características de los herbicidas auxínicos, se discutirán sus principales usos y se describirán los síntomas de daño que causan. De igual forma, se indicará la forma en que estos herbicidas matan a las plantas sensibles.
Auxin and Auxinic Herbicide Mechanism(s) of Action - Part 2 - Advanced
The selective control of broadleaf weeds in cereal grain crops by auxinic herbicides has made this group one of the most widespread and important herbicide families in use. These herbicides are thought to act as hormone mimics. This lesson will detail how these herbicides are related structurally and physiologically to the natural plant hormone, auxin (indole-3-acetic acid; IAA) and explain the biochemical mechanisms which may be involved in their action.
Mecanismo(s) de Acción de los Herbicidas Auxínicos - Parte 2 - Nivel Avanzado
Descripción: El control selectivo de malezas de hoja ancha en cultivos de cereales por los herbicidas auxínicos ha hecho de éstos una de las familias de herbicidas actualmente en uso mas ampliamente distribuidas e importantes. Se cree que estos herbicidas actúan como simuladores hormonales. En esta lección se detallará la relación estructural y fisiológica entre los herbicidas auxínicos y la fitohormona natural auxina (ácido indol-3-acético; IAA por sus siglas en inglés) y se explicarán los mecanismos bioquímicos que pueden estar involucrados en su modo de acción. Se revisará el mecanismo de transporte de célula a célula y la absorción de las auxinas por las células, así como también la forma en que estas moléculas causan elongación celular e inducen la síntesis de etileno. De igual forma, se describirán los receptores, las rutas de transferencia de señales y los cambios en expresión genética inducidos por la fitohormona natural IAA y su relación con la actividad de los herbicidas auxínicos.
Herbicide Classification
This lesson focuses on understanding the classification system into which herbicides are organized. Terms of classification, classification hierarchy, examples of classification and a brief overview of the eight modes of action are all discussed in this lesson. Once this is understood it is much easier to grasp similar herbicides and know why they may exhibit certain symptoms to weeds and plants alike. Objectives: 1. Understand how herbicides are classified and why it is important for managing herbicide resistance 2. Understand the Importance of classification and herbicides by mode of action rather than chemical family 3. Be able to tell the difference between mode of action and site of action 4. Be able to differentiate between herbicide families, modes of action, and sites of action 5. Understand common name, trade names and sites of absorption
Clasificación de los herbicidas
Esta lección se enfoca en entender el sistema de clasificación en el cual están organizados los herbicidas. Terminología como clasificación, jerarquía de clasificación, ejemplos de clasificación y un breve resumen de los ocho modos de acción, se discuten en esta lección. Una vez que esto se entiende, es mucho más fácil comprender herbicidas similares y saber por qué estos pueden exhibir ciertos síntomas en malezas y cultivos.
Foliar Absorption and Phloem Translocation
Herbicides must be absorbed into plants in order to be effective. Herbicide absorption can occur through leaves, roots or both. The process by which herbicides kill weeds, called mode of action, requires herbicide absorption and may also require herbicide movement or translocation within the plant. Translocation means that the herbicide moves from the site of absorption to some other plant part. Foliar applied herbicides that have the necessary characteristics to move in the phloem will translocate to areas of the plant that are actively growing; however, not all foliar-applied herbicides move from the leaves that intercepted the spray solution. Herbicides that are absorbed but not translocated are called contact herbicides, while herbicides that translocate to shoot or root meristems are called systemic herbicides. Absorption and translocation of xylem mobile herbicides will be discussed in another lesson.
Gene Expression Part 2: Expression of Herbicide Resistant ALS Genes in Plants
This lesson describes how changes in the DNA sequence of a gene can alter the synthesis of a protein and thus influence traits such as herbicide resistance.
Herbicides That Act Through Photosynthesis
This lesson will examine herbicides that adversely affect light-related processes, thereby causing damage to plants. There are four basic mechanisms that will be studied in this class of agents: herbicides that inhibit or block synthesis of Protoporphyrin IX; herbicides that inhibit synthesis of carotenoids; herbicides that block Photosystem II electron transfer; and herbicides that divert electrons from Photosystem I. All share the ability to cause cellular damage in the presence of light.
Herbicidas que Actúan A través de la Fotosíntesis
En esta lección se examinarán los herbicidas que afectan los procesos celulares relacionados con la utilización de la luz, causando así daños a las plantas. Existen cuatro mecanismos básicos que serán estudiados: herbicidas que obstruyen la síntesis de protoporfirina IX; herbicidas que inhiben la síntesis de carotenoides; herbicidas que obstruyen la transferencia de electrones en el fotosistema II; y herbicidas que substraen electrones del fotosistema I. Todos ellos comparten la misma habilidad de causar daños celulares en presencia de luz.
Herbicide Discovery and Screening
Historically, herbicides have been discovered by randomly screening collections of chemicals for activity on target weeds. While totally empirical, this approach has been surprisingly successful and has produced essentially all commercial herbicides currently in use. More recently, agrichemical companies have adopted directed strategies using in vitro assays, compound structure/activity relationships, and profiling assays of mRNAs, proteins, and metabolites. These latter approaches, in combination with high-throughput screens, are designed to exploit recent advances in technology and take advantage of our increased understanding of biological systems.
Inhibitors of Aromatic Amino Acid Biosynthesis
This lesson will detail the biochemical mechanisms that are affected by herbicides which inhibit a plant’s ability to synthesize amino acids. The significance of amino acids and proteins will also be described. The herbicide glyphosate, will be studied at length, including the advances made by biotechnology.
Inhibidores de la Síntesis de Aminoácidos Aromáticos
En esta lección se detallarán los procesos bioquímicos que son afectados por los herbicidas que inhiben la síntesis de aminoácidos en las plantas. Se describirá también la importancia de los aminoácidos y las proteínas. De igual manera, se presentará un estudio detallado del herbicida glifosato [N-(fosfonometil)-glicina], incluyendo los avances hechos por la biotecnología.
Herbicide Resistance: Mechanisms, Inheritance, and Molecular Genetics
Explanation of the biochemical mechanisms and genetics of herbicide-resistance in weeds and the management and spread of herbicide-resistant weeds in relationship to the biochemical mechanisms and inheritance of resistance.
Herbicide Discovery and Screening
Historically, herbicides have been discovered by randomly screening collections of chemicals for activity on target weeds. While totally empirical, this approach has been surprisingly successful and has produced essentially all commercial herbicides currently in use. More recently, agrichemical companies have adopted directed strategies using in vitro assays, compound structure/activity relationships, and profiling assays of mRNAs, proteins, and metabolites. These latter approaches, in combination with high-throughput screens, are designed to exploit recent advances in technology and take advantage of our increased understanding of biological systems.
Descubrimiento y selección de herbicidas
Históricamente, los herbicidas se han descubierto por selección al azar de la actividad sobre malezas de interés, con colecciones de químicos. Aunque totalmente empírico, este enfoque ha sido sorprendentemente exitoso y ha producido esencialmente todos los herbicidas comerciales que hoy se usan. Más recientemente, las compañías de agroquímicos han adoptado estrategias direccionadas, usando ensayos in vitro, relaciones estructura del compuesto/actividad, y ensayos de perfilamiento de mARNs, proteínas y metabolitos. Estos últimos enfoques, en combinación con filtros estrictos, están diseñados para explotar avances recientes en la tecnología y para tomar ventaja de nuestro mejor entendimiento de los sistemas biológicos.
Inhibitors of Branched Chain Amino Acid Biosynthesis
Herbicides that inhibit the production of the branched chain amino acids valine, leucine and isoleucine are used for total vegetation management and selective weed control in a wide variety of crops. There are currently four different chemical families that share this MOA. Before the development of glyphosate-tolerance crop technology, branched chain amino acid inhibitors were the mainstay for several major row crops. While this is still a very important herbicide MOA, the major increase in herbicide resistance weeds since 1980 has been the direct result selection pressure from these herbicides. There are currently more weed species resistant to branched chain amino acid inhibitors than any other herbicide MOA.
Plant Pigments and Photosynthesis
This lesson will examine the two major classes of phototsynthetic pigments, chlorophylls and carotenoids, their biochemical structures and their biosynthesis. The organization of these pigments into photosynthetic pigment, which are protein complexes that harvest light and convert its energy into biochemical energy will be explained.
Los Pigmentos Vegetales y la Fotosíntesis
En esta lección se examinarán las dos principales clases de pigmentos fotosintéticos: las clorofilas y los carotenoides. Se analizarán sus estructuras bioquímicas y su biosíntesis, y se explicará además la organización de estos pigmentos en los sistemas fotosintéticos, que son complejos proteicos que colectan y convierten la energía luminosa en energía química.
Transpiration - Water Movement through Plants
This lesson and its animation follows the journey of water through a plant from its uptake by roots to its evaporation from the leaf surface. How this journey is altered by plant characteristics such as stomata and cuticles as well as by changes in the environment will be described.
La Transpiración - Movimiento del Agua a Través de las Plantas
La transpiración es la pérdida de agua en forma de vapor por las plantas. El agua es absorbida del suelo por las raíces y transportada en forma líquida por el xilema hacia las hojas. En las hojas, unos pequeños poros permiten que el agua (H2O) escape a la atmósfera en forma de vapor, al tiempo que se permite la entrada de bióxido de carbono (CO2) para la fotosíntesis. De toda el agua absorbida por las plantas, menos del 5% es retenida y utilizada para crecimiento y almacenamiento. En esta lección se explicará porque las plantas pierden tanta agua, la ruta que ésta sigue dentro de la planta, como pudieran las plantas controlar la pérdida excesiva de agua y como las condiciones ambientales influyen en la pérdida de agua por las plantas.
The Interaction of Light with Biological Molecules
This lesson describes the nature of light, the energy within photons and how this energy may be transferred to biological molecules. In addition, the beneficial and harmful methods for de-exciting molecules will be described.
La Interacción de la Luz con las Biomoléculas
En esta lección se describe la naturaleza de la luz, la energía de los fotones y como dicha energía puede ser transferida a las biomoléculas. Se describen también tanto los procesos benéficos como los procesos dañinos por medio de los cuales las biomoléculas disipan la energía recibida.
Root Absorption and Xylem Translocation
Herbicides must be absorbed into plants in order to be effective. Plant roots and below ground shoots have few barriers to herbicide absorption; however, interactions with soil particles and soil organic matter have significant impacts on the amount of herbicide available for plant absorption. Plant roots and below ground shoots (hypocotyls or coleoptiles) are lipophilic by nature and do not have thick, waxy cuticles like leaves. Lipophilic and hydrophilic herbicides reach the root surface by bulk transport in soil water; however, there are a few examples of herbicides that reach the root as a vapor or gas. Soil-applied herbicides can translocate to the shoot or remain in the root system. Soil-applied herbicides translocate to the shoot in the xylem and tend to accumulate in mature leaves that transpire the most water. The lipophilic/hydrophilic nature of the herbicide will determine if the herbicide translocates to the shoot. Absorption and translocation of phloem-mobile herbicides will be discussed in another lesson.
Metabolism of Herbicides or Xenobiotics in Plants
This lesson will take an in depth view of how plants handle foreign chemicals (xenobiotics) such as herbicides. It will discuss the three main phases that plants use to handle toxic chemicals, which enzymes are involved in these biochemical conversions, how these processes help protect crops again phytotoxic chemicals and consider the importance of these processes to successful weed management.
Inhibitors of Fatty Acid Synthesis and Elongation
Fatty acid synthesis and fatty acid elongation are two parts of a critically important pathway in plants. The endproducts are essential components of cell membranes, waxes, and suberin. Two chemical families of herbicide (groups that share similar chemical structures) inhibit fatty acid synthesis, while fatty acid elongation is inhibited by two other families. This lesson will provide an overview of fatty acid synthesis and elongation, and explain where herbicides inhibit the pathway. Mechanisms of resistance to these herbicides will be described.
Cellular Absorption of Herbicides
Before a herbicide can kill a plant, it must be absorbed by the plant’s leaves or roots and enter a cell which possesses the metabolic pathway the herbicide targets. This lesson follows the fate of the herbicide after it has entered the plant via leaf or root tissue, and explains the factors controlling transport of a herbicide into plant cells. This lesson describes 1) the barriers to herbicide entry, such as the plant cell membrane, 2) the role that the herbicide’s chemical properties have on the rate of cellular absorption, and 3) experimental approaches to understanding herbicide absorption at the cellular level.