Lecture 14 Plant Growth Regulators (PGRs) PDF

L.14 Biology Department SQU College of Science Lecture 14 BIOL3011 Plant growth regulators (PGRs) Plant Physiology  L.14 Biology De...

L.14 Biology Department SQU College of Science Lecture 14 BIOL3011 Plant growth regulators (PGRs) Plant Physiology  L.14 Biology Department SQU College of Science Identify and describe the various classes of plant growth regulators and their Learning roles in plant physiology. Understand the mechanisms by which these Outcome hormones influence plant growth, development, and responses to environmental stimuli. Plant Physiology  L.14 Biology Department SQU College of Science 1 Introduction to plant growth regulators (PGRs) 2 Abscisic acid (ABA) 3 Gibberllins (GAs) Outline 4 Auxins 5 Cytokinins 6 Ethylene 7 Brassinosteroids Plant 8 Comprehensive overview of plant hormones Physiology 1 Introduction to plant growth regulators 1 (PGRs) 1 Introduction to plant growth regulators (PGRs) Plant growth may be defined as an increase in size involving development. It is the result of cell division, cell elongation, cell differentiation and morphogenesis. Morphogenesis is the development of form or shape of cells and organs. Differentiation is the process by which cells undergo biochemical and structural changes to perform specialized functions. 1 Introduction to plant growth regulators (PGRs)  Plant growth is regulated by nutritional and hormonal factors (In Greek language the term 'hormon' means to stimulate).  Hormones, which are chemical messengers, are produced in low concentrations.  They are synthesized in one part of the plant but exert their effects in another.  Growth regulators control the growth of the plant. 1 Introduction to plant growth regulators (PGRs)  Growth regulators regulate the growth of the plant.  They may accelerate the growth or inhibit the growth.  There are five classes of growth regulators:  Auxins  Gibberellins  Cytokinins  Abscisic acid and  Ethylene 1 Introduction to plant growth regulators (PGRs) Plant hormones and their roles in growth and development Control of stem elongation zone division Control of cell division (Auxin and gibberellic (Cytokinin’s and acid) Gibberellic acid) Initiation of flowering Stomatal closure (Flowering hormones (Abscisic acid) from leaves) Growth of young fruits Development of (Cytokinin’s), introduction abscission zone of fruit ripening (ethylene) division (Ethylene and Auxin) Gravitropsim of roots (Auxin) 2 Abscisic acid (ABA) 2 2 Abscisic acid (ABA)  Abscisic acid (ABA) is a class of growth regulator which inhibits the growth and promotes dormancy.  Discovered 1960s.  ABA is synthesized in various parts of the plant, leaves, roots, stem, and seeds. ABA antagonizes the actions of auxins, cytokinins, and gibberellins, playing key roles in inducing seed dormancy and responding to drought stress by regulating stomatal closure. ABA is anti auxin. It prevents curvature of coleoptile. ABA is anti gibberellin. It inhibits germination by inhibiting alpha amylase synthesis.  Chemically it is a sesqui-terpene. 2 Abscisic acid (ABA) Physiological roles of ABA 1. Dormancy  ABA plays a crucial role in inducing buds an seeds dormancy.  Under adverse conditions, such as cold or drought, ABA concentrations in the plant tissues increase. This heightened presence of ABA helps to enforce dormancy, particularly in buds, as a protective mechanism against harsh environmental factors.  While ABA promotes dormancy by inhibiting the sprouting of buds, gibberellins have the opposite effect. Gibberellins can decrease the dormancy imposed by ABA. 2 Abscisic acid (ABA) Physiological roles of ABA 2. Senescence  Senescence is the degradative process leading to the loss of chlorophyll, RNA, proteins,.. etc.  ABA induces the senescence in mature leaves, pollinated flowers and mature fruits. 2 Abscisic acid (ABA) Physiological roles of ABA 3. Abscission  Abscission refers to the shedding of plant parts due to the development of a cork like separating layer at their bases.  ABA induces the shedding of plant parts by promoting the formation of a separating or abscission layer at their bases. e.g. cotton 2 Abscisic acid (ABA) Physiological roles of ABA 4. Stomatal movements ABA promotes stomatal closure when sufficient amount of water is not present in the plant body' there by protecting the plant from wilting. 3 Gibberellins (GAs) 3 1.Physiological effects of gibberellins on plant growth. 2.Commercial uses of gibberellins. 3.Gibberellins vs auxin. 3 Gibberellins (GAs) Physiological effects of gibberellins on plant growth Biosynthesis Gibberellins are synthesized in plants predominantly at apical regions, young leaves, and root tips. Concentration and role High concentrations of gibberellins are found in fruits and germinating seeds, playing a crucial role in growth processes. Transport mechanism Being non-polar, gibberellins are transported in both upward and downward directions through the xylem. 3 Gibberellins (GAs) Diversity More than 130 GAs are identified in plants, fungi, and bacteria. These are named sequentially from GA₁ through GA130. Chemically they are diterpenoids. Synthesized via terpenoid pathway (5C). GAs promotes Seed and bud germination. Stem elongation. Leaf growth. Stimulate flowering and development of fruit. Affect root growth and differentiation. 3 Gibberellins (GAs) 1.Physiological effects of gibberellins on plant growth 1.1.Internodal Elongation (Stem elongation) Gibberellins promote stem elongation in various plants, enhancing vertical growth. Treatment of dwarfism Application of gibberellins helps dwarf plants like beans and maize grow to normal sizes. Specific non-responses Gibberellins do not influence curvature in coleoptiles, highlighting their selective action in plant tissues. Dwarf variety Dwarf variety of pea plant of pea plant treated with gibberellin 3 Gibberellins (GAs) 1.Physiological effects of gibberellins on plant growth 1.2. Flowering Gibberellins promote flowering in many plants. 1.3. Development of parthenocarpic fruits Gibberellins promote the development of parthenocarpic fruits in tomato, apple, almond etc. Gibberellins increase the size of leaves, seeds and fruits. 1.4. Breaking dormancy The temporary suspension of growth and metabolism is called dormancy. Gibberellins break the dormancy in buds and seeds. 1.5. Formation of adventitious roots Gibberellins inhibit the formation of adventitious roots from the cut end of stem. 3 Gibberellins (GAs) 1.Physiological effects of gibberellins on plant growth 1.6. Seed germination Gibberellins promote the germination of cereal seeds such as barley, wheat, rice, etc., by increasing the synthesis of amylase, RNA and proteins.