Plant Hormones and Reactions PDF

Topic 9 Plant Hormones and Reactions Plant hormones are chemical messengers that regulate growth, development, and responses to environmental stimuli (internal and external).  HORMONE...

Topic 9 Plant Hormones and Reactions Plant hormones are chemical messengers that regulate growth, development, and responses to environmental stimuli (internal and external).  HORMONE VITAMIN The site of synthesis is different from the site of action Vitamins are used in the same part without being transported Plant hormones are physiologically active Vitamins by themselves are not physiologically active. They act as co-factor of enzyme. Example:  Major Plant Hormones Auxin Gibberellin Cytokinin Abscisic Ethylene Acid  Hormones in plants HORMONES CAN HAVE HORMONES CAN HAVE 5 MAIN GROUPS BASED EFFECTS ON THE CELLS THAT INHIBITORY RATHER ON CHEMICAL PRODUCE THEM AND, AFTER TRANSPORT, AT THE TARGET THAN STIMULATORY STRUCTURE CELLS OR TISSUES EFFECTS Auxin: The Growth Hormone Cell Elongation Auxin promotes cell elongation, leading to stem and root growth. Phototropism Auxin accumulation on the shaded side of a stem causes bending towards light. Root Development Auxin plays a crucial role in root formation and elongation.  Darwins’ (Charles and son) experiment Under normal When not at tip, Without light on the conditions, shoot tips collar doesn’t prevent tip, no bending bend towards the light bending Conclusion: Light is sensed at the tip, but response not at tip New hypothesis: A substance or chemical is transported Auxin later isolated from shoot tips and established to be involved in cell elongation Drawings depicting seedlings of Zea (Gramineae family) Evidence for the role of auxin in apical dominance High auxin concentration Low auxin concentration Drawings depicting Coleus (Lamiaceae family) Evidence for the role of auxin in the formation of fruit and structures of similar function (e.g. receptacle in strawberry) Normal All achenes Band of achenes conditions removed removed Without seed formation, fruits do not develop. Developing seeds are a source of auxin. What do you expect? Not shown: Auxin replacement restores normal fruit formation and can be used commercially to produce seedless fruits However, too much auxin can kill the plant and thus synthetic auxins used commercially as herbicides Fragaria (Rosaceae family)  Evidence for the role of auxin in adventitious root formation With synthetic auxin Without synthetic auxin Adventitious roots growing from stem tissue Saintpaulia (Gesneriaceae family) Another example of misleading common name The African violet is not in the violet family Parthenocarpy is the natural or artificially induced production of fruit without fertilisation of ovules, which makes the fruit seedless. Gibberellins: Promoting Cell Elongation 1 Stem Elongation Gibberellins stimulate cell elongation in stems, promoting growth. 2 Seed Germination They break seed dormancy and promote germination. 3 Fruit Development Gibberellins contribute to fruit growth and development. Commercial use of GA Without GA With GA Larger fruits that are easier to clean are attractive in markets Thompson seedless grapes (Vitis (Vitaceae family)  What are the effects of GA on the growth of Brassica rapa? Why Brassica rapa? Image from wikipedia.org  What are the effects of GA on the growth of Brassica rapa? Why Brassica rapa? 1. Many economically valuable plants in the (Brassicaceae family) Broccoli, cabbage, cauliflower 2. Members of the Brassicaceae family have become model plant species. Some characteristics that are important for model species include: Relatively small genome Easy to grow Rapid life cycle Broadly and thoroughly studied Not atypical Genetic tools available Cytokinins: Cell Division and Differentiation Cell Division Cytokinins stimulate cell division in roots, shoots, and other tissues. Shoot Development They promote shoot branching and leaf formation. Delaying Senescence Cytokinins can delay leaf aging and senescence. Abscisic Acid: The Stress Hormone Role Function Stress Response Helps plants cope with drought, salinity, and other stresses. Stomata Closure Abscisic acid closes stomata to conserve water during drought. Dormancy Promotes seed dormancy and prepares plants for winter. Plant Hormone Interactions and Regulation Synergistic Effects Antagonistic Effects Some hormones work Other hormones have together to amplify their opposing effects, balancing effects. growth and development. Feedback Loops Hormone levels are tightly regulated through feedback loops. Major Plant Hormones: Their Nature, Occurrence and Effects Conclusion and Future Directions Understanding plant hormones is essential for understanding plant growth and development. Future research will likely focus on developing new strategies for manipulating hormone pathways for agricultural improvement and environmental adaptation.  Group Activity Optimising Crop Yields Using Plant Hormones Propose a method for using plant hormones to enhance crop yields and improve market value. The aim is to identify a practical and innovative application of plant hormones to increase farmers’ profits while maintaining sustainable agricultural practices. Tips: 1. Select the suitable crop 2. Select the appropriate hormone and application time 3. Padlet links will be shared