How hormones help plants respond to different stimuli

Plant hormones and how plants respond to different stimuli

1. LET’S DO PLANT HORMONES WITH GROUP 6

2. GAME

3. HORMONES- ARE CHEMICAL SIGNALS THAT COORDINATES DIFFERENT PARTS OF AN ORGANISM. PLANT HORMONES- NATURALLY OCCURING CHEMICALS PRODUCED WITHIN PLANTS THAT REGULATES GROWTH,DEVELOPMENT,AND RESPONSE TO THE ENVIRONMENT .

4. TYPES OF HORMONES IN PLANTS

5. AUXINS They are a class of plant hormones that play a crucial role in plant growth and development . Common auxin in plants- Indoleacetic acid(IAA)

6. THE ROLE OF AUXINS IN PLANTS

7. CYTOKININ’S Cytokinin’s work with auxins to regulate growth and differentiation. Cytokinin’s promote cytokinesis (cell division). Cytokinin’s are produced mainly in actively growing root tips, then move upward in the xylem into shoot.

8. FUNCTIONS

9. Cytokinin’s delay senescence → (keep leaves green, reduce aging/degeneration, retard aging in some plant organs) by: Inhibiting protein breakdown Prevents important proteins in the leaves from being degraded Keeps the leaf cells functional and healthy Stimulating RNA and protein synthesis Encourages the leaf cells to keep producing new proteins Supports growth, repair, and metabolic activity Mobilizing nutrients from surrounding tissues Redirects nutrients (like sugars and minerals) to the leaf Helps the leaf remain green and active instead of degenerating

10. Promote lateral growth Apical dominance: Auxins from the apical bud promote elongation of the main stem but also suppress growth of lateral/auxiliary buds. Removal of apical bud → auxin levels drop → cytokinin’s can stimulate lateral bud growth (branching).

11. Hormone ratios: High auxin : low cytokinin → root formation. High cytokinin : low auxin → shoot formation / branching. Balanced → normal growth and differentiation.

12. GIBBERELLINS Plant hormones that regulate growth and development - First discovered in rice plants (foolish seedling disease) - Work with other hormones (auxins, cytokinins)

13. Functions of Gibberellins

14. Stem Elongation - Stimulate cell division and elongation in stems - Leads to taller plants, longer internodes - Example: dwarf plants grow taller with gibberellins

15. Fruit Growth

16. Seed Germination - Break seed dormancy - Activate enzymes (e.g., amylase) - Provide energy for embryo growth

17. Agricultural Uses - Increase crop yields - Uniform seed germination - Grow seedless fruits for market

18. BRASSINOSTEROIDS Reproductive Development: BRs are essential for the development of pollen, anthers, and stigmas, as well as for male and female fertility. Cell Growth and Elongation: BRs promote cell expansion and elongation by influencing the mechanical properties of the cell wall. Plant Development: They are involved in numerous developmental processes, including seed germination, root and shoot growth, floral transitions, and the development of vascular tissues.

19. Stress Response: BRs confer resistance against various abiotic stresses, such as drought, cold, heat, and salinity, and can help in biotic stress tolerance. Metabolism and Photosynthesis: They can enhance photosynthetic processes and the activity of antioxidant enzymes.

20. How the brassinosteroid hormone function Detected by Brassinosteroid Insensitive 1 receptor (on the cell membrane) Receptor joins with Brassinosteroid Associated Kinase 1 → signal begins Signal inactivates Brassinosteroid Insensitive 2 (the blocker protein) Brassinazole Resistant 1 and Brassinazole Resistant 2 transcription factors become active Transcription factors move into the nucleus Genes for growth, development, and stress tolerance are switched on

21. Abscisic acid(ABA) Often called a stress hormone because it helps plant survive unfovorable conditions Slows growth Promotes germination only when environment is suitable Prevents seed germination within fruit Light inactivates ABA(sunlight due to plant elongation) Works against growth promoting hormones such as gibberelins and auxins Seed germination occurs when ABA concentration is low Controls stomata opening/closing during drought season The two effects of ABA are seed dormancy and drought tolerance

22. Seed dormancy

23. Abscisic acid

24. What is leaf abscission? Natural process where plants “shed their leaves” Happens at the “abscission zone” at the base of the leaf stalk Controlled by hormones: Auxin ↓ Ethylene ↑

25. Why Do Plants Shed Leaves? Reduce water loss in dry or cold season Recycle nutrients back into the plant Prevent damage from dead or useless leaves

26. What is fruit Ripening? Process where fruits become soft, sweet, and colorful.

27. Why do fruits ripen?

28. ethylene A gaseous plant hormone that regulates a wide range of processes. C2H2

29. How is ethylene produced? Methionine (an amino acid) is converted to S-adenosyl methionine (SAM). SAM is converted to ACC (1-aminocycloproprane-1-carboxylic acid) by ACC synthase. ACC is then converted to ethylene gas by ACC oxidase

30. Ethylene regulates a wide range of processes such as: Stress response Senescene Fruit ripening Leaf abscission

31. Plant respond to stresses such as Drought Flooding Wounding Pathogen attack

32. 2. Senescene It is a programmed aging process in plants that leads to: Decline in cellular function Breakdown of organelles Recycling of nutrients Eventual death cells, organs , or the entire plant nvolves breakdown of cellular components leading to wilting, yellowing, and eventually death of tissues (e.g., flowers, leaves, fruits).

33. Ethylene is called the “ senescence hormone .” It accelerates: Flower wilting (petals lose color, become limp). Leaf yellowing (chlorophyll breakdown). Fruit aging (softening, over-ripening).

34. Diagram of senescene