Chapter 20- growth and development in plants.pptx

Growth and development in plants

1. Chapter 20 Growth and development in plants

2. Growth and development Growth - Irreversible increase in number and size of a cell, organ or whole organism Not uniform through out the life span Development - The changes that takes place in an organism starting from beginning to death It is associated with i . Morphogenesis : process of development of shape and structure of an organism ii. Differentiation : process of change in cells, tissuesor organs to carry out different functions

3. STAGES OF CELLULAR GROWTH Cell division : The number of cells increases due to mitosis Cell enlargement : The size of individual cell increases after cell division Cell differentiation: structure of the cells changes to perform specific functions

4. Comparison of cell division and cell enlargement

5. GROWTH CURVE Sigmoid growth curve : Lag phase : initial phase of growth slow growth rate Log phase : rapid growth and is maximum during the entire life span Stationary phase : rate of growth starts decreasing and finally stops. Grand period of growth: The total time period during which the fastest growth of the organ or organism takesplace

6. Measurement of growth Methods in measuring growth in length Direct method II. Auxanometer * used to measure the rate of growth of shoot length of plants

7. Factors affecting plant growth External growth factors : Light: process of photosynthesis seed germination, growth of seedling, differentiation of various tissues and organs, reproduction Temperature : optimum temp. range:28-30*c, but it may occur 4-45*c all metabolic activity affects Water: photosynthesis biochemical processes 4. Mineral nutrients: metabolic process-inorganic nutrients

8. External growth factors Naturally produced growth hormones 1.Auxin 2.Gibberillins 3.Cytokinins 4.Ethylene 5.Abcissic acid

9. 1. AUXIN Growth promoter Naturally produced auxin - indole-3-acetic acid Synthetic auxin - Indole-3-butyric acid 2,4-dichlorophenoxy acetic acid Naphthalene acetic acid Functions: Promotes cell elongation Suppresses growth of lateral bud apical dominance: In some cases apical bud suppresses the growth of lateral bud Leaf abscission NAA- prevents fruit drop in apples before they are ripe 2,4-D- acts as a dicot weedicide

10. 2.GI BBERILLINS Initially isolated from fungus Gibberella fujikuroi Functions: Height of dwarf plants can be increased Breaks dormancy of seeds and buds It induces parthenocarpy (formation of seedless fruits without fertilization)

11. 3.CYTOKININS Extracted from coconut milk Synthesised in root apex, endosperm of seeds, young fruits Functions: stimulates cell division, cell enlargement and cell differentiation Prevent aging of plants Inhibit apical dominance

12. 4.ETHYLENE Gaseous hormone Found in ripening fruits, young flowers, young leaves FUNCTIONS: Indices ripening in fruits Promotes senescence and abscission of leaves and flowers Increases the width not length

13. 5.ABSCISSIC ACID Naturally occurring growth inhibitor Also known as Dormin Synthesised in leaves Functions : induces dormancy of buds and seeds Induces senescence of leaves Inhibits seed germination and development Causes closing of stomata

14. Practical application of growth regulators Seedless grapes and papayas Early flowering in some plants Early ripened fruits Germination in seeds – auxins Germination of potatoes and onions can be stopped in storage

15. Differentiation Process by which distinct cell types arise from precursor cells and become different from each other E g : vascular tissue, xylem and phloem are differentiated from meristematic cells, procambium and vascular cambium Auxin and cytokinin - vascular tissue differentiation Cells undergo structural changes both in cell wall and protoplasm Dedifferentiation reversal of cell development in plants The living differentiated cells that has lost capacity to divide can regain the capacity of division- dedifferentiation Eg : formation o f meristems , interfascicular cambium and rock cambium from fully differentiated parenchyma cells Redifferentiation

16. SEED GERMINATION 1 . Hypogeal germination 2. Epigeal germination

17. VIVIPAROUS GERMINATION

18. MECHANISM Absorption of water seed swells Seed coat ruptures radicle comes out Root system formation plumule elongates from the embryonic axis develops shoot Factors affecting seed germination Water Temperature Oxygen Light Hormone