Plant Growth and Development Lesson 3 PDF

PLANT GROWTH AND DEVELOPMENT Plant growth refers to the irreversible increase in size, while development involves the progression through different life stages (germination, vegetative growth, flowering, fruiting, and senescence). Key...

PLANT GROWTH AND DEVELOPMENT Plant growth refers to the irreversible increase in size, while development involves the progression through different life stages (germination, vegetative growth, flowering, fruiting, and senescence). Key Growth Processers Phases: Cell Division: Growth starts at the cellular level Embryonic Phase: through mitotic cell Initiated after division. fertilization during seed formation. Cell Elongation: After Vegetative Phase: division, cells elongate, Focuses on root and contributing to overall shoot system plant growth. development. Cell Differentiation: Reproductive Cells specialize into Phase: Involves different tissues and organs flowering, pollination, (roots, stems, leaves). and seed formation. Hormonal Regulation of Growth Auxins: Promote cell elongation and apical dominance. They regulate phototropism and gravitropism. Gibberellins: Stimulate stem elongation, seed germination, and flowering. Cytokinins: Promote cell division and delay leaf senescence. They work in opposition to auxins, encouraging lateral bud growth. Ethylene: Involved in fruit ripening, leaf abscission, and response to stress. Abscisic Acid (ABA): Regulates stress responses, seed dormancy, and stomatal closure during drought.  Environmental Influences on Growth Light: Photoperiodism: The effect of the length of day and night on flowering. Long- day vs. short-day plants. Photosynthesis: Provides the energy required for growth through the conversion of light into chemical energy. Water: Essential for turgor pressure in cells, which is critical for cell elongation. Regulates nutrient uptake and transport. Temperature: Optimum Growth Range: Plants have a temperature range where growth and development are optimal. Thermoperiodism: The effect of daily temperature fluctuations on plant growth, influencing flowering and seed germination. Nutrients: Macronutrients (e.g., Nitrogen, Phosphorus, Potassium) and Micronutrients (e.g., Iron, Zinc) are essential for growth and development  Flowering is the process by which plants transition from FLOWERING vegetative growth to reproductive development, producing flowers for sexual reproduction. ❖ Factors Influencing Flowering: Photoperiod: The length of day and night affects the timing of flowering in plants. This response is known as photoperiodism. Short-day Plants: Require long nights to flower (e.g., chrysanthemums, poinsettias). Long-day Plants: Flower when nights are short (e.g., spinach, lettuce). Vernalization: Some plants require exposure to cold temperatures to initiate flowering (e.g., winter wheat). Hormonal Control: Gibberellins: Promote flowering in some plants, especially in long-day and biennial plants. Flower Stages of Flower Development: Development photoperiod, temperature, and internal ◦ Flower Induction: Signals such as cues trigger the floral meristem's and development. ◦ Floral Initiation: Vegetative meristems Importance transition to reproductive meristems, starting the formation of floral organs (sepals, petals, stamens, and carpels). ◦ Flower Maturation: Floral organs fully develop and open to facilitate pollination. Importance of Flowering: Reproduction: Flowers are the reproductive structures, enabling plants to produce seeds through pollination. Agriculture: Many crops depend on successful flowering for fruit and seed production (e.g., grains, fruits, vegetables). Pollinator Attraction: Flowers attract pollinators (e.g., bees, butterflies) through color, scent, and nectar production, aiding in cross-pollination.  Leaf Senescence The natural, age-dependent process leads to the systematic degradation and recycling of cellular components in leaves. Nutrient remobilization to developing parts like seeds or young leaves. Visible as yellowing due to chlorophyll breakdown. Types of Senescence: Whole plant senescence (e.g., annual plants). Sequential senescence (e.g., older leaves die first). Stress-induced senescence (triggered by drought, pathogens). Molecular Aspects: Hormonal regulation: Decline in cytokinins, increase in ethylene and ABA. Upregulation of senescence-associated genes (SAGs).  Importance of Leaf senescence 1. Nutrient Recycling: Efficient redistribution of nitrogen, phosphorus, and other nutrients to reproductive structures. 2. Stress Response: Senescence as a defense mechanism under stress, conserving energy for survival. 3. Ecosystem Contributions: Organic matter decomposition enriches the soil. 4. Controlled Cell Death: Prevents uncontrolled decay, facilitating efficient nutrient recovery. THANK YOU