Regulation of Plant Growth and Development

Regulation of Plant Growth

  • Hormones

    • Chemical messengers regulating plant growth.
    • Transported via phloem tissue requiring ATP (energy).
    • Interactions with external environmental factors influence growth.

  • Control Functions of Hormones

    • Growth
    • Seed germination
    • Flowering
    • Fruiting
    • Shedding of leaves
    • Color change of leaves

  • Hormones Categorized

    • Growth Inhibiting
    • Present during fall/winter, when growth is less favorable.
    • Growth Promoting
    • Active primarily in spring/summer.

Auxins

  • Description

    • First described group of plant hormones.
    • Growth-promoting hormone produced in shoot tips, seeds, fruits, leaves, and stems (not in roots).

  • Effects of Auxins

    • Promote cell and shoot elongation.
    • Stimulate wood production.
    • Encourage fruit development.
    • Inhibit lateral bud development.
    • Prevent abscission (shedding) of leaves, flowers, and fruits.

Cytokinins

  • Origin

    • Initially identified in coconut ‘milk’.
    • Growth-promoting hormone found in seeds, fruits, and roots.

  • Effects of Cytokinins

    • Promote cell division (cytokinesis).
    • Encourage lateral bud development.
    • Delay leaf senescence (aging).

Gibberellins (Gibberellic Acids)

  • Characteristics

    • Includes many types, more than any other hormone group.
    • Growth-promoting hormones concentrated in seeds.

  • Effects of Gibberellins

    • Stimulate stem elongation through cell division and elongation.
    • Aid breakdown of food reserves in germinating seeds.
    • Water uptake causes swelling and embryo hydration, leading to gibberellin secretion.
    • Gibberellins trigger alpha-amylase secretion for endosperm breakdown to glucose.
    • Embryo directs germination timing, giving an advantage to seed plants.

Abscisic Acid

  • Characteristics

    • Growth-inhibiting hormone predominately found in seeds, mature leaves, and dormant buds.

  • Effects of Abscisic Acid

    • Inhibits cell elongation.
    • Reduces alpha-amylase production.
    • Initiates leaf senescence.
    • Promotes carbohydrate storage in seeds.

Ethylene

  • Characteristics

    • Growth-inhibiting hormone, exists as a gas produced by metabolic processes.

  • Effects of Ethylene

    • Promotes fruit ripening.
    • Triggers leaf, fruit, and flower abscission.
    • Interacts with growth-promoting hormones to regulate cell size and shape.

Seed Germination

  • Requirements

    • Involves breaking dormancy through internal (hormones, food, water absorption) and external factors (sunlight, temperature, moisture).

  • Seed Structure

    • Composed of seed coat(s), embryo, and stored food.

Seedling Development

  • Resultant from cellular reproduction and size increase.
  • Nutritional Needs during Development
    • Nutrients required for growth: CO₂, water, and minerals (K, N, Ca).
    • Deficiencies lead to visible symptoms in plants.

Plant Nutritional Requirements

  • Categories

    • Essential Elements
    • 16 necessary: C, H, O from CO₂ and H₂O.
    • 13 soil nutrients absorbed via roots in water (through xylem).

  • Macronutrients

    • Required in bulk amounts (≥1g/kg dry mass).
    • Examples: N, K, P, Ca, S, Mg.

  • Micronutrients

    • Needed in small amounts (≤0.1g/kg dry mass).
    • Examples: Mo, Cu, Zn, Mn, Cl, B, Fe.

Reproductive Cycle of Flowering Plants

  • Sexual Reproduction

    • Involves the fusion of gametes, alternating generations (sporophyte and gametophyte).
    • Sporophyte: diploid stage producing spores; Gametophyte: haploid stage forming gametes.

  • Evolutionary Trends

    • Sporophyte complexity has increased, while gametophyte size has decreased.

Flower Structure and Function

  • Flowers are reproductive organs of angiosperms, containing essential processes for sexual reproduction (meiosis and fertilization).

    • Characteristics of an Ideal Flower

  • Comprised of sets of modified leaves arranged on a specialized stem.

Pollen and Ovule Development

  • Male Side: Pollen forms in anthers; Pollination transfers pollen to stigma.
  • Female Side: Ovules within the ovary develop into seeds.

Fertilization Process

  • Double Fertilization occurs when one sperm fuses with the egg, and the other with polar nuclei, leading to zygote and endosperm formation.

Plant Genetics

  • DNA

    • Composed of nucleotides with bases A, T, G, C.
    • Contains genotype (genetic info) and phenotype (trait expression).

  • Genetic Crosses

    • Alleles are genes expressed as dominant or recessive traits.
    • Homozygous (same alleles) and Heterozygous (different alleles) distinctions impact inheritance.

  • Punnett Squares

    • Visual representation of genetic crosses predicting offspring genotypes and phenotypes.

  • Mutations

    • Changes in DNA structure/order can lead to new traits, such as albinism in squirrel colors.