Plant Growth and Development

• Growth is an irreversible and permanent increase in the size of a plant, including parameters like cell size, tissue expansion, and overall mass.
• Development refers to a sequence of qualitative structural changes throughout a plant's lifecycle, from germination to aging (senescence).
• Morphogenesis is the acquisition of form and structure during development
• Differentiation is the transformation of generalized cells into specialized ones during development

Stages of Plant Growth

• Seed germination is the stage where the seed absorbs water, breaks dormancy, and starts metabolic activities.
• Seedling grows roots and shoots during seedling development, establishing itself in the soil.
• Adult plant formation occurs when the plant attains maturity with fully developed tissues, organs, and reproductive structures.

Meristems (Growing Regions)

• Apical meristems are located at the tips of roots and shoots
  • Resposible for primary growth, increasing the plant's length
• Lateral meristems are found along the sides of stems and roots.
  • Resposible for secondary growth, increasing the plant's girth

Phases of Cell Growth

• Phase of division (meristematic phase)
  • This involves mitotic cell division in the meristematic zone
  • Produces new cells for growth
• Phase of elongation
  • Cells increase in size, up to 10 times their original length
  • Root penetration happens deeper into the soil
  • Contributes to size and length of plant tissues
• Phase of Differentiation (Maturation)
  • Cells undergo specialization depending on their position in an organ
  • Differentiated cells form complex tissues like vascular bundles and perform specific functions.

Primary vs. Secondary Growth

• Primary Growth:
  • Occurs first and extends plant length above and below ground.
  • Driven by apical meristems.
• Secondary Growth:
  • Occurs after primary growth, increasing diameter and strength.
  • Controlled by lateral meristems.
  • Includes growth from axillary/lateral buds, contributing to plant branching.

Plant Growth and Development Characteristics

• Growth characteristics are measured by increases in fresh or dry weight, leaf area, and plant height.
• Development characteristics include a progression of chronological events such as germination, seedling emergence, leaf appear and senescence.
• Progression of chronological events includes:
  • Leaf appearance
  • Branching
  • Flowering
  • Fruiting
  • Seedling
  • Maturation

Factors Affecting Plant Growth

• Light, water, temperature, and nutrients are essential for plant growth but effect plant processes
• Light regulates the stomata and floral induction in plants
  • Intensity and quality affect plant processes
  • Duration influences leaf production and flowering.
• Water constitutes 90% of the plant body
  • Necessary for cell elongation and expansion, photosynthesis, nutrient transport, and seed germination
  • Absence causes stress and plant death
• Temperature is a key driver for metabolic processes like transpiration, photosynthesis, and flowering
  • Optimal temperature accelerates growth
  • Extremes (above or below optimum) slow down or halt development.
• Plants need macro and micro nutrients
  • Deficiency in even one nutrient can lead to stunted growth and susceptibility to diseases
  • Macronutrients are nitrogen, phosphorus, calcium
  • Micro nutrients are iron, boron, manganese

Plant Growth Curve (Sigmoid Curve):

• Represents growth plotted against time
  • Lag phase is the initial slow growth with seed germination, seedling emergence, and plant establishment
    • Growth percentage is under 25%
  • Log/Exponential Phase is the rapid growth phase with growth percentage from 25-70%
    • Indicators are leaf production, branching and tillering
  • Diminishing Phase is with slower growth and Growth percentage from 70-85%
    • Indicators are flowering and seed production
  • Stationary Phase is is when growth ceases and with growth 85-100%
    • Indicators are ripening, maturity, and senescence

Plant Tissue Systems

• Dermal Tissue System:
  • Forms the "skin" of the plant, for protection
  • Predominantly has parenchyma cells.
  • The epidermis is a single layer of tightly packed cells covering plant surfaces
  • Functions in protection against water loss and pathogens
  • Epidermis that is in plants undergoing secondary growth is replaced by the periderm
  • Secretes a waxy coating called the cuticle on leaves to minimize water loss.
• Periderm with plants that have secondary growth replace the epidermis
  • Cork cambium (meristematic) produces cork (phellem) outward and phelloderm inward.
  • Cork (phellem) is the protective layer, prevents water loss and provides insulation.
  • Phelloderm is the inner layer supporting the cork cambium.
  • Functions in protection against pathogens and excessive water loss ans Insulation for the plant body
• Ground Tissue System:
  • Constitutes the majority of the plant body
  • Functions in Photosynthesis, storage, and structural support.
  • The main cell type is Parenchyma
    • Are living cells at maturity, perform metabolic activities, photosynthesis, food storage, and regeneration, Wound healing and organ regeneration
    • Main sub types
      • Chlorenchyma contains chloroplasts for photosynthesis,
      • Aerenchyma contains large air spaces for gas exchange
  • Collenchyma tissue
    • Are living cells with unevenly thickened walls providing flexible support to leaves and young stems
    • With angular thickening in corners
    • Lamellar thickening on opposite sides and Lacunar with Thickening with intercellular spaces.
  • Sclerenchyma provides strength, and support to mature plant parts.
    • Non-Living cells with thick, lignified secondary walls
    • Fibers: Long, slender cells occurring in bundles
    • Sclereids: Short, irregularly shaped cells present seed coats & nut shells
• Vascular Tissue System
  • Specialized for the transport of water, nutrients, and food
  • Has a secondary role in providing structural support
  • Tissue called Xylem conducts water and dissolved minerals
    • Principal cells: Tracheids and vessel elements
    • Additional cells that are parenchyma and sclerenchyma.
  • Tissue called Pholem transports food (mainly sucrose)
    • Has Sieve tubes and companion cells
    • Fibers and parenchyma.

Generalized Plants

• Protoplasm is is the living content of the cell, with a nucleus being the control center for cell functions.
• Cytoplasm is a gel-like matrix where organelles are suspended
• The cell wall surrounds the protoplasm and provides structural integrity to the plant made predominantly of cellulose
• A growing plant cell secretes a thin primary cell wall that stretches as the cell enlarges; additional layers called the secondary cell wall develop when growth ceases

Types of Permanent Tissue

• Ground tissue such as Parenchyma, Collenchyma, Sclerenchyma
• Tissue such as Xylem and Phloem tissues are also called vascular tissue
• Several tissue such as the internal: Resin/oil vessels, Laticifers and external Hydathodes, Digestive glands can also be called Secretory Tissue

Secretory Tissue

• Specialized cells that secrete substances like resins, oils, and mucilage

Internal Secretory Tissues

• Resin and oil vessels that has Ducts surrounded by epithelial cells secreting essential oils and resins through Lysigeny called (dissolving cells)
  • Laticifers are Cells or series of cells containing latexTypes that are Latex vessels and Latex cells: Unbranched cells

External Secretory Tissues

• Hydathodes or Glands excrete water during guttation
  • Digestive glands are found in insectivorous plants like Drosera, secreting mucilage & digestive enzymes
  • Nectaries are structures secreting nectar to attract pollinators that can be found floral or vegetative parts.

Definition and Structure of the Rhizosphere

• Soil region surrounding a the a plant's root hair interactions happens between roots and microorganisms
• It consists of three zones, defined by their proximity to the root
  • Endorhizosphere includes the cortex and endodermis, where microbes and ions occupy free spaces between cells.
  • The medial zone adjacent to the root, including the epidermis and mucilage is called Rhizoplane
  • Ectorhizosphere, the outermost zone extending into bulk soil

Roots Exudates & Mucilages

• Root exudates are a Broad term including mucilage and soluble compounds
• Mucilages: Polysaccharide-rich, viscoelastic gels with adhesive properties
  • Functions include
    • Attract beneficial microbes
    • Act as bait for pathogens
    • Bind and remove toxic metals

Rhizodeposits

• Substances that roots impart to the surrounding soil
  • Loss of cap and border cells
  • Loss of insoluble mucilage
  • Loss of soluble root exudates
  • Loss of volatile organic carbon
  • Loss of carbon to symbionts
  • Loss of carbon due to death and lysis of root epidermal and cortical cells

Chemical Contributions of the Rhizosphere

• Occurs through Root carbon release amount
  • Forms of carbon released can be organic or inorganic
    • Organic (e.g., organic acids) vs inorganic (e.g., bicarbonate, HCO3-)
• The organic forms influence chemical, physical, and biological processes in the rhizosphere through climatic and soil conditions

Root Hairs

• Functions include absoring water and nutrients and dying after about 3 weeks, creating a compost-like environment that contribute to microbial attraction and nutrient cycling

Microbe-Plant Relationships in the Rhizosphere

• Root carbon release influences the mircobe levels higher compared to bulk soil, leading to microbial competition

Key Micobial relationship

• Rhizobia bacteria converts atmospheric nitrogen to nitrate usable by the plants by residing in root nodules
• Symbiotic association between soil fungi and roots
  • Ectomycorrhiza forms dense hyphae in intercellular spaces (Hartig net) while Endomycorrhiza are more common in penetrating hyphae through cell walls
• Promotion of rhizobacteria happens by Colonizing roots to enhance growth
  • Example using Bacillus subtilis in forming biofilms on root surfaces

Why do crops vital for the future?

• Some of the world relies solely on Dominance of few crops
  • These crops must feed over 7 billion people
• Supply Chain Vulnerability
• Current crops rely on long-distance transportation to markets by raising concerns about diverse global populations; but mainly Climate Challenges

Factors of Sustainable practices

• Utilize crops in sustainable approaches
• Alternative Aquaculture Feeds that can utilizes locally fish based in fishmeal
  • Replace sources of underutilized fish and plants

Expanding future agrculture

• Must utilizes the underutilized to it's fullest potential
• This can be solved bu utilizing Monoculture through research and development
• Embrace multiple cropping systems for resilience against climate shocks.

Linking in Communities and Research

• Knowldge sharing between Communities creates better connections that helps crop knowledge while making it easier for global food systems
• Sustainable production using new approaches and old
  • With climate resilance we can help to develop carbon fixation and future plant needs

Plant growth involves irreversible increases in size, while development encompasses qualitative changes throughout a plant's life. Key processes include morphogenesis, differentiation, and distinct growth stages from germination to maturity. Meristems, such as apical meristems, drive primary growth at root and shoot tips.