Plant Growth and Development Stages

• Growth is defined as the irreversible and permanent increase in size of the plant, its parts, or an individual cell, including factors like cell size, tissue expansion, and overall plant mass
• Development refers to a sequence of qualitative structural changes occurring throughout a plant's life cycle, from germination to senescence (aging)

Development:

• Morphogenesis: the acquisition of form and structure
• Transformation of generalized cells into specialized ones

Stages of Plant Growth:

• Seed Germination is the initial stage, in which the seed absorbs water, breaks dormancy, and starts metabolic activities
• Seedling Development occurs when the seedling grows roots and shoots, thus establishing itself in the soil
• Adult Plant Formation happens when a plant attains maturity with fully developed tissues, organs, and reproductive structures
• Apical Meristem: Located at the tips of roots and shoots. They are Responsible for primary growth, increasing the plant's length
• Lateral Meristem: Found along the sides of stems and roots, and responsible for secondary growth, increasing the plant's girth

Phases of Cell Growth:

• Phase of Division (Meristematic Phase): Involves mitotic cell division in the meristematic zone and produces new cells for growth
• Phase of Elongation: Cells increase in size, up to 10 times their original length, resulting in root penetration deeper into the soil and contributing to the size and length of plant tissues
• Phase of Differentiation (Maturation): Cells undergo specialization based on their position in the organ, and differentiated cells form complex tissues like vascular bundles and perform specific functions
• Primary Growth occurs first and extends plant length above and below ground and is Driven by apical meristems
• Secondary Growth occurs after primary growth, increasing diameter and strength
• It's controlled by lateral meristems and includes growth from axillary/lateral buds, contributing to plant branching
• Plant growth can be measured by increases in fresh or dry weight, leaf area, and plant height

Development Characteristics:

• Progression of chronological events like: germination, seedling emergence, leaf appearance, branching, flowering, fruiting, seedling, maturation, senescence(aging)
• Light is essential for photosynthesis, regulating stomata, and floral induction
• The intensity and quality of light affects plant processes Water constitutes 90% of the plant body
• Necessary for cell elongation and expansion, photosynthesis, nutrient transport, and seed germination
• Temperature is a key driver for metabolic processes like transpiration, photosynthesis, and flowering
• Plants require macronutrients (e.g., nitrogen, phosphorus, calcium) and micronutrients (e.g., iron, boron, manganese)
• Deficiency in even one nutrient can lead to stunted growth and susceptibility to diseases
• The plant growth curve represents growth plotted against time

Phases of plant growth curve:

• Lag Phase: Initial slow growth period with a Growth percentage <25%, seedling emergence, plant establishment
• Log Phase (Exponential Phase): Rapid growth phase with a Growth percentage from 25-70% indicating leaf production, branching, tillering
• Diminishing Phase: Slower growth phase with a Growth percentage from 70-85%, indicating flowering, seed production
• Stationary Phase: Growth ceases at a growth percentage of 85-100%, indicating ripening, maturity, senescence

Plant Tissue systems:

• Dermal Tissue System forms the "skin" of the plant, primarily for protection and generally as a single layer of cells, predominantly parenchyma cells
• Epidermis is a single layer of tightly packed cells covering plant surfaces for protection against water loss and pathogens & secretes a waxy coating called the cuticle on leaves to minimize water loss
• In plants undergoing secondary growth, the epidermis is replaced by the periderm
• Periderm is found in stems of plants with secondary growth, replacing he epidermis
• The Cork Cambium (Meristematic) produces cork (phellem) outward and phelloderm inward with the Cork (Phellem) provides a protective layer that prevents water loss and provides insulation
• Phelloderm is an inner layer supporting the cork cambium

Ground Tissue System:

• Constitutes the majority of the plant body and functions for Photosynthesis, storage, and structural support
• Parenchyma are living cells at maturity performing metabolic activities like photosynthesis, food storage, and regeneration
• Wound healing and organ regeneration occurs due to their ability to divide
• Subtypes: Chlorenchyma contains chloroplasts for photosynthesis
• Aerenchyma: contains large air spaces for gas exchange
• Collenchyma are living cells with unevenly thickened walls, providing flexible support Found in young stems and Angular, Lamellar & Lacunar
• Sclerenchyma are non-live cells with thick, Lignified secondary walls that provide strength and support to mature plant parts

Functions of Types:

• Fibers are long slender cells occurring in bundles (e.g, hemp, flax) while Sclereids are Short, irregularly shaped cells, present in seed coats & nut shells
• Vascular Tissue System is specialized for the transport of water, nutrients, and food that secondarily provide structural support

Composition:

• Xylem functions in conducting water and dissolved minerals with Principal cells: Tracheids and vessel elements (Hollow, non-living cells)
• Addition cells: Parenchyma and sclerenchyma
• Phloem functions to transport food (mainly sucrose) with Principal components: Sieve tubes and companion cells
• Additional Phloem fibers and parenchyma

Plant Cell:

• Protoplasm is the living content of the cell, consisting of The Nucleus & The Cytoplasm
• Nucleus: the control center for cell functions while 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 polysaccharide formed by thousands of glucose molecules.

Growth:

• A growing plant cell secretes a thin primary cell wall that stretches as the cell enlarges
• When growth ceases, additional layers called the secondary cell wall develop, which have a different chemical composition and enhance strength

Types of Permanent Tissue: Ground, Vascular, and Secretory

• Secretory Tissue contains resins, oils and mucilage.
• Specialized cells for production and secretion of substances like resins, oils, and mucilage and those types include internal and external

Tissues:

• Internal Secretory Tissues include Resin & Oil Vessels (Ducts surrounded by epithelial cells secreting essential oils and resins found in citrus plants) and is formed through a process called Lysigeny (dissolving cells)
• Laticifers: Cells or series of cells containing latex (a characteristic fluid)
• External Secretory Tissues include Hydathodes (found in aquatic plants) and Digestive glands, found in insectioverious plants) & Nectaries (found in flowers)
• The rhizosphere is the thin soil region surrounding a plant’s root hair where interactions occur between roots and microorganisms
• It consists of three zones, defined by their proximity to the root: Endorhizosphere, Rhizoplane, and Ectorhizosphere

Layers of Rhizosphere:

• Endorhizosphere includes the cortex and endodermis, where microbes occupy free spaces between cells
• Rhizoplane is adjacent to the root, including the epidermis and mucilage
• Ectorhizosphere is the outermost zone extending into bulk soil
• Root Exudates are a broad term including mucilages and soluble compounds and polysaccharide-rich, viscoelastic gels with adhesive properties
• Rhizodeposits are substances imparted by roots to the surrounding soil

Components of Rhizodeposits:

• Loss of cap and border cells
• Loss of soluble root exudates & volatile organic carbon and carbon to symbionts as well as due to death

Carbon Released:

• Internal Secretory tissues which influences chemical, physical, and biological processes
• Roots release 10-250mg of carbon per gram of root with its organic forms influencing chemical, physical, and biological processes in the rhizosphere
• The composition and amount of compounds released depend on different factors

Factors of Plant type:

• Climatic conditions & nutrient deficiencies or toxicities
• Root hairs are found a few centimeters back from root tips and Absorbs water and nutrients,
• Die after about 3 weeks, creating a compost-like environment

Microbe-Plant Relationships In The Rhizosphere:

• Higher root carbon release leads to microbial competition
• Rhizobia Bacteria: Convert atmospheric nitrogen (N₂) to nitrate, residing in root nodules of legumes
• Mycorrhizal Fungi: Symbiotic association between soil and fungi of two types: Ectomycorrhiza and Endomycorrhiza
• Plant Growth-Promoting Rhizobacteria: Bacteria colonizing roots to enhance growth

Future Cropping Systems:

• Plant-based human food include, Wheat, rice, maize & soybean providing Providing over 50% of plant-based human food while Current crops rely on long-distance transportation to markets
• The vulnerability of supply chains raise the need for resilient supply that that can feed diverse populations while dealing with climate change
• Needs for sustainable agriculture include alternative aquaculture feeds (fish instead of plants) that can utilize locally sourced feeds to avoid major crops Thousands of underutilized plants have potential as future crops

Requirements for Future:

• Research to integrate field studies, lab experiments, community practice
• Need to diversify and develop crops with minimal input
• Developing crops that can thrive on poors soils as well as promoting local diets
• Connection between knowledge networks and foster connections betweek commmunities for more collaboration.

Improve Crops:

• Boost natural ecosystems' ability to fix carbon by enhanceing Yielding & tolerance of crops.
• Develop regenerative crops and chemicals derived from medicinal plants
• Carbon Fixation: ability to fix carbon to support environmental sustainability

Overview of plant growth focusing on irreversible size increase and structural changes during its life cycle. Includes seed germination, seedling development, adult plant formation and apical meristem. Covers morphogenesis and cell specialization.