Plant Growth and Development Colloquium

Plant Growth, Development and Reproduction

• Dr. Luz O. Moreno presented a colloquium on plant growth, development, and reproduction, at the Visayas State University.
• The colloquium was held in 2024, at Visca, Baybay, Leyte.
• Growth and development are coordinated events, starting with germination, followed by vegetative growth, and then the reproductive phase.

How Plants Grow

• Plant growth involves several stages:
  • Seed stage: Seeds are ready to grow
  • Germination: Seeds absorb water and nutrients; roots grow and shoot grows towards the sky, breaking through the ground.
  • Sprouting: Formation of shoot, called a sprout.
  • Pollination: One way plants reproduce
  • Dissemination: Seeds are scattered or dispersed by wind, water, animals, or other forces.
• Growth and development consist of complete, coordinated events.

Growth

• Growth is a process that results in an irreversible increase in size.
• Types of plant growth:
  • Primary growth: Results from the activity of primary meristems, such as apical meristems (e g. tips of roots and shoots).
  • Secondary growth: Results from the activity of secondary meristems, like the vascular cambium, leading to an increase in diameter.
• Usually expressed as dry weight (including grain, height, length, and diameter) with increase in cell numbers through cell division as well as cell size increase in a process called indeterminate growth.
• Plants have this because meristems help them add new tissues and organs as long as they are alive.

Development

• Development encompasses changes throughout the life cycle of an organism (zygote → embryo → mature organism).
• This involves all changes from the beginning to the end of the organism's life cycle.

Differentiation and Organization

• Differentiation is a crucial process where unspecialized cells become specialized cells with unique forms and functions.
• Organization involves the proper placement and integration of differentiated cells, leading to the overall form and structure of the plant organism.

Growth Stages

• Embryogenesis: Development of the embryo from the zygote.
• Vegetative development: Includes:
  • Seed germination to photosynthetic plant.
  • Plant vegetative development (growth of stems, leaves, roots).
• Reproductive development: Includes flowering, pollination, and fertilization.

Phases of Vegetative Stage

• Juvenile stage: From germination to the start of transition.
• Transition stage: Loss of juvenile characteristics gradually and acquisition of the adult characteristics.
• Adult stage: Plant is capable of flowering, responses to stimuli.

Nature of Plant Growth

• Increase in size
  • Cell division
  • Cell enlargement
  • Change in cell density
• Distribution of growth is not uniform.
• Growth centers, such as meristems (production of new cells) and regions of cell enlargement.

Growth Stages

• Embryogenesis
• Vegetative development
• Reproductive develepment

Phases of vegetative

• Juvenile stage
• Transition phase
• Adult plant

Plant Growth Regulators

• Hormones: Substances other than nutrients made by plants – modify/control growth either quantitatively or qualitatively.
• Responses need not be promotive but can also be inhibitory.
• Usually translocated from production sites to action sites.
• Can be effective in minute concentrations.
• Hormones regulate development and plant responses.
• Plant hormones influence plant defense & signaling pathways.
• Hormone effects depend on hormone amount & tissue sensitivity.

Plant Hormones (PGRs)

• Auxins – promote cell elongation.
• Gibberellins – promote cell elongation and division (translated into growth).
• Cytokinins – promote cell division and inhibit senescence.
• Abscisic acid – promote leaf and fruit abscission & dormancy induction of buds and seeds.
• Ethylene - promotes senescence, epinasty, and fruit ripening.
• Other Identified Plant Growth Regulators:
  • Brassinosteroids
  • Salicylic acid
  • Jasmonates
  • Plant peptide hormones
  • Polyamines
  • Nitric oxide
  • Strigolactones
  • Karrikins

Plant Hormones: Classification

• Two major classes:
  • Promoters (auxins, cytokinins, gibberellins, brassinosteroids): Cause faster growth
  • Inhibitors (ethylene, abscisic acid, jasmonic acid): Reduce growth

Two Hormones Affect Plant Differentiation

• Auxin: Stimulates root development
• Cytokinin: Stimulates shoot development
• Ratio of Auxin & Cytokinin determines plant development

Plant Life Processes

• Photosynthesis
• Respiration
• Water absorption and transpiration
• Translocation
• Assimilation

Photosynthesis

• Conversion of light energy into chemical energy.
• Key Processes:
  • Light reactions: Produce ATP & NADPH
  • Calvin cycle: Produces glucose from carbon dioxide.
• Types of photosynthesis:
  • C3: Majority of plants
  • C4: Many grasses and crops
  • CAM: Many succulents.

Factors affecting Photosynthesis (External)

• Light (quality, duration, & intensity): Plants need varying amounts of light.
• CO2 concentration: Higher CO2 levels mean faster photosynthesis.
• Water availability: Impacts the rate of water uptake.
• Temperature: Affects the rate of photosynthesis, with an optimal temperature range.

Factors affecting Photosynthesis (Internal)

• Photosynthetic enzyme systems
• Leaf resistance
• Demand for Ps
• Hormonal regulation
• Genetic control
• Leaf age
• Mineral status

Respiration

• Breakdown of food (glucose) to release energy.
• Occurs in the mitochondria.
• Enzymes control the process.

Cellular Respiration

• Activation of glucose through ATP.
• Glycolysis
• Aerobic (with oxygen present)
• Anaerobic (without oxygen present- fermentation)

Transpiration

• Transpiration is the evaporation of water from plant leaves.
• Controlled by small pores on leaves, called stomata.
• Driven by differences in water potential.
• Includes also guttation which is the loss of water from plants in liquid form.

Water Movement

• Root pressure, capillary action, and transpiration pull (suction pressure).
• Important for transport through xylem cells.

Control of in vitro Culture

• Leaf strip/shoot culture; cytokinin.
• Adventitious shoot / rooting/ root culture; auxin levels.
• Callus development; auxin & cytokinin at equal levels.

General Overview of Role of Plant Hormones in Growth and Development

• Role of hormones varies in the growth stages of the plant from germination to maturity.
  • Gibberellins, Auxin, Cytokinins, Ethylene, ABA; associated with stages of growth.

Sugar Signals Interact with other Signaling Pathways

• Hormones (eg., GA, ABA, ethylene, auxin, cytokinin), metabolic pathways (carbohydrates and nitrogen) Environmental stimuli, and gene regulation all interact to control plant growth and development.

This quiz covers the key concepts discussed in Dr. Luz O. Moreno's colloquium on plant growth, development, and reproduction held at Visayas State University. Explore different stages of plant growth from germination to reproduction and understand the processes involved in a plant's life cycle.