Plant Growth and Development: BIOL 257

BIOL 257: Plant Growth and Development

Course Outline

• Several key processes in plant biology, including growth, growth kinetics, cellular differentiation, morphogenesis, development, and phyllotaxis, will be defined and explored.
• Factors influencing plant growth and development, specifically soil, light, and gravity, will be investigated.
• Plant hormones modulate growth and development in plants.

Course Outline Continued

• Seed types, structures, longevity, dormancy, germination, and quiescence will be examined.
• Phytochrome is a key element.
• Topics such as tissue culture, apical dominance, abscission, and root initiation will be explored.
• Hormone and other herbicides are important factors.
• The study of fruit formation, and parthenocarpy is neccessary.

Course Objectives

• A major objective is to differentiate between the concepts of growth and development in plants.
• Understanding that plant growth and development occur in specific locations.
• Understanding the roles of hormones and environmental factors impacting plant roots, leaves and flowers is critical.

Course Objectives Continued

• Distinguishing between various types of plant movements, including geotropism, phototropism, nastic movement, and turgor is important.
• Ability to differentiate between short-day, long-day, and day-neutral plants is also required.
• Grasping the meaning of abscission and senescence is key.

Reading Materials

• The textbooks Plant Physiology by Frank B. Salisbury and Cleon W. Ross, and Plant Growth and Development-Hormones and Development by Lalit M. Srivastava are recommended
• A variety of websites contain relevant information.

Growth and Development in Plants

• Observation of a seed growing into a mature plant capable of producing flowers and fruit exemplifies growth and development in plants.
• Growth in plants arises from cell division, increasing the number of cells, leading to increased weight, size, and volume.
• Growth is defined by an irreversible increase in the number and size of a cell, organ, or the entire organism.
• Growth rate varies depending on the plants stage of maturity.
• The changes an organism undergoes from its start to its death is called development.

Growth and Development in Plants Continued

• Development encompasses morphogenesis and differentiation.
• Morphogenesis refers to the shaping and structuring of an organism.
• Differentiation involves changes in cells, tissues, or organs to perform specific functions.
• Development includes qualitative and quantitative changes such as growth, differentiation, and maturation throughout an organism's life cycle.

Stages of Cellular Growth

• Organismal growth is always linked to an increase in cell size and cell number.
• Organ or organism growth happens successively in in three stages
• Cell division: the number of cells increases thanks to mitosis.
• Cell enlargement: individual cells increase in size after cell division due to increased protoplasm volume.
• Cell differentiation: cell structure changes to perform specific functions.
• Tissues are created when similar cells with the same function come togehter.

Growth Location

• Entire bodies of lower organisms like algae and bacteria grow.
• Growth is restricted to specific regions in higher organisms like pines, flowering plants and ferns.
• Growth happens at the shoot apex and close to the lateral sides of the body.
• Elongation happens at the tips and lateral growth impacts the thickness of the stem and root tips.

Growth Curve

• The rate of growth varies through the lifespan of a plant or plant part.
• The increase in cell number plotted against the time creates an S-shaped sigmoid growth curve.

Growth Curve Phases

• Lag Phase: The initial phase of slow growth.
• Log Phase: A period of rapid growth, which is the max for the life.
• Stationary Phase: Growth decreases and then halts.
• External and internal factors influence plant growth.

External Growth Factors

• External factors in the environment affect a plant directly or indirectly.
• These factors include light, temperature, water, and mineral nutrients.

External Growth Factors Continued

• Light is essential for photosynthesis, seed germination, growth of seedlings, tissue differentiation and reproduction.
• Plants grown in darkness tend to become tall, yellowish, and weak with small leaves.
• Plants have different temp requirements depending on whether they grow in cold or hot climates.
• For growth of plants, the optimum temperature is 28-30°C though it can happen from 4-45°C.
• Metabolic activity of plants are directly affected by temp variation.
• Plant injuries can be caused by very low temperatures because of chilling and freezing.
• A plant's growth may be haulted by very high temperatures.
• Water absorbtion happen through roots.
• Water is used for photosynthesis and other biochemical processes, and is released through transpiration.
• Plant growth depends on adequate water.
• Nutrient deficiencies and excesses are bad for plants.
• All metabolic processes in plants need inorganic nutrients.
• Deficiency of nutrients may adversely affect plant growth.

Internal Growth Factors

• Plant growth is affected by internal substances made in the plant itself.
• Plant hormones, phytohormones, or growth hormones, are those substances.
• A plant hormone is an organic substance produced in small quantities in one area and transported to other areas to influence growth.
• Synthetic chemicals, or growth regulators, that mimic plant hormones influence plant growth.
• Growth regulators are chemical substances, not naturally produced hormones, that modify or affect growth or development of plants.
• Five Major Classes- naturally produced growth hormones are broadly classified under five major sections.

Internal Growth Factors Continued

• Auxins, gibberellins/gibberellic acid, cytokinins, ethylene, and abscisic acids are examples of plant growth hormones.

Auxins

• Auxin is a growth promoter, generally produced by the growing apex of stems and roots.
• It facilitates shoot and root elongation behind apical meristems.
• The naturally produced auxin is Indole-3-Acetic Acid (IAA).

Auxins Continued

• Chemical synthesis can produce auxins with similar physiological effects of naturally created auxins.
• Examples of synthetic auxins include Indole-3-butyric acid (IBA), 2,4-Dichlorophenoxy acetic acid (2,4-D), and Naphthalene acetic acid (NAA).
• Auxein comes from the Greek word that means "to grow".
• Auxin was frist isolated from Urine.
• Fritz Went did an experiment to see the effects of auxins on oat seedlings.
• Growth stops when an oat coleoptile tip is removed from an early shoot.
• The removed tip goes on a block of agar for about an hour.
• This agar block is then placed on the cut end of the seedling.
• The seedling began to grow which demonstrated that something helps to re-start the plant growth.

Auxin's Functions

• Auxin promotes cell elongation.
• It suppresses growth of lateral buds.
• When the tip of a plant is removed the lateral branches can grow.
• Apical dominance occurs when an apical bud suppresses the growth of lateral buds in most plants.

Auxin Continued Functions

• Auxin delays leaf abscission (leaf fall).
• NAA (Naphthalene acetic acid) is used to prevent fruit drop in apples before they ripen.
• The herbicide weedicide 2, 4-D (2, 4-dichlorophenoxy acetic acid) acts on dicots.

Gibberellins

• Gibberellin, or Gibberellic Acid (GA), was first isolated from the fungus Gibberella fujikuroi.
• These are produced in young leaves roots, and embryos to enhance growth.
• Gibberellins helps in elongation of stems in genetically dwarf plants
• Dwarf plants can increase height by using gibberellins.
• Gibberellins break seed and bud dormancy and also induces parthenocarpy to support seedless fruit production.

Cytokinins

• Cytokinins can be extracted from coconut milk and are synthesized in the root apex, endosperm of seeds, and young fruits.
• Cytokinins encourage cell division.

Cytokinins Functions

• Cytokinins stimulate cell division, cell enlargement, and cell differentiation.
• They also prevent aging of plant parts.
• Also inhibit apical dominance and help in growth of lateral buds into branches

Ethylene

• Ethylene is a gaseous hormone found in ripening fruits, young flowers, and young leaves.
• Ethylene promotes ripening of fruits.
• Also promotes senescence and abscission of leaves and flowers.
• Ethylene increases cell width not length.

Abscissic Acid

• Abscissic acid, also known as Dormin, naturally occurs as a growth inhibitor found in a wide variety of plants and is synthesized in the leaves.
• It is unlike Gibberellin because Abscissic acid induces dormancy of seeds and buds.
• It also promotes senescence of leaves which makes them fall due to the abscissic acid.
• Abscissic acid causes stomata to close and inhibits seed germination and development.

Practical Growth Regulators Applications

• Growth regulators can be used to stimulate, inhibit and modify growth and development in plants.
• Horticulturists can widely use their production.
• Applications of growth regulators help in seed germination with auxins.
• Potato and onion germination during storage is prevented by growth inhibitors.