Plant Growth and Development

Growth and Development

• An organism transforms from a fertilized egg to an adult during its life cycle.
• Development involves various changes with growth being the most noticeable
• Embryonic development refers to the progressive changes before an organism reaches its adult stage.
• Growth constitutes a permanent and irreversible increase in size as an organism matures.

Growth and Development in Plants

• Plant growth and development encompasses cell division, elongation, and differentiation into tissues and organs.
• Growth is an irreversible size increase
• Development follows a programmed sequence from simple to complex.
• Cellular differentiation of structure and function happens as development progresses.

Open Growth

• Plants exhibit a growth pattern considered open growth, throughout its life.
• New organs such as branches, leaves, and roots are added, enlarging from root and shoot tips.
• Growth rate varies across the plant body; it starts slow, accelerates, peaks, and then decelerates.
• In vascular plants, growth occurs via meristems, young tissues with the potential to divide.
• Lower plants can grow throughout, but growth in higher plants is limited to growing points, which are groups of dividing cells called meristems.
• Meristematic cells are located in stems and roots.

Apical Meristems

• Located at the tips of roots and shoots, apical meristems extend the plant body.
• They are perpetual growth zones at root and stem apices.
• They increase cell number at root and stem tips
• Apical meristems are essential for primary growth

Intercalary Meristems

• These are the parts of apical meristem that separate from the apex by permanent tissues.
• Intercalary meristems are located at the base of internodes in numerous plants.
• Intercalary meristems produce leaves and flowers.
• Intercalary Meristems are temporary

Lateral Meristems

• Lateral meristems consist of dividing cells in a cylindrical structure.
• Found in dicots and gymnosperms, examples includes vascular and cork cambium
• Lateral meristems increase stem and root diameter and enable secondary growth.
• Determinate meristems, like those in leaves, flowers, and fruits, grow to a certain size and stop.
• Indeterminate meristems replenish themselves, keeping stems and roots youthful.

Types of Growth

• Primary Growth involves addition of primary tissue by the apical meristem
• Secondary Growth entails adding secondary tissue through intercalary or vascular cambium, increasing thickness.

Phases of Growth

• Multicellular plant growth includes cell division, elongation, maturation, and differentiation.
• Cell division via mitosis increases cell number at root and shoot tips.
• Cells are small, with spherical nuclei and are non-vacuolated
• Daughter cells enlarge and synthesize cytoplasm and cell wall material.

Zone of Elongation

• The zone of elongation is a short distance from the apex of root and shoot.
• Cell volume increases up to 150 times due to water uptake
• The cell wall's plasticity increases and the wall pressure reduces
• New cytoplasm and cell wall material are synthesized.

Maturation

• During maturation the final size of a cell is achieved
• Cells developing into pith, cortex and other tissues do not elongate further along the axis
• Fibers and tracheids elongate lengthwise.

Differentiation

• During differentiation cell enlargement ceases, the cell walls thicken and become pitted
• Thickening appears on the walls of xylem vessels
• Cells of various tissues exhibit differences in spatial dimensions
• New structural features develop

Conditions of Growth

• Growth rate depends on external factors like temperature, light, oxygen, carbon dioxide, water and nutrition
• Internal factors that influence growth include hormones and vitamins.

External Factors Affecting Growth

• Temperature affects the growth rate within 0-35°C.
• Growth rate normally goes up with temperature increasing, and goes down when temperature decreases.
• Optimum temperature is 25-30°C with minimum growth at 5-10°C.
• Growth stops and the plant may die at very high temperatures (35-40°C).
• Light is a key role in plant growth as light is absorbed during photosynthesis
• Light affects growth by intensity, quality and duration.
• Higher light intensity increases cell divisions.
• Red light enhances cell elongation
• Blue light enhances cell division
• Blue light retards cell enlargement
• Ultraviolet rays also retard cell elongation.
• Duration of light impacts the growth of vegetative and reproductive structures
• Duration of light can induce or suppress flowering called photoperiodism.
• Oxygen is needed regularly for growth, because without it metabolic activity wont occur.
• Too much oxygen can inhibit growth.
• Carbon dioxide is needed for photosynthesis, but too much can slow growth.
• Water is necessary for cell elongation, and plant growth ceases without it.
• Nutrition provides energy; increased nutrition boosts growth, while decreased nutrition retards it.

Internal Factors Affecting Growth

• Plant hormones influence growth, such as Indole-3-acetic acid (IAA) that causes cell elongation.
• Vitamins are orgasmic compounds synthesized in the presence of light
• Vitamin deficiencies hinder growth when plants are in the dark

Differentiation

• Post seed germination, a plant's development relies on meristematic tissues.
• Shoot and root apical meristems create all cells of the adult plant.
• Differentiation forms specialized tissues, occurring in five stages:
• Stage 1 is the formation of the embryo.
• Stage 2 involves shoot and root apical meristems within the embryo
• Stage 3 is identifying cambium that is responsible for secondary growth
• Stage 4 involves leaf primordia production from cells becoming leaves, shoots, or roots.
• Pericycle forms root primordia
• Apical meristematic cells directly develop leaf and shoot primordia.
• Stage 5: Fully differentiated tissue forms including xylem, phloem, shoots, leaves and roots

Growth Correlations

• Plant development correlates with growth, organs growing at different rates and the development of parts.
• This relationship is known as correlation.
• Apical dominance is a key correlative effect where the apical bud grows, and lower axillary buds are suppressed.
• Experiments removing the apical bud cause inhibited growth in the lower buds.
• The shoot apex controls lateral bud development.
• Auxin from the terminal bud inhibits lateral bud growth and is known as apical dominance.
• Thimann and Skoog's experiments in 1934 showed apical dominance is caused by auxin inhibiting lateral shoots called inhibitory effect.
• Removing the apex releases lateral buds referred as compensatory effect.
• Cytokinins play a role in apical dominance which allows lateral buds to be released from apical dominance.
• Plants with dense lateral branches exhibit less apical dominance.
• Apical dominance plays a role in tap root development, and inhibits sprouting of lateral buds.
• Applying synthetic auxin prevents eye sprouting and extends storage by one to three years.

Growth and Development in Animals

• Embryology studies growth and differentiation of organisms from a single fertilized egg into a complex being like its parents.
• Development involves sequenced, irreversible steps setting up each subsequent step.
• Similarities exist in animals' development due to evolution.
• Development stages include;
  • Gamete formation: Sperm and egg formation
  • Fertilization: Egg and sperm fuse to form a zygote
  • Cleavage: Zygote divides, and blastomeres form
  • Gastrulation: Germ layers form
  • Organogenesis: Body organs form, and cells interact and differentiate
  • Growth: Organs increase in size to develop adult body form

Chick Development

• Chick development serves as a basic model for organ system differentiation and body formation in vertebrates.
• The chick egg (yolk) is surrounded by coverings from the female reproductive tract
• Fertilization is internal and happens when the ovum enters the oviduct.
• The shell is secreted as the egg goes through the shell gland (uterus).
• Development is paused once the egg is laid unless the temperature reaches the mother's body temperature
• Artificial incubation requires temperatures between 36-38°C, to complete development of a chick at twenty-one days

Cleavage

• After fertilization, the egg goes through mitotic divisions known as cleavage.
• In bird eggs, cell division is isolated to the protoplasm disc on the yolk's surface at the animal pole.
• It is commonly called discoidal cleavage
• Cleavage furrows start in cytoplasmic region
• The first two cleavage planes are vertical
• The third plane is horizontally parallel to the surface and thus cuts cytoplasm and separates from the yolk
• Successive cleavages are irregular, and cell number increases.

Morula

• Cleavage forms a packed mass of blastomeres called morula.
• It is is a disc of cells two or more layers in thickness (blastoderm) lying near the yolk.
• Smaller and defined cells exist in the center of the blastoderm
• Cells are flattened are larger those at the periphery.

Blastula

• The morula stage is short lived which changes into blastula characterized by segmentation cavity/blastocoele.
• Blastoderm: discoidal cap of cells above the blastocoele.
• Zone of junction: marginal blastoderm area with cells adhered to the yolk.

Gastrulation

• Gastrulation is cell movement and rearrangement in the embryo
• Blastoderm divides into two layers: epiblast (upper layer) and hypoblast (lower layer).
• The epiblast forms presumptive ectoderm and mesoderm
• the hypoblast forms presumptive endoderm
• Hypoblast cells grow over the yolk surface to form the endodermal lining of the yolk sac.
• Central blastoderm cells separate from the yolk and form a pool of fluid
• Area translucida is the translucent appearance
• Area opaca is the peripheral part of the blastoderm attached to the yolk, which transmits lights
• Presumptive mesoderm and ectoderm are in the upper blastoderm layer.

Notochord and Mesoderm Formation

• The mesodermal cells of the chick migrate medially and caudally from both sides
• This create primitive streak, a midline thickening.
• More and more presumptive mesodermal cells gather, the blastoderm’s shape goes from circle to pear.
• The primitive streak's anterior end forms the primitive node, or notochordal cells, and the remainders are mesodermal cells.
• Thus, the primitive streak represents the dorsal and lateral lips of the blastopore.
• Migration of cells occurs between the epiblast and hypoblast
• This form the primitive groove
• The primitive groove is marked by the primitive ridges.

Hensen’s Node

• Closely packed cells form a local thickening called Hensen's node at the cephalic end of the primative streak
• Hensen's node is the site of invagination.
• Cells push in from Hensen's node region to form the notochord that is shaped like a rod beneath the ectoderm
• The notochord is a structural feature for a chick embryo of about 18 hours
• Ectoderm spreads and organizes into cells merging with the yolk and the marginal area that is called the germ wall.
• The cavity between yolk and endoderm now termed the primitive gut was called gastrocoele.
• Dorsal mesoderm and somites form from Hensen's node.
• The lateral plate mesoderm is split into somatic/splanchnic mesoderm
• Coelom is between somatic and splanchnic mesoderm
• Somites are seen in 25-26-hour embryos
• Somites are compact cell masses near neural folds.

Neurulation

• The presumptive neural ectoderm are on the dorsal surface of the gastrula
• As gastrula elongates, the band thickens to form a neural plate.
• Neural plate shows as a thickened ectoderm in 18-hour chicks
• Neural groove happens from longitudinal folding in 21–22-hour embryos
• Neural plate folding is seen in 24-hour embryos
• The anterior end forms the future brain
• The remainder forms the spinal cord.
• Neural plates sink, the neural folds fuse and convert the neural groove into neural tube
• The cavity enclosed is known as neurocoel
• There are anterior/posterior neuro-pores at each end, which later close.

Development Mechanisms

• From a single zygote cell, a multicellular person is created
• The zygote has genome with form of chromosomes from the eggs and sperms.
• During cleavage, the zygote divides into many cells with full instructions from the parents.
• Some genes are active and some switch off during differentiation.
• The nucleus and cytoplasm shows the importance during development
  • Experiments:
  • Hans Dietrisch shook and broke apart a sea urchin egg at the two-cell stage in 1892
  • Both half embryos developed into normal larvae
  • Conclusion: Both cells had the original zygote's genetic data
  • Spemann divided the salamander zygote into two with human hair
  • One half had nucleus and other had not nucleus
  • Cleavage only completed in the nucleated half
  • the nucleated side reached a 16-cell stage
  • Cleavage nuclei crossed narrow cytoplasmic bridge to the anucleate side
  • Immediately this side started to divide.
  • Spemann again separated embryo halves; both had nuclei
  • He seperated the two halves of embryo and both them developed into complete embryos
  • Even separating from a 16-cell embryo, a single cell can form a full embryo.
  • Nucleated halves sometime develop into abnormal ball of cells.

Gray Crescent

• Development is reliant of the gray crescent's position
• Gray crescent lacks pigment
• If gray crescent absent, then no further development takes place'

Spemann's Conclusions

i) All cells have the same nuclear data. ii) Cytoplasm in the gray crescent contains data needed for development

Further Differentiation

• All cells have identical nuclear material, so what causes the cells to differentiate and become fully developed?
• Cells undergo differentiate and become committed to determinative molecules in two ways:

1. During cleavage, cytoplasmic segregation of determinative takes place.
2. Induction/interaction takes place with neighboring cells.

Cytoplasmic Role in Development

• Cytoplasmic parts have morphogenetic determinants that differentiate cells.
• Determinants are present in blastomeres.
• cytoplasm of ascidian fertilized egg contains cytoplasm of five colours that are segregated into different blastomeres Clear cytoplasm produces larval epidermis. Yellow cytoplasm produces muscle cells. Gray vegetal cytoplasm produces gut. Grey equatorial cytoplasm produces notochord and neural tube.

Nucleus's Role in Development

• Gene controlled substances can be recognized in cytoplasm
• Through experiment, nucleus produces active substances in some cases.
• An the algae named Acetabularia has a rhizoid attached to the ground from which has a long stalk with an umbrella shaped cap at its top.
• Two species, Acetabularia mediterranea(regular shaped cap) and A. crenulata (irregular shaped cap) were identified.
• Haemmerling showed that new one regenerated if the cap removed.
• He harvested nucleus containing rhizome from an alga of species A. mediterranea
• He the grafted in piece containing nucleus of another species named A. crenulata.
• The newly regenerated cap was removed, it will contain A. crenulata's character.
• Alga's nucleus determined cap structure
• Cytoplasm genes express according to nucleus type

Conclusions:

• Gene and cytoplasm play role in development
• Nucleus contains all data for an individual's characteristics
• Cytoplasm select data

Differentiation Concept:

• Fertilized egg has unequally distributed cytoplasmic parts
• These cytoplasmic parts have morphogenetic determinants that control the functioning of a specific cell type
• Differentiation contains complete data for development an individual.

Spemann's experiments on amphibian embryo

• Piece of ectoderm from frog’s embryo was grown in separate dish.
• The frog unable formed normal nervous system but had defective nervous system
• Isolated piece would not developed
• Separated flap of ectoderm from the mesoderm
• The frog did not develop system
• Mesoderm does effect the ectoderm
• Simulating the ectoderm cells can stimulate nervous system.

Embryonic Induction:

• Some cells are capable to evoke in other a development reponse
• Work was reported by Hans Spemann in 1924
• Two embryos of salamander was taken at the gastrula stage
• They removed a piece of dorsal blastopore lip of one the embryos
• The piece was transplanted to a ventral area of a salamandar gastrula.
• The developing embryo contained induced tissue with grafted tissue
• It seen that balstopore induced embryo development
• Spemann called the dorsal lip area, the primary organizer for its ability to undergo secondary embryo development

Aging:

• Aging is process that is inevitable
• Aging has negative physiological changes in the body
• Signs of old age are loss of hair, pigmented areas in the skin, agility and fat
• Conditions are loss of poor vision, weakness and forgetfulness
• immunity is decreased

Degeneration

• Organ and tissue degeneration takes place
• For example, cartilage degenration is in joins
• Elastic tissues disappear from the tunicia media
• Resulting in artiosclerosis
• Coronary arteries consist of blood clotting

Aging Process

• The aging is unknown
• Cells have specific division
• Deterioration affects the memory Intracelluar changes take aging
• Collagen acquires protein while dense tissues and cartilage are lost.
• Mutation lead to tsues degeneration
• Aging can be slowed from nutrition or life expecatancy e.g abstinance from smoking
• Gerontology study of aging
• By the time for half century 14.5millon age has a increase compared to 8millon
• Age of 80 has a increase of 12millio. compared to 5milion
• The human life has a increased to 125 year
• The objective the aging is to increase to more heatlhspan

Regenration

• There is ability restore or regain injured body part.
• Sponges great great regeneration abilities
• Sponges can replace parts or grow new body.
• The regeneration process has a slow or may takes years
• As example lobster can pincer that are losse, they can regenerate
• Starfish can break arm or can separate devloping each individual
• Earthworm or head can be regenerated
• Amphians can regenerated mosty as they are small and yong
• Amphian limb are eaisyli regenerated
• Lizard can easy discard tail
• Freature and repair wounds help the regenerat

Plants Relation

• Regeneration is an basis of plant propagation
• Most parts develop into new or a single cell to dvelp a new plat
• Some part form soil may take many plants for new pant

Process of regeneration

• Type of cell develop for missig parts are replaced by the differertion of cells
• As example flatworm cells or neoblasts that in planira are mobilived and differntiate in amputation parts
• Another organism example are Newt can some some tissure cells are amputated
• Afterwords they proceed in same and differnt cell

ABORMAL DEVELOPMENT

• some parts can show abnormal devolpments
• Tertaogy is study of bilogy
• abormal devlopemt as result abnormal factors
• Abormalites and devlopments are des turbed or gen -Factors of enviroment and defect
• abormal or defect genes
• develpmet or also affect for sex chormosmes -examplee heampohlla they only affect to men
• the domiant gene and how genes are domiant or recieves
• Chromsomoal defect affect one of the chomrmosmes As results they can affect sunydormes Example of Kline feters syndrom or trisomy sect
• Example of Tumer they are most in which one sex chormosme misssing
• condtions the tallness and aggerivenes
• Enviroment factos are contribue of abnormalites As tetragions as Example x rays
• Because that some effect the develoemts are change due to mutaions
• nutriton defenies
• The absene of vitaime can the the defenites may killed the cells