Angiosperm Gametophyte and Embryo Development

• Angiosperms have an alternation of life cycle with gametophyte and sporophyte stages

Female Gametophyte

• Develops within the ovule, surrounded by two integuments to form the seed coat
• The megasporangium undergoes meiosis to produce 4 haploid megaspores
• One megaspore survives and undergoes mitosis without cytokinesis, forming a cell with 8 nuclei

Male Gametophyte

• Pollen sacs develop in the anther within the microsporangium
• Microsporocytes undergo meiosis, forming 4 haploid microspores and creating male gametophytes

Embryo Development

• The zygote's initial mitotic division results in a basal cell and a terminal cell
• The basal cell develops into the suspensor, transferring nutrients and anchoring the embryo
• The terminal cell forms the early embryo, connected to the suspensor, where cotyledons begin to form
• Cotyledons form and the embryo elongates
• The shoot apex exists between cotyledons and the root apex is where the proto embryo attaches to suspensor
• Apical stems at the root and shoot are necessary for primary growth

Mature Seed Structure

• During maturation, the seed dehydrates and enters dormancy
• The embryo and its food supply are enclosed by a hard seed coat formed from the integuments
• Cotyledons store food from the endosperm before germination
• The embryonic axis below the cotyledon attachment point is called the hypocotyl, which terminates at the radicle
• The epicotyl is located below the miniature seeds, collectively called the plumule
• Thin cotyledons store nutrients in the endosperm
• Thick cotyledons absorb nutrients from the endosperm
• Cotyledons in monocots are shield-shaped, specialized, and called the scutellum, pressing against the endosperm for nutrient absorption

Seed Dormancy

• Seed dormancy depends on imbibition, which is the water uptake due to low water potential in the dry seed
• Seed dormancy causes a change for the embryo and the resumption of growth
• Enzymes digest storage material, providing nutrients to growing regions of the embryo
• The radicle emerges initially, establishing roots that anchor the plant before the shoot breaks through the soil

Germination

• In many eudicots, a hook forms from the hypocotyl to push the plant through the soil
• Light exposure causes the hook to straighten and the shoot tip to rise
• In monocots, shoots grow straight through the coleoptile

Reproduction

• Fragmentation is the separation of a parent plant to create multiple plants, a common type of asexual reproduction
• Apomixis is asexual reproduction from a diploid cell without pollination and there is no need for sperm
• Vegetative reproduction, arising from vegetative fragments and often stronger than seedlings, is beneficial in a environment
• Angiosperms have mechanisms to avoid self-fertilization and ensure genetic diversity
• Dioecious plants cannot self-fertilize due to lacking stamens or carpels, needing a separate individual
• Self-incompatibility exists where plants can reject pollen from themselves or closely related individuals using a biochemical block

Totipotent Cells

• Totipotent cells can divide and asexually generate a clone of the parent

Vegetative Propagation

• Vegetative propagation is vegetative reproduction which is assisted by humans
• Callus is the mass of dividing & undifferentiated cells that form where the stem is cut and forms adventitious roots
• The stock is the plant that provides the roots
• The scion is the bud/twig grafted onto the stock

Transgenic Species

• Transgenic species are genetically modified to express a gene from another species

Biofuels

• Biofuels are an energy source derived from burning biomass
• Biofuels can be produced by rapidly growing crops for rapid regeneration

Plant Adaptations

• Etiolation includes morphological adaptations while growing in the dark
• Etiolation involves unexpanded leaves, short stunted roots, pale stems, and not needing an extensive root system with unexpanded leaves
• Detiolation involves greening and expanded leaves
• Detiolation activates enzymes for photosynthetic processes and supplies chemical precursors for chlorophyll

Auxin

• It plays a key role in phototropism
• Auxin stimulates proton pumps in the plasma membrane
• Auxin stimulates stem elongation, fruit development, gravitropism, and lateral root formation
• Proton pumps lower the pH in the cell wall, activating expansins to loosen the wall and allow elongation
• It promotes leaf arrangement
• It stimulates adventitious root formation and is used in vegetative propagation
• An overdose of auxin leads to ethylene production, which inhibits growth

Adventitious Roots

• Plant roots that form from non-root tissues

Cytokinins

• Cytokinins stimulate cytokinesis
• Cytokinins are produced in actively growing tissues
• Cytokinins are mainly synthesized in roots and are transported to other organs
• Cytokinins stimulate seed germination
• Cytokinins promote lateral bud growth
• Cytokinins work with auxin to control cell division & differentiation
• Cytokinins inhibit protein breakdown, anti-aging, and mobilize nutrients from surrounding tissue

Apical Dominance

• Terminal buds release auxin & cytokinins to suppress lateral bud growth
• Removing the terminal bud makes the plant bushier

Gibberellins

• Gibberellins are for seed germination, stem elongation, and fruit growth
• Auxin & gibberellins should be present for fruit growth
• Gibberellins signals seed germination after water imbibition

Abscisic Acid

• Abscisic acid is used in seed dormancy
• Abscisic acid inhibits growth
• Abscisic acid promotes drought tolerance
• Abscisic acid ensures sees germinate in optimal conditions and prevents early germination
• Abscisic acid rapidly causes stomata to close, increasing drought tolerance

Ethylene

• Ethylene is for ripening, stress, and wound response
• Triple response allows for a growing shoot to avoid obstacles by slowing stem elongation, thickening the stem, and horizontal growth
• A burst of ethylene is associated with apoptosis
• Ethylene is for fruit ripening
• Ethylene is for senescence and programmed cell death of organs

Brassinosteroids

• Brassinosteroids are chemically similar molecules to animal sex hormones
• Brassinosteroids stimulate cell elongation & division in stem segments
• Brassinosteroids promote xylem differentiation and leaf abscission

Photomorphogenesis

• Phytochromes regulate the plant's response to light
• Red light increases germination, while far-red light inhibits germination
• Pfr induces vertical growth, while Pr inhibits vertical growth

Photoperiodism

• Short-day plants flower when the light period is shorter than a critical length, they do not flower if exposed to light during the dark.
• Long-day plants flower when the light period is longer than a critical length and are unaffected when exposed to light during dark period
• Vernalization is the pretreatment with cold to induce flowering

Gravitropism

• Plants can detect gravity using statoliths
• Roots show positive gravitropism, and shoots show negative gravitropism

Thigmotropism

• Thigmotropism is the growth related response to touch
• Thigmotropism occurs in climbing plants

Action Potential

• Action potential involves rapid leaf movement in response to mechanical stimulation
• Action potential is the transmissions of electrical pulses

Flooding

• Flooding leads to enzymatic destruction of root cortex cells to create air tubes for plant survival through oxygen deprivation

Salt Stress

• Salt stress reduces water uptake
• Plants respond by producing solutes tolerated at high concentrations
• Plants keep the water potential of the cell more negative than the soil

Heat Stress

• Heat stress denatures plant enzymes
• Heat shock proteins protect other proteins from heat stress
• Transpiration helps with cooling

Defense System

• Pathogens can enter through openings like the stomata
• The epidermis & periderm are the first line of defense

Plant Hormores

• Auxin: primary growth
• Cytokinins: Stimulates mitosis for growth, Regulates cell differentiation, and affects how quickly/slowly plants age
• Gibberellins: Found in reproductive parts, Causes flowers to mature, and Makes food bigger
• Abscisic acid: Accumulates when plants are exposed to stressful conditions and Conserves resources through dormancy
• Ethylene: Regulates fruits & flowers and Volatile gas, released by maturing plants