Plants and Colonization of Land

Plants and Colonization of Land

• Introduces the plant kingdom
• Includes vascular and non-vascular plants
• Plants are multicellular, eukaryotic, photosynthetic autotrophs with cellulose cell walls
• Plants are primarily terrestrial, with some secondarily aquatic species.
• Plants have complex bodies adapted for terrestrial life
• Plants possess a waxy cuticle and conduct carbon dioxide + oxygen diffusion through stomata
• Photosynthetic cells contain chlorophyll A and B, along with yellow and orange carotenoid pigments
• Carbohydrates are stored as starch in chloroplasts and plastids.
• Mitosis occurs in all plants through typical phases.
• Generalized view of plant reproduction and life cycle
• Reproduction is primarily sexual, with asexual propagation capabilities in most plants
• Gametes are produced within gametangia, which have protective sterile cell jackets
• All plants have a life cycle with alternating generations of haploid gametophytes and diploid sporophytes
• Sporophyte and gametophyte generations differ morphologically (heterotrophs) in all extant plants.

Colonization of Land

• For the first 3 billion years, the terrestrial surface was lifeless
• Geochemical evidence suggests cyanobacteria existed on land around 1.2 billion years ago
• Plants, fungi, and animals colonized land about 500 million years ago
• Land plants evolved from green algae known as charophyceans, their closest relatives
• Land plants and charophyceans share four key traits
• Land plant and charophycean cells have rosette cellulose-synthesizing complexes
• Both contain peroxisome enzymes that minimize organic product loss due to photorespiration
• Flagellated sperm structure is similar in some land plants and charophyceans
• Phragmoplast formation during cell division is similar in land plants and charophyceans
• Terrestrial adaptations are key to modern land plants (flowering plants)
• First plant evolution stage: plants originated from aquatic charophyta ancestors about 475 million years ago (Ordovician period),
• Early terrestrial adaptations included sporopollenin-toughened spores and jacketed gametangia to protect gametes/embryos
• Vascular tissue evolved relatively early
• Most bryophytes lack vascular tissue, but some have it
• Second major plant evolution period: diversification of vascular plants about 400 million years ago (early Devonian period)
• The earliest vascular plants lack seeds, such as ferns and similar seedless vascular plants
• Third plant evolution period: origin of seeds, advancing land colonization by protecting the plant embryo from desiccation
• First vascular plants with seeds appeared about 350 million years ago (Devonian period)
• Seeds were not enclosed (naked seeds), such as those of gymnosperms
• Fourth major plant evolution episode: emergence of flowering plants during the Mesozoic era (130 million years ago)
• Flowers are complex reproductive structures bearing seeds within protective ovaries
• The majority of modern plants are flowering plants

Plant Kingdom

• Non-vascular plants (bryophytes) are represented by phyla or divisions
• Phylum groupings include Bryophyta (mosses), Hepatophyta (liverworts), and Anthocerophyta (hornworts)
• Bryophyte life cycle is gametophyte-dominated
• Bryophytes have two adaptations for land: a waxy cuticle for water retention
• Gametes develop within gametangia (multichambered organs with sterile jackets to keep gametes moist)
• Male gametes, antheridia, produce flagellated sperm
• Female gametes, archegonia, produce one egg
• Egg fertilization occurs within the archegonium → zygote → embryo
• Bryophytes lack vascular tissue, water moves over the plant's surface through diffusion
• Phylum Bryophytes (mosses) are familiar bryophytes, forming mats
• Plants grip substratum with root-like rhizoids, and photosynthesis occurs in upper parts with leaf-like appendages
• Phylum Hepatophyta (liverworts) are less conspicuous
• Some liverworts have bodies divided into lobes, resembling a lobed liver
• Example: Marchantia species, with gametangia resembling miniature trees and small sporophytes with short stalks
• Phylum Anthocerophyta (hornworts) resemble liverworts but have sporophytes that are elongated capsules that grow like horns

Vascular Plants

• In vascular plants dominant sporophyte versus gametophyte
• The life cycle with a dominant sporophyte generation is larger and more complex
• The gametophyte is reduced even more so through the evolution of seed plants
• Xylem and pholem are the two connecting tissues of the vascular system
• Xylem provides microscopic water pipes with lignified walls for support and water transport
• Phloem is a living tissue of elongated cells arranged into tubes for distribution of sugar, amino acids, and other organic nutrients
• Leaves increase the surface area of vascular plants for capturing more solar energy for photosynthesis
• Earlier plants (lycophytes) have small leaves (microphylls) with a single vein
• Other vascular plants have megaphylls with a highly branched vascular system
• Seedless vascular plants include phylum Lycophyta (club mosses, ground pine), Selaginella (spike mosses), and Isoetes (quillworts)
• Lycopods are among the most primitive vascular plant groups, evolving first during the Devonian period (340-280 million years ago)
• Giant lycopods became extinct when the swamps began to dry out
• Surviving lycopods are represented by 1200 species (Lycopodium and Selaginella)
• Many Lycopodium species are tropical epiphytes
• Phylum Pterophytes include ferns, Equisetum (horsetail), and Psilotum (whisk fern)
• Ferns are widespread seedless vascular plants, with over 12,000 species
• Ferns are most diverse in temperate forests
• Ferns typically have compound leaves called fronds, divided into leaflets
• Fronds grow as coiled tips (fiddleheads) and sprout from a prostrate rhizome
• Large tropical ferns can grow like trees with upright stems, reaching meters in height
• Many fern sporangia are arranged in clusters (sori) equipped with spring-like devices (elaters) for spore dispersal

Seed Vascular Plants

• Seed vascular plants have gametophytes that are even more reduced than in ferns
• Pollination replaced swimming as the mechanism for delivering male gametes (sperms) to female gametes (eggs)
• The seed evolved instead of the zygote developing into a young sporophyte
• Angiosperms have xylem consisting of tracheids and vessel elements
• The zygote of seed plants develops into an embryo, packaged with a food supply within a seed coat.

Gymnosperms

• Gymnosperms include four phyla: Cycadophyta, Ginkgophyta, Gnetophyta, and Coniferophyta
• Phylum Coniferophyta have reproductive structures called cones
• Pines, firs, spruce, larches, junipers, cedars, cypresses, and redwoods belong to Coniferophyta
• There are only 550 conifer species
• Conifers are mostly evergreen with needle-shaped leaves adapted to dry conditions (xerophytes)
• Lumber and paper pulp are mostly obtained from conifer woods
• Phylum Ginkgophyta’s extant species is Ginkgo biloba, characterized by fan-shaped leaves that turn gold in autumn.
• Ginkgo is believed to improve memory
• Phylum Cycadophyta has seeds that develop on reproductive leaves
• Phylum Gnetophyta includes Welwitschia, Gnetum, and Ephedra.

Angiosperms

• Angiosperms are categorized into two classes: monocotyledons (monocots) and dicotyledons (dicots)
• Monocots include grasses, lilies, orchids, palms, lawn grass, sugarcane, and grain crops (corn, wheat, rice)
• Dicots include roses, peas, buttercups, sunflower, oak, maple
• Angiosperms typically use insects and other animals to transfer pollen from male to female plants
• Xylem becomes more specialized for water transport during angiosperm development
• In gymnosperms, xylem consists mainly of tracheids
• A complete flower has sepals (regularly green), petals (brightly colored), stamens (filament and anther), and carpel (pistil: stigma, style, ovary, and ovules)
• Flowering plants (anthophyta) consist of leaves, stems, and roots
• These organs undergo primary growth (shoot apex and root apical meristems) or develop adventitious structures from other tissues (adventitious)
• Leaves differentiate into a blade or lamina and a petiole (stalk)
• Flowers may be clustered into aggregations called inflorescences
• Peduncle: stalk of the inflorescence; pedicle: stalk of an individual flower
• Calyx: collective term for sepals; corolla: collective term for petals
• Perianth consists of both the calyx and corolla
• Androecium is the collective term for stamens; gynoecium for carpels
• Stamens are also called micro sporophytes
• Carpels are also known as megasporophylls
• The ovary is partitioned into chambers called locules
• Placenta: portion of the ovary where ovules are attached
• Partial placentation has ovules born along the ovary wall
• Axial placentation has ovules born of ancestral ovary tissue and partitioned into locules
• Free Central Placentation has ovules on a central tissue column without partitioning of the locus
• Some flower ovaries form a single ovule, leading to apical or basal placentation

Flower Structure

• Other flower variations include perfect flower, imperfect flower, monoecious plant, diecious plant, complete flower, incomplete flower
• Superior ovary means the sepals, petals, and stamens attach to the receptacle below the ovary (hypogenous flower)
• Semi-inferior ovary is the perigynous flower where petals, stamens, and sepals are attached to the margin of the ovary extension.
• Inferior ovary or epigenous flower, the sepals, petals, and stamens originate from the top of the ovary

Flower Symmetry

• Actinomorphic (regular) flower: the corolla is made of petals similar in shape that radiates from the center
• Zygomorphic (irregular, bilaterally symmetrical) flower: one or more whorls differ from other whorl members
• Coalescence: parts of the flower may fuse to other members of the same whorl
• Adnation: if part of the whorl is united or fused with another whorl

Angiosperm Reproduction

• Sexual reproduction in angiosperms involves flower formation, fertilization, fruits, and seeds
• Asexual reproduction doesn't involve flowers, fruits, or seeds and relies on a single parent instead of two
• Flowering plants exhibit an alternation of generations, where the sporophyte generation (2n) reproduces the male (1n) and female (1n) gametophytes
• They are heterosporous and produce microspores and megaspores
• Microsporogenesis forms pollen grains: spores that give rise to male gametophytes (pollen grains) are produced in anthers
• The pollen sac (2n) inside each anther produces four small haploid microspores through meiosis
• Each microspore divides again by mitosis, resulting in an immature haploid male gametophyte
• A male gametophyte (pollen grain) consists of three cells: two sperm cells (generative cells) and a tube nucleus cell (pollen tube)
• Pollen grain walls are toughened for protection
• The outer pollen surface is the exine
• Megasporogenesis forms the female gametophyte (development of megaspores)
• A diploid megaspore mother cell (megasporocyte) in each ovary ovule undergoes meiosis, forming four haploid cells
• Three of the four cells disintegrate, leaving one functional megaspore (embryo sac)
• The functional megaspore goes through cell division to form 8 cells arranged in the embryo sac
• Pollination is the transfer of pollen grains from the anther to the stigma, facilitated by wind, insects, or birds
• In fertilization, pollen grain lands on the stigma of the same species
• Germination forms a pollen tube
• The germinated pollen grain, containing a tube nucleus and two sperm, constitutes a mature male gametophyte
• As the pollen tube passes through the style, it reaches the micropyle
• One sperm nucleus unites with the egg, forming a zygote (2n)
• Another sperm unites with the two polar nuclei, forming a 3n endosperm nucleus
• Then, the pollen nucleus disintegrates
• The endosperm nucleus (3n) forms the endosperm
• The zygote forms the embryo
• The Integument forms the Seed coat

Compatibility

• Flowers like garden peas are self-compatible, known as selfing
• Many angiosperm species have mechanisms to prevent self-fertilization (self-incompatible)
• Most flowering plants are self-incompatible to encourage cross-fertilization
• Barriers preventing self-fertilization could be morphological or genetic, encouraging fertilization

Embryo Development

• Early divisions of the zygote produce the embryo (sporophyte) and the suspensor
• The suspensor anchors the embryo and transfers nutrients to the growing embryo
• Soon the cotyledons (seed leaves) can be seen
• At this point, the dicot embryo is heart-shaped and later becomes torpedo-shaped
• At this stage, the shoot apex and root apex can be distinguished
• Monocots differ from dicots by having only one cotyledon
• Another difference lies in how nutrients are stored:
• In monocots, the cotyledons rarely store food but absorb and transfer nutrients from the endosperm.
• Bean seed as an example of a dicot
• Corn kernel as an example of a monocot
• If cotyledons are parted in dicots, alimentary plants can be seen
• Plumule (epicotyl) is the stem portion above cotyledon attachment
• Hypocotyl is the stem portion below cotyledon attachment
• Radicle contains the root apical meristem and becomes the root's 1st primary growth
• In corn kernels (monocot), the outer covering is the pericarp, and the bulk of the food storage is in the endosperm
• Cotyledons do nopt play a storage role
• The plumule and radical (in monocots) are enclosed in the protective sheath called coleoptile and coleorhiza

###Seed Dormancy

• Resumption of growth or germination of the embryo or seed is dependent upon many external and internal factors
• Among the external factors
  • Water
  • Oxygen
  • Temperature
• Respiration may be anaerobic during the early stages of germination
• But when the seed coat ruptures, the seed switches to aerobic respiration
• Sometimes seeds fail to germinate despite having favorable external conditions
• The two most common causes for seed dormancy are the impermeability of the seed coat to water and the physiological immaturity of the embryo
• Collectively those changes that allow seeds to germinate are called after ripening
• Dormancy is a great survival value to the plant

###Seed to Seedlings

• After the seed imbibes water and germinates, the first organ to emerge is the radical (embryonic root)
• Next, the shoot tip must breakthrough the soil surface - in many dicots, it makes a hook in the hypocotyl and pushes it above ground
• Stimulated by light, the hypocotyl straightens up, raising the cotyledons and the epicotyl above the surface
• The elevated epicotyl spreads its plumule and the first foliage leaves start to make photosynthesis

From Seed to Fruit

• The ovary and other portions of the flower or inflorescence develop into a fruit once ovules becomes seeds
• The wall/pericarp often thickens and becomes differentiated into the exocarp (outer layer), the mesocarp (middle layer), endocarp (inner layer)
• Mostly in fleshy fruits, the pericarp consists of all three parts
• In dry fruits, the pericarp usually does not have the mesocarp
• A fruit is a mature ovary
• Fruits are usually classified as
  • Simple is when the fruits develop from one carpel or several united carpels
  • Multiple fruits: Develop from a separate carpel of one gynoecium (Ex: raspberries and strawberries

Plant Reproduction

• Asexual reproduction (Vegetative) is when offspring are derived from a single parent without genetic recombination
• This forms a genetic clone
• There are 2 types of asexual reproduction
  • Fragmentation: separation of a parent plant into parts that develop into whole plants, this is a common method
  • Apomixis: is when a diploid cell inside the ovule helps give rise to an embryo and its dispersed from wind or other factors

Plant Biotechnology

• Is possible to grow plants by culturing a small explant(take a piece of tissue from a parent plant or even a single parentyme cell) on an artificial medium containing nutrients
• This help produce a mass of undifferentiated tissue (callus)
• Then that small plant is transferred to the soil once the hormonal balance is applied so the callus can be differentiated into shoots and roots

Plant Growth & Organs

• The plant body has a hierarchy of organs, tissues and cells
• Plants have organs made of different tissues that are a group of cells with a common function, structure or both
• An Organ consists of several types of tissues together that carry out a function
• The basic morphology of vascular plants is that they are organized in a root system(below soil) and shoot system(above soil, stem, leaves, flower, ect)
• Taproot system: Found in most dicots and gymnosperms, consisting of a main vertical taproot, that develops from the root apex that gives rise to lateral roots
• Fibrous system: mat of generally thin roots spreading out below the soil surface

Root Modifications

• Prop roots: emerge from the stem nodes and they support tall heavy plants
• Storage roots: store food of water
• Buttress roofs: aerial roots that look like buttons to support tropical frees
• Pneumatophores Roots: also known as air roots are produced by mangrove that inhibit tidal swamp

Stems

• Stem: is an organ consisting of altering systems of nodes and internodes(The partial part between the 2 nodes
• Stolons are horizontal s stems that grow along the surface
• Bulbs: A vertical underground shoot, mostly of the enlarged bases of leases that store food
• Rhizome: a horizontal stem that grows just below the surface, Aerial stems and adventitious roots develop from the nodes
• Tubers enlarged stems specialized for storing food
• Primary growth occurs because shoots and roots grow from the apical meristem
• It increases the length of a plant

Plant Tissue

• Primary meristems are developed from apical meristel, epidermis, ground tissues and primary vessel tissues (pholem)
• Secondary growth is associated with The lateral meristems vascular cambium (secondary vascular tissue)
• Vascular cambium New cork cells

Tissue Types

• Dermal- The entire bodies of non-woody plants(herbaceous) are covered by a layer of epidermis the walls of the outer epidermal cells are covered with a waxy cuticle
• Ground tissue:
  • Ground tissues make the bulk of plant Parenchyma Collenchyma Sclerenchyma
  • Parenchyma is the least specialized cell, that is found in all organs, there are also chloride pass and live cells
• Collenchyma has ticker walls and forms bundles beneath the epidermis to give support
• Sclerenchyma cells are non living at functional maturity and they’re 2 types fibers or selereids
• Vascular tissue is the vascular system that contains xylose and water in order to help trasnport nutirnrs