KINGDOM PLANTAE Chapters 29 & 30
Kingdom: PLANTAE Characteristics • Multicellular • Mostly photosynthetic, contain chlorophyll and other pigments • - some parasitic or carnivorous • Cell walls made of cellulose • Food stored as starch • Subdivided into two main division – Bryophytes (non-vascular plants) and Tracheophytes (vascular plants) • Approximately 261,849 Species
Plants evolved from multicellular green algae Proof: • Plants are multicellular, eukaryotic, photoautotrophs like most algae • Plants contain cellulose in cell walls, just like green algae, brown algae and dinoflagellates • Plants contain chloroplasts with chlorophyll a and b like most algae
Charophytes – green algae that are the closest relatives of plants Belong to: Phylum chlorophyta Class Charophycea. They are common pond dwellers.
Proof of Relation between charophyceans and modern land plants • Cellulose-synthesizing protein rosettes found in the cells of both. In other algae, these complexes are linear. • There is more cellulose present in the cell walls of charophyceans and plants than other algae
Proof of Relation between charophyceans and modern land plants • Peroxisomes of land plants and charophyceans contain special enzymes to prevent damage from photorespiration. Other algae do not have these enzymes. • In pond charophytes, a layer of durable polymer called sporopollenin keeps their zygotes from drying out during dry spells. Spores of some land plants are also covered with sporopollenin. • The flagellated sperm of certain land plants (like mosses) resemble sperm of charophyceans. • The cytokinesis of land plants and charophyceans is identical – the formation of a phragmoplast (a fancy name for the lining up of the vesicles from the Golgi body). • Both – nuclear DNA and chloroplast DNA of land plants and charophyceans are closely related!
The Move to Land • The move to terrestrial environments occurred in the Silurian period of the Paleozoic Era (about 500 million rears ago) • The new terrestrial plants were faced with many new challenges as a result of the relative lack of water present in terrestrial environments.
A Dilemma for terrestrial plants • Algae could get water, O2 / CO2 as well as other nutrients from one single medium: The water they resided in. • Plants have to obtain their requirements from 2 different media: Air and soil • Plants have evolved two systems to deal with this: The subterranean root system and an aerial shoot system
The Challenges Also Include: • support of the plant against gravity, • finding and taking in water for metabolic processes, • reproduction with motile gametes (algae have swimming sperm) • greater variability and extremes of climate, and • spatial separation of nutrients. • Different groups of plants have dealt with the problems created by lack of water in various ways. These solutions will be discussed with each group of plants where appropriate
Alternation of Generations Female – ovule Male – Pollen grain
Spores • Spores are usually haploid and unicellular and are produced for asexual reproduction • Spores are produced by diploid sporophytes. They can be dispersed by wind and germinate when they land in an ideal location. • When they germinate, they produce haploid gametophytes. • The haploid gametophytes produce haploid gametes (sperm and egg) • Sperm and egg fuse to give rise to a diploid sporophytes.
Alternation of generations • Sporophytes – are the mature, green plants that we see all around us, They are diploid. • They produce haploid spores via meiosis. • The haploid spores give rise to haploid gametophytes (sperm or egg producing units). • Gametophytes – they are multicellular reproductive parts of a plant that are haploid. • The female gametophyte is termed the megaspore which is located inside the ovule • The male gametophyte is termed the microspore which is located inside the pollen grain. • The haploid megaspore and microspores produce haploid gametes (egg and sperm). • When the sperm fertilizes the egg, a diploid sporophyte is created.
Spores versus Gametes • Spores are the units of asexual reproduction, because a single haploid spore develops into a new haploid organism (a haploid gametophyte). • By contrast, gametes are the units of sexual reproduction, as two haploid gametes need to fuse to create a new diploid organism (a diploid sporophyte).
Homo vs. Heterosporous • Homosporous – The sporophyte produces only one type of spore which gives rise to one type of gametophyte that is both male and female. These gametophytes then produce both sperm and eggs. Example: Ferns, Mosses • Heterosporous – The sporophyte gives rise to two different spores (Male - Microspore and female - megaspore). Each gives rise to a separate gametophyte (Male gametophyte – pollen, female gametophyte – ovule). The female gametophyte will produce eggs and the male will produce sperm.
Kingdom Plantae cont’d Non-vascular Plants – Short, live close to the ground in moist soil. Produce spores. No true leaves or roots. Sometimes all these 3 non-vascular divisions are collectively called BRYOPHYTES Division Heptophyta (Liverworts) Division Anthocerophyta (Hornworts) Division Bryophyta (Mosses)
Need rainwater so flagellated sperm from antheridia can swim to the eggs in the archegonia. MOSSES ARE HOMOSPOROUS – one spore type creates both male and female gametophytes.
Origin of Vascular plants • Life cycle with a Dominant sporophyte (unlike mosses, where the gametophyte generation is dominant) • Tissue called Xylem conducts water and minerals from root to rest of plant • Tissue called Phloem conducts sugar from leaves (source) to rest of plant (sink) • Lignin in xylem and phloem walls in addition to cellulose. • True roots and leaves.
Kingdom Plantae cont’d Vascular Seedless Plants – Produce spores for reproduction Division Psilotophyta (Whisk Ferns) Division Sphenophyta (Horsetails) Division Lycophyta (Club Mosses) Division Pterophyta (Ferns)
Like mosses, ferns have flagellated sperm that rely on water to swim from antheridium to archegonium FERNS ARE HOMOSPOROUS
Family: Welwitschia Kingdom Plantae cont’d Vascular Seed Plants – Produce seeds for reproduction, sperm are encased in pollen, but seeds are not encased in ovaries – Gymnosperms or “Naked seeds” Division Gnetophyta (Gnetophytes) Lives in deserts Division Cycadophyta (Cycads)
Kingdom Plantae cont’d Vascular Seed Plants – Produce seeds for reproduction (Also known as gymnosperms) Division Ginkgophyta (Ginkgos) Oldest trees on Earth. Existed during the time of the dinosaurs. Division Coniferophyta (Conifers) All evergreens: Firs, Cedars, Junipers, etc. Gymnosperms are heterosporous
Kingdom Plantae cont’d Vascular Seed, Flowering Plants – Produce seeds for reproduction Seeds encased in ovaries – Division Anthophyta or Angiosperms Two types of flowering plants: Monocotyledons Dicotyledons
Comparison of generations in Mosses, Ferns and Flowering plants
Differences between ovule and pollen Male gametophyte or pollen (came from the male microspore) (Later divides into 2 sperm cells) Female gametophyte or ovule (came from the female macrospore)
Ovule Structure • Ovules form in the ovary. Each contains 8 haploid nuclei, in 7 cells including : • 1 egg nucleus • 2 polar nuclei (in one cell) • 3 antipodals • 2 synergids • All nuclei are haploid (n)
Pollen Structure • Pollen grains are formed in anthers. Each contains: • 1 Tube nucleus • 1 generative nucleus that divides into 2 sperm nuclei after the pollen lands on the stigma
Fertilization and seed Production (pollen grain)
Fertilization • The tube cell creates a pollen tube which tunnels all the way through the carpel and enters the embryo sac. • The synergids of the embryo sac burst the end of the pollen tube. • Meanwhile, the generative cell has followed the pathway digested by the tube cell. Along the way it has divided to produce two sperm cells. • The two sperm cells exit the pollen tube and enter the ovule. • One sperm cell unites with the egg. This process is called syngamy (union of gametes). This produces a diploid zygote. The zygote will divide and grow and differentiate to become a new embryonic plant with root, stem, and leaf. Ultimately it will become an adult plant. • The other sperm cell unites with the central cell. This is a second syngamy! This produces a triploid endosperm cell (one from sperm and one each from the two polar nuclei). • The endosperm cell divides to form a nutritive tissue inside the seed. It accumulates nutrients from the mother plant and stores them away for the developing embryo inside the seed. The nutrients are stored as starch, protein, and/or oil.
Stamens and Seed (Ovule) Fruit (Ovary) After Fertilization • The mature ovule becomes the seed. The seed contains the embryo. The integuments become the seed coat that surrounds the endosperm and embryo. The mature carpel (and sometimes associated tissues) becomes the fruit.
The radicle is the first part of the embryo to push out of the seed. This will be the first root. The hypocotyl is the lower section of the stem and the epicotyl is the upper part or actively growing part of the stem . Seed germination of seeds depends on imbibition – the absorption of water from the soil, due to the lower water potential in the dry seed. Alpha-amylase is released by the outer coat of the endosperm, to breakdown the starch stored in the endosperm – food for the growing seedling.