Plant Bio Week 10

Evolutionary advantages of producing seeds

1. Nutrients 2. Protection (from animals, fungi, dessication) 3. advantages of being diploid (2 copies of every gene: masks deleterious recessive alleles, also if one damaged other one ok) 4. No need for H2O for fertilization

Pine seedling germination

1. Seed root grows down- this primary root is called the radicle 2. Seed has cotyledons inside the juvenile, inside-seed leaves (8 cotyledons per seed) 3. Hypocotyl region (in middle of seedling) turns into hook shape and pulls the shoot out as it elongates 4. Plumule, the new developing leaves, comes up from the hypocotyl

Extinct gymnosperms

1. seed ferns (pteridospermales) 2. cordates 3. cycadoites (bennetitales)

Coniferophyta overview

550 species, dominant plants in northern latitudes, most are evergreen and are trees, monopodial growth (are apical dominant, meristem is branches that come out of cone in whorls- 1 whorl per year). Most are xerophytes (bc northern latitudes- lots of frozen inaccesible H2O and low humidity- drought conditions)

Eusporangia

All vasc plants except ferns. Multicellular origin, one tapetum layer

Cycadophyta

Another kind of gymnosperms, besides conifers. 11 genera, 300 species, have whorls of leathery leaves (evergreen, though they look like palm), unbranched stem, monopodial, vascular cambium (slow secondary growth), >2 meters tall but can be more than 18, have a taproot, secondary roots are called coralloid roots and they are aerial (aboveground), have mutualistic associations with cyanobacteria which live within the root cells and fix nitrogen, nasty secondary componds (neurotoxins in leaves stems seeds, also carcinogens in stems and leaves, but theyre water soluble so can be rinsed away if rinsed thoroughly)

Sallvinia

Another water fern. Finely divided lower leaves act as pots?? See moodle 11/18. Know they're leaves bc sporangia present on the lower leaf. Heterosporous

Fasicle

Bundle of needles produced by a short shoot. Short shoots have determinate growth; produce bn 1-8 needles, depending on species

How to ID ferns

Diff clusters of sporangia

Cycad reproduction

Dioecious- they have male and female cones/plants. As with pines male plants have microsporophylll, microsporangia, microspores, etc. But unlike pines have flagellated sperm. Ovules can be some of largest in plants. Some insect species have coevolved w cycads, many are insect pollinated (ie weevils pollinate zamia furfuraceea), also beetles can pollinate or can be wind pollinate. Seeds are brightly colored and large so might have been dispersed by an animal species that has since gone extinct. No seed dormancy- dry out quickly

Similarities bn moss and fern life cycles

Diploid spores, need H2O to reproduce, have archegonia and antheridia

Types of ferns

Ferns, whisk ferns, adder's tongue, tree ferns, horsetails

Gymnosperm life cycle through time

For male: pollination, pollen tube grows and digests nucellus, after one year generative cell divides so there's 2 sperm nuclei, at 15 mo pollen reaches egg For female: 4 megaspores produced, one makes it (within 1st month), at 7 months megagametophyte grows using energy from nucellus, at a little over a year 2000 free nuclei have formed from mitosis, at 15 months 2-3 archegonia w eggs in each; when pollen reaches egg zygote forms (15 mo), embryo develops and at 2 years seed is ready for dispersal

Pine needles (why evergreen?)

Grow in areas that have low nutrient availability, also grow in northern latitudes so short growing season. For this reason, not cheap to produce- that's one reason they stay on all year. Wouldn't want to throw away tough, durable, expensive leaves. Also having leaves that stay on all year means that can begin photosynthesizing as soon as growing season begins in the spring- no need to waste time making new leaves.

example of convergent evolution

Heterospores

Characteristics of seeds?

Heterosporous (Homosporous = Sporangium, spore, gametophyte) Megasporangium, megaspore, megagametophyte Microsporangium, microspore, microgametophyte Megaspores not released from megasporangium Only 1 megaspore mother cell per megasporangium After meiosis, only 1 megaspore survives Endosporic megagametophyte Gametophyte is NOT independent Embryo within megagametophyte, within megasporangium Integument surrounding the megasporangium Micropyle - Pollen-receiving structures No water needed for fertilization

Evolution of seeds

Heterosporous reproduction, ovule=megasporangium and integument (integument surrounds and protects megasporangium), micropyle=pollen-receiving structure, no H2O needed for fertilization, only 1 megaspore mother cell (also called megasporocyte) per megasporangium (in ovule), after meiosis only one megaspore survives, megaspores stays INSIDE the megasporangium (no dispersal!), endosporic megagametophyte (megagametophyte forms inside the megaspore), embryo within megagametophyte, within megasporangium

Horsetails

Hollow stems with solid nodes, whorled branches at nodes, siphonostele (has pith), reduced leaves, fertile stalk or strobilus at top of veg stalk (in some), eusporangiate, spores with elators for dispersal (projections on spores twist and move when they dry), gametophytes are longer lived than other groups, have both antheridia and archegonia at once, require H2O for fertilization, homosporous

Heterosporous have ______, __________, and _____________. Homosporous have

Homosporous have spores within a sporangia on a sporophyll. Heterosporous have mega/microspores in mega/microsporangia

Cavitation catapult

In leptosporangiate ferns. Outer layer of annulus dries, breaks open at the lip cells, contracts, and then cavitation in the cells of the annulus causes it to spring back

Marsilea

In polypodiopsida. Creeping rhizome with quadrifoliate leaves, sporangia form on fertile pinnae, pinnae curl over sporangia, produces sporocarps which can be dormant for decades. After weathering add water and sori come out of sporocarps. Water ferns are heterosporous- they make big spores (megaspore which produces female gametophytes) and small spores (microspores which produce male gametophytes) See moodle 11/18

Evolution of the integument

Leaf-like things over evolutionary time fuse (bc advantageous) then leave opening for pollen grains to come in at top (the micropyle) (see moodle 11/20)

Marattiopsida example

Marattiopsida is an order, tree ferns (psaronious) are an example- now extinct, lived during carboniferous. Trunk made of leaf bases, aerial roots

Gymnosperm life cycle

Megaspore mother cell inside ovule, 4 megaspores produced and all but final one deteriorate, megagametophyte w 2 eggs develops, zygote forms, microspore mother cell goes through meiosis and then mitosis, gametophyte inside, pollen grain disperses, lands and goes in through micropyle, grows pollen tube in, sperm and egg fuse, proembryos form, embryos develop suspensors which push embryos to middle of megagametophyte, one of the 2 embryos dies (usually), so only 1 embryo left, seed disperses, seedling grows into pine

Example of spore development: pines

Megaspore mother cells inside megasporangium, meiosis occurs, 4 cells form, only one lives, that cell goes through mitosis (first only the NUCLEI are replicating but no cell div then once 2000 nuclei begins dividing into cells), then grows into megagametophyte (inside the megasporangium), then produces archegonia, ovule=gametophyte that grow inside, male gametophytes enter, micropyle closes and seals it off, pollen sends out pollen tubes to fertilize eggs in the archegonia, pollen tube reaches egg cell, fertilization occurs (2n), zygote forms and develops into an embryo, embryo is surrounded by female gametophyte, thin later called nucellus outside, female gametophyte and nucellus are stored resources for development

Difference bn moss and fern life cycles

Moss is gametophyte dominant, sporophyte dependent. Sporangium (just one) includes capsule. Fern is sporophyte dominant, independent, leaf has many sporangia in a cluster

Gymnosperms

NEW: fertilization doesnt require water, reproduce via seeds (seed=embryo, stored food, seed coat). See moodle 11/20 for other traits

Cones in pine life cycle (where on the tree? how do they disperse?)

Pine trees typically have both male and female cones. Female cones on top, male cones lower (encourages outcrossing- if pollen were on top, it would rain down on cones of same tree. Also may aid in seed dispersal- bc seeds higher up). In many cones, when time for dispersal, cones turn down and seeds fall out. In some species, whole cone disintegrates, scales fall off. Or with serotiny, cones stay sealed and are covered with a coating that can only be broken down by fire. Seeds remain dormant in cone until fire comes; advantageous bc can disperse when little competition and good nutrients (ash). Some cones are bird dispersed, some wind dispersed

How does pollen drop aid in pollination

Pollen lands in pollen drop which is on the external surface of the megagametophyte, pollen sends a chemical signal which causes the pollen drop to be absorbed into the gametophyte (and the pollen is pulled in along with it), integument closes up, megagametophyte grows for a year, releases sperm nuclei, one fuses w the egg nucleus (no motil swimming sperm w pines), embryo forms

Male microsporangiate cones in gymnosperms

Produce pollen but NO ANTHERIDIA (even though megagametophytes/females produced archegonia). Have microsporophyll (the sporophyll is the leaf associated w the sporangia) on microsporangium, which come off an axis. Microspore mother CELLS produce haploid microspores, 4 microspores develop into a gametophyte (endosporeic-happens inside the microspore. microgametophyte-the pollen grain grows inside the microspore), inside microspore, goes through mitosis - get 4 cells (2 of them degenerate), one of the cells that's left is the generative cell (produces sperm) and the other is the tube cell (produces pollen tube)

Progymnosperms

Produce spores, secondary xylem and phloem, bifacial vasc cambium, heterosporous, have a eustele (vasc tissue in discrete bundles)

Two classes of eusporangiate ferns

Psilotopsida, Marattiopsida

Female microsporangiate cones

See moodle 11/20

Serotiny

Seed release occurs in response to environmental trigger. cones stay sealed and are covered with a coating that can only be broken down by fire. Seeds remain dormant in cone until fire comes; advantageous bc can disperse when little competition and good nutrients (ash).

Fern life cycle

Spores develop, haploid, wind dispersed, young gametophytes germinate and grow into mature gametophyte (aka prothallus) which is short lived, produces archegonia and antheridia, embryo forms once sperm (which rely on H2O) go down neck canal of archegonia and fuse w egg, sporophyte grows from gametophyte and gametophyte disappears, sporophyte is diploid and dominant, produce sporangium (hollow group of cells in which spores produced), group of sporangia is a sorus, spores disperse

Ginkos (ginkophyta)

The only species left is ginko biloba. Are deciduous gymnosperms. Tolerant of pollutants, radiation. Seeds are edible, seed is green and can photosynthesize. Male strobili fertilize female ovules (pollination in spring then fertilize in winter), flagellated sperm, have 2 ovules on tips but only 1 develops

Structure of pinaceae needle

Thick/waxy cuticle, sunken stomata (reduce evapotranspiration), hypodermis (a layer of compact thick walled cells which is underneath the epidermis, reduces dessication), low surface to volume ratio (bc round), endodermis in the LEAF (not in the root) with special transfusion tissue around the vascular tissue which moves H2O and nutrients to the endodermal layer from the vasc tissue (also intended to reduce H2O loss), long and thin needles which shed weight of snow, reduce breakage and loss of leaf material, monopodial branches also maybe good for shedding snow

Leptosporangia

Unique to ferns- a derived trait. One initial cell, 2-layered tapetum which is involved in producing nutrients for developing spores. Annulus-catapult spore discharge (annulus cells dry out, lip opens and forces H2O out of annulus cells, cavitation in annulus cells happens which causes sporangium to pull back and then flip forward, catapulting the spores)

Azolla

Water fern. Associated w cyanobacteria, N fixation in rice patties, also heterosporous

Psilotopsida

Whisk ferns. Eusporangiate (like club mosses and gymnos), one frond (has fertile part and blade, which is the sterile part), 1 leaf per year, no fiddlehead, subterranean gametophytes (no chlorophyll, have assoc w myc fungi), includes grape fern and adder's tongue. Dichotomously branched, scalelike leaves, protostele, no true roots, evolutionary loss of traits- a reversal (traits are derived, not ancestral)

Sorus

group of sporangia (sporangia are hollow groups of cells in which spores produced)

Sporangium (ferns)

hollow group of cells in which spores produced

How are pine needles produced

produced on structure called short shoot (which comes off branches, or "long shoots"). Short shoots have determinate growth; produce bundle of needles at tip called fasicle, get only certain # of needles per short shoot (between 1-8 needles, depending on species). needles retained for 2-4 years.