Biology 191-Lecture 26

-The first plant hormone discovered

-Found in seed embryos, maristems of apical buds, and young leaves

-growth phenomena

-stimulates cell elongation, root growth, cell differentiation and branching, regulates development of fruit, enhances apical dominance, functions in phototropism and gravitropism, promotes xylem differentiation, and retards leaf abscission

-Found in maristems of apical buds and roots, young leaves and embryos

-Promotes seed and bud germination, stem elongation and leaf growth, stimulates flowering and development of fruit, and affects root growth and differentiation

-Found in tissues of ripening fruit, nodes of stems, and aging leaves and flowers

-Also produced naturally

-Promotes fruit ripening, opposes some auxin effects, promotes or inhibits growth and development of roots, leaves and flowers, depending on species.

-Plants possess surprisingy sophisticated systems for responding to environmental conditions like: light, gravity and touch

-receptors and hormone-mediated signal transduction

-they rely exclusively on chemical messengers

-Receptor: NPH1 in stems and leaves; light spectrum; short wave length

-Signal Transduction:NPH1 autophosphorylates; the remainder of system is unknown, but involves CRY1 and CRY2 proteins

-Response: Phototropism occurs

-Adaptive Value: Stems grow toward lights with wavelengths needed for photosynthesis

-Receptor: Phytochrome in seeds and elsewhere

-Signal Transduction: Phytochrome changes to Pfr form and activates response

-Response: Seed germinates

-Adaptive Value: Sunlight triggers sprouting in species that require full sun

-Receptor: Phytochrome in stem

-Signal Transduction: Phytochrome changes to Pf form and induces responser; mechanism is unknown

-Response: stems lengthen

-Adaptive Value: Species that require full sun attempt to escape shade

-Receptor: Integrin proteins located in cell membrane or in amyloplast membrane?

-Signal Transduction: Details unknown, but auxin is involved

-Response: Cells on opposite sides of root or shoot elongate; tissue curves

-Adaptive Value: Roots grow down; shoots grow up

-Land plants evolved from green algae

-Closest relatives are charophyceans (freshwater green algae)

-Eukaryotic
-multicellular
-possess chloroplasts in addition to mitochondria
-exhibit alternation of generations

-Blue-green algae aka cyanophytes
-prokaryotes engulfed by plants for photosynthetic activity
-shared, derived characteristics include: haploid gametes, but no adults; alternate haploid/diploid stages

-ribosomal RNA
-everything but viruses have them
-can find homological sequences
-used extensively

-non-tracheophyte plants with protected embryos
• lack phloem and xylem
• includes liverworts, hornworts and mosses
• require water for reproduction; confined to wet environments
-sporophyte dependent on gametophyte

-Possess cells joined into tubes that transport water (xylem) or nutrients (phloem)
• includes lycophytes (club mosses), ferns and horsetails
• require water for fertilization
-Large sporophyte, small, independent gametophyte

• evolution of seed a major advance in occupation of
terrestrial habitats
• seed is a sporophyte embryo packaged along with a
protective coat
-Reduced gametophyte dependent on sporophyte

-"naked seeds"
– lack enclosed chambers (ovaries) in which
angiosperm seeds develop
– includes cycads, ginkos, conifers: pines, firs,
redwoods

-flowering plants
– most diverse and economically important
– double fertilization with triploid endosperm

-haploid multicellular organism (n)
-produce gametes by mitosis

-diploid multicellular organism (2n)
-produce spores by meiosis

develops directly into adult

must combine with other gamete to form zygote

-non-vascular plants
-18,600 species

-vascular, but seedless
-13,015 species

-seed plants
-721 species

-flowering seed plants
-250,000 species
-abundant, diverse, comparable to animal lineages

-threat of dessication
-transporting water through the plant body
-establishing an upright body to compete for sunlight
-transporting gametes without water

-Sunlight and CO2 more available
-cuticle and stomata
-vascular tissue
-lignin in cell walls and an erect growth habit
-reduced gametophytes; male gametophyte travels to female as pollen
-specialized methods of photosynthesis: C4 and CAM

-pores on leaf surface
-restrict water are to water loss

-produces wood
-allows for skeleton of plant and height

-most plants have it
-with water

-grasses have modification
-conserve water

-succulent plants
-open stomates at night instead of day when temps. is low and humidity is low
-take in CO2 and use it during day

-pollen tube discharges two sperm into female gametophyte within ovule

-double fertilization occurs
-one sperm fertilizes egg while other combines with two nuclei in central cell of female gametophyte and initiates development of food-storing endosperm
-endosperm nourishes developing embryo

-sporophyte-dominant
-gamtophytes:
female-ovule
male-pollen grains are haploid (produces gametes through mitosis)

a) Wings enable maple fruits to be easily carried by the wind eg. sycamore (maple) seeds

b)seeds within berries and other edible fruits are often dispersed in animal feces

c)the barbs of cockleburs facilitate seed dispersal by allowing these fruits to hitchhike on animals

d)plants have lost of mold; many chemicals produced by plants to inhibit mold growth

e)fleshy fruits adapt to increase attractiveness to animals

angiosperms

important to human productivity

wheat, rice, maize, potatoes, cassava, and sweet potatoes

-CORN!
-most food produced in US is derived from a cornfield in Iowa
-corn has distinctive C13 profile on mass spectrophotometer

soda: 100% of carbon from corn
burger: 56% of carbon from corn

-most exhibit determinate growth, meaning the growth of indiv. ceases when adult stage is reached

-growth is indeterminate, meaning indiv. continues to grow after adult stage is reached
-growth is generated by specific regions of active cell divisions called meristem

groups of cells that retain ability to produce new organs indefinitely

cell divisions in meristem

• Germ-line sequestered early in development in most animal groups(exceptions include cnidarians)
• Cells lose totipotency early due to differentiation
• Mutations in somatic cells not transmitted to offspring

• Meristem is perpetually embryonic tissue (retains totipotency)
• Mutations that occur in meristem during development of individual can be transmitted to offspring
• Restricted case of the evolution of acquired characters
-can live thousands of years

-corals, anemones, hydras, and jelly-fishes
-dont have early germ-line sequences