Topic 93 U Undifferentiated cells in the meristems of plants allow indeterminate growth Most plants have indeterminate growth cells divide indefinitely most animals have d eterminate growth ID: 626209
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Slide1
Growth in plants
Topic 9.3Slide2
U:
Undifferentiated cells in the meristems of plants allow indeterminate growth
Most plants
have indeterminate growth = cells divide indefinitely (most animals have determinate growth)Most plant cells are totipotent = total ability of a single cell to divide & produce all the differentiated cells in organism (only an animal zygote/early embryo is totipotent)Meristem = undifferentiated cells that are dividing Primary meristems: Root apical meristem = tip of growing root Shoot apical meristem = tip of growing stemSecondary meristems: Lateral meristem = cause stem to grow laterally (in diameter); in dicotsSlide3
U:
Mitosis & cell division in the shoot apex provide cells needed for extension of stem & development of leavesSlide4Slide5
U:
Plants hormones control growth in shoot apex
Hormone = chemical message produced & released in one part of organism to have an effect in another partAuxins = plant growth hormonesIAA = indole-3-acetic acid (type of auxin)Promotes elongation of cells in stemsMade in shoot apical meristem & transported down stem to stimulate growthShoot Tip - No matter what the concentration, IAA promotes growth in the shoot area of a plant (though higher concentrations promote growth more) .Root Tip - High concentrations of auxin inhibit growth while small amounts are enough to promote growth in the root with indole acetic acid.Slide6
Apical Dominance
Axillary buds
= lateral (side) buds Apical dominance
= lateral buds closer to shoot tip are inhibited by auxin (presence of auxins in the lateral areas between root and shoot tip prevent lateral growth)can be disrupted by pruning (cutting off) the shoot tip – the lack of diffusible auxins means they cannot inhibit growth in the lateral budsOther hormones: Cytokinins = hormones produced in root; promote axillary bud growthGibberellins = hormones that contribute to stem growthSlide7
Before & after pruningSlide8
If you want bushier, thicker plants, cut them back!Slide9
a
uxins
vs
cytokininsSlide10
U:
Plants respond to environment by tropisms
Plant hormones control growth rate and direction of growth
Direction influenced by light & gravityStems grow towards brightest lightIn absence of light, plants grow upTropism = directional growth in response to external stimuli (light & gravity)Phototropism = growth towards lightGravitropism = growth in response to gravityGeotropism = growth towards EarthSlide11
U:
Auxin influences cell growth rates by changing the pattern of gene expression
1
st stage in phototropism = light absorption by photoreceptors called phototropin (blue-light receptors)Phototropins bind to receptors, which control transcription of genes that code for PIN3 proteins that transport auxin from cell to cellSlide12
U:
Auxin efflux pumps can set up concentration gradients of auxin in plant tissue
Auxin
transported to shady side of stemCells on shady side elongate, curving stem towards lightLeaves attached to stem will receive more light & photosynthesize faster
Auxin transported to bottom of cells
Auxin inhibits root cell elongation
Top cells elongate faster than bottom cells, causing root to bend downwardSlide13
App:
Micropropagation
of plants using tissue from the shoot apex, nutrient agar gels and growth hormones
Micropropagation = in vitro process; rapidly produces many identical plants Stock plant has desirable traitDepends on totipotency of plantsTissues sterilized & cut into pieces called explantsUsually meristems used (least differentiated)Placed in sterile growth media with hormonesEqual auxin & cytokinin leads to forming callus (undifferentiated mass)If A:C is greater than 10:1 (increased concentration of auxin), what develops? roots
If A:C is less than 10:1 (increased concentration of
cytokinin
), what develops?
ShootsSlide14
App:
Use of
micropropagation
for rapid bulking up of new varieties, production of virus-free strains of existing varieties & propagation of orchids and other rare speciesAdvantages of micropropagation:Virus-free plants! (apical meristems usually virus-free)Desirable traits are clonedFasterLess space Preservation of species (e.g. orchids)Easier than germinating seedsCan be stored in liquid N (cryopreservation)Can be used for wild replanting or commercial https://www.youtube.com/watch?v=6j5U5eeEQtUSlide15
NOS: developments in scientific research follow improvements in analysis & deduction:
Improvements in analytical techniques allowing the detection of trace amounts of substances have led to advances in the understanding of plant hormones and their effect on gene expression
“Microarrays” have improved genetic research
:DNA microarray analysis is a technique that scientists use to determine whether genes are turned on or offScientists know a gene is ON if mRNA is presentallows scientists to perform experiment on thousands of genes at same timehttp://learn.genetics.utah.edu/content/labs/microarray/Slide16
Microarrays of plant hormone expression
Researchers found:
genes are expressed at higher levels on the bottom
cells in gravitrophically stimulated cells on rootsGenes are expressed at higher levels on shady side of phototrophically stimulated cells on stems