growth regulators Flashcards
what are the phases in plant growth and development
1) seed dormancy
2) germination
3) seedling growth,differenciation and maturation
4) flowering
5) seed and fruit production
what are plant growth regulators
naturally occurring organic compounds which have profound effects on physiology, growth and development
what are some important properties of plant growth regulators
1) growth promotion or inhibition
2) can act in combination or antagonistically
3) transported in different ways such as by the phloem, xylem, parenchyma cells or diffusion
outline the signal transduction pathway which must occur for the plant growth regulator to have an effect
1) hormones bind to proteins associated with membranes of the affected cells
2) the binding activates a membrane receptor which alters intracellular molecules releasing secondary messengers
3) the secondary messengers create a responce
what do auxins do for plants
a plant growth hormone which causes cell enlargement and tissue differentiation
how are auxins transported around the plant
polar transport from the apex to the base (basipetal transport) in parenchyma surrounding vasucualr bundles at 1cm an hour
what is meant by polar transport by auxin molecules
the movement in one direction within a plant, basipetically in shoots by a mechanism that requires energy and carrier proteins
what plants are often used to explant the mechanism of auxin transport
arabidopsis mutants
what are some effects of auxin
1) apical dominance= where the growth of the lateral meristem is supressed by hormones produced in the apical meristem
2) tropisms
3) tissue differentiation
what is meant by apical dominance
where auxin inhibits axillary bud growth so buds remain dormant until the apical tip is removed therefore suppressing growth of the lateral meristem
what are tropisms
growth responses to features such as gravity or light which may be positive or negative
what happens as a result of stems being positively phototropic
usually positively phototropic, when blue light is detected by the protein-flavin complex auxin accumulates on the shaded side causing plants to growth towards the light
who conducted experiments with oat coleptiles
Cholodny-Went 1927 who described the tendencies for the shoot to grow towards light and the roots to grow downwards due to the asymmertrical distribution of auxin
what is the name of the blue light receptor involved in phototropism and what type of protein is it
photoropin is a flavoprotein (contains a nucleic acid derivative of riboflavin
how does the curvature responce come about in phototropism
the presence of blue light causes the redistribution of auxin with greater concentrations on the shaded side
- auxins cause acidification of the cell wall therefore loosening the wall matric
- causing increased turgour pressuure resulting in cell elongtion and bending towards the light
how does auxin promote tissue differentiation
auxin transported by polar transport mechanisms to a wound
here cells in the pith differentiate into new vascular tissue and connect tissues above and below the wound
what protein inhibits the auxin response gene
AUX/IAA protein
what is ubitquitin
a small regulatory protein which is found in most tissues which can affect proteins
how is the auxin responce gene turned on
auxin-ubiquitin E3 ligase complex binds to AUX/IAA protein which becomes ubiquniated
the portein is tagged for proteolysis via a 26S proteasome and is broken down
the auxin responce gene is no longer repressed and is turned on
what are gibberellins and their effects
a plant growth regulator which promotes cell divison and enlargement, seed germination, maturation, flowering initiation and fruit formation
how is gibberellin transported
non-polar, bidirectional in the phloem
where can dwarf mutants result from
1) mutations in gibberellin biosynthesis pathway
2) mutations in genes which control responces to gibberellin
- can be seen in mendels experiements with varieties of peas
how is gibberellin involved in germination
many seeds need light or a cold period to break dormancy however gibberellin does this as well by promoting amylase activity in seeds
outline how gibberellin promotes amylase activity
1) GA synthesised by the embryo and released into the endosperm
2) GA diffuse into the aleurone layer where cells synthesis amylase and secrete it into the endosperm
3) startch and other molecules are broken down
4) endosperm solutes are absorbed by the scutellum and transported to growing embryo
outline the gibberellin signal transduction pathway
the receptor in the cell wall is inhibited by a repressor with two regions ( DELLA domain and GRAS domain) which
what are the effects of cytokinin’s
1) cell exansion in dicots
2) chloroplast development
3) delay leaf senesence
4) promote movement of nutrients
how are cytokinis transported
long distance in the xylem
what does the interaction between cytokinin and auxin result in
tissue culture differentiation
outline the cytokinin signal transduction pathway
1) receptors are transprotein kinases
2) cytoknin binds to receptor
3) activates histidine kinase activity and a phosphate is transferred to a protein
4) the phosphorylated protein moves to the nucleus and transfers a phosphate
5) gene transcirption cascade begins in the nucleus
what are histidine kinases
multifunctional transmembrane proteins in a class of enzymes which play a role in signal transduction across the cell membrane
what are trans-membrane protein kinases
they can chemically modify proteins via the addition of phosphate groups
what are the main affects of abscisic acids
it is a growth inhibitor, initates seed and bud dormany and embryo development and senescence
how is ABA transported
root to shoot in the xylem
shoot to root in the phloem
what is the role of dormancy
promotes production of seed storage proteins
prevents premature germination
as ABA decreases dormancy breaks
what is found in plants under high stress
higher amounts of ABA- found it induces stomatal closure in leaves during drought
how does ABA induce the closure of stomata
1) ABA binds to receptor inc ell membrane and clacium acts as a secondary messenger
2) calcium opens anion channels causing membrane polarisation
3) K+ channels open and pottassium enters decreasing turgour pressure cuasing cells to become flaccid and close
what are the main effects of ethylene
fruit ripening, leaf and flower senescene, absiccion, root hair development
how is ethylene transported
diffusion as a gas
what happens when seedling are exposed to ethylene in the dark
1) short hypocotyl root
2) thickened hypotyl
3) horizontal growth
what gene codes fdor the ethylene receptor porteins
ETR1
what is stratification
when seeds need cold exposure to break dormancy
what is vernalisation
when buds need a cold period before initating new growth
