growth regulators

Question 1

what are the phases in plant growth and development

Answer 1

1) seed dormancy
2) germination
3) seedling growth,differenciation and maturation
4) flowering
5) seed and fruit production

Question 2

what are plant growth regulators

Answer 2

naturally occurring organic compounds which have profound effects on physiology, growth and development

Question 3

what are some important properties of plant growth regulators

Answer 3

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

Question 4

outline the signal transduction pathway which must occur for the plant growth regulator to have an effect

Answer 4

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

Question 5

what do auxins do for plants

Answer 5

a plant growth hormone which causes cell enlargement and tissue differentiation

Question 6

how are auxins transported around the plant

Answer 6

polar transport from the apex to the base (basipetal transport) in parenchyma surrounding vasucualr bundles at 1cm an hour

Question 7

what is meant by polar transport by auxin molecules

Answer 7

the movement in one direction within a plant, basipetically in shoots by a mechanism that requires energy and carrier proteins

Question 8

what plants are often used to explant the mechanism of auxin transport

Answer 8

arabidopsis mutants

Question 9

what are some effects of auxin

Answer 9

1) apical dominance= where the growth of the lateral meristem is supressed by hormones produced in the apical meristem
2) tropisms
3) tissue differentiation

Question 10

what is meant by apical dominance

Answer 10

where auxin inhibits axillary bud growth so buds remain dormant until the apical tip is removed therefore suppressing growth of the lateral meristem

Question 11

what are tropisms

Answer 11

growth responses to features such as gravity or light which may be positive or negative

Question 12

what happens as a result of stems being positively phototropic

Answer 12

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

Question 13

who conducted experiments with oat coleptiles

Answer 13

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

Question 14

what is the name of the blue light receptor involved in phototropism and what type of protein is it

Answer 14

photoropin is a flavoprotein (contains a nucleic acid derivative of riboflavin

Question 15

how does the curvature responce come about in phototropism

Answer 15

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

Question 16

how does auxin promote tissue differentiation

Answer 16

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

Question 17

what protein inhibits the auxin response gene

Answer 17

AUX/IAA protein

Question 18

what is ubitquitin

Answer 18

a small regulatory protein which is found in most tissues which can affect proteins

Question 19

how is the auxin responce gene turned on

Answer 19

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

Question 20

what are gibberellins and their effects

Answer 20

a plant growth regulator which promotes cell divison and enlargement, seed germination, maturation, flowering initiation and fruit formation

Question 21

how is gibberellin transported

Answer 21

non-polar, bidirectional in the phloem

Question 22

where can dwarf mutants result from

Answer 22

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

Question 23

how is gibberellin involved in germination

Answer 23

many seeds need light or a cold period to break dormancy however gibberellin does this as well by promoting amylase activity in seeds

Question 24

outline how gibberellin promotes amylase activity

Answer 24

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

Question 25

outline the gibberellin signal transduction pathway

Answer 25

the receptor in the cell wall is inhibited by a repressor with two regions ( DELLA domain and GRAS domain) which

Question 26

what are the effects of cytokinin’s

Answer 26

1) cell exansion in dicots
2) chloroplast development
3) delay leaf senesence
4) promote movement of nutrients

Question 27

how are cytokinis transported

Answer 27

long distance in the xylem

Question 28

what does the interaction between cytokinin and auxin result in

Answer 28

tissue culture differentiation

Question 29

outline the cytokinin signal transduction pathway

Answer 29

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

Question 30

what are histidine kinases

Answer 30

multifunctional transmembrane proteins in a class of enzymes which play a role in signal transduction across the cell membrane

Question 31

what are trans-membrane protein kinases

Answer 31

they can chemically modify proteins via the addition of phosphate groups

Question 32

what are the main affects of abscisic acids

Answer 32

it is a growth inhibitor, initates seed and bud dormany and embryo development and senescence

Question 33

how is ABA transported

Answer 33

root to shoot in the xylem
shoot to root in the phloem

Question 34

what is the role of dormancy

Answer 34

promotes production of seed storage proteins
prevents premature germination
as ABA decreases dormancy breaks

Question 35

what is found in plants under high stress

Answer 35

higher amounts of ABA- found it induces stomatal closure in leaves during drought

Question 36

how does ABA induce the closure of stomata

Answer 36

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

Question 37

what are the main effects of ethylene

Answer 37

fruit ripening, leaf and flower senescene, absiccion, root hair development

Question 38

how is ethylene transported

Answer 38

diffusion as a gas

Question 39

what happens when seedling are exposed to ethylene in the dark

Answer 39

1) short hypocotyl root
2) thickened hypotyl
3) horizontal growth

Question 40

what gene codes fdor the ethylene receptor porteins

Answer 40

ETR1

Question 41

what is stratification

Answer 41

when seeds need cold exposure to break dormancy

Question 42

what is vernalisation

Answer 42

when buds need a cold period before initating new growth