Bio220 Final Plant Internal Signaling Part I

Front 1

Reason for Plant Growth

Back 1

Plants cannot move therefore they respond to changes in environment by changes in growth patterns

Front 2

Plant growth

Back 2

Cell walls are rigid and don't allow for movement of cells past each other: shape of organs dependent on growth

growth dependent on division and expansions.

Front 3

Preprophase Band

Back 3

A ring of microtubules bisecting the cell in the outer layer of cytoplasm

in rapid growth areas plane is perpendicular to growth areas

Front 4

Plant growth: expasnion

Back 4

Growth after divisional growth can be rapid and is caused by water uptake.

Lower water potential leads to water going into the cells (the large central vacual) causes volume to increase.

enzymes get released into the primary cell wall break hydrogen bonds between cellulose microfibrals: loosening the structure

Cell growth perpendicular to cellulose microfibrals

Front 5

Differentiation

Back 5

Plant cells arise from a totipotent ancestrial cell

Differences in gene expresion lead to different protein compliments which determine cell function and morphology

Front 6

Control of Differentiation

Back 6

Differentiation can be determined based on positional information or location of the cells

Front 7

How plants function

Back 7

Using plant hormones: Have no nervous system, therefore they integrate functions by distributing chemical signals in the body.

Front 8

Plant Hormones

Back 8

Modifies structure and function in response to the environment
Example Phototropism

Front 9

Phototropism (definition)

Back 9

Is the altered growth pattern in response to light
can be positive growth or negative growth

most plants show a positive phototropism due to greater growth on the shaded side of the stem (petiole)

Front 10

Phototropism (discovery)

Back 10

Darwin and son discovered that signal comes from the tip of the stem in grasses

1. Shoot with no tip, or covered tip, shows no phototropism
2. Shoot covered with transparent tip, or with lower parts of stem covered, shows positive phototropism

Front 11

Phototropism (tip of signal)

Back 11

shown to be a chemical signal when tip was separated signal was still present after tip was reatached with a gelatin permeable to large proteins.

Front 12

Phototropism (hormone)

Back 12

called auxin causes stem to grow based on where the auxin is released

Front 13

Auxin (function)

Back 13

only an intermediate amount of apical meristem produce growth

Activates proton pumps which pump H+ into cell wall. H+ activates expansins weakening the cell wall

because H+ is pumped out K+ is pumped in down the electrochemical gradient. making the solute potential increases. Cell then increases

Front 14

Auxin (transport)

Back 14

Produced in the apical Meristem (top most branch)

and transported down the stem (from root to shoot)

Cotransport with hydorgen imports Auxin into the basil membrane.

Carriers at basil membrane export the auxin

Front 15

Other functions of Auxin

Back 15

1. Stimulates cell growth/ differentiation in the vascular cambium (secondary growth)
2. Stimulates formation of roots in stem cuttings
3. Stimulates growth of fruits in some plants (auxin produced by seeds)
4. Inhibits growth of axillary buds (source of apical dominance)

Front 16

Various Plant Hormones

Back 16

Auxin

Cytokinins

Gibberellins

Abiscus Acid

Ethylene

Front 17

Cytokinins

Back 17

work with auxin to promote cell division and differentiation

Front 18

Gibberelins

Back 18

causes stem elongation by stimulating both cell division and expansion – responsible for bolting; breaking of dormancy

produced from fungi found in rice plants.
in the apical meristem

Front 19

Abiscus Acid

Back 19

-- Slows down metabolism, maintains dormancy in seeds (antagonistic to gibberellins)

Front 20

Ethylene

Back 20

A gas, it is involved in senescence, fruit ripening (Commercial fruits are now stored in ethylene-free or ethylene-enriched environments for storage or artificial ripening).

Front 21

Tropisms

Back 21

Morphological responses to the enviroment.

Front 22

Phototropism (overview)

Back 22

ii. Ensures maximal exposure to light through inhibition of growth on lit side of plant
iii. Sensation of light occurs at shoot tip (cryptochromes) : blue light receptors

Front 23

Thigmotropism

Back 23

Changes in growth patterns due to touch.

example vines crawling up a tree.

Front 24

Circadiane Rythmes

Back 24

Sensitivity to day and night cycles (photoperiodism)

circadian rhythm depends on light sensitive structures and signaling compounds to spread information through the plant

Front 25

Example of photoperiodism

Back 25

PHOTOPERIODISM is the reason for most seasonal responses example: control of flowering.

Front 26

flowering types

Back 26

1. Short-day, flower in response to night lengths longer than a certain minimum. Therefore flower in the fall.
2. Long-day, flower in response to night lengths shorter than a certain maximum. Therefore flower in the spring.
3. Day-neutral, flower in response to internal cues (e.g., plant maturity); flowering not photoperiod-sensitive.

Front 27

Flowering mechanism

Back 27

Flowering responds to night length.

Just a flash of light to long will supress flowering.

Signal is hormonal therefore by grafting two plants together the signal produced by one plant impacts the other.

Front 28

Phytochromes

Back 28

are red/far-red sensitive pigments composed of a protein covalently attached to a non-protein chromophore

Front 29

Phytochromes

Back 29

i. Red light darkness (~660 nm) induces a conformational change that makes the phytochrome more sensitive to far-red light