Exam 2 Sensory Systems In Plants

Question 0

Phototropism

Answer 0

Growth response in direction of (blue) light

Question 1

Gravitropism

Answer 1

Growth response to gravity.
Positive: Eg. Roots
Negative: Eg. Stems

Question 2

Photomorphogenesis

Answer 2

Ex. Seedling development
In the dark seedlings have apical hook, is thin and white, leaves are small.
In the light seedlings shoot turns green, leaves expand, decrease in stem growth

Question 3

Phytochrome

Answer 3

A receptor that can be present in 2 forms.

Pr (red) and Pfr (far red)-biologically active form

Question 4

Pfr enters the nucleus and triggers…

Answer 4

Changes in gene expression, which leads to photomorphogenesis.

Question 5

Plant hormones are

Answer 5

Organic substances that at low concentrations can affect development and function.

Question 6

Classical Plant hormones list:

Answer 6

Auxins. Cytokinins. Gibberelins. Ethylene. Abscisic acid.

Question 7

Other plant hormones:

Answer 7

Brassinosteroids, jasmonic acid, strigolactones

Question 8

Auxin (indole acetic acid)
Site of synthesis:
Transport:

Answer 8

Shoot tip (leaf primordia) and developing seeds

Polar(from shoot tip to lower portions of plant)

Question 9

Effects of auxin

Promotion of cell expansion:

Answer 9

Auxin induces the secretions of protons into the cell wall. This promotes the activity of enzymes that make the wall more extensible.

Question 10

Effects of auxin

Phototropism

Answer 10

Auxin produced at the shoot tip moves preferentially to the shaded side of the seedling. Promotes the formation of adventitious roots (roots originating in stems or leaves)

Question 11

Cytokinins
Site of synthesis:
Transport:

Answer 11

Root tip and developing fruits

Transport through the xylem and it accumulates in young leaves and seeds promoting cell division

Question 12

Cytokinins

Effects

Answer 12

Delay of leaf and flowering senescence (aging)

Promotion of growth of lateral buds

Question 13

Organogenesis

Answer 13

Formation of new organs

Balance between auxin and cytokinins affects this.

Question 14

Gibberellins
Site of synthesis:
Transport:

Answer 14

Young tissues, developing seeds

Through xylem and phloem

Question 15

Gibberellins effects
Promotion of stem elongation:
Promotion of fruit growth:

Answer 15

Many dwarf plants are mutants impaired in the synthesis of gibberellins (dwarf corn or mustard plants)

E.g. Seedless grapes

Question 16

Ethylene gas
Site of synthesis:
Transport:

Answer 16

In most tissues in response to stress or wounding.

Diffusion

Question 17

Ethylene effects
Inhibits stem elongation:
Leaf, flower, and fruit senescence and abscission (drop):

Answer 17

Shaking and touching stimulates ethylene production, results in short thick stems.

Stimulates activity of enzymes that break the glue between cell walls.

Question 18

Ethylene triggers..

Answer 18

Fruit ripening

Question 19

Abscisic acid (ABA)
Site of synthesis:
Transport:

Answer 19

Mature leaves in response to water, stress, seeds, roots

Through xylem and phloem

Question 20

ABA effects
Prevents premature germination and is involved in desiccation tolerance:
Causes closure of stomata

Answer 20

Corn mutants that do not synthesize ABA germinate on the cob.

Mutants arabidopsis and tomato plants that don’t synthesis ABA are always wilted.

Question 21

Plant defenses
Physical:
Chemical:

Answer 21

Thorns, spikes, cuticle
Poisonous compounds
Eg. Jack beans produce canavanine(kills insects)
Poison oak produces urushiol
Castor beans produce ricin (protein that blocks translation)

Question 22

Induced defense response

Eg. Plant response to insect herbivory

Answer 22

Plants synthesize molecules that inhibit insect digestion. (Jasmonic acid)

Question 23

Induced defense responses
Virulent pathogen:
Aviral pathogens:

Answer 23

Pathogen eventually kills plant.

Plant responds to pathogen, have genes that code for receptors. Production of antimicrobial activity (hydrogen peroxide, phytoalexins)