Exam 2 Sensory Systems In Plants Flashcards
(24 cards)
Phototropism
Growth response in direction of (blue) light
Gravitropism
Growth response to gravity.
Positive: Eg. Roots
Negative: Eg. Stems
Photomorphogenesis
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
Phytochrome
A receptor that can be present in 2 forms.
Pr (red) and Pfr (far red)-biologically active form
Pfr enters the nucleus and triggers…
Changes in gene expression, which leads to photomorphogenesis.
Plant hormones are
Organic substances that at low concentrations can affect development and function.
Classical Plant hormones list:
Auxins. Cytokinins. Gibberelins. Ethylene. Abscisic acid.
Other plant hormones:
Brassinosteroids, jasmonic acid, strigolactones
Auxin (indole acetic acid)
Site of synthesis:
Transport:
Shoot tip (leaf primordia) and developing seeds
Polar(from shoot tip to lower portions of plant)
Effects of auxin
Promotion of cell expansion:
Auxin induces the secretions of protons into the cell wall. This promotes the activity of enzymes that make the wall more extensible.
Effects of auxin
Phototropism
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)
Cytokinins
Site of synthesis:
Transport:
Root tip and developing fruits
Transport through the xylem and it accumulates in young leaves and seeds promoting cell division
Cytokinins
Effects
Delay of leaf and flowering senescence (aging)
Promotion of growth of lateral buds
Organogenesis
Formation of new organs
Balance between auxin and cytokinins affects this.
Gibberellins
Site of synthesis:
Transport:
Young tissues, developing seeds
Through xylem and phloem
Gibberellins effects
Promotion of stem elongation:
Promotion of fruit growth:
Many dwarf plants are mutants impaired in the synthesis of gibberellins (dwarf corn or mustard plants)
E.g. Seedless grapes
Ethylene gas
Site of synthesis:
Transport:
In most tissues in response to stress or wounding.
Diffusion
Ethylene effects
Inhibits stem elongation:
Leaf, flower, and fruit senescence and abscission (drop):
Shaking and touching stimulates ethylene production, results in short thick stems.
Stimulates activity of enzymes that break the glue between cell walls.
Ethylene triggers..
Fruit ripening
Abscisic acid (ABA)
Site of synthesis:
Transport:
Mature leaves in response to water, stress, seeds, roots
Through xylem and phloem
ABA effects
Prevents premature germination and is involved in desiccation tolerance:
Causes closure of stomata
Corn mutants that do not synthesize ABA germinate on the cob.
Mutants arabidopsis and tomato plants that don’t synthesis ABA are always wilted.
Plant defenses
Physical:
Chemical:
Thorns, spikes, cuticle
Poisonous compounds
Eg. Jack beans produce canavanine(kills insects)
Poison oak produces urushiol
Castor beans produce ricin (protein that blocks translation)
Induced defense response
Eg. Plant response to insect herbivory
Plants synthesize molecules that inhibit insect digestion. (Jasmonic acid)
Induced defense responses
Virulent pathogen:
Aviral pathogens:
Pathogen eventually kills plant.
Plant responds to pathogen, have genes that code for receptors. Production of antimicrobial activity (hydrogen peroxide, phytoalexins)
