topisms

tropism

directional growth in response to a stimulus

IAA

an auxin which regulates cell elongation

phototropism

growth towards light (positive) away (negative)

geotrophism

growth in response of gravity

SHOOTS: GRAVITROPISM (negative)

• IAA diffuses from tips to lower side of shoot

• IF VERTICAL: cells elongate upwards

• so shoot bends upwards (away from gravity)

ROOTS: gravitrophism (positive)

• IAA accumulates underside of root tip

• to inhibit cell elongation

• so the upper side only elongates, causing the root to bend downward into the soil.

• good for mineral uptake

SHOOTS: phototrophism (positive)

EVEN LIGHT SOURCE:

• IAA evenly distributed within tips of shoot

• causing upwards cell elongation

UNILATERAL LIGHT SOURCE:

• IAA accumulates on shaded side, resulting in higher concentration there

• causing the shaded side to elongate and bend toward the light

→ maximises LDR

ROOTS: phototropism (negative)

light not required, want to anchor plant into soil away from light.

• IAA accumulates towards shaded side (lower)

• to inhibit cell elongation

• roots elongate on lighter side so root bends away from light (shaded side stays hidden)

summarise role of growth factors in flowering plants

• specific growth factors move from growing regions (shoot tips/ root tips) where they’re produced

• to other tissues where they regulate growth in response to directional stimuli (tropisms)