Plant Tropisms and Auxin Dynamics

Flashcards covering the mechanisms of plant tropisms, the role of Indole Acetic Acid (IAA), and experimental findings regarding phototropism.

Tropism

The bending of a plant towards (positive) or opposite (negative) to the direction of a stimulus, caused by a unilateral stimulus leading to unequal growth.

Unilateral stimulus

A stimulus coming from one side only, which results in unequal production or distribution of growth hormone and subsequent unequal plant growth.

Auxin (IAA)

Indole Acetic Acid, a plant growth hormone produced at the tips of shoots and roots that is transported to regions of active growth to affect cell elongation.

Positive response

A type of tropism where the plant grows or bends towards the direction of the stimulus.

Negative response

A type of tropism where the plant grows or bends away from the direction of the stimulus.

Shoot Auxin Concentration Range

The concentration of auxin that promotes growth in shoots, ranging from $10^{-2}$ to $10^{1}\text{ ppm}$.

Minimum Root Auxin Requirement

The minimum concentration of auxin required for roots, which is approximately $10^{-4}\text{ ppm}$, a level that has no effect on shoot growth.

Phototropism

A plant response to light, mainly exhibited by the shoot, where the tips bend towards the sunlight.

Charles Darwin

The "father of evolution" who conducted the earliest experiments on phototropism using seedling coleoptiles.

Coleoptile

The shoot tip of a young seedling used in experimental studies of plant growth and tropism.

Shaded side (Shoot)

The side of the shoot where higher auxin concentration accumulates due to unilateral light, causing more growth by cell elongation.

Illuminated side (Shoot)

The side of the shoot facing the light source, which receives less auxin concentration compared to the shaded side.

Shaded side (Root)

The side of the root where high auxin concentration inhibits cell elongation, causing the root to bend away from light.

Positive phototropism

The specific response where a plant shoot bends towards a light source.