Lesson 5: Plant-Environment Interactions

Chlorophyll

The primary pigment for photosynthesis, converting light energy into chemical energy.

Phytochrome

A pigment-containing molecule associated with photomorphogenesis, existing in active (Pfr) and inactive (Pr) forms.

Phototropism

Directional growth of plants toward light, positively in stems and often negatively in roots.

Etiolation

A survival mechanism where seedlings grown in the dark become long, slender, and pale to reach light.

Gravitropism

Orientation based on gravity; roots grow down (positively gravitropic) and shoots grow up (negatively gravitropic).

Auxin (Indoleacetic Acid - IAA)

A plant hormone that causes cell enlargement and is responsible for phototropism and gravitropism.

Cytokinins

Hormones produced in root tips that promote cell division and work against auxin for bud growth.

Ethylene

A gaseous plant hormone that promotes fruit ripening and can be delayed by carbon dioxide.

Abscisic Acid (ABA)

A hormone that maintains dormancy in seeds and triggers stomatal closing by moving potassium ions.

Gibberellins

Hormones involved in stem elongation and flowering, with over 100 types identified.

Vernalization

A chilling period required for the temperature-dependent pathway to flowering.

LEAFY (LFY)

A master regulatory gene defining the development of floral parts.

Photoperiod

The proportion of light to uninterrupted darkness, critical for the flowering of short-day and long-day plants.

Thigmotropism

Directional growth in response to contact, such as tendrils twining around a support.