PLANT HORMONES

AUXIN

• Stimulates cell elongation, regulates apical dominance, promotes root formation, and mediates tropisms (e.g., phototropism, gravitropism)

CYTOKININ

• Promotes cell division and differentiation, regulates shoot and root growth, delays senescence (aging)

GIBERELLIC ACID

• Stimulates stem elongation, seed germination, and flowering, promotes fruit growth

ABSCISIC ACID

• Inhibits growth, induces seed dormancy and stomatal closure in response to stress (e.g., drought, salinity)

ETHYLENE

• Promotes fruit ripening, senescence (aging), and abscission (shedding) of leaves and fruits, regulates responses to stress

BRASSINOSTEROIDS

• Promote cell elongation, differentiation, and division, regulate flowering, seed germination, and stress responses

OLIGOSACCHARINS

• Induce defense responses against pathogens and herbivores, promote seed germination, and regulate root growth and development

PHOTOMORPHOGENESIS

• Definition: Light-triggered developmental processes in plants.

• Examples: Regulation of seed germination, stem elongation, leaf expansion, and flowering.

• Key Players: Photoreceptors such as phytochromes and cryptochromes.

PHOTOTROPISM

• Definition: Growth response of plants to light direction.

• Positive : Growth towards the light source.

• Negative : Growth away from the light source.

PHYTOCHROME

• A light receptor involved in various plant responses to light.

SEED GERMINATION

• Inhibited by far-red (pfr) light and stimulated by red (pr) light in many plants.

SHOOT ELONGATION

• results in etiolation with the absence of red light - become normal once they are exposed to red light, which increases the amount of pfr.

• Etiolated plants show long, weak stems, and smaller leaves due to longer internodes

PLANT SPACING

• Involved both red and far-red light

• happens when shading plants results in increase in far-red light compared to red light

• when plants are close to one another, there is more far-red light which causes plants to grow taller, allowing then to get more sunlight than the rest.

PHOTOTROPISM

• a directional response due to a directional stimulus like light

• Includes the bending of young stems and other plant parts towards the source of light, particularly the blue wavelength

GRAVITROPISM

• the growth response of plants to gravity.

• helps roots penetrate soil and anchor the plant.

• enables shoots to grow towards light for photosynthesis.

• Examples: Root growth downward (positive gravitropism) and shoot growth upward (negative gravitropism).

TIGHTMOTROPISM

• a directional growth response of a plant or a plant part in response to a contact with an object

TIGHTMONASTY

• response of a plant to touch

SEED DORMACY

• state of suspended growth or development in seeds, allowing them to remain viable until favorable conditions for germination occur.

ABSCISSION

• the natural shedding or dropping of plant organs, such as leaves, at specific stages of development or in response to environmental cues