Test Your Knowledge on Plant Hormones

Effects of Plant Hormones:

• Survival of plants depends on their ability to respond to changes in their environment
• Plants respond to several types of stimuli including light, gravity, physical objects, herbivory, water, and physical touch
• Plants do not possess a nervous system; their responses rely on chemical substances that are released or altered in response to a stimulus
• Phytochromes are plant pigments that react to different types of light, leading to different plant responses
• Phytochrome pigments exist in two forms: PR (inactive) and PFR (active)
• Absorption of different wavelengths of light causes a reversible conversion between the PR and PFR forms of phytochrome
• Phytochrome is responsible for seed germination: red light triggers germination while far-red light prevents it
• Phytochrome controls flowering: long day plants flower when the nights are short, high levels of PFR activate flowering, and PFR activates expression of genes that stimulate flowering
• Phytochromes are also involved in plant responses to light and gravity by acting as transcription factors
• PFR can move into the nucleus via the nuclear pores and bind to a protein known as phytochrome-interacting factor 3 (PIF3)
• PIF3 can initiate transcription and activate various different genes, controlling many different aspects of plant growth and development
• The length of night can be detected by a plant because it determines the quantities of different forms of phytochrome in the leaf