Plant hormones are chemical substances that regulate the growth and development of plants.
Name the five major types of plant hormones.
The five major types of plant hormones are auxins, gibberellins, cytokinins, ethylene, and abscisic acid.
What role do auxins play in plants?
Auxins promote cell elongation, root formation, and differentiating xylem and phloem tissues.
How do gibberellins affect plant growth?
Gibberellins stimulate stem elongation, seed germination, and flowering.
What is the main function of cytokinins in plants?
Cytokinins promote cell division and delay leaf senescence.
Which plant hormone is responsible for fruit ripening?
Ethylene is responsible for fruit ripening and some aspects of plant aging.
How does abscisic acid affect plants under stress?
Abscisic acid helps plants respond to stress by closing stomata and inducing dormancy during unfavorable conditions.
Describe the interaction between auxins and cytokinins in plant tissue cultures.
Auxins and cytokinins balance cell differentiation and growth; a higher auxin-to-cytokinin ratio promotes rooting, whereas the inverse ratio promotes shoot formation.
What are the effects of ethylene exposure on seedling growth?
Ethylene exposure can lead to the 'triple response' in seedlings: inhibited stem elongation, thickening of the stem, and horizontal growth.
Why is gibberellin often used in agriculture for fruit production?
Gibberellins are used to enhance fruit size and quality and to promote seedless fruit development through parthenocarpy.
What role do cytokinins play in leaf senescence?
Cytokinins delay leaf senescence by maintaining chlorophyll and protein levels, keeping leaves green and functional longer.
How does abscisic acid influence seed germination?
Abscisic acid inhibits seed germination by maintaining seed dormancy, ensuring germination occurs only under favorable conditions.
What is the significance of ethylene in plant responses to stress?
Ethylene is involved in various stress responses, including promoting leaf abscission and defense against pathogens.
How do auxins contribute to the tropic responses of plants?
Auxins regulate plant growth towards light (phototropism) and against gravity (gravitropism) by uneven distribution in plant tissues.
What is a practical application of cytokinins in agriculture?
Cytokinins are applied to promote shoot development and delay leaf aging in crops, enhancing yield and shelf-life.