Plant Growth Regulators (Lecture 10)

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Questions and Answers

What is the primary effect of plant growth retardants on plant growth?

Cause significant growth defects and malformations

Promote cell division and elongation

Reduce stem elongation and increase green color of leaves (correct)

Increase root growth and leaf production

What is the role of sterols in plants?

Hormone production

Root growth promotion

Cell wall formation

An essential component of cell membrane (correct)

Which of the following is NOT a characteristic of plant growth retardants?

Produce significant growth defects (correct)

Block specific sites in PGR biosynthesis

Have little effect on leaf production

Reduce stem elongation

What is the effect of plant sterols on cholesterol levels in animals?

Decrease serum cholesterol concentration Signup and view all the answers

What is the main site of action for plant growth retardants in the gibberellin biosynthetic pathway?

Key steps in GA biosynthesis Signup and view all the answers

Which of the following is an example of a plant growth retardant?

Ancymidol Signup and view all the answers

What is the primary goal of reducing plant height in floricultural crops?

To enhance aesthetic quality without affecting plant growth Signup and view all the answers

Which plant growth retardant is most effective in reducing the height of Poinsettias?

Chlormequat chloride (CCC) Signup and view all the answers

What is the effect of applying daminozide to Chrysanthemum?

It produces shorter, more rigid, and darker green leaves Signup and view all the answers

Which plant growth retardant is commonly used to control the height of bedding plants like Zinnia and Geranium?

Paclobutrazol Signup and view all the answers

What is the primary purpose of using plant growth retardants in turf grass?

To control grass growth on difficult-to-maintain sites Signup and view all the answers

What is the effect of daminozide on anthocyanin production in sweet cherry fruits?

It advances anthocyanin production Signup and view all the answers

What is the effect of daminozide on fruit drop in apples?

It decreases fruit drop Signup and view all the answers

What is the effect of daminozide on flower bud formation in apples and pears?

It stimulates flower bud formation Signup and view all the answers

What is the main benefit of using paclobutrazol in fruit trees?

Maintain tree height for spraying and harvesting efficiency Signup and view all the answers

Which of the following plant growth retardants is used to reduce stem height and diameter in cereal crops?

Chlormequat chloride Signup and view all the answers

What is the main benefit of using chlormequat chloride in grapes?

Increase fruit set Signup and view all the answers

What is the main use of maleic hydrazide in onion and potatoes?

Prevent bud sprouting Signup and view all the answers

What is a critical factor in successful control of plant height using plant growth retardants?

All of the above Signup and view all the answers

Why is soil drenching considered a more effective method of application for plant growth retardants?

It allows for a more exact amount of chemical to be applied Signup and view all the answers

Why are plant growth retardants less effective at high temperatures?

They are more prone to phytotoxicity Signup and view all the answers

What is a critical factor in achieving uniform coverage when applying plant growth retardants?

Stem contact Signup and view all the answers

Study Notes

Plant Growth Retardants (GR)

Synthetic organic compounds that cause retardation/inhibition of cell division and/or elongation
Produce no significant growth defects/malformations
Have little effect on the production of leaves or on root growth
Reduce stem elongation, increase green color of leaves
Block specific sites in pathways of PGR biosynthesis, especially Gibberellins biosynthesis

Gibberellins Biosynthetic Pathway

Gibberellins are affected by GR
GR inhibits key steps in GA biosynthesis

Sterols

An essential component of cell membranes
Plants and animals produce sterols
Cholesterol is exclusively an animal sterol
Plant sterols (phytosterols) are different, with 40 identified, including sitosterols, campestrols, and stigmasterols
Plant sterols lower serum concentration of cholesterol

Use of Plant Growth Retardants

Reduce plant height, especially in floricultural crops
Examples of GR: ancymidol, chlomequat, daminozide, flurprimidol, mefluidide, paclobutrazol, tetcyclacis, and unicozole
Used to manipulate size, shape, and overall quality of plants

Specific Applications

Floricultural Crops

Poinsettia: Chlormequat chloride, CCC, is most effective in reducing height
Chrysanthemum: Daminozide, Ancymidol, and Paclobutrazol are used to reduce height and improve quality
Easter Lily: Ancymidol, Paclobutrazol, and Triademefon are used to reduce height

Bedding Plants

Zinnia and Geranium: Daminozide and Paclobutrazol are used to control height

Turf Grass

GRs are used to control growth, especially in difficult-to-maintain areas
Examples of GRs: Chlorflurenol, Paclobutrazol, Melfluidide

Fruit Production

Daminozide advances anthocyanin production in fruit skin and flesh in sweet cherry
Daminozide increases anthocyanin synthesis, decreases fruit drop, and reduces fruit softening during cold storage in apples

Flower Bud Formation

Daminozide stimulates flowering in apples and pears

Tree Size

Paclobutrazol is effective for controlling shoot elongation in fruit trees

Lodging Control

Chlormequat chloride reduces stem height and diameter, leading to increased yield in wheat, barley, and rye

Fruit Set

Chlormequat chloride increases fruit set in grapes

Other Miscellaneous GR

Maleic hydrazide prevents bud sprouting in onion and potatoes
Citrus abscision agents induce abscision in citrus for mechanical harvesting

Application of Plant Growth Retardants

Successful control of plant height using GR depends on crop, stage of crop, concentration, method of application, volume of application, coverage, and environmental conditions
Foliar spray and soil drenching are two methods of application
Uniform coverage is essential, and stem contact is crucial for effective application

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Description

Learn about plant growth retardants, synthetic organic compounds that inhibit cell division and elongation, and their effects on plant growth and development.