Plant Growth and Development

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Questions and Answers

What is the primary role of cytokinins in plants?

To stimulate bud formation and tissue differentiation (correct)

To induce root growth

To promote leaf senescence

To enhance fruit ripening

Which of the following is a characteristic function of ethylene in plants?

Promotes root development

Stimulates leaf growth

Enhances chlorophyll production

Induces leaf senescence and abscission (correct)

How does abscisic acid (ABA) primarily function in response to environmental stresses?

By promoting shoot growth

By enhancing stomata opening

By increasing leaf photosynthesis

By inducing stomatal closure (correct)

What discovery is credited to W.W. Garner and H.A. Allard?

The concept of photoperiodism Signup and view all the answers

Which condition does not primarily trigger an increase in abscisic acid levels in plants?

Low light intensity Signup and view all the answers

What is the main distinction between growth and development in plants?

Growth involves cell division and enlargement, while development involves phase transitions. Signup and view all the answers

How are vitamins different from hormones in plants?

Vitamins are not physiologically active and act as co-factors. Signup and view all the answers

Which of the following is an example of a postulated hormone?

Florigen Signup and view all the answers

What defines synthetic hormones in the context of plant growth regulators?

They are produced artificially but mimic the activity of natural hormones. Signup and view all the answers

Which of the following hormones is classified as a growth promoter?

Auxins Signup and view all the answers

What role do nutritional factors play in plant growth?

They are the raw materials required for growth. Signup and view all the answers

Which statement is true about plant hormones?

Plant hormones are active in locations different from where they are synthesized. Signup and view all the answers

What is the characteristic of growth in plants?

Growth involves an irreversible increase in size and mass. Signup and view all the answers

What is the main function of auxins in plants?

Promote growth along the vertical axis Signup and view all the answers

What is the role of the hormone 'florigen' in plants?

It induces flowering. Signup and view all the answers

Which of the following statements about the production of auxins is correct?

Auxins are produced in areas of active growth Signup and view all the answers

What discovery did F.W. Went contribute to the understanding of auxins?

He successfully discovered and isolated auxins from oat coleoptiles Signup and view all the answers

Which type of plant flowers when day length is shorter than a critical day length?

Short-day plants Signup and view all the answers

Which synthetic auxin is known for its use in herbicides?

2,4-D (2,4-Dichlorophenoxy acetic acid) Signup and view all the answers

What defines a plant classified as a Long-day Plant (LDP)?

Flowers when day length is longer than a critical day length Signup and view all the answers

What is critical day length?

The photoperiod required to induce flowering Signup and view all the answers

What effect does auxin have on lateral bud development?

Suppresses lateral bud growth in the presence of apical buds Signup and view all the answers

What is the primary cause of cell elongation induced by auxins?

Increase in osmosis and cell wall plasticity Signup and view all the answers

Which of the following characteristics apply to Day-neutral Plants (DNP)?

Flowering is controlled endogenously Signup and view all the answers

How do natural auxins differ from synthetic auxins?

Natural auxins are produced continuously by plant tissues Signup and view all the answers

Which of the following is NOT a method by which auxins promote cell elongation?

Inhibiting wall synthesis Signup and view all the answers

What effect does a short flash of light during the night have on plants with a critical night length?

It makes the plant behave as if it has been exposed to a long day. Signup and view all the answers

Which form of phytochrome absorbs red light?

Pr Signup and view all the answers

What is the primary purpose of vernalization in plants?

To induce early flowering through cold treatment. Signup and view all the answers

What did Klippart discover about the temperature requirement for flowering in wheat?

Low temperatures are necessary for flowering in winter wheat. Signup and view all the answers

What happens to the Pfr form of phytochrome under continuous darkness?

It converts to Pr form. Signup and view all the answers

Which of the following plants is typically affected by vernalization?

Winter wheat Signup and view all the answers

What type of light wavelength reverses responses in plants when exposed?

Far red light Signup and view all the answers

Why do dry seeds not respond to vernalization?

They require hydration to respond to cold treatment. Signup and view all the answers

Study Notes

Growth and Development

Growth is a continuous, irreversible change in size, volume, and weight of a plant.
Development is a phase to phase irreversible, qualitative change in plant body.
Plant growth and development are influenced by internal factors including nutrients and chemical messengers such as hormones and vitamins.

Hormones and Vitamins

Hormones are synthesized in one part of the plant and have an action in a different part.
Vitamins are used in the same part without transport.
Vitamins function as co-factors for enzymes.

Plant Growth Regulators

The term "phytohormone" was suggested by Thimann (1948) for plant hormones.
Plant hormones are also known as growth hormones, growth regulators, growth promoting substances, or growth factors.
Plant growth regulators include all plant hormones but also non-nutrient chemicals that influence growth.

Classification of Plant Growth Regulators

Plant hormones are classified by origin and function.
Natural Hormones are naturally produced by plant tissues (e.g., Indole Acetic Acid - IAA).
Synthetic Hormones are artificially produced and have similar physiological activity to natural hormones (e.g., 2,4-D, NAA).
Postulated Hormones are spontaneously produced in the plant but their structure and function are not yet fully understood (e.g., Florigen, Vernalin).
Growth Promoting Hormones (e.g., Auxins, gibberellins, cytokinins) increase growth.
Growth Inhibiting Hormones (e.g., ABA, ethylene) inhibit growth.

### Auxins

Derived from "Auxein," meaning "to grow/increase".
Promote growth along the vertical axis when applied in low concentration.
Discovered by Arpad Paàl in 1919 who observed bending of oat coleoptiles after asymmetrically placing cut tips.
F.W. Went isolated the growth substance from oat coleoptile tips (1926) and Kogl and Haagen-Smit (1931) named it "auxin."
Auxins promote cell elongation and division, apical dominance, and root initiation.
Natural auxins are produced continuously by plants (e.g., IAA) and synthetic auxins are manufactured (e.g., 2,4-D, NAA).

### Cytokinins

Promote cell division and promote lateral bud growth (counteract apical dominance).
Synthesized mainly in roots and transported upwards to the shoots.
Used in tissue culture to induce shoot development.
May slow or prevent leaf senescence.

Ethylene

A gaseous plant hormone.
Produced in actively growing meristems, ripening fruits, senescing flowers, germinating seeds, and injured tissues.
Diffuses readily throughout the plant.
Promotes leaf senescence and abscission.
Can increase the number of female flowers in some plants.
Degreens citrus fruits - breaking down chlorophyll to reveal underlying color.

Abscisic Acid (ABA)

A growth inhibitor.
Synthesized in leaves and moves readily through the plant.
Counteracts growth-promoting effects of auxins and gibberellins.
Involved in leaf and fruit abscission, seed dormancy, and bud dormancy.
Induces stomatal closure in response to stress (e.g., water, heat, or salinity).

### Photoperiodism

Discovery: W.W. Garner and H.A. Allard discovered photoperiodism studying flowering in a tobacco plant in 1920.
The biological measurement of relative lengths of day and night.
The control of flowering is based on changes in day length.
Mechanism: Phytochrome pigment in plant leaves is responsible for sensing light and initiating flowering.
Phytochrome exists in two forms: Pr (absorbs red light) and Pfr (absorbs far red light).
Pr is converted to Pfr upon exposure to red light, and Pfr converts back to Pr in darkness.
Photoperiodism is used commercially to manipulate plant growth. For example, increasing day length can be used to prevent winter dormancy and autumnal fall.

### Classifications of Photoperiodic Responses

Short-Day Plants (SDP) flower when day length is shorter than a critical day length (e.g., soybean, chrysanthemum).
Long-Day Plants (LDP) flower when day length is longer than a critical day length (e.g., oat, radish, spinach).
Long-Short Day Plants (LSDP) flower after a sequence of long days followed by short days (e.g., Jasmine, Bryophyllum).
Short-Long Day Plants (SLDP) flower after a sequence of short days followed by long days (e.g., winter rye).
Day-Neutral Plants (DNP) are insensitive to day length and flower based on internal factors (e.g., Balsam, Maize).

### Critical Day Length

The photoperiod required to induce flowering
Varies from species to species.
Must not be exceeded in short-day plants and must be exceeded in long-day plants.
A single inductive cycle is necessary for flowering.
Night break phenomenon: A brief flash of light during the night can disrupt the short-day response in plants.
Light quality: Far Red light promotes short-day responses, while red light promotes long-day responses.

### Vernalization

Promotion of flowering with cold treatment.
Dry seeds don't respond to cold treatment.
Shortens the vegetative period, resulting in early flowering.
Plants without cold treatment may have delayed flowering or remain vegetative.
The cold treatment is usually applied to seeds or growing plants for a period of time.

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Description

This quiz explores the concepts of plant growth and development, highlighting the roles of hormones and vitamins in these processes. It also covers the classification of plant growth regulators and their impact on plant health. Test your knowledge on how internal factors influence the growth and development of plants.