Plant growth Regulators introduction

Question 1

what are plant hormones?

Answer 1

Phytohormones are chemical compounds present in very low concentrations in plants. They regulate plant development, growth, longevity and reproductive processes.

Question 2

Auxin

Answer 2

Auxins are hormones that promotes stem elongation, cell division and inhibits growth of lateral buds in the plants.

They are found in young shoot and root tips.
It usually occurs in undifferentiated cells.
Auxins can be produced naturally(by the plants) and synthetically(in a lab).
Synthetic one can be used in high concentration as a herbicides, causing drastic growth.
Eg. The herbicides, 2,4- D.
Is synthesized in meristem and enlarging Auxins decreases in light and increases in dark.
tissues of plants.

Question 3

Types of auxins

Answer 3

Natural auxins
IAA(indole acetic acid)
IBA(indole butyric acid)

2.Synthetic auxins
NAA(Napthalene acetic acid)
2,4-D(dichlorophenoxy acetic acid)

Question 4

commercial applications of synthetic auxin

Answer 4

prevention of fruits and leaf drop
prevention of sprouting of potatoes and onion bulb
induction of parthenocarpy fruits
induction of flowering in pineapple
control xylem differentiation and promote cell division

Question 5

Auxin in plant growth

Answer 5

1. Control seedling Orieantation
2. stimulate shoot elongation
3. promote root development
4. Fruit development

Question 6

Homemade hormone products

Answer 6

Willow and salix species(contain IBA & SA)
Aspirin, reported as rooting agents

Question 7

What is the chemical formula and structure of Auxin?

Answer 7

Indole 3 acetic acid- C10H9NO

Question 8

Gibberellins

Answer 8

• . Gibberellins is isolated from fungus gibberella fujikuroi
  It is one of the major plant promotors
• It is an organic endogenous compund (Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism.) found in the plant body.
• Gibberellins are a very potent hormone produced in the plant cell’s plastids
  Their natural occurrence in plants control their development.
  Examples: GA3, GA4, GA7, +90PLUS GA compounds
  Used in concentration between 0.01 to 10 mg/l

Question 9

why is Gibberellin considered a plant growth promoter?

Answer 9

Gibberellins are involved in the natural process of breaking dormancy and other aspects of germination
It regulates plant growth.

• Regulate various developmental processes:
• Stem elongation
• Root development
• Germination
• Dormancy
• Flower development
  Elongate stems to proper length
  Promote fruit set
  The transition of ovary to a
  young fruit is called fruit set
  Increase fruit size

Question 10

USES/Commercial Applications of GA

Answer 10

Brewing industries use GA3 to speed malting process
Increase sugarcane yield
Used to hasten maturity
Promote early seed production
Helps malting in barley
Used in grape growing industry.

Question 11

CYTOKININS

Answer 11

Cytokinins are a group of plant growth substances specifically known as phytohormones( (phytohormones) are chemicals produced by plants that regulate their growth, development, reproductive processes, longevity, and even death.) that participate in promoting cell division especially in plant roots and shoots.

Question 12

Chemical formula and structure of GA

Answer 12

C19H22O6
[]https://en.wikipedia.org/wiki/Gibberellic_acid(http://)

Question 13

what are some examples of synthetic and natural cytokinin? know their strucuture also

Answer 13

Natural cytokinin- Zeatin, Isopentenyl adenine
Sythetic cytokin- kinetin, Adenine and Benzylamino purine

Question 14

DISCOVERY OF CYTOKININS and CHARACTERISTICS OF CYTOKININS

Answer 14

Cytokinins were first discovered by Folke Skoog.
Skoog discovered coconut milk as cytokinesis promoting substance.
Later named as ‘Cytokinins’.
Many similar discoveries were made by different scientists later on

Plant growth hormones.
Mainly induce shoot growth.
Responsible for lateral growth of the plant.
Produced mainly in root tips.
Work from bottom up.
Exist both naturally occurring and synthetic cytokinins.

Question 15

Functions of Cytokinins in Plants

Answer 15

Increase cell division.
Produce new leaves.
Stimulate morphogenesis.
Help in overcoming apical dominance.
Delay senescence.
Adventitious root formation.
Transport of nutrients.
Responses to environmental stress.

Question 16

EFFECTS OF EXCESS CYTOKININs

EFFECTS OF DEFICIENT CYTOKININS

Answer 16

EFFECTS OF EXCESS CYTOKININs
Causes Necrotic lesions.
Wilting of leaves.

EFFECTS OF DEFICIENT CYTOKININS
low growth of shoot
Occurrence of morphological changes like dwarfism and smaller leaves.

Question 17

what is the chemical formula and structure of cytokinin?

Answer 17

https://www.ebi.ac.uk/chebi/chebiOntology.do?chebiId=CHEBI:23530

Question 18

Ethylene

Answer 18

Phytohormones are naturally synthesized hormones in plants that act as growth promoter.
Simple gaseous hydrocarbon produced naturally in plants
Its chemical formula is C2H4
Galston and Davis proposed that it was a hormone that induced ripening in fruits and inhibited growth in plant vegetative tissue.https://byjus.com/neet/plant-hormones/

Question 19

Factors affecting ethylene production

Answer 19

Auxin stimulates ethylene production
As it retards the mitotic division of the meristem of roots, shoots, and auxiliary buds.
Red light suppresses ethylene production
With the exposure of plants to red light the production of auxin is stimulated that leads to the suppression of ethylene.
Temperature
With the increase in temperature the production of ethylene increases.

Question 20

functions and practical uses of Ehtylene?

Answer 20

Release from dormant state
Growth
Ripening
Abscission
Senescence

Sprouting of storage organs
Thinning
Feminising Effect
Fruit ripening
Anesthetic

Question 21

Abscisic acid(ABA)

Answer 21

In the mid 1960s 3 inhibitors were reported:
Inhibitor b
Abscission II
Dormin
A plant hormone which functions in many plant development processes, including seed and bud dormancy, the regulation of the size of plant parts and acts as antitranspirant.
it is one of the stress hormones released by plants during drought conditions, temperature, cold and light.
Synthesized in all types of plant cells that contains chloroplast or other plastids.
It is produced in the roots of a plant as well as the terminal bud at the top of the plant.
Especially in Phloem sap, xylem sap, nectar.

Question 22

Chemical name, formula and structure of Abscissic acid

Answer 22

C14 H20 O4
https://byjus.com/neet/plant-hormones/

Question 23

functions of Abscisic acid(ABA)

Answer 23

Promote Leaf senescence(ageing )
Initiates abscission( fall )zone of fruit and leaves.
It stimulate the closure of stomata of leave decreasing the transpiration.
Responsible for seed dormancy by inhibiting cell growth(inhibits seed germination )
Inhibits fruit ripening

Uses
Flowering
Rooting
Antitranspirant
Dormancy
Controlled growth

Question 24

what is the difference between sythetic and natural PGRs?

Answer 24

Plant growth regulators (PGRs) are substances that influence the growth, development, and physiological processes of plants. The main difference between synthetic and natural PGRs lies in their origin:

1. Natural PGRs: These are compounds naturally produced by plants or other organisms. Examples include auxins, cytokinins, gibberellins, abscisic acid, and ethylene. Natural PGRs often play essential roles in regulating various aspects of plant growth and development, such as cell elongation, seed germination, flowering, and fruit ripening.
2. Synthetic PGRs: These are artificially synthesized compounds designed to mimic the effects of natural PGRs or to exert specific effects on plant growth and development. Synthetic PGRs are often developed for agricultural purposes, such as promoting flowering, increasing fruit size, enhancing root development, or controlling plant height. Examples of synthetic PGRs include synthetic auxins like 2,4-D (2,4-dichlorophenoxyacetic acid), synthetic cytokinins like kinetin, and synthetic gibberellins like GA3 (gibberellic acid).

While both natural and synthetic PGRs can have significant impacts on plant physiology, the main difference lies in their origin and production methods. Natural PGRs are derived from biological sources, whereas synthetic PGRs are chemically synthesized in laboratories. Additionally, natural PGRs may have evolved within plants to serve specific functions in their growth and development, while synthetic PGRs are engineered for specific agricultural or horticultural purposes.

Question 25

What is the relationship between a PGR and Plant pest and Disease?

Answer 25

The relationship between plant growth regulators (PGRs) and pests/diseases in plants can be complex and multifaceted:

1. Indirect Effects: PGRs can indirectly influence the susceptibility of plants to pests and diseases by altering their growth and development. For example, PGRs that promote vigorous growth may make plants more attractive to certain pests or susceptible to certain diseases. Conversely, PGRs that regulate plant defense mechanisms or enhance stress tolerance may help plants resist pest infestations or disease infections.
2. Direct Effects: Some PGRs have direct antimicrobial or insecticidal properties that can affect pests and diseases. For instance, certain synthetic PGRs may have pesticidal properties that directly target pests or inhibit the growth of pathogenic microorganisms, thereby reducing disease incidence.
3. Modulation of Defense Mechanisms: PGRs can modulate plant defense responses against pests and diseases. They may enhance the production of defense compounds such as phytoalexins, lignins, and secondary metabolites, which can deter pests or inhibit pathogen growth. Additionally, PGRs can regulate the expression of genes involved in plant defense pathways, thereby enhancing the plant’s ability to withstand pest attacks or disease infections.
4. Integrated Pest and Disease Management: PGRs are often used as part of integrated pest and disease management (IPM/IDM) strategies, where they are combined with other control measures such as cultural practices, biological control agents, and chemical pesticides. PGRs may be employed to enhance plant resistance, mitigate stress, or promote recovery from pest or disease damage, thereby reducing the reliance on conventional pesticide applications.
5. Risk of Imbalance: However, improper or excessive use of PGRs can sometimes lead to unintended consequences, such as increased susceptibility to certain pests or diseases, phytotoxicity, or disruption of ecological balance. Therefore, it’s essential to use PGRs judiciously and in accordance with recommended guidelines to minimize potential risks to plant health and ecosystem integrity.

In summary, the relationship between PGRs and pests/diseases involves a combination of direct and indirect effects, modulation of plant defense mechanisms, and considerations within the broader context of integrated pest and disease management strategies.

Question 26

Difference between Growth and Development

Answer 26

Growth mainly refers to the quantitative increase in plant body such as increase in length of the stem and root, the number of leaves, the fresh weight and dry weight etc. On the other hand, germination of seed, formation of flowers, fruits and seeds, emergence of lateral buds, falling of leaves and fruits are qualitative changes, referred to as development.

Question 27

Plant growth Regulators

Answer 27

Plant growth regulators or plant regulators are the organic compounds other than nutrients which modify or regulate physiological processes in an appreciable measure in the plants when used in small concentrations. They are readily absorbed and these chemicals move rapidly through the tissues when applied to different parts of the plant.
Plant hormones or phytohormones are also regulators but produced by the plants in low concentrations and these hormones move from the site of production to the site of action.

The term plant growth regulators’ is relatively new in use. In earlier literature these were mentioned as Hormones. Hormone is a Greek word derived from “hormao” which means to stimulate. Now the term phytohormone is used in place of plant hormone.
Growth and development of the plant body are controlled by two sets of internal factors, namely, nutritional and hormonal. Nutritional factors supply the plant necessary mineral ions and organic substances such as proteins, carbohydrates and others. These constitute the raw materials required for growth. However, utilization of these substances for proper development of the plant is controlled by certain chemical messengers, called plant growth substances or plant growth regulators, which in minute amounts increase or decrease or modifies the physiological processes in plants.

Question 28

What is the difference between plant Growth Regulator and Plant Hormones

Answer 28

Therefore, the difference between the plant regulator and plant hormone is in that the former one is synthetic and the latter one is natural from the plant source.
“All plant hormones are plant growth regulators, but not all plant growth regulators are plant hormones,”

Question 29

What is the importance of Plant Growth Regulators?

Answer 29

• Propagation ( rooting in stem cuttings, Layering, grafting and budding)
• Flowering control
• control of sex orieantation of the plants
• Fruit set
• Fruit Drop
• Fruit Quality and size
• Ripening of Fruits
• Parthenocarpy

Question 30

Rooting of cuttings:

Answer 30

Certain kind of plants may not successfully root under normal condition and with the aid of plant regulators; they can be easily made to induce rooting. The most commonly employed growth regulators for rooting are auxins like IBA, IAA, and NAA. Among these chemicals IBA is most ideally used since, it is the most effective one.

Concentrations ranging from100-500ppm are used for long dip method of treatment of cuttings for 12-24 hours and high concentrations of 10,000 to 20,000 for quick dip method for a few seconds. The concentrations differ according to the type of cutting i.e. herbaceous, Semi-hard wood and hard wood cuttings. Applications in the form of dust as talcum preparation or in the form of a paste in lanolin are also used.

Question 31

Layering:

Answer 31

Another usage of plant regulators in plant propagation is in aiding rooting of air layering. Layering is the practice of inducing rooting on shoots/stems while it is still attached to the parent plant. This is practiced in fruit trees like guava, pomegranate etc.
The main principle of layering is that a part of the aerial portion of the intact plant is girdled. This results in severing of phloem. Consequently, hormones and food substances coming from the leaves accumulate above the girdled portion. When the ring of bark is removed from the stem, the growth regulators like IBA or IAA in powder or in Lanolin paste is applied at the distal end of the bark-removed portion to promote root formation

Question 32

Grafting and Budding:

Answer 32

Grafting of plants is a widely used horticultural practice of multiplying the desired genotypes in mango, citrus and others. For this, a portion of the plant is inserted in to another plant of the same species or sometimes compatible plants of different species or genera. There are mainly two types of grafting: bud grafting and scion grafting. Whatever may be the method employed, the principle remains the same. When the cambium of a stock plant comes into physical contact with the cambium of a scion both from new xylem and phloem simultaneously together.
Consequently, these become united and grow as one plant. Since, auxins have the property of promoting cell division of cambium these are often employed. Before grafting, either stock or scion or both are dipped in auxin solution. This promotes an early union and consequently, a better success of grafted plants.

Question 33

Control of flowering:

Answer 33

The plant growth regulators are used for the regulation of flowering in certain crops. In pineapple flowering is irregular and harvesting becomes a problem and hence to regulate flower production, plant regulators are used. The treatment generally consists of pouring a required quantity of (50ml), the solution containing 0.25 to 0.5 mg of the chemical of NAA in the central core of plants. In recent studies, Cycocel and Alar at 5000ppm and Ethrel at 100-200ppm have been shown to induce flowering in mango during an off year. In Jasminum grandiflorum, the flowering period is extended by the application of Cycocel at 500ppm.
Flowering can also be induced in certain vegetables such as radish, beet root and carrot with the application of GA.

Question 34

Fruit set:

Answer 34

Various growth regulators like IAA, IBA, IPA, NAA, 2, 4-D, and GA have been found to improve fruit set in many crops. Among these chemicals 2, 4-D and NAA (Planofix) have been found in general to be most effective in increasing the fruit set. The optimum concentrations for this purpose are 10-20 ppm of auxins and 10-100ppm of GA in different crops. Spraying the flower cluster thoroughly 4-6 days after full bloom with 100 ppm GA increased the fruit set in grape. It has been found that in chillies spraying of Planofix @ 1ml in 4.5 liters of water at 60th and 90th day after planting is beneficial for good fruit setting.

Question 35

Fruit drop:

Answer 35

Losses resulting from pre-harvest drop of fruits have long been a serious problem. When the growth regulators have been put in to use in apples and pears, pre-harvest fruit drop can be checked by the application of 2,4-D effectively. Pre harvest fruit drop in citrus is controlled with 2,4-D at a concentration of 20ppm2,4-D, 10- 15ppm of NAA and 2,4,5-T at 15 to 30ppm at pea stage and marble stage and 2,4D at 20ppm and 2,4,5-T at 10-15ppm in mandarins. At 10ppm and NAA at 20ppm have effectively prevented fruit drop in mango. Application of planofix containing NAA at‖ pea stage and marble‖ size of the fruits completely controlled early fruit drop in Guava.

Question 36

Parthenocarpy:

Answer 36

Partenocarpic fruit set could be induced in a number of vegetables like cucurbits, bhendi, brinjal, chillies and tomato and fruits like guava, straw berry, citrus, watermelon etc.IAA,IBA,NAA,NAD,2,4-D,IPA and GA are effective in different plants. Application of GA at 100 ppm induced complete seedless in grapes.

Question 37

Fruit ripening:

Answer 37

The plant growth regulators can be employed to hasten or delay fruit ripening. Plant growth regulators like 2, 4, 5-T at concentrations of 25 to 100ppm has been found to hasten the ripening in some varieties of plums and peaches. In banana ethrel treatment at 2500ppm induces ripening in 24 hours. Application of 2, 4-D at 16ppm delays ripening in Washington navel oranges.
In tomatoes all fruits on a plant won‘t mature and ripen at a time .This is a serious disadvantage for mechanical harvesting .Ethephon applied 1-2 weeks before harvest promotes de-greening and ripening of tomatoes. Application of smoke is commercially employed to hasten and ripen bananas, the active ingredient responsible being ethylene.

Question 38

Fruit size and quality:

Answer 38

Increase in berry size in grape varieties was reported when GA was applied at 40ppm at bud and flower stages. Higher concentrations resulted in the increase in the length of berries.

Question 39

Sex expression:

Answer 39

Plant regulators can be employed to modify the sex expression in crops. In cucurbitaceous vegetables the production of male flowers will be always more in number than the female flowers and this sex ratio can be narrowed down by the application of ethrel at 100 to 250ppm, if sprayed four times at weekly intervals commencing from 10 to 15 days after sowing. This growth regulator not only increases the number of female flowers to male flowers, but also produces female flowers at earlier nodes. Application of GA, the sex ratio is shifted towards maleness in several
cucurbits. Certain plant regulators are employed to induce male sterility in crop plants, so that such male sterile plants can be used as a female plant in the hybridization work. Complete male sterility in okra can be obtained by spraying with 0.4% of MH. A single spray one week before floral bud initiation offers male sterility for 10 days and a subsequent spray at floral initiation extends the effect to 22 days.

Question 40

Preparation of growth regulators

Answer 40

Solution form: To prepare an alcoholic solution of any plant growth regulator, dissolve 1 gm. of growth regulator in 50 ml of ethyle alcohol or methyl alcohol or methylated spirit and then dilute this with an equal volume of water to make 100ml of solution containing 10,000 ppm of growth regulator.
This acts as stock solution for further dilutions with distilled or de-ionized water. Stored in well-stoppered bottles in a refrigerator, the solutions retain their activity indefinitely.
Dust form: To prepare a dust containing 10,000ppm of growth regulator dissolve 1gm of the regulator in 40 ml of methylated spirit of 95% alcohol and stir this into 100g of pharmaceutical talc to form a smooth paste. This should be done in a dark room away from strong light. Stir the paste while it is drying until it becomes a fine dry powder. This prepared dust remains active for six months or more if stored in a closed opaque container in a refrigerator. From this stock, before using, dilute the growth regulator by mixing the stock with talc powder.
Lanolin pastes: These are particularly convenient for use in air layering but now regarded as an obsolete treatment for cuttings and are made by stirring the growth regulators into the molten lanolin and then allowing it to cool. To make a paste containing 5,00ppm of growth regulator melt 200gm of lanolin and thoroughly stir into this molten lanolin 1gm of required growth regulator. This prepared paste will keep indefinitely if stored in a well stoppered opaque glass vessel in a refrigerator.