Plant hormones MCQ Quiz in मल्याळम - Objective Question with Answer for Plant hormones - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

The correct answer is ABA

Explanation:

• Abscisic Acid (ABA) plays a pivotal role in plant development and adaptive stress responses, particularly in the acquisition of desiccation tolerance during seed development. This desiccation tolerance is crucial for seeds, as it ensures their survival during dry conditions and maintains their viability until environmental conditions are favorable for germination.
• ABA accumulates in the seed as it begins to mature, signaling the embryo to initiate changes that prepare it for desiccation. These changes include the synthesis of protective proteins, deposition of storage compounds, and cessation of growth.
• ABA specifically influences the expression of a wide array of genes, including those coding for Late Embryogenesis Abundant (LEA) proteins. LEA proteins are highly hydrophilic, meaning they can protect cellular structures and enzymes by preventing aggregation during dehydration, essentially stabilizing the cell's internal environment.
• Other proteins induced by ABA include seed storage proteins that serve as nutrient reserves for the growing embryo upon germination.
• ABA also regulates the closure of aquaporins, which are channels in the cell membrane that control water flow. By modulating aquaporin activity, ABA decreases water loss, further preparing the seed for desiccation.
• Additionally, ABA influences the accumulation of osmoprotectants -molecules that protect cells against the detrimental effects of dehydration by stabilizing proteins and membranes and by balancing cell osmotic potential.

The correct answer is Option 3

Explanation:

Statement A: Incorrect. Ethylene is not synthesized from phenylalanine. This pathway, involving phenylalanine ammonia-lyase (PAL), is significant in the production of other compounds, such as flavonoids and lignin, not ethylene.

Statement B: Partially incorrect. While the ethylene signal transduction pathway does initiate with ethylene binding to its receptor (e.g., ETR1), these receptors are located at the endoplasmic reticulum membrane, not in the cytosol. ETR1 and its homologs serve as receptors for the plant hormone ethylene, which regulates various aspects of plant growth and development, including seed germination, root hair development, and fruit ripening.These receptors contain an N-terminal ethylene-binding domain located in the ER lumen, which binds to ethylene molecules. 

Statement C: Correct. This statement accurately describes the biosynthesis pathway of ethylene. The conversion of methionine to ethylene involves specific enzymatic steps: methionine is first converted to S-adenosylmethionine (SAM), then SAM is converted to 1-aminocyclopropane-1-carboxylic acid (ACC) by the enzyme ACC synthase, and ACC is finally converted to ethylene by the enzyme ACC oxidase.

Statement D: Correct: The statement accurately describes the negative regulation of the ethylene signaling pathway in the absence of ethylene. The ethylene receptor ETR1 (and others in its family), when not bound by ethylene, activates CTR1, a negative regulator kinase. CTR1 then represses the ethylene response pathway, part of which involves the degradation of EIN3/EIL1 transcription factors which are central to activating ethylene response genes.

Conclusion: Therefore, the correct statements are C and D

The correct answer is Option 2

Explanation:

• Brassinosteroids are synthesized from plant sterols, with campesterol serving as a direct precursor for brassinolide, the most active form of BRs.
• The conversion of campesterol to brassinolide involves several enzymatic reactions. Among the enzymes involved, the cytochrome P450 monooxygenase (CYP) enzymes play a critical role in this biosynthesis pathway.
• These enzymes are involved in specific hydroxylation steps that are essential for converting precursors into active brassinosteroids.
• The reactions catalyzed by the CYP enzymes occur at various positions on the sterol backbone, introducing necessary hydroxyl groups that contribute to the biological activity of the final brassinosteroid product.
• This process is complex and finely tuned, involving multiple steps and enzymes beyond just the CYP family. Furthermore, the ER (endoplasmic reticulum) serves as a critical site for these biosynthetic reactions, where CYP enzymes are localized.

Key Points

• Brassinosteroids are not synthesized directly from glucose via glycosyltransferase enzymes. They are synthesized from sterols, most directly from campesterol.
• The biosynthesis of brassinosteroids does not exclusively involve the addition of methyl groups to cholesterol without requiring CYP enzymes.Hydroxylation reactions catalyzed by CYP enzymes are essential steps in the pathway.
• Active brassinosteroid levels are not kept constant; they are regulated through a balance of synthesis, inactivation, and catabolic reactions, depending on the plant's developmental stage and environmental conditions. This ensures that BR levels are dynamically managed to meet the plant's physiological needs.

The correct answer is Option 3

Explanation:

Strigolactones are a class of plant hormones that were initially recognized for their role in inhibiting shoot branching and facilitating the establishment of mycorrhizal associations.

Mechanisms of Action in Drought Stress Response

• Alteration of Root Architecture: One of the ways strigolactones help plants to cope with drought is by modifying root architecture. Under drought conditions or in response to strigolactone signaling, plants can adapt by growing deeper or more extensive root systems. This architectural adjustment allows the plant roots to access water from deeper soil layers that are less affected by evaporation. Additionally, strigolactones can influence lateral root formation and root hair density, which are important for maximizing water uptake from the soil.
• Promotion of Water Uptake: By altering root architecture, strigolactones indirectly promote water uptake. A deeper or more branched root system increases the soil volume explored by roots, enhancing the plant's ability to access and absorb water. This is critical during periods of drought when surface water is scarce, and plants must rely on moisture present in deeper soil layers.
• Regulation of Other Physiological Processes: While the main recognized action of strigolactones in drought tolerance relates to root architecture, research suggests they might also be involved in regulating other physiological processes that contribute to drought resilience. For example, there could be interactions between strigolactones and other plant hormones that are directly involved in stomatal closure, such as abscisic acid (ABA), thereby influencing the plant's overall water loss through transpiration.

The correct answer is Option 4 i.e. A and C.

Explanation-

The observation that exogenous application of gibberellic acid (GA3) stimulates stem elongation in a dwarf maize mutant while having little effect on a tall wild-type mutant is consistent with the known role of gibberellins in plant growth and development.

Gibberellins are a class of plant hormones that play a crucial role in promoting stem elongation, cell division, and overall plant growth.

Key Points A. Gibberellins are ubiquitous in plants and are also present in several fungi.

• This statement is correct. Gibberellins are a group of diterpenoid acids that function as plant hormones. They are produced by all plants and regulate a wide range of growth and developmental processes, including seed germination, stem elongation, leaf expansion, and flower and fruit development. The discovery of gibberellins traces back to the study of a fungus, Gibberella fujikuroi (now known as Fusarium fujikuroi) that infected rice plants and caused the plants to grow excessively tall. The "foolish seedling" disease, as it was called, was found to be due to the production of a type of gibberellin (GA3) by the fungus.

B. GA1 is the most abundant gibberellin produced in the fungus Fusarium fujikuroi.

• While GA1 is a naturally occurring gibberellin, this statement is not correct. The fungus Fusarium fujikuroi is known to produce Gibberellin A3 (GA3), as its major product, not GA1. GA3 was the first to be discovered and remains the most extensively studied type of gibberellin.

C. The exogenous application of gibberellin, GA3 stimulates dramatic stem elongation in the dwarf maize mutant but has little effect on the tall, wild-type plant.

• This is a correct statement. Several dwarf plant varieties, including mutants of maize, have deficiencies in either the production of or the response to gibberellins. When these dwarf plants are treated with exogenous GA3, they often exhibit large increases in stem elongation. Conversely, wild-type plants that already produce and respond to sufficient quantities of gibberellins generally do not exhibit dramatic changes in growth with additional gibberellin.

D. The application of exogenous gibberellins causes upregulation of the GA20 oxidase and GA3 oxidase genes.

• In plants, the biosynthesis of gibberellins is controlled by a series of enzymes, including GA20 oxidase and GA3 oxidase. However, when exogenous gibberellins are applied, their biosynthesis is generally reduced rather than increased. This is a common example of negative feedback regulation, where the accumulation of a final product (in this case, gibberellins) inhibits its own production. So this statement is incorrect.

Key Points

• Auxin efflux is mediated by PIN auxin efflux carriers proteins.
• The PIN proteins (named after the pin-shaped inflorescences formed by the pin mutant of Arabidopsis) are a plant-specific family of transmembrane proteins that transport the auxin.
• Directional auxin movement is associated with the tissue-specific distribution of PIN proteins.
• They are asymmetrically localized on the plasma membrane of cells and their asymmetrical distribution also determines the directionality of intercellular auxin flow.
• Until now, eight members of the PIN protein family have been isolated in Arabidopsis and are commonly referred to as PIN1 to PIN8.
• The PIN1, PIN2, PIN3, PIN4, and PIN7 proteins are localized at the plasma membrane, acting as auxin efflux carriers.
• PIN1 (localized basally in vascular parenchyma cells) mediates the vertical transport of auxin (IAA) from the shoot to the root along the embryonic apical-basal axis.
• Other proteins that play a role in auxin efflux are ABCB proteins (ATP-binding cassette subfamily B).
• The ABC transporters comprise a super-family of membrane proteins.
• On the basis of sequence similarity, protein size and other features, the plant ABC proteins can be divided into eight sub-families, ABCA - ABCH.
• Among the ABCB subfamily, ABCB1, ABCB4, and ABCB19 have been well characterized as auxin transporters.
• However, recent studies showed that other ABCBs like ABCB14 and ABCB15 also are associated with polar auxin transport.
• ABCB19 mediates rootward auxin transport in the stele.
• Many auxin transport inhibitors (phytotropins) are presumed to bind to the IAA-efflux protein and prevent auxin efflux.
• Synthetic compounds TIBA (2,3,5-triiodobenzoic acid) and NPA (Naphthylphthalamic acid) act as auxin efflux inhibitors, thus blocking polar transport.
• In roots, on the other hand, there appear to be two transport streams.
• An acropetal stream, arriving from the shoot, flows through xylem parenchyma cells in the central cylinder of the root and directs auxin toward the root tip In the primary root, acropetal transport of auxin towards the root tip is a PIN-dependent process.
• Auxin flow towards the tip is maintained by the action of PIN1 and PIN4 proteins present in the stele.
• In the columella, the action of PIN3 and PIN7 redirects auxin flow laterally to the lateral root cap and the epidermis, where the apically localized PIN2 mediates the upward flow of auxin to the elongation zone.
• The PIN2-based shootward epidermal auxin flow is further supported by the action of AUX1 and ABCB4 transport proteins.

Explanation:

• In the columella, the action of PIN3 and PIN7 redirects auxin flow laterally to the lateral root cap and the epidermis, where the apically localized PIN2 mediates the upward flow of auxin to the elongation zone.
• The PIN2-based shootward epidermal auxin flow is further supported by the action of AUX1 and ABCB4 transport proteins.

Hence the correct answer is option 1.

Concept:

• Plant hormones are naturally occurring small molecule compounds and play particularly important roles in the normal functioning of plant.
• According to structural and chemical diversity, plant hormones are grouped into several classes, including auxins, cytokinins (CKs), abscisic acid (ABA), gibberellins (GAs), ethylene, jasmonic acid (JA), salicylic acid (SA), brassinosteroids (BRs), and strigolactones (SLs).
• The important roles of plant hormones is the regulation of plant growth and development 

Explanation:

• Plant hormones (phytohormones) are chemicals produced by plants that regulate their growth, development, reproductive processes, longevity, and even death.
• These small molecules are derived from secondary metabolism and are responsible for the adaptation of plants to environmental stimuli.
• Plant hormones appear to be ubiquitous, that is, they are present in all higher plants (and many are also present in lower plants, and even in fungi and bacteria).
• This universality of plant hormones is remarkable.
• The effects of plant hormones are quite complex, one plant hormone often having a wide range of effects.
• Light, temperature, and moisture are particular environmental signals, and these affect the biosynthesis, catabolism, and translocation of plant hormones.
• Plants do not have particular glands or tissues where hormone is synthesized solely.
• A plant hormone is synthesized in one part of a plant and translocated to another part in very low concentrations it causes physiological response.

Correct option: 3) They are synthesized in specific glands and tissues.

Concept:

• Gibberellins are a class of plant hormones that regulate various aspects of plant growth and development.
• They are involved in promoting stem elongation, seed germination, flower and fruit development, and other processes.
• Gibberellins were first discovered in Japan in the 1930s as a result of research on a fungus that caused abnormal growth in rice plants.
• The name "gibberellin" comes from the fungus Gibberella fujikuroi, which was the source of the first gibberellin to be isolated.
• Gibberellins are synthesized in various parts of the plant, including the shoot apical meristem, young leaves, and developing seeds.
• They are transported through the plant via the phloem and xylem.
• The effects of gibberellins on plant growth and development are complex and depend on a variety of factors, including the species of plant, the stage of growth, and the environmental conditions.
• For example, in some plants, gibberellins promote stem elongation and can be used to increase the height of crops such as rice and wheat.
• In other plants, gibberellins are involved in flower and fruit development and can be used to promote flowering and fruiting in some crops.
• Overall, gibberellins play a key role in regulating plant growth and development, and their effects are important for agriculture and horticulture.

Explanation:

• The hormone which substitutes the long photoperiod required for flowering is Gibberellin.
• Gibberellins are a group of plant hormones that regulate various growth and developmental processes in plants, including the promotion of flowering.
• In some plant species, gibberellins can substitute for the long photoperiod required for flowering, allowing the plants to flower even under short-day conditions.
• In many plants, the timing of flowering is regulated by day length or photoperiod.
• Some plants require a long period of daylight to flower, while others require a
• short period of daylight or even darkness. This is because the length of the day and night cycles affect the levels of certain plant hormones, including gibberellins, which play a role in regulating flowering.
• Gibberellins are a group of plant hormones that promote stem elongation, seed germination, and flowering in many plant species.
• In some plants, gibberellins can substitute for the long photoperiod required for flowering, allowing the plants to flower even under short-day conditions.
• This is because gibberellins can promote the expression of flowering genes, which leads to the development of flower buds.

Auxin - 

• Auxin is a class of plant hormones responsible for regulating various aspects of plant growth and development.
• It plays a crucial role in cell elongation, phototropism (bending towards light), gravitropism (response to gravity), apical dominance (suppression of lateral bud growth), and root development.
• Auxin also participates in tropic responses, such as the bending of plant parts in response to stimuli.

Gibberellin - 

• Gibberellins are a group of plant hormones that regulate plant growth and development, particularly stem elongation.
• They are involved in diverse processes, including seed germination, flowering, fruit development, and stem elongation.
• Gibberellins promote stem elongation by stimulating cell division and elongation, causing plants to grow taller.
• They also play a role in breaking seed dormancy and promoting flowering.

Cytokinin - 

• Cytokinins are plant hormones involved in cell division and differentiation.
• They are crucial for promoting cell proliferation and growth in various plant tissues, such as shoots, roots, and developing embryos.
• Cytokinins interact with auxin to maintain proper balance and control of plant growth.
• They also regulate processes like shoot formation, delay in leaf senescence (aging), and influence nutrient mobilization.

Brassinosteroid - 

• Brassinosteroids are a group of plant hormones that regulate multiple physiological processes in plants.
• They play a role in promoting cell elongation, cell division, and differentiation.
• Brassinosteroids are involved in various aspects of plant growth and development, including seed germination, stem elongation, vascular development, and stress responses.
• They also contribute to the regulation of flowering, pollen tube elongation, and fruit development.

Important Points

Transmembrane Receptor:

• A transmembrane receptor is a type of receptor protein that spans the cell membrane.
• These receptors have an extracellular domain that binds to specific signaling molecules, such as plant hormones, and an intracellular domain that transmits the signal into the cell.
• When a hormone binds to the extracellular domain of a transmembrane receptor, it initiates a cascade of molecular events inside the cell, leading to a cellular response.
• The hormone Cytokinin and Brassinosteroid (B in column I) are associated with transmembrane receptors (a in column II).

Soluble Receptor - 

• A soluble receptor, also known as a cytoplasmic receptor, is a receptor protein found within the cytoplasm of the cell.
• Unlike transmembrane receptors, soluble receptors do not span the cell membrane.
• Instead, they are located inside the cell and are capable of directly interacting with certain signaling molecules, including plant hormones.
• When a hormone binds to a soluble receptor, it triggers a series of intracellular events that result in a cellular response.
• The hormone Auxin and Gibberellins (A in column I) are associated with soluble receptors (b in column II).

Explanation:

(i) Response mediated by phosphorylation/dephosphorylation:

• Phosphorylation and dephosphorylation are common regulatory mechanisms in cellular signaling pathways.
• Phosphorylation refers to the addition of a phosphate group to a protein or molecule, while dephosphorylation is the removal of a phosphate group.
• This reversible modification of proteins through phosphorylation and dephosphorylation can trigger various cellular responses.
• In the context of plant hormone signaling, a response mediated by phosphorylation/dephosphorylation indicates that the binding of the hormone to its respective receptor activates a cascade of phosphorylation events, resulting in the activation or inactivation of downstream signaling components.
• These phosphorylation events can regulate enzyme activities, alter protein-protein interactions, or modulate gene expression, leading to specific cellular responses.

(ii) Response mediated by proteasome-mediated protein degradation:

• Proteasome-mediated protein degradation is a process in which proteins are targeted for degradation by the proteasome, a cellular complex responsible for breaking down proteins.
• In this response type, the plant hormone signaling pathway leads to the selective degradation of specific proteins.
• When the hormone binds to its receptor and triggers the signaling pathway, it can induce the tagging or modification of target proteins, marking them for degradation by the proteasome.
• The targeted degradation of these proteins can regulate their abundance, stability, or activity, influencing the overall cellular response to the hormone.

Therefore, the correct answer is option 2: (A) - (b) - (ii) and (B) - (a) - (i).

The correct answer is C and D only

Concept:

Polar auxin transport is a fundamental mechanism in plants that regulates growth and development. Auxins are a class of plant hormones responsible for processes such as cell elongation, root development, and tropic responses. This transport is directional and occurs from the shoot apex to the root apex. The polar nature of auxin transport is facilitated by specific cellular mechanisms involving active transport and protein carriers.

• Auxin transport occurs via specialized pathways that ensure the hormone's movement in a controlled and polarized manner.
• Protein carriers such as PIN and AUX/LAX proteins play a significant role in mediating this transport across plant cell plasma membranes.

Explanation:

• Statement C: Polar auxin transport is specific for active auxins, including both natural ones such as indole-3-acetic acid (IAA) and synthetic auxins like 2,4-D. This specificity is crucial for the regulation of plant growth processes. Thus, this statement is correct.
• Statement D: The process is mediated by protein carriers located on the plasma membrane, primarily PIN proteins and AUX/LAX transporters, which actively move auxins in a polar manner. 

Incorrect Statements:

• Statement A: Polar auxin transport does not proceed via the symplast (cytoplasmic continuity between cells). Instead, it involves active transport across the plasma membrane mediated by protein carriers. Therefore, this statement is incorrect.
• Statement B: The velocity of polar auxin transport is slower than the phloem translocation rates. Phloem translocation is a much faster process, driven by pressure flow mechanisms. Thus, this statement is incorrect.