Q.While eating watermelons, all of us wish it was seedless. As a plant physiologist can you suggest any method by which this can be achieved?

Plant hormones, also known as phytohormones, are chemical messengers that regulate growth, development, and responses to environmental stimuli in plants. They often act in concert, with some hormones promoting a particular process while others inhibit it, creating a delicate balance that controls the plant's life cycle. Understanding these antagonistic and synergistic relationships is key to solving this type of problem.

Here's a breakdown of each combination:

1. Analyze Combination I: Senescence

   • Physiological effect: Senescence refers to the process of aging in plants, leading to the eventual death of organs (like leaves) or the entire plant.
   • Positive role (promotes senescence): Abscisic Acid (ABA). ABA is known as a stress hormone and plays a significant role in promoting senescence and abscission (shedding of leaves, fruits). This is correct.
   • Negative role (inhibits/delays senescence): Gibberellins (GA). Gibberellins, along with cytokinins, are known to delay senescence and maintain the youthful state of plant tissues. This is also correct.
   • Therefore, combination I is correct.

2. Analyze Combination II: Seed germination

   • Physiological effect: Seed germination is the process by which a seed sprouts and develops into a seedling.
   • Positive role (promotes germination): Ethylene. While gibberellins are the primary promoters of germination, ethylene can also promote germination in certain seeds (e.g., peanuts, lettuce) by breaking dormancy. This is correct.
   • Negative role (inhibits germination): Abscisic Acid (ABA). ABA is the primary hormone responsible for inducing and maintaining seed dormancy, thereby inhibiting germination. This is correct.
   • Therefore, combination II is correct.

3. Analyze Combination III: Seed dormancy

   • Physiological effect: Seed dormancy is a state where a seed will not germinate even under favorable environmental conditions, allowing it to survive adverse periods.
   • Positive role (promotes dormancy): Abscisic Acid (ABA). As discussed, ABA is crucial for establishing and maintaining seed dormancy. This is correct. …

Plant hormones, also known as phytohormones, are chemical messengers that regulate various physiological processes in plants, including growth, development, and reproduction. Flowering, a crucial reproductive stage, is tightly controlled by a complex interplay of these hormones. In pineapple, specific hormones are known to trigger the transition from vegetative growth to reproductive growth, leading to flower formation.

Here's how auxin and ethylene induce flowering in pineapple:

1. Understanding Auxin's Role: Auxins are a class of plant hormones primarily known for promoting cell elongation, root initiation, and apical dominance. However, in pineapple, high concentrations of auxins, particularly synthetic auxins like NAA (Naphthaleneacetic acid), are widely used to induce uniform flowering. The exact mechanism involves a complex signaling pathway, but it's understood that auxin application can lead to the production of ethylene, which then acts as the direct trigger for flowering.

2. Understanding Ethylene's Role: Ethylene is a gaseous plant hormone known for its role in fruit ripening and senescence. Crucially, it is also a potent inducer of flowering in certain plant species, including pineapple. When applied exogenously or produced endogenously in response to auxin, ethylene triggers the physiological changes necessary for flower initiation. This makes ethylene a key player in the commercial induction of flowering in pineapple, ensuring a synchronized harvest. …

The key here is to know the specific, often opposing, roles of the five major plant hormones: auxin, cytokinin, gibberellin, ethylene, and abscisic acid (ABA). Each process listed has a clear "positive" (promoting) hormone and a "negative" (inhibiting) hormone. Let's check each row one by one.

1. Row I: Apical dominance — Positive: Auxin, Negative: Cytokinin

   Apical dominance is the suppression of lateral bud growth by the shoot tip. Auxin, produced at the tip, is the positive signal that maintains this suppression. Cytokinin, produced in roots, promotes lateral bud growth, thus acting negatively on apical dominance. This combination is correct.

2. Row II: Seed germination — Positive: Ethylene, Negative: ABA

   Seed germination is promoted by gibberellins and, in many seeds, by ethylene (which breaks dormancy in some species). ABA is the classic inhibitor of germination, maintaining dormancy. So ethylene as positive and ABA as negative is correct for many seeds (e.g., peanut, sunflower). This combination is correct.

3. Row III: Seed dormancy — Positive: ABA, Negative: Ethylene

   Seed dormancy is induced and maintained by ABA — it is the positive regulator of dormancy. Ethylene often breaks dormancy and promotes germination, so it acts negatively on dormancy. This combination is correct. …

Plant hormones belong to distinct chemical families, and understanding their molecular origins helps classify them correctly. This question tests whether you can connect each hormone to its biochemical precursor or category.

The key is to recall the chemical nature of each plant growth regulator:

Cytokinins are adenine derivatives. Kinetin, the first discovered cytokinin, is 6-furfurylaminopurine—literally adenine with a side chain. All natural cytokinins (zeatin, etc.) share this adenine core, which is why they can interact with nucleic acid metabolism.

Abscisic acid (ABA) is a carotenoid derivative. It's synthesized from the cleavage of C₄₀ carotenoids (specifically violaxanthin and neoxanthin) in plastids, yielding the C₁₅ structure of ABA. This is why ABA is classified as an isoprenoid/terpenoid.

Synthetic auxins include compounds like 2,4-D, IBA, and naphthaleneacetic acid (NAA). These are man-made analogs of indole-3-acetic acid (IAA), designed to mimic auxin activity but resist degradation by the enzyme IAA oxidase.

The respiratory climacteric is the sharp rise in respiration and ethylene production during fruit ripening. Climacteric fruits (banana, mango, tomato) show a burst of ethylene synthesis that autocatalytically triggers ripening. Ethylene is the gaseous hormone responsible for this phenomenon.

Now we match:

1. A. Adenine derivatives → II. Kinetin …

Evaluate each statement against known phytohormone physiology.

1. I — Ethylene initiates sprouting of potato tubers. Correct. Ethylene breaks bud/seed dormancy and initiates sprouting of potato tubers.

2. II — Gibberellins promote senescence. Incorrect. Gibberellins delay leaf senescence and delay fruit ageing; they do not promote senescence. …

The key here is to understand what each plant hormone does — not just memorise a table, but know the why behind the regulation. Apical dominance, seed germination, seed dormancy, and senescence are all processes where one hormone promotes and another opposes the effect. The table gives a "positive" (promotes) and "negative" (inhibits) regulator for each role. Let's check each one.

1. I – Apical dominance: Auxin produced in the shoot tip suppresses the growth of lateral buds. Cytokinin, applied to lateral buds, can overcome this suppression and promote branching. So auxin is positive (promotes apical dominance) and cytokinin is negative (opposes it). This match is correct.

2. II – Seed germination: Ethylene is known to break dormancy and promote germination in many seeds (e.g., peanut, sunflower). Abscisic acid (ABA) is the classic inhibitor of germination — it maintains dormancy. So ethylene is positive, ABA is negative. This is correct.

3. III – Seed dormancy: ABA induces and maintains dormancy; ethylene (or gibberellin) breaks it. Here the table says ABA is positive (promotes dormancy) and ethylene is negative (breaks dormancy). That is correct. …

The core concept here revolves around plant hormones (phytohormones) and specific agricultural techniques that influence plant growth and development. Each hormone has distinct roles, and certain practices are employed to achieve desired outcomes in plants. Understanding these specific functions and applications is key to correctly matching the lists.

Here's a step-by-step breakdown:

1. Analyze A) Decapitation:

   • Concept: Decapitation refers to the removal of the shoot apex (apical bud) of a plant. The apical bud produces auxins, which inhibit the growth of lateral (axillary) buds, a phenomenon known as apical dominance.
   • Effect (List-II): When the apical bud is removed, the inhibitory effect of auxin on lateral buds is lifted. This promotes the growth of III) Lateral buds, leading to a bushier plant.
   • Application (List-III): This technique is commonly used in horticulture to encourage branching and increase yield. For instance, in ii) Tea plantation, decapitation (pruning) is done regularly to promote the growth of more lateral branches and leaves, which are the harvested parts.
   • Match: A-III-ii

2. Analyze B) Zeatin:

   • Concept: Zeatin is a naturally occurring cytokinin, a class of plant hormones. Cytokinins are primarily involved in cell division (cytokinesis) and differentiation.
   • Source (List-II): Cytokinins are abundant in rapidly dividing tissues and are also found in various plant extracts. I) Coconut milk is a well-known natural source rich in cytokinins, including zeatin-like substances, and is often used in plant tissue culture media.
   • Effect/Context (List-III): Cytokinins promote cell division and expansion, delay senescence (aging), and promote the growth of lateral buds. Their role in active growth zones contributes to the formation and expansion of iv) New leaves.
   • Match: B-I-iv

3. Analyze C) Ethylene:

   • Concept: Ethylene is a gaseous plant hormone with diverse effects, often associated with ripening, senescence, and stress responses.
   • Effect (List-II): One of the specific physiological effects of ethylene is the promotion of II) Root hair formation. Root hairs significantly increase the surface area of roots for water and nutrient absorption. …

The concept first: hormones are known by their signature effects

Plant growth regulators overlap a great deal — several of them influence growth, several influence ageing. What examiners test is the signature effect, the one for which each hormone is the textbook answer. Fix those, and matching questions become mechanical.

• Auxins — apical dominance (they impose it), rooting of cuttings, parthenocarpy, herbicides (2,4-D).
• Gibberellins — bolting, stem elongation, "delay of senescence" in fruit, malting in brewing, increasing sugarcane cane length.
• Cytokinins — cell division, overcoming apical dominance, lateral shoot growth, and delaying leaf ageing (the Richmond–Lang effect).
• Ethylene — fruit ripening, epinasty, triple response, root hair formation, breaking dormancy in potato tubers.
• Abscisic acid (ABA) — the stress hormone: stomatal closure, dormancy, and seed development and maturation.

Step-by-step matching

1. "Inhibit apical dominance." Apical dominance is the suppression of lateral buds by auxin coming down from the apex. The hormone that antagonises this and lets the lateral buds grow is the cytokinin — which is why removing the apex (or applying cytokinin) makes a plant bushy.
2. "Delay senescence." Gibberellic acid ($\mathrm{GA_3}$) delays senescence — the standard textbook example is spraying citrus fruits so they can be left on the tree longer, extending the marketing period. $\Rightarrow$ Gibberellic acid.
3. "Promote root hair formation." Ethylene promotes root growth and root hair formation, thereby increasing the surface for absorption of water and minerals. $\Rightarrow$ Ethylene. …

Concept & Intuition

Each phytohormone has a signature action and chemical class. Reading each List-I clue and pinning it to its unique hormone resolves the match.

Step-by-step

• A) Delay in nutrient mobilization $\to$ IV) Cytokinins. Cytokinins delay senescence (the Richmond-Lang effect): they retain nutrients in the tissue and slow their mobilization away from leaves.
• B) Promoting root-hair formation $\to$ III) Ethylene. Ethylene stimulates root-hair initiation and elongation in the root epidermis. …

Plant growth regulators are a fascinating mix of chemistry and biology. Each PGR has a distinct chemical origin — some are terpenes, some are indole compounds, some are purine derivatives — and each triggers specific physiological responses. The trick here is to know both the chemical class and the function, and to avoid mixing up similar-sounding compounds (like IBA vs IAA, or 2,4-D vs ABA).

Let’s examine each statement one by one.

1. Statement A: Terpenes — hastens malting process — 2,4 D

   Terpenes are a large class of compounds derived from isoprene units. Among PGRs, abscisic acid (ABA) and gibberellins are terpenes. But 2,4-D is a synthetic auxin (an indole-like compound, not a terpene). Also, hastening the malting process (germination of barley) is a function of gibberellins, not 2,4-D. So this match is wrong on both counts — chemical class and function.

2. Statement B: Carotenoid derivatives — stimulates the closure of stomata — ABA

   This is spot on. ABA is synthesized from carotenoids (via violaxanthin) in plastids. Its well-known role is to trigger stomatal closure under water stress. So B is correct.

3. Statement C: Indole compounds — Increases the internodal length — IBA …