Part B - SAGs, SDGs, hormones, TFs: NAC, WRKY, ROS signaling

पहले topic को छोटे-छोटे terms और concepts में बेसिक MCQs से clear करो, फिर उसी पर advance / exam-oriented प्रश्न practice करो।

Leaf senescence (SAGs, SDGs, hormones, TFs: NAC, WRKY, ROS signaling)

Leaf abscission

Rhizobacteria & plant interaction

Pathogen invasion (necrotroph, biotroph, hemibiotroph)

30 MCQs (basic → medium level) बनाता हूँ ताकि हर term crystal clear हो जाए।

🌱 30 Basic-to-Medium MCQs on Plant Senescence & Pathogen Interaction

Section A: Senescence Basics (SAGs, SDGs, Hormones)

1. Genes that are up-regulated during senescence are called:

a) SDGs

b) SAGs

c) WRKYs

d) Auxin

2. Genes that are suppressed during senescence are termed:

a) SAGs

b) SDGs

c) NAC genes

d) Cytokinins

3. Which of the following is not a positive regulator of senescence?

a) Ethylene

b) ABA

c) Jasmonic acid

d) Cytokinin

4. Which hormone delays leaf senescence?

a) Ethylene

b) Cytokinin

c) ABA

d) Brassinosteroids

5. NAC transcription factors regulate leaf senescence and are named after:

a) NAM, ATAF, CUC

b) WRKY, ROS, ABA

c) ABA, GA, JA

d) SAG, SDG, PR

6. A functional NAM-B1 allele in wheat causes:

a) Delayed senescence

b) Early senescence and nutrient remobilization

c) Pathogen resistance

d) ROS scavenging

7. WRKY transcription factors are plant-specific TFs characterized by:

a) Zinc finger motif

b) WRKYGQK sequence

c) Helix-turn-helix domain

d) RNA-binding domain

8. Knockout mutants of WRKY53 in Arabidopsis show:

a) Early senescence

b) Delayed senescence

c) No effect on senescence

d) Enhanced ABA signaling

9. ROS, especially H2O2, act as:

a) Growth promoters

b) Senescence signals

c) Structural barriers

d) Nutrient remobilizers

10. Which senescence regulator functions in a negative feedback loop?

a) NAC NAM-B1

b) WRKY53

c) Cytokinin oxidase

d) PR proteins

Section B: Leaf Abscission

11. Abscission occurs in:

a) Guard cells

b) Vascular cambium

c) Abscission zone

d) Root tips

12. High auxin levels keep tissues:

a) Ethylene sensitive

b) Ethylene insensitive

c) ROS sensitive

d) ABA insensitive

13. When auxin levels drop, ethylene effect becomes:

a) Weaker

b) Stronger

c) Constant

d) Absent

14. Leaf abscission is an example of:

a) Constitutive defense

b) Developmental programmed cell death

c) Inducible defense

d) Stress tolerance

Section C: Rhizobacteria & Plant Interaction

15. Rhizobacteria enhance nutrient uptake by:

a) Producing antibiotics

b) Producing siderophores

c) Producing toxins

d) Reducing ethylene

16. Example of a rhizobacterium discussed is:

a) Agrobacterium tumefaciens

b) Pseudomonas aeruginosa

c) Bacillus subtilis

d) Rhizobium leguminosarum

17. Siderophores secreted by rhizobacteria help plants by:

a) Capturing phosphate

b) Capturing iron

c) Releasing nitrogen

d) Inhibiting auxin

18. Plants regulate rhizobacterial population through:

a) Root exudates affecting quorum sensing

b) Lignin deposition

c) Abscisic acid signaling

d) Cell wall enzymes

Section D: Pathogen Entry & Lifestyle

19. Pathogens may penetrate plant cuticle by:

a) Stomatal closure

b) Secreting lytic enzymes

c) ROS production

d) PR proteins

20. Natural openings used by pathogens include:

a) Stomata

b) Hydathodes

c) Lenticels

d) All of the above

21. Necrotrophic pathogens obtain nutrition by:

a) Keeping host cells alive

b) Killing host cells

c) Symbiotic relation

d) Avoiding host tissue

22. Biotrophic pathogens:

a) Kill host tissues rapidly

b) Maintain host cells alive

c) Use dead cells as food

d) Colonize only roots

23. Hemibiotrophs:

a) Show only biotrophic phase

b) Show only necrotrophic phase

c) Start as biotrophs, later necrotrophic

d) Are non-pathogenic

24. Example of necrotrophic activity is:

a) Production of toxins & cell wall degrading enzymes

b) Formation of haustoria

c) Maintenance of host plasma membrane integrity

d) Symbiotic nitrogen fixation

Section E: ROS & Senescence Regulation

25. ROS levels during senescence:

a) Decrease

b) Increase

c) Stay constant

d) Are removed completely

26. Antioxidant concentration during senescence:

a) Increases

b) Decreases

c) Constant

d) No role

27. H2O2 treatment in Arabidopsis induces expression of:

a) WRKY53

b) NAM-B1

c) PR-1

d) GA7

28. At the time of bolting, Arabidopsis shows:

a) Decrease in H2O2

b) Increase in WRKY53 & H2O2

c) Drop in ABA

d) Loss of NAC genes

Section F: Hormonal Regulation Summary

29. Which of the following promotes senescence?

a) Auxin

b) Gibberellin

c) Cytokinin

d) ABA

30. Which of the following represses senescence?

a) Ethylene

b) Cytokinin

c) ABA

d) Jasmonic acid

✅ Answers + Explanations

Section A: Senescence Basics

1. b) SAGs – Senescence Associated Genes are upregulated during senescence.

2. b) SDGs – Senescence Downregulated Genes are suppressed.

3. d) Cytokinin – यह senescence को delay करता है, बाक़ी hormones promote करते हैं।

4. b) Cytokinin – Delays leaf yellowing और senescence को रोकता है।

5. a) NAM, ATAF, CUC – यही तीन gene families NAC नाम में शामिल हैं।

6. b) Early senescence & nutrient remobilization – NAM-B1 functional allele N remobilization को तेज करता है।

7. b) WRKYGQK sequence – WRKY TFs का hallmark sequence यही है।

8. b) Delayed senescence – WRKY53 knockout mutants late senescence दिखाते हैं।

9. b) Senescence signals – ROS (specially H₂O₂) act as signaling molecules in senescence.

10. b) WRKY53 – यह खुद ROS और senescence signals से activate होता है और फिर feedback regulation करता है।

Section B: Leaf Abscission

1. c) Abscission zone – वहीं से leaf/fruit separation होता है।

2. b) Ethylene insensitive – High auxin ethylene की sensitivity suppress कर देता है।

3. b) Stronger – Auxin कम होने पर ethylene का action dominant हो जाता है।

4. b) Developmental programmed cell death – Abscission एक developmental PCD का example है।

Section C: Rhizobacteria & Plant Interaction

1. b) Producing siderophores – Fe³⁺ को chelate करके plant को available कराते हैं।

2. d) Rhizobium leguminosarum – Root nodulation वाला classical rhizobacterium।

3. b) Capturing iron – यही siderophore का function है।

4. a) Root exudates affecting quorum sensing – Plants root exudates से rhizobacterial population regulate करते हैं।

Section D: Pathogen Entry & Lifestyle

1. b) Secreting lytic enzymes – Cutinase, cellulase, pectinase से entry करते हैं।

2. d) All of the above – Stomata, hydathodes, lenticels सभी natural openings हैं।

3. b) Killing host cells – Necrotroph toxins + CWDE release करके cells मारते हैं।

4. b) Maintain host cells alive – Biotrophs host को जीवित रखते हैं।

5. c) Start as biotrophs, later necrotrophic – Hemibiotroph lifestyle यही है।

6. a) Production of toxins & cell wall degrading enzymes – Necrotroph का hallmark।

Section E: ROS & Senescence Regulation

1. b) Increase – Senescence के दौरान ROS accumulation बढ़ता है।

2. b) Decreases – Antioxidant enzymes कम हो जाते हैं → ROS levels uncontrolled।

3. a) WRKY53 – H₂O₂ treatment से senescence regulator WRKY53 activate होता है।

4. b) Increase in WRKY53 & H2O2 – Bolting stage पर senescence signals active होते हैं।

Section F: Hormonal Regulation Summary

1. d) ABA – Senescence को promote करता है।

2. b) Cytokinin – Senescence को repress करता है।

🌱 CSIR NET Life Science – Part B Questions (Set 2: Q31–Q50)

Q31. CAM pathway plants fix CO₂ at night through:

A. PEP carboxylase → Malate

B. Rubisco → 3-PGA

C. Pyruvate carboxylase → Oxaloacetate

D. Malic enzyme → Pyruvate

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Q32. In photosynthesis, the primary electron acceptor of PSII is:

A. Ferredoxin

B. Pheophytin

C. Plastocyanin

D. Plastoquinone

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Q33. In competitive enzyme inhibition:

A. Vmax increases, Km constant

B. Vmax decreases, Km increases

C. Vmax constant, Km increases

D. Both Vmax and Km decrease

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Q34. The Shine-Dalgarno sequence in bacteria helps in:

A. DNA replication

B. Transcription termination

C. Ribosome binding during translation

D. RNA splicing

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Q35. Which of the following is an example of post-translational modification?

A. Polyadenylation

B. Acetylation of histones

C. 5’ capping

D. RNA editing

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Q36. During glycolysis, substrate-level phosphorylation occurs at:

A. Glucose → G6P

B. 1,3-BPG → 3PG

C. Fructose-6-P → F1,6BP

D. Pyruvate → Lactate

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Q37. Which hormone mainly induces stomatal closure during drought?

A. Cytokinin

B. Gibberellin

C. Abscisic acid

D. Auxin

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Q38. In animal cells, oxidative phosphorylation occurs in:

A. Cytoplasm

B. Endoplasmic reticulum

C. Mitochondrial inner membrane

D. Lysosome

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Q39. In immunology, opsonization refers to:

A. Lysis of bacteria

B. Coating of pathogen for enhanced phagocytosis

C. Complement inactivation

D. Antibody switching

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Q40. A major nitrogen-fixing symbiont in legumes is:

A. Agrobacterium tumefaciens

B. Rhizobium

C. Azotobacter

D. Frankia

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Q41. The oxygen-evolving complex of PSII contains:

A. Mg and Fe

B. Mn and Ca

C. Zn and Cu

D. Mo and Fe

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Q42. Which amino acid is a precursor for auxin biosynthesis?

A. Methionine

B. Tryptophan

C. Tyrosine

D. Phenylalanine

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Q43. A ribozyme is:

A. Protein enzyme only

B. DNA molecule with catalytic activity

C. RNA molecule with catalytic activity

D. Lipid-based enzyme

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Q44. An ecological niche is best described as:

A. Physical place where an organism lives

B. Functional role and habitat of an organism

C. Population density in ecosystem

D. Feeding relationship only

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Q45. Which DNA repair mechanism uses photolyase enzyme?

A. Mismatch repair

B. Photoreactivation

C. Base excision repair

D. Nucleotide excision repair

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Q46. Okazaki fragments are synthesized on:

A. Leading strand

B. Lagging strand

C. Both strands equally

D. mRNA template

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Q47. In the lac operon, lactose acts as:

A. Corepressor

B. Inducer

C. Activator

D. Repressor

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Q48. Endosymbiotic theory suggests mitochondria originated from:

A. Cyanobacteria

B. Purple bacteria (α-proteobacteria)

C. Archaea

D. Viruses

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Q49. In cell cycle, the spindle checkpoint ensures proper attachment of:

A. Centrosomes to nucleus

B. Microtubules to kinetochores

C. Ribosomes to mRNA

D. DNA polymerase to template

Q50. The most abundant immunoglobulin in human serum is:

A. IgM

B. IgA

C. IgG

D. IgE

Answer: C

✅ Final Answer Key (Q31–Q50)

Ans –

31 – (A)

32 – (B)

33 – (C)

34 – (C)

35 – (B)

36 – (B)

37 – (C)

38 – (C)

39 – (B)

40 – (B)

41 – (B)

42 – (B)

43 – (C)

44 – (B)

45 – (B)

46 – (B)

47 – (B)

48 – (B)

49 – (B)

50 – (C)