45. Given below are statements related to different aspects of plant growth and development.
    A. Leaf longevity is increased in ethylene insensitive mutants eir1-1 and ein2 of Arabidopsis.
    B. Programmed cell death (PCD) is responsible for the formation of prickles, thorns and spines in plants.
    C. Senescence and PCD occur only in the development of vegetative tissues and does not occur in reproductive tissues
    D. Re-differentiation of organelles is an integral component during initial stages of senescence in plants.
    Which one of the following represents the combination of all correct statements?
    (1) A, C and D (2) B and C
    (3) A, B and D (4) C and A

Explanation:

• (A) Leaf longevity is increased in ethylene insensitive mutants eir1-1 and ein2 of Arabidopsis — This is correct. Ethylene is a hormone that promotes senescence; mutants insensitive to ethylene show delayed senescence and increased leaf lifespan.

• (B) Programmed cell death (PCD) is responsible for the formation of prickles, thorns, and spines in plants — This is correct. PCD shapes these structures by selectively eliminating cells, contributing to their development.

• (C) Senescence and PCD occur only in the development of vegetative tissues and do not occur in reproductive tissues — This is incorrect. Senescence and PCD also occur in reproductive tissues, for example during seed maturation, flower development, and pollen formation.

• (D) Re-differentiation of organelles is an integral component during initial stages of senescence in plants — This is correct. Early senescence involves remodeling organelles such as chloroplasts which undergo transformation and degradation.

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Introduction

Plant growth and development involve complex processes regulated by hormones and programmed cellular events. Ethylene regulates leaf aging, programmed cell death shapes defense structures like spines, and organelle remodeling is a hallmark of early senescence, indicating dynamic cellular control over life cycle progression.

Ethylene’s Role in Leaf Longevity

• Ethylene promotes leaf senescence; mutants reduced in ethylene sensitivity such as eir1-1 and ein2 display delayed senescence, contributing to increased leaf lifespan.

• This modulation offers insights into hormonal control of plant aging and stress responses.

Programmed Cell Death in Protective Structures

• PCD sculpts prickles, thorns, and spines by controlled cell elimination during development, creating physical barriers for defense.

• This exemplifies PCD’s role beyond merely cell death, contributing to plant morphology and protection.

Senescence and PCD Beyond Vegetative Tissues

• Contrary to statement C, senescence and PCD are also critical in reproductive tissues, instrumental in processes such as flower and fruit maturation.

Organelle Re-differentiation during Senescence

• Organelles such as chloroplasts undergo structural re-differentiation during early senescence, marked by degradation and change in function.

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Summary Table: Plant Growth and Development Statements

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Conclusion

Statements A, B, and D correctly describe processes in plant growth related to hormonal regulation, developmental programmed cell death, and cellular remodeling during senescence. Statement C is incorrect.