Question

Senescence is an active developmental cellular process in the growth and functioning of a flowering plant is indicated in
A. Annual plants
B. Floral parts
C. Leaf abscission
D. Vessels and tracheids

Answer 1

Hint:Senescence refers to the process by which cells stop dividing and are permanently growth-arrested without cell death. Any type of damage in DNA or stressed condition can induce senescence. Senescence in the plants is the slow aging of plants. This aging can be stress-related or age-related

Complete answer: Leaf senescence occurs by chlorophyll degradation and plays an important role in transferring nutrients from old leaves to growing and storage parts of the plant. New organs are produced in the plants and older ones undergo senescence. The process of senescence is highly influenced by plant hormones. Promoters of senescence are ethylene, abscisic acid, jasmonic acid, and salicylic acid are promoters of senescence. Cytokinins are important to prevent senescence in the later developmental stages.
Senescence is indicated in leaf abscission. Hence option C) is correct.
Theories that explain hormonal induction of senescence
Shoot pruning: This theory states that ethylene is responsible for the shedding of leaves at later stages. ABA and strigolactones push water minerals and growth hormones and this leads to more and more production of ABA and strigolactones which drain all the nutrients until sugar and oxygen deficiencies are present which lead to the formation of gibberellins and ethylene. When ethylene is produced the leaf excises.
Root pruning: Ethylene, GA, BA, Eth are released during oxygen and sugar shortages in the roots and they drain oxygen, minerals, water and growth hormones from the root cell which leads to the death of root cells.

Hence The correct answer is option C) is correct.

Note: The shedding of plant parts is known as abscission. Parts that are no longer necessary undergo senescence and are discarded by the plant. Leaves are mostly shed during autumn. Plant parts undergo cytological and biochemical changes, macromolecules are degraded and remobilization of nutrients occurs from aging parts to growing or storage organs.