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Eduncle posted an MCQ
October 20, 2019 • 18:30 pm 0 points
  • CSIR NET
  • Life Sciences

Given below are statements related to different aspects of plant growth and development.

Given below are statements related to different aspects of plant growth and development. (A) Leaf longevity is increased in ethylene-insensitive mutants etr 1-1 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) Redifferentiation 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 ?

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    Eduncle Best Answer

    Ethylene signaling in Arabidopsis begins at a family of five ethylene receptors that regulate activity of a downstream mitogen-activated protein kinase kinase kinase, CTR1. Triple and quadruple loss-of-function ethylene receptor mutants display a constitutive ethylene response phenotype, indicating they function as negative regulators in this pathway. No ethylene-related phenotype has been described for single loss-of-function receptor mutants, although it was reported that etr1 loss-of-function mutants display a growth defect limiting plant size. In actuality, this apparent growth defect results from enhanced responsiveness to ethylene; a phenotype manifested in all tissues tested. 
    Programmed cell death (PCD) in plants is a crucial component of development and defence mechanisms. In animals, different types of cell death (apoptosis, autophagy, and necrosis) have been distinguished morphologically and discussed in these morphological terms. PCD is largely used to describe the processes of apoptosis and autophagy (although some use PCD and apoptosis interchangeably) while necrosis is generally described as a chaotic and uncontrolled mode of death. In plants, the term PCD is widely used to describe most instances of death observed.  
    Leaf senescence is manifested by color change from green to yellow (due to chlorophyll degradation) or to red (due to de novo synthesis of anthocyanins coupled with chlorophyll degradation) and frequently culminates in programmed death of leaves. However, the breakdown of chlorophyll and macromolecules such as proteins and RNAs that occurs during leaf senescence does not necessarily represent a one-way road to death but rather a reversible process whereby senescing leaves can, under certain conditions, re-green and regain their photosynthetic capacity. This phenomenon essentially distinguishes senescence from programmed cell death, leading researchers to hypothesize that changes occurring during senescence might represent a process of trans-differentiation, that is the conversion of one cell type to another. In this review, we highlight attributes common to senescence and dedifferentiation including chromatin structure and activation of transposable elements and provide further support to the notion that senescence is not merely a deterioration process leading to death but rather a unique developmental state resembling dedifferentiation.

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