Q.48 ‘Quiescent Center’ is present in
(A) leaf meristem
(B) root apical meristem
(C) shoot apical meristem
(D) floral meristem
The Quiescent Center is present in the root apical meristem. This region consists of slow-dividing stem cells that organize surrounding active cells in the root tip, discovered by F.A.L. Clowes in 1956.
Correct Answer
(B) root apical meristem
The quiescent center (QC) forms a hemisphere of up to 1,000 low-mitotic cells at the root apex, behind the root cap, acting as a stem cell niche for root growth maintenance. It replaces damaged meristematic cells during stress, ensuring root persistence.
Option Analysis
-
(A) leaf meristem: Incorrect. Leaf meristems at leaf margins or tips lack a quiescent center; they feature active cell division without a defined slow-dividing QC region.
-
(B) root apical meristem: Correct. The QC resides here as inactive cells with low DNA/RNA/protein levels, surrounded by initials for epidermis, cortex, and stele.
-
(C) shoot apical meristem: Incorrect. Shoot meristems have central and peripheral zones for leaf/stem production but no quiescent center; all zones divide actively.
-
(D) floral meristem: Incorrect. Floral meristems produce flower organs determinately without a QC; they derive from shoot meristems lacking this structure.
The quiescent center in root apical meristem serves as a key organizing hub in plant roots, enabling continuous growth through low-activity stem cells. This structure, vital for root development, distinguishes root tips from other meristems.
What is Quiescent Center?
The quiescent center comprises slow-dividing cells forming a hemisphere at the root tip, with minimal DNA, RNA, and protein synthesis. Discovered by F.A.L. Clowes in maize roots, it acts as a reserve for meristem repair.
Location in Root Apical Meristem
Found universally in higher plant root apices, between the root cap and active initials, the QC (4 cells in Arabidopsis, up to 1,000 elsewhere) maintains surrounding stem cells via auxin signaling.
Functions and Significance
-
Maintains stem cell niche for tissue production (epidermis, cortex, stele).
-
Provides regeneration post-damage or stress.
-
Ensures root meristem stability during growth.
Absent in leaf, shoot apical, or floral meristems, highlighting root-specific organization.
