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Tunica carpus theory

The Tunica-Corpus theory describes the structure of shoot apices. It states that the apical meristem is divided into two regions: the tunica and corpus. The tunica forms the outer one to several layers with anticlinal cell divisions, while the corpus forms the inner central region with more random cell divisions. This theory best describes the zonation pattern observed in apical meristems and is widely used to understand the development of vegetative and floral structures.

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TUNICA CARPUS THEORY Presented to : Mam Tiba Presented by: Zeenat Meeran
GENERAL  Meristem: Divisible and unspecialized cell. Divided and become specialized in relation to their function.
TYPE Type Location function Apical meristem Tip of stems and roots Growth: increase length at tip Intercalary meristem Between the tip and base stem and leaves Growth: increase the length between the nodes Laterlal meristem Sides of stems and roots Growth : increase in diameter
CHRACTERISTICS  Shape: Isodermatic ,spherical, oval or polygonal.  Arrangement: Compactly and lack intercellular space.  Dense cytoplasm, large distinct and prominent nucleous.  Have capacity to divide.
SHOOT APEX  Shoot apex- where new leaves and tissues of the stem arise Theories about zonation of shoot apex: A. Apical cell theory B. Histogen theory C. Tunica-corpus theory
APICAL CELL THEORY  Hofmeister (1857) cell visible in early stages of development and dividing like a single apical cell.  Nageli (1878) a single apical cell is structural and functional unit, which governs the entire process of apical growth.
HISTOGEN THEORY  Henstein(1868) three distinct meristematic zones. Dermatogen: outermost and uniseriate layer Periblem: middle region composed of isodiamatric cell. Pelrome: central and inner mass Each develop from independent group of initials (histogens)
TUNICA CARPUS THEORY  Schmidt, 1924  TUNICA and CORPUS  2 regions can be distinguished by their plane of cell division  Apices are best described by this theory.  This concept used to describe apical structure of vegetative and floral part.
 Dome like part of apical meristem have one to several outer layers.  Regularly arranged.  Arise from specific group of initials.  The tissue mass beneath the superficial layers more random arrangement.
Tunica  One to several layered  Plane of division almost entirely anticlincal
Carpus  Central region  Plane of division may be quit randomly TYPES A. Usual – 1. CMC 2. rib meristem 3. peripheral B. Opuntia - + cambium-like transition zone
 Central zone– (waiting meristem)- promeristem - corpus + portions of tunica - gives rise to:  Rib zone or pith rib meristem - below central zone; center location - becomes the pith  Peripheral zone or peripheral meristem - encircles the other zones - most meristematic (eumeristem) - densest protoplast and smallest dimensions - gives rise to leaf primordia, procambium, cortical ground tissue
Origin  Evidences of surface layer in apex.  Was deduced arrangement and aspect of cell is fixed.
Satina et al.(1940): Two outer most layer of tunica Whereas third layer contributing cell to the carpus
Baker (1945):  Self-perpetuating tunica No.38
Dermen (1945)  oxycoccus  Distinct apical layer  Histogenicaly independent
At was long thought that precilincal layers in th chimeras plant was not true tunica
 Thiekle (1954-1957)  Untrue  Trandence spp.  No preclinical division  Elsewhere in surface layer
 True tunica variable in number(1-9)  Now recognized  Parallel layer vary in number  With ontogeny of plant  With seasonal growth
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