Parenchyma

1. 1/13/2010
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Parenchyma
Parenchyma
yLiving cells; variable in morphology and physiology
yThin primary walls; polyhedral
yConcerned with vegetative activities of the plant
yphotosynthesis, assimilation, respiration, storage,secretion,
d iand excretion
y“Para” – beside; “en chein” ---to pour
yGround tissue or fundamental tissue
yDevelopmentally, undifferentiated
Parenchyma
yCan resume meristematic activity (dedifferentiate)
--wound healing, regeneration, formation of
adventitious roots and shoots
yTotipotent
Parenchyma cells may occur in continuous masses as
parenchyma tissue or be associated with other cell
types in morphologically heterogeneous tissues
yPith, cortex of stems and roots
yMesophyll of leaves
yFlesh of succulent fruits
yEndosperm seeds
yVascular rays, vertical files of living cells in X and P
The Contents of Parenchyma Cells Are a Reflection of
the Activities of the Cells
yChlorenchyma --- mesophyll of leaves
- vacuolated; numerous chloroplasts; extensive intercellular
space system
S llySecretory cells
- dense protoplasts,esp. rich in ribosomes,
- and have either numerous Golgi bodies or a massively
developed ER

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yParenchyma cells in storage organs, endosperm, cotyledons
- Starch storing – amyloplasts
yParenchyma storing protein/oils ---Proteinoplast/
Elaioplasts
yParenchyma of flowers and fruits ---Chromoplasts
yParenchyma with anthocyanin or tannins or crystals in their vacuoles
yParenchyma – abundant with water/water storage tissue
Walls of parenchyma
yThin, non lignified primary wall
yPlasmodesmata common
yWood– thick, secondary lignified wall
yTransfer cells –with cell wall ingrowthsg
-- transfer of solute over short distances
-- X and P of small, or minor,veins in cotyledons and foliage leaves
of many herbaceous eudicots
-- leaf traces, placentae, embryo, embryo
-- glandular structures (nectaries, salt glands, glands of
carnivorous plants)
Shape
ypolyhedral shape--having
many sides, or facets
yIsodiametric
yFacets tend to approach to 14 (in homogenous parenchyma)(in homogenous parenchyma)
yorthic tetrakaidecahedronÆa
geometrically perfect 14-sided
fi gure is a polyhedron with 8
hexagonal and 6 quadrilateral
facets
Arrangement
yUsually with intercellular
spaces– mesophyll; schizogenous
yAlmost no intercelluar spaces---
endosperm (compact)
yAerenchyma – well developed
air spaces; aquatic and semiair spaces; aquatic and semi-
aquatic angiosperms or water-
logged organs
--enhances the diffusion of air
from the leaves to the roots
--maintain levels of oxygen suffi
cient to support respiration.