Download PRIMARY GROWTH AND DEVELOPMENT OF SHOOTS

PRIMARY GROWTH AND DEVELOPMENT OF SHOOTS
Seed germination
Primary growth of stem and root
--cell division: mitosis and cytokinesis gives more cells
--cell enlargment: plastic stretching of wall gives larger
tissue
--differentiation: cell wall, organelles, enzymes (gained or
lost)--gives specialized functions
Strategies: location and timing of growth
Determinate growth
--"Pre-set" size, determined genetically or
e n vironmentally
--cells divide, expand, then differentiate (losing
a b i lity to divide)
--leaves, flowers, fruits, seeds, (most animal organs)
show determinate growth
Indeterminate growth
--no pre-set size, "continual" growth
--cells divide, expand, differentiate in different
l o cations, maintaining dividing population
("meristem")
--axes of root and shoot (in mammals, blood, skin)
show indeterminate growth
Determinate growth and differentiation (leaves, flowers, etc.)
“Stem
cell”
Mitosis
Cytokinesis Cell expansion Differentiation
i
to k
is
nes
sio
pan
l ex
Cel
Indeterminate growth and differentiation (stems, roots)
s
os i
Mi t
“Stem
cell”
Mitosis
Cytokinesis Cell expansion Differentiation
i
to k
Cy
is
nes
sio
pan
l ex
Cel
Stem longitudinal section
--cell division shown by dots
(dark regions, 3H-thymidine
autoradiography)
--overlap of regions: division
with expansion, expansion
with differentiation
--change in plane of division
to make new shapes, e.g.,
leaves
--no migration of cells
Apical meristem
(cell division)
Subapical
meristem
(division and
expansion)
Elongation,
differentiation
Where do leaves come
from? Periclinal divisions
Differentiation of cells to form tissues shown best by xsection of stem
Epidermis
Cortex
Pith rays
Pith
Xylem
Phloem
Summary
•Seed contains embryo
•Stem and root meristems
•Cotyledons (seed leaves)
•Stem and root meristems enlarge by cell division
(anticlinal), cell enlargement, differentiation
•Leaves and axillary buds form by periclinal cell
division