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Summary BOT 2601 LEARNING UNIT 1
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- University Of South Africa (Unisa)
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BOT 2601 LEARNING UNIT 1PLANT GROWTH, DEVELOPMENT AND CELLULAR ORGANISATION:
Textbook reference: chapter 1 pg. 3-49
THE PLANT BODY:
The plant body consists of a central axis, distinguished into a
central aerial shoot and a subterranean root
Growth of the aerial shoot gives rise to new organs and
tissues acropetally, from the base of the shoot upwards
In roots, new organs and tissues are initiated basipetally,
from the base of the root downwards
PLANT GROWTH:
Growth is a genetically programmed developmental
process involving cell division, enlargement and maturation
Roots and shoots become extended apically, increasing in
length
This manner of growth is traceable to a small region of cells
at the tip of the stem and the root that is characterised by
the formation of new, differentiated cells by repeated
subdivision and cell expansion
These regions of growth and active cell division are
meristems
MERISTEM FUNCTION:
Meristems consist of undifferentiated cells, also called initials. Initials give rise to derivatives
Cell differentiation is the process where derivatives differentiate into different specialised cells
Meristems can be identified by their topographic positions and capacity for cell division:
o Meristems restricted to the extreme tips of stems, branches and roots are called apical meristems and
their activity results in primary growth and an increase in axis length
o Promeristem refers to the core of centrally positioned initial cells and their intermediate derivatives
that have yet to show differentiation to a more specialised function
Tissues that arise directly from these apical regions are called primary tissues. They contribute to growth in
length and limited growth in width of organs
- The growing tip of the shoot consists of meristematic cells that result in growth of organ length and the
formation of regularly spaced, undifferentiated subapical mounds of cells on the flank of the apical dome.
These cell groups are called primordia. They develop into new leaves, branches or floral parts
- The apical meristems of roots are subapical and results in increase in root length and produces cells to form
the outer root cap
- Leaf primordia that are more removed from the apex become larger as they grow outward. The upper or
adaxial surface of the leaf primordium is directed towards the stem apex, while the lower or abaxial surface
faces away from the side. The resulting dorsiventral symmetry is associated with 2 sides that are
morphologically and anatomically different
- In the upwards angle or axil is a small mound of cells that become the bud. This is the axillary bud
primordium. It contains the axillary meristem, which when stimulated will give rise to a branch root that is
indistinguishable from the primary shoot
The primary body of the plant and its primary tissues include all the tissues that arise from the apical
meristems
Lateral meristems, called cambia, are regions of dividing cells in a continuous thin sheet on the outer axis,
responsible for axis thickness. Lateral meristems participate in secondary growth and formation of secondary
tissues that form the secondary plant body.
The major lateral meristems are the vascular cambium that forms secondary conducting tissues and the cork
cambium that deposits an outer zone of periderm
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