This BOT2601 summary includes diagrams and in depth information summarized from the prescribed textbook (Integrative Plant Anatomy Dickson, WC 2000) in a concise way without excluding valuable information.
PLANT GROWTH, DEVELOPMENT AND CELLULAR ORGANIZATION
,All plant bodies consist of a central axis divided into two regions
Above ground shoot
Below ground root
Shoot is further differentiated into the
lateral photosynthetic appendages
the leaves
the axial component on which the leaves are attached
the stem
Reproductive organs, sporangia/ sporophylls form at reproductive maturity
PLANT GROWTH
Growth: genetically programmed developmental process involving cell division, selective cell
enlargement and maturation
Roots, similar to shoots, also become extended apically increasing in length
Growth is traceable to small regions known as meristems, these are regions of potentially unlimited
growth and active cell division.
All growth an organ formation of the plant is initiated and largely controlled by meristems
Concept of meristems: collection of actively dividing cells (initials) plus their most recent
derivatives
Vegetative meristems are indeterminate (not limited in their capacity to continue the
development of the axis
Actual elongation of the axis occurs by means of cellular enlargement
Process in a 10- o 1000- fold increase in cell volume
Associated with an increase in internal turgor pressure and irreversible changes in the cell wall
Vascular plants are characterized by a “open growth pattern” in which new cells, tissues and organs are
regularly initiated throughout the plant’s life. This type of growth relies upon the existence of small
,aggregations of cells that occur at specific sites in the plant body, retaining the genetic potential of
active cell division.
In addition to initiating new tissues and organs and controlling the pattern of cell and tissue
differentiation, meristems communicate signals to and from the remained or the plant body, while at
the same time maintaining themselves as organized, formative regions.
Long been assumed that variation in the behavior of meristems, frequency and orientation of division
planes, major factors in determining the shape if plant organs.
Agreement that the remarkably complex process of overall plant growth is dependent upon the
presence of permanently ‘embryonic’ meristematic tissue
MERISTEM FUNCTION
It is possible to identify meristems by their topographic positions and by their capacity for cell division
Restricted to the extreme tips of stems, branches and roots called apical meristems
Their activity results in primary growth associated increase in axis length
Promeristems refers to the core of centrally positioned initial cells and their immediate derivatives that
have yet to show visible evidence of differentiation and a progression to a more specialized for or
function
Primary tissues: tissues that arise directly from these apically located regions
They contribute to grow in length s well as to limited growth in the width of organs
Growing tip of shoot consists of a pool of meristematic cells whose derivatives result not only in
organ length but also in the formation of regularly spaced, undifferentiated subapical mounds of
cells on the flanks of the apical dome
These cell groups are called primordia
Develop into new eaves, branches or floral parts in regular sequence flowing a course of
development that is species specific
Apical meristem of roots is subapical
, Contributes derivatives to the root tissue that account for an increase in root length but also
produces cells distally to form the outer root cap
Exact boundary between the core of actively dividing cells and the proliferative subapical zone is often
difficult to clearly demarcate. Differential expansion and multiplication of cells or groups of cells is
important in these growth processes
Leaf primordia that are more removed from the apex become progressively larger as they grow outward
Upper or adaxial surface of the leaf primordium is directed toward the stem apex
Lower or abaxial surface faces away from the side
Resulting dorsiventral symmetry is associated with two sides that are morphologically and
anatomically different
Upward angle or axil (formed by leaf and petiole with the stem) is a small mound of cells that represents
the forerunner of a bud, his is the axillary bud primordium
It contains the axillary meristem, which when simulated will give rise to a branch shoot
indistinguishable from the primary shoot
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