shoot system
TRANSCRIPT
Shoot System-Stem-
Prepared by:
Group III
BS Bio 1-C
StemsThe main body of the
portion above the ground of the tree, shrub, herb, or other plant; the ascending axis, whether above or below the ground of a plant, in contradiction to the descending axis or root.
MAJOR FUNCTIONS
OF STEMS
-Stems support
-Stems Conduct
-Stem produce new ling tissue
STEMS SUPPORT Provides mechanical support and raise leaves into the
air, thus facilitating photosynthesis. Flowers and fruits are also produced in position, for facilitating pollination and seed dispersal.
STEMS CONDUCTo Provides a pathway for movement of water and mineral
nutrients from roots to leaves and for transfer of foods , hormones and to other metabolites from one part to another.
STEMS PRODUCE NEW LIVING TISSUEo Provide new living tissue for normal metabolism of
plant.
EXTERNAL PLANT
MORPHOLOGY
A stem is an organ consisting of
An alternating system of nodes, the points at
which leaves are attached
Internodes, the stem segments between
nodes
An axillary bud is a structure that has the potential to form a lateral shoot, or branch
An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot
Apical dominance helps to maintain dormancy in most non-apical buds
Lenticels are structure that permit the passage of gas inward and outward.
Leaf scar are characteristic scar on stem axis made by leaf abscission.
Bud scales are small modified leaves for protection from desiccation.
Dormant shoot apex with its protective scales is a BUD.
Bud Scars are the scars left from the removal of bud.
Leaf primordium is an immature leaf of the shoot.
Intercalary meristem the portion of the internodes above the node . Made up of actively dividing cells responsible for the elongation of the monocot stem.
Fig. 35-12
Apical bud
This year’s growth(one year old)
Bud scale
Axillary buds
Leafscar
Budscar
Node
Internode
One-year-old sidebranch formedfrom axillary budnear shoot tip
Last year’s growth(two years old) Leaf scar
Stem
Bud scar left by apicalbud scales of previouswinters
Leaf scar
Growth of twoyears ago(three years old)
Shoot Apex
Organization
The outer group consisting of one or more peripheral cell layer is known as the TUNICA. These cells divide anticlinally(perpendicular to the surface of the shoot apex)
The CORPUS lies below the tunica and initially has a single layer of cells. Corpus cells divide anticlinallyand periclinally(parallel to the surface of the shoot apex.)
Shoot Apex organization
A shoot apical meristem is a dome-
shaped mass of dividing cells at the shoot
tip
Leaves develop from leaf primordia
along the sides of the apical meristem
Axillary buds develop from
meristematic cells left at the bases of leaf
primordia
Fig. 35-16
Shoot apical meristem Leaf primordia
Youngleaf
Developingvascularstrand
Axillary budmeristems
0.25 mm
Primary Meristems
Protoderm- the outermost layer of cells.
It develops into epidermis--- the special
primary tissue that covers and protects all
underlying primary tissues. The epidermis
prevents excessive water loss and yet
allows for exchange of gases necessary for
respiration and photosynthesis.
Primary Meristems
Ground meristem- Comprises the
greater portion of meristematic tissue of
the shoot tip. Primary tissues forming
from the ground meristem are:
a) Pith- in the very center of stem
b) Cortex- in a cylinder just beneath the
epidermis and surrounding the vascular
tissues. Sometimes pith and cortex are
connected by pith rays.
Primary Meritsems
Procambium cells give rise to
primary vascular tissues
namely;
a) Primary phloem
b) Primary xylem
STEM ANATOMY,
PRIMARY
STRUCTURE
• Meristems are perpetually embryonic tissue and allow for indeterminate growth
• Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots
• Apical meristems elongate shoots and roots, a process called primary growth
Stems undergo primary growth which results in the formation of primary tissues. These include the
Epidermis
Ground tissue
primary vascular tissues (primary xylem and primary phloem)
The young dicot stem
Summary of Primary Development
Protoderm Epidermis
Ground meristem Cortex
Apical Meristem Pith and pith rays
Procambium Phloem
Vascular Cambium
Xylem
Primary Growth development The term stele is applied to the part of the stem that includes
primary vascular tissues, pith, and pith rays. The primary plant body is composed of the above primary tissues.
The main functions of these primary tissues may be summarized as shown below.
Epidermis: Protects underlying tissues.
Vascular tissues
Phloem: Conducts Food
Vascular Cambium: produces secondary phloem and secondary xylem
Xylem: conducts water and mineral salts , and gives strength to stem.
Cortex: Stores food and in young stems, manufactures food, strengthens and protects.
Pith: Stores food
Pith rays: Store food, and conduct water, mineral salts, and food radically.
The young dicot stemThe stellar type exhibited by a dicot
stem is a EUSTELE.
The type of xylem maturation is known as Endarch.
Secondary growth is present.
THE MONOCOT STEM
Fig. 35-17b
Groundtissue
Epidermis
Keyto labels
Cross section of stem with scattered vascular bundles(typical of monocots)
Dermal
Ground
Vascular (b)
Vascularbundles
1 mm
The monocot stem
The vascular bundles are scattered throughout the ground tissue. The type of stele exhibit is ATACTOSTELE.
In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring.
They do not have secondary growth.
Fig. 35-17
Phloem Xylem
Sclerenchyma(fiber cells)
Ground tissueconnectingpith to cortex
Pith
Cortex
1 mm
Epidermis
Vascularbundle
Cross section of stem with vascular bundles forminga ring (typical of eudicots)
(a)
Keyto labels
Dermal
Ground
Vascular
Cross section of stem with scattered vascular bundles(typical of monocots)
(b)
1 mm
Epidermis
Vascularbundles
Groundtissue
Eustele vs. Atactostle
STEM
ANATOMY, SECONDA
RY STRUCTURE
• Secondary growth occurs in stems and
roots of woody plants but rarely in leaves
• The secondary plant body consists of the
tissues produced by the vascular cambium
and cork cambium
• Secondary growth is characteristic of
gymnosperms and many eudicots, but not
monocots
Woody dicot (Tillia sp.)
Stem anatomy, secondary structure
These tissue layers form the Periderm.
The outermost layer is the phellem,
consisting of cork cells.
Immediately inner to it is the phellogen, or
the cork cambium, consisting of flattened
dividing cells.
The third layer is the pheloderm, few cell
layers in thickness.
Fig. 35-19a1
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Primary and secondary growth
in a two-year-old stem
(a)
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondary
xylem
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Fig. 35-19a2
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Primary and secondary growth
in a two-year-old stem
(a)
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondary
xylem
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Fig. 35-19a3
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Primary and secondary growth
in a two-year-old stem
(a)
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondary
xylem
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Cork
Bark
Most recent corkcambium
Layers ofperiderm
Fig. 35-19b
Secondary phloem
Vascular cambium
Secondary xylem
Bark
Early wood
Late wood Cork
cambium
Cork
Periderm
0.5
mm
Vascular ray Growth ring
Cross section of a three-year-
old Tilia (linden) stem (LM)
(b)
0.5 mm
The Vascular Cambium and Secondary
Vascular Tissue
The vascular cambium is a cylinder of meristematic
cells one cell layer thick
It develops from undifferentiated parenchyma cells
In cross section, the vascular cambium appears
as a ring of initials
The initials increase the vascular cambium’s
circumference and add secondary xylem to the
inside and secondary phloem to the outside
Secondary xylem accumulates as wood, and consists of tracheids, vessel elements (only in angiosperms), and fibers
Early wood, formed in the spring, has thin cell walls to maximize water delivery
Late wood, formed in late summer, has thick-walled cells and contributes more to stem support
In temperate regions, the vascular cambium of perennials is dormant through the winter
Tree rings are visible where late and early
wood meet, and can be used to estimate a
tree’s age
Dendrochronology is the analysis of tree ring
growth patterns, and can be used to study
past climate change
As a tree or woody shrub ages, the older
layers of secondary xylem, the heartwood,
no longer transport water and minerals
The outer layers, known as sapwood, still
transport materials through the xylem
Older secondary phloem sloughs off and
does not accumulate
Fig. 35-22
Growth
ring
Vascular
ray
Secondary
xylem
Heartwood
Sapwood
Bark
Vascular cambium
Secondary phloem
Layers of periderm
The Cork Cambium and the
Production of Periderm
The cork cambium gives rise to the secondary plant body’s protective covering, or periderm
Periderm consists of the cork cambium plus the layers of cork cells it produces
Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm
Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air
A plant can grow throughout its life; this is
called indeterminate growth
Some plant organs cease to grow at a certain
size; this is called determinate growth
Annuals complete their life cycle in a year
or less
Biennials require two growing seasons
Perennials live for many years
Sequoia sempervirens
Pinus aristata
Monocot vs.Dicot
Parameter Monocot Dicot
Extent of cortex No distinct cortex Cortex found at the
outer part of ground
tissue
Presence or absence of
pith
Absent Present
Type of stele Atactostele Eustele
Presence or absence of
vascular cambium
Absent Present
Modified StemModification of the stem would depend on
the need of the plant to survive…
… like the animals it learns how to
adapt.
Bulb – consist of small amount of vertical stem and a massive quantity of thick, fleshy storage leaves.
- most of them consist of concentric rings of scales attached to a basal plate.
.
Other bulbous plants
Daffodil Reticulate iris
Stolon / runner = with long
internodes just below the
surface of the ground that
typically terminating in a new
plant
= use for propagation
Fig. 35-5c
Stolons
Stolon
Corm - formed from a swollen bases
of stems.
- A corm consists of one or
more internodes with at least one
growing point
Examples of Corm
Crocuses Gladioli
Rhizome= the stem is
horizontal and underground
with short internodes and
bearing with scale-like leaves.
Other rhizome plants
Johnson grass
Sorghum halepenseCogon grass
Imperata cylindrica
Tuber = a thick under ground
storage stem, usually not upright
= bearing outer buds
= lacking protective scales
Fig. 35-5d
Tubers
Aerial MODIFICATIONS OF STEM
•TENDRILSIN grapes
Axillary bud is modified into tendrils.
•CLADOPHYLL /
PHYLLOCLADE
The entire shoot is flattend & leaf like.
References
• Campbell, N.A., J.B Reece and L.G. Mitchell. 1999. Biology. 5th ed. USA: The Benjamin/Cummings Publishing Co. Inc.
• Weier, E.T., R.C Stocking., M. G Barbour and Rost T. L.1982. Botany an Introduction to Plant Biology. 6th ed. USA: John Willey and Sons Inc.
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