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‫ریخت زایی و اندام زایی گیاهی‬
‫دکتر محمد رضا واعظی‬
‫‪Roots, Stems & Leaves‬‬‫‪The Primary Plant Body‬‬
Structure & Function of Roots
‫ساختمان و عمل ریشه‬
• Roots anchor plants and absorb water and minerals
• Some roots are useful as human food because they
store carbohydrates
• Roots are important sites of hormone and secondary
compound production in plants
• The roots of some plants help support stems
• Pneumatophores (‫ )ریشه های ریه ای‬help provide oxygen to
underwater roots of some mangroves (‫حرا‬
ّ ‫)گیاهان مشابه‬
• Some plants produce other types of specialized roots
Taproot (‫ )ریشه راست‬systems and fibrous root systems.
(a) In taproot systems, as in this dandelion (‫)گل قاصد‬, lateral roots
branch off from a larger main root called a taproot. Taproot systems
are typical of most dicots (‫ )دولپه ایها‬and gymnosperms. (b) A fibrous
root system has no main root, and the root system is usually
shallower (‫)سطحی تر‬. Fibrous root systems are found in most
monocots and seedless vascular plants.
The Root Apical Meristem
‫مریستم نوک ریشه‬
• The root apical meristem produces
primary tissues
• Root cells enlarge and begin to specialize
in the zone of elongation (‫)منطقه طویل شدن‬
• Specialized cells and tissues are present
above the zone of maturation (‫)منطقه بالغ شدن‬
The Organization of The Root System-1
‫تشکیالت سیستم ریشه‬
• A. The organization of the Root Apical
Meristem:
– The quiescent center and its role
– The root cap and its role
The root apical meristem. (a) First several millimeters of a dicot root
shows root hairs forming in the region of maturation. Farther up the root,
lateral roots begin to form. (b) The root cap . (c) The root apical meristem
produces the cells of the root itself and cells of the root cap. The root apical
meristem consists of a quiescent zone (‫ )منطقه سکون‬of slowly dividing cells
surrounded by a narrow region of more rapidly dividing cells.
The Root System -2
• B. The Primary Root Meristem and their
Tissue Products:
– Protoderm –epidermis
– Procambium – Vascular Tissues (phloem &
xylem)
– Ground Meristem - cortex
Just beyond the root apical meristem are regions of increased cell division:
the protoderm, procambium, and ground meristem. Above them are regions
of cell elongation and cell maturation. Each region gradually blends into the
next.
The Root System -3
• C. Division, growth & differentiation zones
of the root primordium
• 1. Zone of cell division
• 2. Zone of elongation
• 3. Zone of differentiation (maturation)
The Root System - 4
• D. Tissue Organization of the Mature Primary
Root:
• 1. Epidermis (‫)روپوست‬
• 2. Cortex (‫)پوست‬
• 3. Endodermis with casparian strip (‫)حلقه کاسپاری‬
• 4. Pericycle (‫)دایره محیطیه‬
• 5. Vascular Cyliner (stele) (‫)استوانه آوندی‬
The primary structure of roots. (a) Most roots have a protostele—a
solid central cylinder of vascular tissue. In all primary roots, the
vascular tissue is surrounded by one or more layers of pericycle and
next by one layer of endodermis. (b) Monocot roots have a stele with
rings of xylem and phloem surrounding a core of parenchyma.
An emerging lateral root. Also known as branch roots or secondary
roots, lateral roots originate in the root pericycle and grow out through
the cortex and epidermis. This series of micrographs shows an
emerging lateral root of a salix. The view of the root itself is a cross
section, while the view of the lateral root is a longitudinal section.
The endodermis. (a) Water and minerals can pass between the cells
of the epidermis and cortex, but they must pass through the cell
membranes of the endodermis because of the Casparian strip. (b)
This view of two layers of the endodermal cylinder shows how the
Casparian strip forces water and dissolved minerals from the soil to
pass through endodermal cells instead of around or between them.
The Root System - 5
• F. Roots with specialized functions
– 1. Aerial roots (‫)ریشه های هوایی‬
– 2. Buttress roots (‫)ریشه های نگهدار‬
– 3. Contractile roots (‫)ریشه های قابل انقباض‬
– 4. Pneumatophores (air roots) (‫)ریشه های ریه ای‬
– 5. Parasitic roots (‫)ریشه های انگلی‬
– 6. Storage roots (‫)ریشه های ذخیره ای‬
Aerial root in epiphytic (‫ )داردوست‬orchid. In epiphytic orchids,
aerial roots absorb water from the air.
Aerial root as prop root. In corn, aerial roots serve as prop (‫)نگهدارنده‬
roots to stabilize the plant.
Climbing aerial root. Adventitious climbing roots of Boston
ivy (Parthenocissus tricuspidata) help anchor the plant to
vertical surfaces.
Buttress roots. Large buttress roots produced by some
tropical trees help stabilize the plant in thin soils.
Storage roots. A number of plants, such as Hamburg parsley
(Petroselinum hortense), store water or food in their roots.
Pneumatophores (air roots). Pneumatophores, such as those of
the white mangrove (Laguncularia racemosa), supply oxygen to
plants growing in swamps where the water may become
deoxygenated.
The Root System - 6
• G. Roots & their associations with fungi
(‫)ریشه های همراه با میکوریزا‬
(endomycorrhizal & ectomycorrhizal)
Mycorrhizae are mutualistic associations of roots and fungi.
The Root System - 7
H. Roots of certain plants establish associations with nitrogen
fixing bacteria (‫)باکتریهای تثبیت کننده ازت‬.
• Some plants form associations with species of nitrogen-fixing
bacteria—bacteria that can convert nitrogen gas from the air into
ammonium, which is incorporated into various organic molecules.
• Plants can then take up fixed nitrogen from these bacteria and
incorporate it into amino acids, nucleotides, and other vital nitrogencontaining compounds.
• This is virtually the only biological pathway by which inorganic
nitrogen can enter food chains.
• Plants in the legume family, Fabaceae, are particularly important for
humans because their mutualistic associations with nitrogen-fixing
bacteria enrich the soil by adding nitrogen.
The shoot apical meristem. The shoot apical meristem itself consists of a
central group of slowly dividing cells surrounded by a narrow region of
more rapidly dividing cells. This longitudinal section shows the leaf
primordia emerging on both sides of the shoot apical meristem. As the stem
grows, new leaf primordia arise along the flanks of the apical meristem.
Just beyond and below the apical meristem, the protoderm, procambium,
and ground meristem are regions of increased cell division. Cell elongation
and cell maturation occur below these regions.
Shoot System - II
• B. Primary tissues of the stem
– 1. Epidermis
– 2. Cortex
– 3. Vascular tissue
– 4. Pith
IV. The Transition Zone Between
Roots & Stems
)‫منطقه انتقال بین ریشه و ساقه (یقه‬
V. Specialized Forms of Stems
‫شکلهای تخصصی شده ساقه‬
•
•
•
•
•
A. Stolons (‫)ساقه رونده‬
B. Rhizomes (‫)ساقه زیرزمینی‬
C. Tubers (‫)ساقه غده ای‬
D. Bulbs (‫)پیاز‬
E. Corms (‫)کورم‬
VI. Leaves of the Primary Plant
Body
• A. Formation of leaf primordia - Phyllotaxy
Leaves - II
• B. Basic patterns of leaf arrangement (‫)نظم‬
– 1. Alternate (‫)یک درمیان‬
– 2. Opposite (‫)متقابل‬
– 3. Whorled (‫)فراهم‬
Leaves - III
• Tissues of the Leaf
– 1. Upper epidermis & the cuticle
– 2. Palisade mesophyll (‫)مزوفیل نردبانی‬
– 3. Spongy mesophyll (‫)مزوفیل حفره ای‬
– 4. Vascular bundle (veins, ‫ )رگبرگ‬and their
arrangements
– 5. Lower epidermis & stomates (‫)روزنه‬
Leaves - IV
• D. The process of leaf abscission (‫)ریزش برگ‬
– Deciduous (‫ & )برگ ریز‬non-deciduous trees
Leaves - V
• Specialized (modified) forms of leaves
– 1. Spines (‫)خاردار‬
– 2. Tendrils (‫)پیچک دار‬
– 3. Bracts (‫)برگه‬
• Xerophytes
– 4. Succulent (‫)گوشتی‬
– 5. insectivore (‫)حشره خوار‬