Download Bi 151 – Plant Morpho

9/14/2014
Bi 151
Plant Morpho-anatomy
Lecture 5
Meristems, Growth and Differentiation
Jan Lorie M. Robil, M.Sc.
Meristems
Meristems
• ‘merismos’ - division
• embryonic tissue regions that are primarily
concerned formation of new cells.
• restricted to certain parts of the plant
• Initials
– result of evolutionary specialization
– a.k.a. initiating cells or meristematic initials
– cells that maintains the meristems as
continuing source of new cells
• Derivatives
– products of initials
– divides to give rise to somatic or body cells
Initials
Classification of Meristems
• analogous to stem cells
• totipotency
• Based on their position to plant body
– able to produce entire spectrum of cells
– develop into complete plant
– Apical meristems
– Lateral meristems
– Intercalary meristems
• plasticity
– evolutionary response to sessile form of life
– adjust to environmental conditions
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Classification of Meristems
• Based on the nature of cells that give rise
to their initial cells
– Primary
• protoderm → epidermal tissues
• procambium → primary vascular tissues
• ground meristem → fundamental/ground tissue
– Secondary
• cork cambium (phellogen) → periderm
• vascular cambium → secondary vascular tissues
How will you categorize fascicular and interfascicular cambia?
Growth Patterns of Meristems
• Periclinal division
Periclinal Division
– parallel to the axis
– increase in thickness of the organ
• Anticlinal division
Radial Anticlinal Division
– surface growth of the organ
– perpendicular to the axis
• Radial anticlinal – parallel with the radius
• Transverse anticlinal – perpendicular to the long
axis
Transverse Anticlinal Division
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Differentiation
Differentiation
• succession of changes in form, structure,
and function of progenies of meristematic
derivatives, and their organization into
tissues and organs.
• Histogenesis – tissues e.g. xylem, phloem
• Organogenesis – organs
• Morphogenesis – specific form
• Senescence - Programmed Cell Death
• histological diversity results from changes
in individual cells.
• controlled by a number of genetic,
physiological and even physical factors
– environmental cues (biotic and abiotic)
– hormones
Apical Meristems
• refers to a group of meristems at the apex
of shoot or root
• lay the foundation of the primary plant
body
• First organized when the plant is still an
embryo in the seed
Equisetum
Polypodium
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What is the evolutionary selective
advantage to having an apical cell?
• It divides less rapidly than its derivatives,
thus helping prevent the multiplication of
abnormalities.
Tunica-Corpus Organization
Tunica-Corpus Organization
Initial region of apical meristem consists:
• Tunica
– one or more peripheral layers of cells
– divides in planes perpendicular to the surface
• Corpus
– a mass of cells several layers deep
– divides in various planes
Features Of The Tunica-corpus
• Separate tiers of apical initials occur at the
distal position at the apex = stratified
meristems
• tunica is one or more layers thick and it
divides anticlinally.
• Corpus provides the bulk, tunica the
mantle or covering of the shoot.
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Cyto-histological Zonation
• differentiation of regions with distinctive
cytological characteristics
• prominent in most Gymnosperms and
Angiosperms
• Central Zone
• Rib Zone
• Peripheral Zone
Stem LS showing shoot apex with a core and mantle organization, apical cell,
central mother cell zone, peripheral zone, pith meristem; Prepared slide
Shoot Apex
• can produce both vegetative or
reproductive (i.e. foliar and floral structures)
• produces lateral organs (e.g. branches, twigs)
• contains the primary meristems
• starts with an apical cell that gives rise to
all cells
Root Apex
• Consider the longitudinal zones of root
• Calyptrogen. Meristem that creates and
resupplies parenchyma to the root cap.
• This meristem is adjacent to a dermatogen
that produces the epidermis
• Thus, the root cap and epidermal cells
have independent origins – only in
Monocot
Solenostemon (Coleus) the tunica is two-layered
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