Download Microscopy

S1 L3 Evaluation of plant drugs
1. Botanical
B. Microscopy
Cell types
Anna Drew
Microscopy
• Powdered plant material identified
• Via observation of the types and form of individual
diagnostic structures present
• Presence of structures
• -> morphological group
• Size, shape, frequency of characters
• -> exact species
• Aided by identification tables
• Essential to recognise the diagnostic
structures!
Microscopy
• Very good analytical technique
• Quicker than extracting & running a chromatogram
• Quick way to check if it is a different plant or
material contaminated
• Magnification
M = Me x Mo
eyepiece objective
Low power
x 10
x 10
= x 100
High power
x 10
x 40
= x 400
Adjuncts on microscope
• (a) Polarized light
• Polarized material in the eyepiece
• With the analyser below it is arranged to get darkness
• Crystalline material may rotate planes to show bright
• Micromeasurement
• Micrometer eyepiece – scale (100 divisions)
• Micrometer slide to calibrate the scale
• Focus micrometer slide and align with eyepiece scale to
calibrate it for low and high powers
• Then replace with plant slide – can measure objects in
micrometres
1. PARENCHYMA (ground tissue)
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Indicates plant tissue is present
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Least specialized plant cells
Thin and somewhat flexible cell walls
Generally have a large central vacuole
Living at maturity
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Found in all plant organs as a continuous tissue
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cortex and pith of stems
ground tissue of petioles
mesophyll of leaves
endosperm of seeds
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Also forms part of complex tissues such as vascular tissues
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Most metabolic functions are carried out by parenchyma cells
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Photosynthesis
Storage
Secondary growth
Wound healing
Most parenchyma cells have the ability to differentiate into other cell types
under special conditions
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During repair and replacement of organs after injury
Can resume meristematic activity to produce adventitious roots and shoots
• Typical
Thin rounded cellulose walls
Air spaces
Isodiametric (rounded) cell
Modifications of parenchyma
• Leaf tissue
Epidermal cell
Palisade mesophyll cell layer
Spongy mesophyll cells
• Lignified
Pits in cell walls
Lignin in cell wall
- Indicates secondary thickening
- Constituent of woody material
• Reticulate
Large pit (surface view)
- Eg Fennel fruit (Foeniculum vulgare)
2. COLLENCHYMA
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Closely related to parenchyma
Thicker primary cells walls (usually with uneven thickness)
Living at maturity
Role in support of herbaceous plants
– Example - the "strings" of celery
• Occur in groups just beneath the epidermis
– beneath cork in bark
– at the midrib of leaf below and above vascular bundle
Cellulose thickening
3. SCLERENCHYMA (support cells)
• Thick secondary cell walls (showing simple pitting)
• Dead at functional maturity
• Cannot increase in length - occur in parts of the plant which have
quit growing in length
• Two types:
• FIBRES
– long, slender cells with a more or less regular secondary cell
wall
– Usually occur in groups or strands
» Commercial examples – flax, jute, hemp (for making rope)
– In dicots found in vascular tissue as xylem / phloem
– In monocots they may enclose the vascular bundle or support it
either side
– Sometimes form columns from lower to upper epidermis
– Fibre position, aggregation and general appearance makes
then valuable diagnostic aids
– Function: support
• Typical
Lignin
Pit (surface view)
Lumen
Pit (section view)
Cascara bark
Diagnostic features:
• Very narrow lumen
• Found in groups
• Very thick – hard to
see the lumen
Zingiber officinale
(ginger) fibres viewed
under high power
Cinchona bark fibres (viewed under low power)
Diagnostic features:
• Found singly, not in a group
• Very large
• Funnel-shaped lumen
• Striated wall
(Some ends blunted)
• SCLEREIDS (stone cells)
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Shorter or blunter cells with an irregular shape
Widely distributed in plants
Can vary considerably in shape
Typically:
» Isodiametric
» Thick secondary walls
» Numerous pits
– May occur in layers or groups or alone
– Found:
» in epidermal, ground or vascular tissue
» In stems – continuous sheath on the periphery of a
vascular region
» In leaves – throughout or at ends of small veins
» In fruits – singly or in groups
» Hardening of seed coats during ripening often results from
layers of sclereids
– Function:
» protection (seed coats)
• Brachysclereid ‘stone cells’
Pits in surface
Thick wall
Lumen
Eg Pyrus communis - pear
• Astrosclereid
• TS Water lily
• Lignified
• Branched
• Single cell
• Osteosclereid
• Cinnamon bark
• Horseshoe shape
• One wall much thinner
• Irregular sclereid
Cascara bark
Wild cherry bark
Irregular, solid, many in groups
Very irregular, sometimes
branched, (“jigsaw” piece)
4. VESSELS AND TRACHEIDS
Xylem:
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Vessel
• End walls of
linear parenchyma
cells breakdown to
form continuous
tubes or channels
• Only found in
Angiosperms
Thick secondary cell walls, often deposited unevenly in a
coil-like pattern so that they may stretch
Dead at functionally maturity
Water/ion conduction – vessels and tracheids*
storage - parenchyma
support – fibres and sclereids
Tracheid
• More primitive
• Pits allow water
to pass from one
to another
• Less efficient at
conducting water
• More like a fibre
Lignin arrangements:
HERBACEOUS
Annular
Spiral
WOODY PLANTS – to conduct more water
Reticulate
Eg
Gentian
root
Rhubarb
Sclariform
Eg Male
fern
rhizome
Bordered
pitted
Eg
Liquorice
root
Gentiana lutea (Gentian) root vessels (viewed under high power)
Tracheids of Atropa belladonna
root (viewed under high power)
5. PHLOEM
– Not strong tissue – collapses (as it grows)
– Not good diagnostically
– Involved in transport of sucrose, other organic compounds, and
some ions
– Living at functional maturity
• Protoplast may lack organelles and nucleus, though
– End walls connect to each other via sieve-plates
– Two types of cells in the phloem
• Sieve-tube members - actual conduit for sucrose transport
• Companion cells - has a nucleus that may also control the sievetube element and may aid in sucrose loading
Companion
cell
Sieve
plate
Holes in
patches sieve plate
at an angle
Sieve area conducts to
next cell
6. LEAF EPIDERMIS
(a) THE CUTICLE
Separate outer layer made of cutin, a fatty substance
Characteristic feature of epidermis
Sometimes striated – diagnostic feature
Atropa belladonna
Mint
Senna
Digitalis
(b) EPIDERMAL CELLS
• Continuous layer of cells covering surface of plant
• Elongated parts of plant, stem or petiole, cells elongated
• Leaves, petals, ovaries, ovules cells have wavy anticlinal
walls and are roughly isodiametric
• In some plants they have special features
» Papillae
» Cell inclusions (tannins, crystals)
(c) STOMATA
• Openings in epidermal cell layer
• Each stoma is bounded by two specialised guard cells
• These control opening and closing of the pore by changing
their shape
Anomocytic
Digitalis
Anisocytic
Paracytic
Diocytic
Belladonna
Senna
Mint
7. TRICHOMES (Hairs)
• Protective
• Highly variable appendages
– Glandular – secretory
– Non-glandular (covering) hairs, scales, papillae and absorbing
hairs of roots
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Can occur on any part of the plant
Persist throughout life of plant
When lost scar (or cicatrix) is left
Good diagnostic feature
Unicellular
Multicellular
Senna
Hyoscyamus
Warty - Digitalis
Cannabis sativa
Anise
Stellate
Witch
hazel
Glandular
Hyoscyamus
Digitalis
Belladonna
Unicellular stalk
Belladonna
Multicellular stalk
8. PERIDERM (Cork)
• Protective tissue
• Replaces epidermis in stems and roots that have
continuous secondary growth
• Comprises:
» Cork tissue (phellem)
» Cork cambium (phellogen)
» Parenchyma (phelloderm)
• Phellogen can arise in epidermis, cortex, phloem
» Produces phellem to outside
» Produces phelloderm to the inside
• Cork particularly diagnostic
• Characterised by suberisation – suberin – a fatty
substance which covers (lignified) primary cell wall
• Cork cells vary in thickness, colour
9. POLLEN
• Produced in anthers
• Varies considerably in size, shape, external
characters
• Can be useful diagnostically for drugs containing
floral parts