s1 l3 evaluation of plant drugs 1. botanical b. microscopy cell types anna drew
TRANSCRIPT
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)
– Indicates plant tissue is present
– Least specialized plant cells– Thin and somewhat flexible cell walls– Generally have a large central vacuole– Living at maturity
– Found in all plant organs as a continuous tissue• cortex and pith of stems• ground tissue of petioles• mesophyll of leaves• endosperm of seeds
– Also forms part of complex tissues such as vascular tissues
– Most metabolic functions are carried out by parenchyma cells• Photosynthesis• Storage• Secondary growth• Wound healing
– Most parenchyma cells have the ability to differentiate into other cell types under special conditions
• During repair and replacement of organs after injury • Can resume meristematic activity to produce adventitious roots and shoots
Modifications of parenchyma
• Leaf tissue
Epidermal cell
Palisade mesophyll cell layer
Spongy mesophyll cells
• Lignified
- Indicates secondary thickening- Constituent of woody material
Pits in cell walls
Lignin in cell wall
2. COLLENCHYMA
• 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
Cascara bark
Diagnostic features:
• Very narrow lumen
• Found in groups
• Very thick – hard to see the lumen
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)
– 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)
• Osteosclereid
• Cinnamon bark
• Horseshoe shape
• One wall much thinner
• Irregular sclereid
Cascara bark
Irregular, solid, many in groups
Wild cherry bark
Very irregular, sometimes branched, (“jigsaw” piece)
4. VESSELS AND TRACHEIDS
Xylem:» 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
Vessel
• End walls of linear parenchyma cells breakdown to form continuous tubes or channels
• Only found in Angiosperms
Tracheid
• More primitive
• Pits allow water to pass from one to another
• Less efficient at conducting water
• More like a fibre
Lignin arrangements:
Annular Spiral Reticulate SclariformBordered pitted
HERBACEOUS WOODY PLANTS – to conduct more water
Eg Gentian root Rhubarb
Eg Male fern rhizome
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 sieve-
tube element and may aid in sucrose loading
Holes in patches -sieve plate at an angle
Sieve area - conducts to next cell
Sieve plate
Companion 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 SennaDigitalis
Mint
(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
7. TRICHOMES (Hairs)
• Protective• Highly variable appendages
– Glandular – secretory
– Non-glandular (covering) hairs, scales, papillae and absorbing hairs of roots
• 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
Glandular
Senna
AniseStellate
Witch hazel
Hyoscyamus
Warty - DigitalisCannabis sativa
Digitalis
Belladonna
Unicellular stalk Multicellular stalk
Hyoscyamus
Belladonna
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