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)

– 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

• 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

- Indicates secondary thickening- Constituent of woody material

Pits in cell walls

Lignin in cell wall

• Reticulate

- Eg Fennel fruit (Foeniculum vulgare)

Large pit (surface view)

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

• 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)

– 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

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

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

• 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

9. POLLEN

• Produced in anthers• Varies considerably in size, shape, external

characters• Can be useful diagnostically for drugs containing

floral parts