Plant Architecture Plant Architecture --exploring functionality and formexploring functionality and form

The structure of a plant is akin to that of this greenhouse. Each individual piece has very little capacity to resist either torsional or compressive force individually. Yet, when assembled it is self-supporting. The key lies in architecture and engineering.

The Palm House, Kew Gardens, RichmondPhoto credit: Prof D Cutler, RGB Kew

The Palm House, Kew Gardens The Palm House, Kew Gardens November 2002November 2002

What architecture?What architecture?What are the contributing What are the contributing components?components?How do these components How do these components interact?interact?

tracheidstracheids fibersfibers

girdersgirders

STRENGTHSTRENGTHturgorturgor

vesselsvessels

collenchymacollenchyma

shapeshape

architectural contributorsarchitectural contributors

Efficient architectureEfficient architecture

Formation of a structure that has the ability to withstand stress and strain with the minimumminimum of lignin expenditure.The shapeshape of the unit, vs. expenditure on lignin

What is architecture?What is architecture?What contributes to What contributes to successful architecture?successful architecture?How do these components How do these components interact?interact?

tracheidtracheid fibersfibers

girdersgirders

STRENGTHSTRENGTHturgorturgor

vesselvessel

collenchymacollenchyma

shapeshape

stems stems

In the stem, architecture In the stem, architecture contributes to the design contributes to the design and interaction of and interaction of components that enhance components that enhance capacity to withstand capacity to withstand stress and strain, with the stress and strain, with the minimum energy minimum energy expenditure on the expenditure on the biosynthesis of biosynthesis of ligninlignin, , thickened, or supporting thickened, or supporting structures.structures.

Leaf architectureLeaf architecture

In the leaf, architecture In the leaf, architecture contributes to a design in contributes to a design in which components which components interactinteract, , thereby thereby enhancingenhancing the the capacitycapacity of the leaf (and of the leaf (and perhaps the stem as well if perhaps the stem as well if monocot) to monocot) to withstand stresswithstand stressand strainand strain, with , with minimum minimum involvement of lignin involvement of lignin biosynthesisbiosynthesis or the formation or the formation of other thickened of other thickened supporting structures.supporting structures.

High investment costsHigh investment costs

fibersfibers

tracheidstracheids

turgorturgor

vesselsvessels

girdersgirders

©© D Cutler RBG KewD Cutler RBG Kew

Ghania radula, Ghania radula, TS leafTS leaf

This leaf is an example of a huge This leaf is an example of a huge investment in support structures investment in support structures –– ““WW”” ––shaped beams support and separate the shaped beams support and separate the photosynthetic tissues, which lie in this photosynthetic tissues, which lie in this heavilyheavily--grooved structure.grooved structure.

shapeshape

Investment in rootsInvestment in roots

Architecture may be influenced by the Architecture may be influenced by the need for an need for an efficient transportefficient transport and and translocationtranslocation systems. systems. Most secondary roots are massive Most secondary roots are massive structures, anchoring and supporting structures, anchoring and supporting the mass of the aerial parts above the mass of the aerial parts above ground.ground.

root structureroot structure

Vicia fabaVicia faba TS RootTS Root

©© D Cutler RBG KewD Cutler RBG Kew

This cross section of This cross section of Vicia fabaVicia fabaroot typifies the structure of a root typifies the structure of a developing dicotyledonous developing dicotyledonous rootroot. There is very little . There is very little mechanical tissue present mechanical tissue present here here –– the only lignified the only lignified tissues are associated with the tissues are associated with the vascular core. vascular core.

Why?Why?

Shape and structureShape and structure

Collection and supportCollection and support

Many leaves have a Many leaves have a recurved structure, which recurved structure, which often carries over to the often carries over to the petiole, producing a petiole, producing a guttergutter--like structurelike structurewhich is also an which is also an inexpensive way of inexpensive way of creating supporting creating supporting strands.strands.

What else could be What else could be involved in mechanical involved in mechanical support?

Prunus amygdalusPrunus amygdalus petiole, petiole, gutteringguttering

©© D Cutler RBG KewD Cutler RBG Kew

support?

shapeshape turgorturgor

fibresfibres

Recurvature, gutteringRecurvature, guttering

©© D Cutler RBG KewD Cutler RBG Kew

Greyia sutherlandii Greyia sutherlandii TS petioleTS petiole

Recurvature of the vascular Recurvature of the vascular tissue adds additional tissue adds additional strength to the whole strength to the whole structure, as seen in this structure, as seen in this cross section of cross section of Greyia Greyia sutherlandii.sutherlandii. This is a This is a minimalist support system.minimalist support system.

What else could be involved What else could be involved in mechanical support?in mechanical support?

shapeshape

turgorturgor

fibresfibres

ShapeShape

Triangulation results in a Triangulation results in a fairly strong structure, fairly strong structure, which again requires very which again requires very little expensive lignin little expensive lignin biosynthesis.biosynthesis.

This leaf is also extremely This leaf is also extremely unpalatable, as it has high unpalatable, as it has high tannin content. tannin content.

The contributors are:Oscularia deltoidea

©© D Cutler RBG KewD Cutler RBG Kew The contributors are:

shapeshape turgorturgor

Triangulation in leavesTriangulation in leaves

Xanthorrhhoea australis Xanthorrhhoea australis leaf TSleaf TS

This leaf contains This leaf contains pockets of mesophyllpockets of mesophyll, , embedded between embedded between thick sclerenchyma thick sclerenchyma strands. This leaf has strands. This leaf has a central translucent a central translucent parenchymatous core parenchymatous core (may be a water (may be a water storage area?).storage area?).

©© D Cutler RBG KewD Cutler RBG Kew

Developing hollow tubesDeveloping hollow tubes

The core becomes hollow The core becomes hollow –– massive strength gainmassive strength gain

Core tissue Core tissue –– stem stem and differentiating and differentiating leaf materialleaf material

Useful shapes. Tubes, hollow Useful shapes. Tubes, hollow cylinders, pentagons, hexagons & cylinders, pentagons, hexagons & combinations of thesecombinations of these

Composite structure Composite structure –– some considerations some considerations

What about shape and its effect on strength?What about shape and its effect on strength?What role does orientation play?What role does orientation play?

?? ????

Compression & tension – which of these structures is effective?

Shape vs. strengthShape vs. strength

Polygonium officinalePolygonium officinale

Angular stems are not Angular stems are not of necessity of necessity necessarily very necessarily very strong. In strong. In Polygonium Polygonium officinale, officinale, thethestrength of the stem strength of the stem lies in its angularity. lies in its angularity. BUTBUT lack of lack of mechanical tissues mechanical tissues means low shear means low shear strength (low strength (low resistance to lateral resistance to lateral forces).forces).

© D Cutler RBG Kew

Shape vs. strengthShape vs. strength

Adding reAdding re--enforcing enforcing to the corners of this to the corners of this square tube (using square tube (using collenchyma or collenchyma or sclerenchyma) sclerenchyma) results in a flexible, results in a flexible, light yet rigid light yet rigid structure.structure.

Massive cornersMassive corners

Mechanical tissue

large regions of mechanical large regions of mechanical tissue, coupled with large tissue, coupled with large vascular bundles in the vascular bundles in the corners of the stem, and a corners of the stem, and a hollow centre means hollow centre means increased strength with increased strength with relatively light construction relatively light construction costscosts.

Stelar structure Stelar structure -- Corrugation Corrugation

Corrugated boardCorrugated board

Xylem, forms tubular Xylem, forms tubular rere--enforcingenforcing

Stelar structure Stelar structure –– Rings within rings,Rings within rings,& corrugation& corrugation

Stelar structure Stelar structure -- Layering & corrugation Layering & corrugation

Alternation of mechanical support tissue with a band of xylem creates a strong ‘corrugated’effect

To Juncus

BeamsBeamscompositecompositesimplesimple

Cojoined Cojoined ‘‘II’’ beams beams transfer stress transfer stress laterally and laterally and vertically, providing vertically, providing high sheer strengthhigh sheer strength

Anarthria scabridaAnarthria scabrida

Leptocarpus simplexLeptocarpus simplex© D Cutler RBG Kew

© D Cutler RBG Kew

Pit props and armour platingPit props and armour plating

© D Cutler RGB Kew

Willdenovia striataWilldenovia striata

Many species have evolved Many species have evolved verticallyvertically--orientated strands of orientated strands of fibers, as longitudinal fibers, as longitudinal strengthening agents, as well as strengthening agents, as well as to resist collapse of the leaf, to resist collapse of the leaf, during torsional bending.during torsional bending.Sclereids separate verticallySclereids separate vertically--orientated mesophyll cells in orientated mesophyll cells in this example. Note that the this example. Note that the epidermis is heavily lignified as epidermis is heavily lignified as well.well.

Pit propsPit props

Compression preventionCompression prevention

Hypodisus striatus Hypodisus striatus – culm, girdersculm, girders© D Cutler RGB Kew

Leptocarpus simplex, Leptocarpus simplex, culm, pit propsculm, pit props© D Cutler RGB Kew

helping plants breathe #1helping plants breathe #1

Diaphragms have evolved Diaphragms have evolved in many species. They may in many species. They may be partly lignified. In this be partly lignified. In this example, parenchymatous example, parenchymatous cells have pulled apart at cells have pulled apart at the corners, (through the corners, (through schyzogenous separation) schyzogenous separation) to leave a large number of to leave a large number of small interconnected air small interconnected air spaces.spaces.

PontedariaPontedaria pedicel diaphragmpedicel diaphragm

© D Cutler RGB Kew

helping plants breathe #2helping plants breathe #2

Stem diaphragms have evolved as very Stem diaphragms have evolved as very effective bubble traps, thereby improving effective bubble traps, thereby improving flotation in hydrophytes, and or COflotation in hydrophytes, and or CO22exchange in mesophytes as well exchange in mesophytes as well Organizationally, composed of modified Organizationally, composed of modified parenchyma cells, called stellate parenchyma parenchyma cells, called stellate parenchyma (good example in (good example in Canna Canna leaves as well)leaves as well).

Zinia latifolia Zinia latifolia stem diaphragm, lignifiedstem diaphragm, lignified©© D Cutler RGB Kew . D Cutler RGB Kew

Hard hollow cylinder and aeration.Hard hollow cylinder and aeration.

Juncus maritimusJuncus maritimus©© D Cutler RGB KewD Cutler RGB Kew

sclerenchyma

aerenchyma

Not quite squareNot quite square…….concavo convex.concavo convex

Crossed girders Crossed girders ‘‘XX’’ confer confer high resistance to inward high resistance to inward compression at the corners compression at the corners –– this modified this modified ‘‘guttergutter’’shape, relies principally shape, relies principally therefore on shape and not therefore on shape and not mechanical tissues to keep mechanical tissues to keep it erect.it erect.

What else is necessary What else is necessary here?here?

EuphorbiaEuphorbia sp, stem

© D Cutler RGB Kewturgorturgor

ConcavoConcavo--convex #2convex #2

StapeliaStapelia sp, stemsp, stem

©© D Cutler, RGB KewD Cutler, RGB Kew

As in the previous example, As in the previous example, this cross section of a this cross section of a StapeliaStapelia stem, has a deeply stem, has a deeply concavoconcavo--convex structure, convex structure, which will add significantly which will add significantly to the mechanical to the mechanical supportive capacity, of this supportive capacity, of this otherwise simple, relatively otherwise simple, relatively undifferentiated stem.undifferentiated stem.

What else is needed to What else is needed to maximise support capacity?maximise support capacity?

turgorturgor

Monocot epidermis, tough stuff!Monocot epidermis, tough stuff!

The epidermis in The epidermis in monocotyledonous monocotyledonous leaves, is composed of leaves, is composed of long and short cells, long and short cells, which parallel the vein which parallel the vein system.system.

Silica bodies can be seen Silica bodies can be seen in the epidermal cells a in the epidermal cells a vein. vein.

This is a resilient This is a resilient structure

Molinia sp Molinia sp Leaf epidermisLeaf epidermis©© D Cutler, RGB KewD Cutler, RGB Kew

structure

Whatever the caseWhatever the case……....

& whichever it is, xylem & whichever it is, xylem or sclerenchyma, or sclerenchyma, parenchyma or parenchyma or collenchyma, plants do collenchyma, plants do possess a degree of possess a degree of mechanical strength mechanical strength which is determined, which is determined, directed, and related to directed, and related to the environment within the environment within which they exist.which they exist.

Alternatively, it is their Alternatively, it is their expression of mechanical expression of mechanical strength that determines strength that determines their niche.their niche.

References:References:

Additional ReadingAdditional ReadingA few core articles may be made available to you.A few core articles may be made available to you.Behnke, HBehnke, H--D and RJ SjD and RJ Sjöölund (eds) 1990. lund (eds) 1990. Sieve elements. Comparative structure, Sieve elements. Comparative structure,

induction and Development. Springer ISBN 3induction and Development. Springer ISBN 3--540540--5078350783--3. (I have a personal 3. (I have a personal copy).copy).

Carlquist, S.1988. Carlquist, S.1988. Comparative Wood Anatomy. Springer ISBN 3Comparative Wood Anatomy. Springer ISBN 3--540540--1882718827--4. 583.04 4. 583.04 Car.Car.

Fahn, A 1967 Fahn, A 1967 Plant Anatomy. Pergamon Press. 581.3 Fah. (There may be a newer Plant Anatomy. Pergamon Press. 581.3 Fah. (There may be a newer edition out thereedition out there……))

DF Cutler and CEJ Botha DF Cutler and CEJ Botha Plant AnatomyPlant Anatomy –– an Applied Approach an Applied Approach prepublication formatprepublication formathttp://botany.ru.ac.za/BOTANY2/applied.pdfhttp://botany.ru.ac.za/BOTANY2/applied.pdf

Internet Information SourceInternet Information Source: WWW; BIOSIS; ISI Web of Knowledge: WWW; BIOSIS; ISI Web of Knowledge ScienceDirectScienceDirect ; Google; Google