shoot primary growth - christian brothers universityfacstaff.cbu.edu/~jmoore25/botanyppt/shoot...

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10/6/2011 1 Shoot Primary Growth Ch 25 Outline Origin & growth of primary stem tissues Primary structure of stem Relation between vascular tissues of the stem & leaf Morphology and structure of the leaf Grass leaves Development of the leaf Leaf abscission Transition between the Vascular Systems of the Root & Shoot Development of the flower Stem and Leaf modifications Primary Shoot functions • Support • Conduction – Food Wt Water

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Page 1: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

10/6/2011

1

Shoot Primary Growth

Ch 25

Outline• Origin & growth of primary stem tissues• Primary structure of stem• Relation between vascular tissues of the stem & leaf• Morphology and structure of the leaf• Grass leaves• Development of the leaf• Leaf abscission• Transition between the Vascular Systems of the Root

& Shoot• Development of the flower• Stem and Leaf modifications

Primary Shoot functions

• Support• Conduction

– Food W t– Water

Page 2: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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Origin and Growth of the Primary Tissues of the Stem

• Apical meristem adds cells to the primary plant body– Also, repetitively produces leaf primordia and

bud primordia– Results in repeated units called phytomeres

• Leaf primordia– Develop into leaves

• Bud primordia– Develop into lateral shoots

Protects apical meristem

R t d itRepeated units

• Shoot apical meristem – Tunica-corpus organization

• Tunica consists of the outermost layer or layers of cells that divide anticlinally– Perpendicular to the surface of meristem

• Corpus consists of a body of cells that lie beneath tunica layers.– Initials of corpus occur beneath the tunica and

add cells to the corpus by dividing periclinally• Parallel with the apical surface

Page 3: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Number of tunica layers varies from species to species.

• Angiosperms have apices consisting of three superimposed layers:three superimposed layers:– L1, L2, L3 – Outermost = L1– Innermost = L3

Central Zone

Peripheral zone

Two layered tunica

Initial layer of

Coleus blumei

Initial layer of corpus is L3.

Page 4: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Central zone – Mitotically quiescent

• Peripheral zoneMit ti ll ti– Mitotically very active

http://www.trainingreference.co.uk/free_pictures/gallery_3/horse_chestnut.jpg

Young shoots tightly packed in buds; protected by bud scales.

Bud scales: highly modified leaves initiated late in the previous growing season.

Page 5: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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Buds open to reveal oldest rudimentary leaves.

Internodal elongation has separated the nodes from one another.

Terminal bud is a mixed bud,containing both leaves and flowers.

Lateral buds produce only

http://farm2.static.flickr.com/1142/1470553921_3c4422524c_o.jpg

p yleaves.

Page 6: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Primary stem tissues go through periods of growth similar to the root– Stem cannot be divided along its axis into regions of

cell division, elongation, and maturation like roots.• Shoot gives rise to leaf primordia in such rapidShoot gives rise to leaf primordia in such rapid

succession that nodes & internodes can not be distinguished at first.

• Thus, increase in length of stem occurs by intrenodal elongation:– This may occur simultaneously over several

internodes.

• Apical meristem of shoot gives rise to same primary meristems found in root:– Protoderm, procambium, and ground

meristemmeristem.• These meristems develop into the mature

tissues of the primary plant body:– Epidermis, primary vascular tissues, and

ground tissue.

Page 7: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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Primary structure of the stem

• In seed plants other than monocots, the vascular system of the internode appears as more or less continuous cylinder within the ground tissuethe ground tissue.

• In others, the primary vascular tissues develop as a cylinder of discrete strands, or bundles, separated from one another by ground tissueground tissue.

• In stems of most monocots and some herbaceous eudicots, the arrangement is more complex. Vascular bundles appear scattered throughout the ground tissuescattered throughout the ground tissue.

Page 8: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Tilia americana– Vascular cylinder is composed of vascular

bundles that are separated from one another by inconspicuous regions of ground y p g gparenchyma call interfascicular regions.

Page 9: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Sambucus canadensis– The interfascicular regions pith rays are

relatively wide, hence the procambial strands and primary vascular bundles form a system p y yof discrete strands around the pith. Very similar to Tilia

Young stem, showing protoderm, ground meristem, and three discrete procambialstrands.

Mature sieve element

Primary tissues farther along in development

Page 10: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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Stem near completion of primary growth.

Cambia not formed yet!!!

Will become woody.

Sambucus has wide interfascicular regions—great portion of vascular cambium develops from interfascicular parenchyma

Herbaceous stems

• Undergo little or no secondary growth.• Medicago sativa (alfalfa) exhibits some

secondary growth.G th i il t S b– Growth similar to Sambucus.

Very discrete

Page 11: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Ranunculus (buttercup): herbaceousness– Vascular bundle resembles many monocots– VB’s retain no procambium after primary

vascular tissues maturevascular tissues mature• Hence, bundles never develop a vascular

cambium • Lose potential for future growth

Bundles are closed; All procambial cells mature precluding secondaryprecluding secondary growth.

Page 12: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Zea mays – Exemplifies stems of

monocots. – Vascular bundlesVascular bundles

appear scattered throughout the ground tissue in transverse section.

– VB’s are closed

Mature vascular bundle surrounded by a sheath of thick-walled sclerenchyma cells.

Relation between Vascular Tissues and Stem and Leaf

• Extensions from the vascular system in the stem toward the leaves – Leaf traces

• The wide interfascicular regions or gaps of ground tissue in the vascular cylinder located above the level where leaf traces diverge toward the leaveswhere leaf traces diverge toward the leaves– Leaf trace gaps

• Leaf trace extends from its connection with a bundle in the stem (stem bundle) to the level which it enters the leaf.

• Buds commonly develop in the axils of leaves, and their vascular system is connected with the main stem by branch traces

Page 13: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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Leaf arrangement• Phyllotaxy

– Arrangement of leaves on the stem• Most common helical or spiral.

– Quercus & Morus• Other plants have a single leaf at each node

– i.e, grasses –phyllotaxy is distichous• When leaves are formed in pairs at each

node – Phyllotaxy = opposite (Acer & Lonicera)

Page 14: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• If each pair is at a right angle to previous pair:– Decussate phyllotaxy

Lamiaceae (Coleus)– Lamiaceae (Coleus)• Three of more leaves at each node

– Whorled phyllotaxy– Culver’s root (Veronicastrum virginicum)

Helical

Whorled

Opposite

Helical

Morphology & Structure of the Leaf

• Blade or lamina – The expanded portion

• Petiole– Stalklike portion

• Simple leavesSimple leaves – Blades not divided into distinct parts

• May be deeply lobed• Compound leaves

– Divided into leaflets – each with own petiole– Two types

• Pinnately & Palmately• Pinnately – leaflets arise from either side of an axis rachis

Page 15: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Distinguishing leaflets from leaves.• 1. buds are found in the axils of leaves –

simple and compound – but not in leaflets.

• 2. leaves extend from the stem in various planes, whereas leaflets of a given leaf all lie in the same plane.

Mesophyll

• Mesophyll– Ground tissue of the leaf– Palisade parenchyma

Spongy parenchyma– Spongy parenchyma

• Where photosynthesis takes place– Chloroplasts

• Thylakoids

Page 16: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• VB’s found throughout mesophyll– Known as veins in leaves

• VenationNetted or reticulate– Netted or reticulate

• Veins arranged in branching pattern with successively smaller veins branching from larger ones.

• Angiosperms

– Parallel • Veins that extend along the long axis of the leaf• Monocots

Sun vs. Shade leaves

• Light can have substantial effects on leaf development.– Sun leaves

• Grown under high light intensities• Grown under high light intensities– Shade leaves

• Develop under low light intensities

Page 17: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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• Quercus rubra sun vs shade leaves

Sinuses very shallow Petioles rarely reddish

• Sun leaves thicker• Internal surface area of the mesophyll is

higher in sun leavesSh d l t d t d t hi h li ht• Shade leaves not adapted to high light intensities – Lower maximum photosynthetic rates

Sun Leaf

Shade Leaf

Page 18: Shoot Primary Growth - Christian Brothers Universityfacstaff.cbu.edu/~jmoore25/BotanyPPT/Shoot Primary Growth.pdf · Shoot Primary Growth Ch 25 ... • Development of the flower •

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Leaf Abscission

• Separation of leaf from stem– Occurs near base of petiole– Creates an abscission zone

• After separation occurs (i.e., leaf falls) the protective layer is recognized as a leaf scar on the stem.

Overview • Shoot apical meristem produces leaf primordia, bud

primordia, and stem primary tissues.• Three basic types of organization exist in the primary

structure of stems.• Leaves and stems are closely elated physically and

developmentally.• Leaf structure variation is related to habitat.• Leaves exhibit determinate growth, stems exhibit

indeterminate growth.• Separation of a leaf from a branch by abscission is a complex

process.• A flower is a determinate stem tip bearing modified leaves.• Stems may serve food-storage or water-storage functions.