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Home , Cambium, Cork cambium, Cortex (botany), Epidermis (botany), Guard cell, Lenticel

Morphogenesis in Vascular

Plants Cells

Fig. 35.24 Developmental plasticity in fanwort (Cabomba caroliniana) Fig. 6.8b

Plastids Localized & synthesis • Proplastid: reduced from in megasporocyte; passed to ova; produce functional in • : , accessory pigments, starch • The was covered with synthesis a negative and exposed • Leucoplast: chloroplast loses to light for several hours. pigments in dark Starch was produced in the exposed areas that • : accessory can be detected with pigments only iodate (dark areas of the photo). • : starch synthesis – (D. A: WALKER, 1983) only

Cytokinesis & primary wall formation in dividing cells

• Primary wall – deposited during division • Plasmodesmata form • Short-chain cross-linked microfibrils in gel-like matrix gap (communicating) • Strong, but flexible & porous junctions between cells • Middle lamella – gel (inter-cell glue) • Secondary wall (not in all tissues) • Long-chain cellulose microfibrils • Arranged in parallel cross-linked pattern • Sometimes reinforced with aromatic polymers (e.g., ) Figs. 6.27 & 6.29 • Irreversibly stronger & waterproof Fig. 12.10b

Heyer 1 Morphogenesis in Vascular Plants

1. Proliferation – plane & symmetry of Multicellular Growth & Development cell fiber 1. Proliferation – mitotic cell divisions Plane of cell division 2. Hypertrophy – enlarging or elongating cells 3. Differentiation – formation 4. Morphogenesis – pattern formation (a) Planes of cell division Developing guard cells

Unspecialized epidermal cell “mother cell”

(b) Asymmetrical cell division

Fig. 35.28

2. Hypertrophy – cell elongation 3. Differentiation – Major plant tissue types A. Meristematic tissue i. Apical Cellulose ii. Lateral meristems microfibrils B. Dermal tissue i. ii. Periderm C. 5 µm Nucleus i. ii. Collenchyma 1. enzymes activated → weaken cross-links between microfibrils iii. Sclerenchyma 2. Central takes on by → cell expands 3. Cell can only expand perpendicular to microfibrils → directional elongation D. 4. New microfibrils constructed between old ones and new cross-links form i. – & vessel elements ii. – sieve-tube elements & companion cells Fig. 35.30

A. Meristematic tissue A. Meristematic tissue

• Meristematic tissue: contains undifferentiated cells that continue to divide throughout their to produce all of the other plant tissues. • Apical : growth of end of , , & axillary . • (Analogous to “stem cells” in ) – Makes primary meristem tissues: • Protoderm → epidermis tip (shoot apical meristem • Ground meristem → ground tissue and young ) M • Procambium → primary xylem & phloem Lateral meristems: initial • Lateral meristem: in woody plants, Vascular D cambium M derivative adds girth Axillary meristem D mitosis – Contains secondary meristem derived from primary D • • Meristem cells divides: apical 1. One daughter cell (initial) remains undifferentiated to replace original meristem cell. meristems 2. Second daughter cell (derivative) divides to produce specialized cells.

Fig. 35.11

Heyer 2 Morphogenesis in Vascular Plants

Apical meristem in a root tip A. Meristematic tissue

[differentiation]

[hypertrophy]

[proliferation]

Fig. 35.13

Apical meristem in a shoot tip 3. Differentiation – Major plant tissue types A. Meristematic tissue i. Apical meristems ii. Lateral meristems B. Dermal tissue i. Epidermis ii. Periderm C. Ground tissue i. Parenchyma ii. Collenchyma iii. Sclerenchyma D. Vascular tissue i. Xylem – tracheids & vessel elements ii. Phloem – sieve-tube elements & companion cells Fig. 35.16

B. Dermal tissue B. Dermal tissue — Epidermis • Leaf epidermis with guard cells & stomata • Covers the outer surface of the plant • Root hairs • Resists desiccation, infection, and herbivory i. Epidermis (from protoderm) – surface of primary plant body • Secretes waxy cuticle • Produces specialized cells: • Guard cells around stomata for • : bristles to resist desiccation & herbivory (cotton) • Root hairs to increase surface area for absorption

Heyer 3 Morphogenesis in Vascular Plants

Epidermis — Cuticle Epidermis — Cuticle Diagram illustrating layers and composition of the cuticle

• Upper surface of a chamomile • These cuticle folds have several functions:

 they enhance the intense velvet effect of the flower color

 increase the water-repellent quality of the flower surface

 strengthen the stability of the

 could be recognized by landing Layers of cuticle proper: insects as additional information • right: concerning the 'right' landing strip. • left: tracheophyte Budke J M et al. Ann Bot 2011;aob.mcr079

B. Dermal tissue 3. Differentiation – Major plant tissue types A. Meristematic tissue i. Apical meristems • Covers the outer surface of the plant ii. Lateral meristems • Resists desiccation, infection, and herbivory i. Epidermis (from protoderm) – surface of primary B. Dermal tissue plant body i. Epidermis ii. Periderm (from cork cambium) – replaces epidermis ii. Periderm on surface of (woody) areas C. Ground tissue • Cork – thicker, tougher & more water-proof i. Parenchyma • secondary walls permeated with waxy ii. Collenchyma iii. Sclerenchyma

Onset of cork formation from cork cambium: D. Vascular tissue 1 cork (= phellem); 2 cork cambium (= phellogen); 3 collenchyma; 4 ; 5 parenchyma; 6 sclerenchyma; i. Xylem – tracheids & vessel elements 7 phloem; 8 cork (= phelloderm) (http://www.vcbio.science.ru.nl/en/virtuallessons/cambiumcork/) ii. Phloem – sieve-tube elements & companion cells

C. Ground Tissue — C. Ground Tissue — Parenchyma Parenchyma • Leaf parenchyma • Most common/least specialized cell type in plants (mesophyll) with – Including most photosynthetic cells (leaf mesophyll) chloroplasts (chlorenchyma) – And most non-photosynthetic storage tissues • Capable of dividing and live a long time – Can differentiate into other tissue types • Wound healing, asexual propagation, etc. • Root parenchyma • Thin primary cell walls and reduced/absent secondary walls (cortex) with . • Large central vacuoles [starch grains stain red]

Heyer 4 Morphogenesis in Vascular Plants

C. Ground Tissue — C. Ground Tissue — Collenchyma Sclerenchyma • Thicker primary cell walls than parenchyma. No secondary walls • Thick, lignified secondary walls • Usually stacked to form long strands or cylinders, often just • Harder & more rigid than collenchyma, but cannot elongate below epidermis • Cells die when wall is done. Left for structural support • Used for flexible support, esp. in young stems & pertioles – May persist for decades! • Mature cells remain viable and elongate with growing stem • Elongated sclerenchyma forms fibers (, ) • Short sclerenchyma forms sclerids (nut shells, grit)

Cross-section of fibers

sclerids

(lignin stains red)

3. Differentiation – Major plant tissue types D. Vascular tissue — Xylem A. Meristematic tissue i. Apical meristems Xylem: elongated cells with thick lignified cell walls. ii. Lateral meristems • Cells die, walls remain. B. Dermal tissue • Pits in secondary cell wall; porous primary wall filters i. Epidermis water as it flows across ii. Periderm – Supportive tissue C. Ground tissue – Produce vessels to conduct water, minerals and ions i. Parenchyma from the root tips to the leaf tips ii. Collenchyma  Tracheids: longer, narrower, with overlapping tapered iii. Sclerenchyma ends D. Vascular tissue  Vessel elements: shorter & fatter, aligned end-to-end i. Xylem – tracheids & vessel elements → “micropipes” (vessels) — in angiosperms only ii. Phloem – sieve-tube elements & companion cells

D. Vascular tissue — Xylem D. Vascular tissue — Phloem Phloem vessels to transport organic fuel, mostly sucrose, from source tissues to sink organ  Sieve-tube elements: moderately elongated cells with very thin primary cell walls / no secondary walls. • Aligned end-to-end with sieve plate in walls between adjacent cells. • Cells persist alive, but without nuclei or vacuoles • Phloem flows from cell to cell through sieve pores and plasma membranes  Companion cells: aligned parallel to sieve-tube element cells (descended from same mother cell)  Tracheids: longer, narrower, with overlapping tapered ends • connect through plasmadesmata  Vessel elements: shorter & fatter, aligned end-to-end • Synthesize to support sieve-tube element cell → “micropipes” (vessels) — in angiosperms only • In source tissues, secrete into phloem  Usually associated with sclerenchyma fibers for tensile strength, • In & pterophytes, sieve cells are similar to sieve-tube and rays of parenchyma tissue for lateral water transport elements, but retain nuclei. No companion cells

Heyer 5 Morphogenesis in Vascular Plants

Multicellular Growth & D. Vascular tissue — Phloem Development 1. Proliferation – mitotic cell divisions 2. Hypertrophy – enlarging or elongating cells 3. Differentiation – tissue formation 4. Morphogenesis – pattern formation Embryo () ⇒ Roots ⇒ Shoots ⇒ Stems  Usually associated with sclerenchyma fibers for tensile strength, and rays of parenchyma tissue for lateral water/ transport ⇒ Leaves • In gymnosperms & pterophytes, sieve cells are similar to sieve-tube ⇒ Reproductive organs elements, but retain nuclei. No companion cells

Root & Shoot Primary Systems Growth Shoot tip (shoot apical meristem and young leaves) Roots & shoots lengthen • by proliferation of apical meristems, • followed by hypertrophy, and • early differentiation into primary meristem tissues

Root apical meristems

Primary Growth in a Root Tip Primary Growth in a Root Tip 1. Apical meristem secretes growth-regulating factors → Inhibits differentiation • Development of lateral roots originates in (outermost layer 2. Once apical meristem has moved far enough away, of ) to form vascular core () of the lateral root. differentiation proceeds 3. Some regions of pericycle, once released from root tip inhibition, become [differentiation] new apical meristems for growth of lateral branches

[hypertrophy]

[proliferation]

Fig. 35.15

Heyer 6 Morphogenesis in Vascular Plants

Primary Growth in a Shoot Tip Primary Growth in the 1. Apical meristem projects laterally to form leaf primordia Shoot 1. Apical meristem projects 2. Hypertrophy of region between laterally to form leaf primordia creates internode primordia at nodes lengths between leaves 2. Leaf primordia develop 3. Once apical meristem extends far into leaves at nodes enough away, primary meristems 3. Hypertrophy of internode in stem and leaves differentiate region between primordia 4. Islands of meristem left behind at creates internode lengths upper axis of leaf primordia between leaves → axillary buds 4. Islands of meristem left behind at upper axis of leaf primordia → axillary buds 5. may become apical meristem of lateral stem branch

Primary Growth in a Shoot Tip Primary Growth in a Shoot Tip

1. In non-growing season (winter), apical meristem goes dormant (apical bud) protected by hardened leaf primorida (bud scales) 2. When growing season Fig. 36.3 resumes (spring), • axillary buds at successive nodes arranged in spiral pattern scales fall of leaving • Phyllotaxy (“leaf order“): the arrangement of the leaves on bud scar and apical the stem of a plant — unique for that species bud extends again – Determines the amount of self-shading of lower leaves by upper leaves

Fig. 36.4 Fig. 35.12

Primary Growth in a Shoot Tip Secondary Growth in a Woody Stem

Apical dominance: Apical buds 1. Proximity of apical bud causes axillary buds to remain dormant. 2. Once shoot tip growth Discussed in moves apical bud away, Axillary buds Lab! axillary buds may be stimulated to become new apical bud to form shoot or branch 3. Removal of apical bud (grazing/pruning) likewise removes and results in formation

Fig. 35.19

Heyer 7 Morphogenesis in Vascular Plants

Developmental Phase Changes of Meristem Developmental Phase Changes of Meristem and and Determinate Development of Leaves Specific Development of developmental & environmental cues → Axillary buds develop as floral buds → flower instead of branch • Nodes of floral axis develop as whorled floral primordia instead of leaf primordia Fig. 35.24 • First internode → • Distal internodes Fig. 35.33 very short

Reproductive Phase Changes of Meristem and Floristic Development

• Meristem identity : leaf primordia → floral primordia • Organ identity genes: which floral primordia node becomes which floral component – The ABC hypothesis

Fig. 35.28

Heyer 8