B6A4PlantStructureF09

B6A4PlantStructureF09 - Morphogenesis in Vascular Plants...

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Unformatted text preview: Morphogenesis in Vascular Plants Plants Cells Structure & Function in Vascular Plants •Plants have indeterminate growth ¸ ¸ Continue to grow throughout life Continue to have mix of embryonic, developing, & mature organs •Plants have phenotypic/developmental plasticity Fig. 35.1 Developmental plasticity in fanwort ( Cabomba caroliniana ) Plastids • Proplastid : reduced from chloroplasts in megasporocyte ; passed to ova; produce functional plastids in embryo • Chloroplast : chlorophyll, accessory pigments, starch synthesis • Leucoplast : chloroplast loses pigments in dark • Chromoplast : accessory pigments only • Localized Photosynthesis & Starch synthesis Amyloplast : starch synthesis only Cytokinesis & primary wall formation in dividing plant cells • • Cell Walls & Junctions Cell Walls & Junctions • Plasmodesmata form gap (communicating) junctions between cells Heyer The leaf was covered with a negative and exposed to light for several hours. Starch was produced in the exposed areas that can be detected with potassium iodate (dark areas of the photo). (D. A: WALKER, 1983) • Primary wall – deposited during cell division •Short-chain cross-linked cellulose microfibrils in gel-like matrix •Strong, but flexible & porous • Middle lamella – pectin 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., lignin ) •Irreversibly stronger & waterproof 1 Morphogenesis in Vascular Plants 1. Proliferation – plane & symmetry of cell division Multicellular Growth & Development cell fiber Plane of cell division 1. Proliferation – mitotic cell divisions 2. Hypertrophy – enlarging or elongating cells 3. Differentiation – tissue formation (a) Planes of cell division 4. Morphogenesis – pattern formation Developing guard cells Unspecialized epidermal cell Guard cell “mother cell ” (b) Asymmetrical cell division Fig. 35.25 2. Hypertrophy – cell elongation 3. Differentiation – Major plant tissue types A. Meristematic tissue i. Apical meristems ii. Lateral meristems Cellulose microfibrils B. Dermal tissue i. Epidermis ii. Periderm 5 µm Vacuoles Nucleus 1. Cell wall enzymes activated Æ weaken cross-links between microfibrils 2. Central vacuole takes on water by osmosis Æ cell expands 3. Cell can only expand perpendicular to microfibrils Æ directional elongation 4. New microfibrils constructed between old ones and new cross-links form Fig. 35.27 A. • • Meristematic tissue Meristematic tissue : contains undifferentiated cells that continue to divide throughout their lives to produce all of the other plant tissues. (Analogous to “stem cells” in animals) initial mitosis D derivative D mitosis D Meristem cells divides: 1. One daughter cell ( initial ) remains undifferentiated to replace original meristem cell. 2. Second daughter cell ( derivative ) divides to produce specialized cells. Heyer i. Parenchyma ii. Collenchyma iii. Sclerenchyma D. Vascular tissue i. Xylem – tracheids & vessel elements ii. Phloem – sieve-tube elements & companion cells A. Meristematic tissue • Apical meristem: growth of end of roots, shoots, & axillary buds. – Makes primary meristem tissues: • Protoderm Æ epidermis Shoot tip (shoot apical meristem • Ground meristem Æ ground tissue and young leaves) • Procambium Æ primary xylem & ploem M M C. Ground tissue • Lateral meristem: in woody plants, adds girth – Contains secondary meristem derived from primary Axillary bud meristem Lateral meristems: Vascular cambium Cork cambium • Vascular cambium • Cork cambium Root apical meristems 2 Morphogenesis in Vascular Plants A. Apical meristem in a root tip Meristematic tissue [differentiation] [hypertrophy] [proliferation] 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 B. Dermal tissue Dermal tissue — Epidermis B. • • • Covers the outer surface of the plant 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 gas exchange • Trichomes: bristles to resist desiccation & herbivory (cotton) • Root hairs to increase surface area for absorption • • Heyer Leaf epidermis with guard cells & stomata • Root hairs 3 Morphogenesis in Vascular Plants Epidermis — Cuticle B. Dermal tissue • • i. Upper surface of a chamomile flower These cuticle folds have several functions: they enhance the intense velvet effect of the flower color, increase the waterrepellent quality of the flower surface, strengthen the stability of the petals and finally does it seem as if they could be recognized by landing pollinators insects as additional information concerning the 'right' landing strip. 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 Epidermis (from protoderm) – surface of primary plant body ii. • • Covers the outer surface of the plant Resists desiccation, infection, and herbivory Periderm (from cork cambium) – replaces epidermis on surface of secondary growth (woody) areas • C. Cork – thicker, tougher & more water-proof Ground Tissue — Parenchyma • Most common/least specialized cell type in plants – Including most photosynthetic cells (leaf mesophyll) – 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. • Thin primary cell walls and reduced/absent secondary walls • Large central vacuoles D. Vascular tissue i. Xylem – tracheids & vessel elements ii. Phloem – sieve-tube elements & companion cells C. Ground Tissue — Parenchyma • Leaf parenchyma (mesophyll) with chloroplasts (chlorenchyma) C. Ground Tissue — Collenchyma • Thicker primary cell walls than parenchyma. No secondary walls • Usually stacked to form long strands or cylinders, often just below epidermis • Used for flexible support, esp. in young stems & pertioles • Mature cells remain viable and elongate with growing stem • Root parenchyma (cortex) with amyloplasts. [starch grains stain red] Heyer 4 Morphogenesis in Vascular Plants Ground Tissue — Sclerenchyma C. 3. Differentiation – Major plant tissue types A. Meristematic tissue • Thick, lignified secondary walls • Harder & more rigid than collenchyma, but cannot elongate • Cells die when wall is done. Left for structural support i. Apical meristems ii. Lateral meristems B. Dermal tissue – May persist for decades! i. Epidermis ii. Periderm • Elongated schlerenchyma forms fibers (hemp, flax) • Short schlerenchyma forms sclerids (nut shells, pear grit) C. Ground tissue Cross-section of fibers i. Parenchyma ii. Collenchyma iii. Sclerenchyma sclerids (lignin stains red) D. Vascular tissue i. Xylem – tracheids & vessel elements ii. Phloem – sieve-tube elements & companion cells D. Vascular tissue — Xylem D. Vascular tissue — Xylem Xylem: elongated cells with thick lignified cell walls. • Cells die, walls remain. • Pits in secondary cell wall; porous primary wall filters water as it flows across – Supportive tissue – Produce vessels to c onduct water, minerals and ions from the root tips to the leaf tips ÿ Tracheids: longer, narrower, with overlapping tapered ends ÿ Tracheids : longer, narrower, with overlapping tapered ends ÿ Vessel elements : shorter & fatter, aligned end-to-end Æ “micropipes ” (vessels ) — in angiosperms only ÿ Vessel elements: shorter & fatter, aligned end-to-end Æ “micropipes” ( vessels) — in angiosperms only ÿ Usually associated with sclerenchyma fibers for tensile strength, and rays of parenchyma tissue for lateral water transport D. Vascular tissue — Phloem Phloem vessels to transport organic fuel, mostly sucrose, from source tissues to sink organ ÿ 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 sap flows from cell to cell through sieve pores and plasma membranes ÿ Companion cells : aligned parallel to sieve-tube element cells (descended from same mother cell) • Cytoplasms connect through plasmadesmata • Synthesize proteins to support sieve-tube element cell • In source tissues, secrete sugars into phloem • Heyer In gymnosperms & pterophytes , sieve cells are similar to sieve-tube elements, but retain nuclei. No companion cells D. Vascular tissue — Phloem ÿ Usually associated with sclerenchyma fibers for tensile strength, and rays of parenchyma tissue for lateral water transport • In gymnosperms & pterophytes , sieve cells are similar to sieve-tube elements, but retain nuclei. No companion cells 5 Morphogenesis in Vascular Plants Multicellular Growth & Development 1. 2. 3. Root & Shoot Systems Proliferation – mitotic cell divisions Hypertrophy – enlarging or elongating cells Differentiation – tissue formation 4. Morphogenesis – pattern formation Embryo (seed) fi Roots fi Shoots fi Stems fi Leaves fi Reproductive organs Primary Growth in a Root Tip Primary 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 1. Apical meristem secretes growth-regulating factors Æ Inhibits differentiation 2. Once apical meristem has moved far enough away, differentiation proceeds 3. Some regions of pericycle , once released from root tip inhibition, become [differentiation] new apical meristems for growth of lateral branches [hypertrophy] Root apical meristems Primary Growth in a Root Tip • [proliferation] Primary Growth in a Shoot Tip 1. Apical meristem projects laterally to form leaf primordia Development of lateral roots originates in pericycle (outermost layer of vascular bundle) to form vascular core (stele) of the lateral root. 2. Hypertrophy of region between primordia creates internode lengths between leaves Developing vascular strand Heyer 3. Once apical meristem extends far enough away, primary meristems in stem and leaves differentiate 4. Islands of meristem left behind at upper axis of leaf primordia Æ axillary buds 6 Morphogenesis in Vascular Plants 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 resumes (spring), scales fall of leaving bud scar and apical bud extends again Fig. 36.3 • axillary buds at successive nodes arranged in spiral pattern • Phyllotaxy (“leaf order“): the arrangement of the leaves on the stem of a plant — unique for that species – Determines the amount of self-shading of lower leaves by upper leaves Primary Growth in a Shoot Tip Apical dominance: Secondary Growth in a Woody Stem Apical buds 1. Proximity of apical bud causes axillary buds to remain dormant. 2. Once shoot tip growth moves apical bud away, axillary buds may be stimulated to become new apical bud to form shoot or branch Discussed in Lab! Axillary buds 3. Removal of apical bud (grazing/pruning) likewise removes apical dominance and results in lateral shoot formation Developmental Phase Changes of Meristem Reproductive Phase Changes of Meristem Determinate Development of Leaves Floristic Development and and • Meristem identity genes: leaf primordia Æ floral primordia • Organ identity genes: which floral primordia becomes which floral component – The ABC hypothesis Heyer 7 ...
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This note was uploaded on 09/02/2011 for the course BIOL 6a taught by Professor Staff during the Fall '10 term at DeAnza College.

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