Chapter 35 Plant Structure, Growth, and Development

Roots support stem and leaves, send water and minerals; Leaves make food, stem supports and exchanges the two

Epidermis protects and absorbs Collenchyma and sclerenchyma support Parenchyma stores Xylem and phloem conduct Meristems allow for growth Root hairs increase surface area

Epidermis outside Under that is ground tissue In the center is vascular tissue

Fibrous: Shallow mat of thread-like roots Large surface area for absorption and anchoring Taproot: One large vertical root with branches Firm anchor, gets to deep resources, thick for storage Root hairs: Extensions of epidermal cells Increase surface area Adventitious: Roots originating aboveground In corn they help support

Epidermis protects Collenchyma and sclerenchyma support Parenchyma stores Xylem and phloem conduct Meristems allow for growth

Leaves are attached at nodes alternating with internodes Apical buds emerge just above the leaves At the tip, the terminal bud contains the apical meristem

Terminal bud inhibits the growth of lateral buds; decreases with distance Removal stops inhibition; growth of lateral buds = bushy

Stolons grown across the ground and may root Rhizomes are enlarged underground stems for storage/dormancy Tubers are the swollen ends of rhizomes for storage/dormancy Bulbs have a short underground stem with leaves for storage/dormancy

Spongy parenchyma performs photosynthesis Epidermis protects Collenchyma and sclerenchyma support Xylem and phloem conduct

Stomata control gas exchange Structure: Leaf = blade + petiole 1 blade = simple; > ≥2 = compound

Monocots: many similar leaf veins run parallel Dicots: branching, tapering veins

Dermal: Protects surfaces; extensions important in absorption Epidermis thickened by cuticle; bark including cork Vascular: Transports water, minerals, metabolic products; supports Xylem and phloem Ground: Photosynthesis, storage, support Parenchyma, collenchyma, sclerenchyma Bulk of the young plant

Parenchyma Cells: Thin walls with no secondary; large central vacuole Carry on most of the metabolic functions Ex.: leaf mesophylls, starch-storing cells in roots Collenchyma Cells: Thicker primary cell walls; no secondaries Support without restraining growth Ex. strings in celery, turgid cortex cells Sclerenchyma Cells: Thick secondary cell walls with lignin Stiff, cannot expand; terminally differentiated ~Two forms: -Long fibers as in flax -Short, irregular sclereids in nut shells Water-Conducting cells of the Xylem: Water-conducting; secondary walls reinforced by spirals/rings ~Types: -Tracheids: overlapping, joined at thin-walled pits -Vessel elements: end-to-end, joined by perforations -Both dead and empty at maturity Sugar-Conducting Cells of the Phloem: End-to-end sieve tube members joined by sieve plates No nuclei, ribosomes, vacuole Tended by companion cells

Meristems Stem cell tissues at the tips and in a layers under the bark

Primary growth: Apical meristems lengthen the roots and shoots Herbaceous plants, first year for woody plants Secondary growth: Growth in girth by lateral meristems Woody plants

Annuals must grow from seed each year: grains and legumes Biennials grow the first year, flower the second: carrots and beets Perennials live many years: grasses, trees

Dicot xylem in center with spokes; phloem between spokes Monocot xylem and phloem surround pith

From the tip: root cap and zones of cell division, elongation, maturationEpidermis outside; mixed parenchyma, collenchyma, sclerenchyma; endodermis; vascular stele

Similar arrangement from the tip Grasses have intercalary meristems allowing growth at each node Epidermis outside -Dicot: cortex, ring of vascular bundles, pith in center -Monocot: scattered vascular bundles in ground tissue

Epidermis outside with guard cells surrounding stomata Two layers of photosynthetic parenchyma -Tightly packed palisade mesophyll on top -Loose spongy mesophyll below inside the stomata Veins have xylem above phloem

Two lateral meristems ~Vascular cambium -Between the xylem and phloem -Cells divide to form xylem inside, phloem outside ~Cork cambium produces bark including corks cells with suberin As the apical meristems lengthen the stem, lateral meristems make it thicker Secondary xylem (wood) collects inside the vascular cambium Cells are wider in the wetter spring = springwood Cells are narrower in the drier summer = summerwood Roots have similar growth patterns Vascular cambium in the stele adds xylem inside, phloem outside Secondary xylem shows annual growth rings Cork cambium produces tough bark

Traits: Fits in test tubes Six week generations Small genome, sequence in hand Results: in situ hybridization shows where specific RNAs appear Mutations affecting flower development have been isolated

Plane: Plane not important in maize tangled-1 mutants Leaf shape is normal even though division planes aren't Symmetry: Asymmetrical division signals key events Also establishes polarity from the first division of the zygote

Cellulose fibrils resist stretching Fibrils are synthesized around the cell to restrict expansion in particular directions

Lineage-based: More important in animals Involves transcription factors like Hox genes Position-based: More important in animals Depends on cell to-cell commmunication