Bald cypress Taxodium distichum in a swamp in North Carolina

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1 Bald cypress Taxodium distichum in a swamp in North Carolina Bald cypress is another deciduous gymnosperm. It is native to the SE United States. It can tolerate a wide range of soil conditions. It is not reliably hardy in MN but there is one on the St. Paul campus.

2 In saturated soil bald cypress produces knees to obtain oxygen for the root system

3 Cells, Tissues and Organs (continued) Introduction to plant architecture Epidermis of a reed

4 Root hair cells: epidermal cells of the root with projections. The function is to increase surface area for water and nutrient absorption. Not every root epidermal cell becomes a root hair cell. Note: root hairs are cellular extensions, lateral roots are multicellular.

5 Cell growth: two mechanisms 1) tip growth (root hairs, pollen tubes) and 2) diffuse growth (almost all other cells).

6 In diffuse growth orientation of cellulose microfibrils determines the polarity of cell expansion. The orientation of cellulose is determined by interaction of cellulose synthase with microtubules.

7 Plant cells normally expand 10 to 100-fold in volume. The cell wall expands by stress relaxation. Expansins (cell wall protein) are responsible for acidinduced stress relaxation. Cell expansion is driven by turgor pressure (positive hydrostatic pressure) within cells. Model for expansin action: External or hormonal signals activate plasma membrane proton pumps (H + -ATPase) that acidify the wall space. This could be localized. Under acidic conditions expansins loosen the wall by modifying cross linking of cellulose.

8 Define primary growth: Growth in vascular plants resulting from the production of primary tissues by a primary meristem. Primary meristem: Meristematic tissue in vascular plants derived from an apical meristem. Primary meristems are procambium, protoderm, and ground meristem. Primary tissues: tissues derived from an apical meristem. (Secondary tissues are derived from secondary meristems)

9 Phyllotaxy: arrangement of leaves on the stem Alternate: one leaf per node node internode Opposite: two leaves per node Distichous: one leaf per node, arranged in only two rows

10 opposite alternate whorled spiral

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12 Distichous (two rows of leaves) alternate Decussate (four rows of leaves) opposite You can have distichous opposite also.

13 Vascular tissues: Primary phloem and xylem are always found together in vascular bundles. In stems and roots the phloem is oriented to the outside. Primary phloem Primary xylem Vascular bundle of clover

14 What are the similarities and differences between xylem and phloem? Both are types of vascular tissue, both are found in vascular bundles, and both form tubes that conduct solutes for long distances in plants. In the xylem the tracheids and vessel elements that form the conducting tubes are dead at maturity. In the phloem the sieve elements that form the conducting tubes are living at maturity. Transport in the xylem is driven by negative pressure. Transport in the phloem is driven by positive pressure.

15 What are the differences between plant and human vascular tissue? The conduits or conducting tubes in plants are single cells and they are multicellular in humans. In humans, one of the main functions of the functions of vascular tissue is to carry O 2 and CO 2. Not in plants. In both plants and humans delivery of sugar is a main function of the vascular tissue. In humans, cells circulate in the vascular tissue. Not in plants.

16 xylem shoot tip epidermis mesophyll phloem node bud flower pith xylem phloem cortex node internode Vascular tissues Dermal tissues leaf epidermis seeds (inside fruit) Ground tissues Shoot system Root system cortex xylem phloem primary root lateral root root hairs epidermis root tip root cap

17 Cross section of a clover (eudicot) stem. vascular bundle pith cortex ground tissue epidermis

18 Cross sectional diagram of a eudicot stem (Helianthus, sunflower).

19 Cross section of a buttercup (eudicot) root cortex vascular cylinder epidermis

20 Cross sectional diagram of a eudicot root

21 Cross section of a lilac leaf mesophyll (ground tissue) vascular bundle epidermis Fig. 4-3c, p. 53

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23 Cross section of a monocot stem epidermis vascular bundles ground tissue

24 Plant Cells are under positive pressure. Turgor pressure: the positive hydrostatic pressure of a cell. This pressure is generated by water accumulation driven by a negative solute potential. The rigid cell wall prevents the cell from bursting. A negative solute potential means that the cell accumulates solutes and that water is attracted and enters the cell by osmosis. Importance of turgor pressure: plant structure, cellular movement, cell growth, nutation (tissue movement).

25 Turgor pressure and plant srtucture: low turgor and wilting.

26 Turgor pressure and guard cell movements Higher turgor Lower turgor

27 Modified stems: Bulbs modified shoots, underground stems surrounded by modified fleshy leaves. Examples: onion, daffodils, garlic. Function: storage. Corms fleshy stems with modified papery leaves. Examples: gladiolus. Function: storage. bulb corm Tubers horizontal underground fleshy stems. Example: potato, the eyes are axillary buds. Function: storage. tuber Sunflower Germination in continuous light

28 Rhizomes horizontal underground stems that survive harsh winters and allow plants to spread. Examples: bamboo, irises, canna lillies, Stolon horizontal stem, also called a runner. Used to explore for suitable habitat. Examples: strawberry, some grasses.