Stems and Transport in Vascular Plants. Herbaceous Stems. Herbaceous Dicot Stem 3/12/2012. Chapter 34. Basic Tissues in Herbaceous Stems.

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Winifred Norris
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Bud scale Terminal bud Stems and Transport in Plants One year's growth Terminal bud scale scars Axillary bud Leaf scar

732 Herbaceous Stems : protective layer covered by a water-conserving cuticle Stomata: permit gas exchange Tissue: Xylem:

Basic Tissues in Herbaceous Stems Herbaceous eudicot (dicot) stems vascular bundles arranged in a circle (in cross

1 Bud scale Terminal bud Stems and Transport in Plants One year's growth Terminal bud scale scars Axillary bud Leaf scar Node Internode Node Chapter 34 Lenticels Terminal bud scale scars Bundle scars A Woody Twig Fig. 34-1, p. 732 Herbaceous Stems : protective layer covered by a water-conserving cuticle Stomata: permit gas exchange Tissue: Xylem: conducts water and dissolved minerals Phloem: conducts dissolved sugar Ground tissue: and function primarily for storage Basic Tissues in Herbaceous Stems Herbaceous eudicot (dicot) stems vascular bundles arranged in a circle (in cross section) distinct cortex and pith Monocot stems vascular bundles scattered in ground tissue Herbaceous Stems Herbaceous Dicot Stem Ground tissue 1

Monocot Stem Phloem fiber cap Phloem Xylem Vessel element bundle 250 µm Fig.

733 Ground tissue bundles Phloem Sieve tube element Companion cell Xylem

bundle) Fig. 34-3a, p. 734 Fig. 34-3b, p.

from shoot Apical meristems Seconday tissues (xylem,, and periderm of stems

2 Monocot Stem Phloem fiber cap Phloem Xylem Vessel element bundle 250 µm Fig. 34-2b, p. 733 Ground tissue bundles Phloem Sieve tube element Companion cell Xylem Vessel element Air space 500 µm 100 µm Bundle sheath (surrounds the vascular bundle) Fig. 34-3a, p. 734 Fig. 34-3b, p. 734 Primary tissues (epidermis, cortex, pith, xylem, and ) of stems develop from shoot Apical meristems Seconday tissues (xylem,, and periderm of stems Develop from Lateral Meristems ( Cambium,Cork Cambium) Apical Primary Lateral meristems tissue meristems tissues Meristematic cells Primary xylem Primary Cork xylem (wood) (inner bark) 2

Time 3/12/2012 Growth Production of secondary tissues, wood, bark occurs in some

in two directions secondary xylem (to the inside) secondary (to the outside)

primary xylem pith xylem (wood) (outer bark) Fig. 34-4a, p. 735 Fig. 34-4b, p.

gradually crushed or turn apart and sloughed off) 1X2X3X4X 2P1P 1X2X3X 2P1P

3 Time 3/12/2012 Growth Production of secondary tissues, wood, bark occurs in some flowering plants (woody dicots) and all cone-bearing gymnosperms Cambium divides in two directions secondary xylem (to the inside) secondary (to the outside) Primary xylem Remnant of primary Remnant of cortex epidermis (inner bark) Primary primary xylem pith xylem (wood) (outer bark) Fig. 34-4a, p. 735 Fig. 34-4b, p. 735 xylem (wood) (outer bark; remnants of primary, cortex and epidermis are gradually crushed or turn apart and sloughed off) 1X2X3X4X 2P1P 1X2X3X 2P1P (inner bark) 1X2X xylem 2P1P primary xylem pith 1X 2X 1P 1X 1P Second division of vascular forms a cell. Fig. 34-4c, p X cell Division of vascular forms two cells, one xylem cell and one vascular cell. cell when secondary growth begins. Fig. 34-5, p

Cork Cambium Lateral meristem that produces periderm cork parenchyma and cork cells Cork cells to

for storage in a woody stem Primary xylem Annual ring of secondary xylem xylem (wood) and remnants

4 Cork Cambium Lateral meristem that produces periderm cork parenchyma and cork cells Cork cells to outside of cork suberin and waxes make it waterproof Cork parenchyma to inside of cork primarily for storage in a woody stem Primary xylem Annual ring of secondary xylem xylem (wood) and remnants of primary, cortex, and epidermis Expanded ray Xylem ray Heartwood Sapwood 0.5 mm Fig. 34-6, p. 737 Fig. 34-8, p µm Cross section of 3-year-old Tilia stem Summerwood Springwood Summerwood of preceding year Annual ring of xylem Fig. 34-9, p. 739 Water Movement Water and dissolved minerals move from soil into root tissues (epidermis, cortex) Water and minerals move upward, from root xylem to stem xylem to leaf xylem Water entering leaf exits leaf veins and passes into atmosphere 4

Transport Sugar molecules from photosynthesis are transported in throughout plant, including into roots. Most water that plant absorbs is transpired into atmosphere.

740 Water Potential A measure of the free energy of water Pure water = 0 water = lots of free energy no solutes Water with dissolved solutes has lowered water potential (a negative number) Water

5 Transport Sugar molecules from photosynthesis are transported in throughout plant, including into roots. Most water that plant absorbs is transpired into atmosphere. Once inside roots, water and minerals are transported upward in xylem to stems, leaves, flowers, fruits, and seeds. Roots obtain water and dissolved minerals from soil. Fig , p. 740 Water Potential A measure of the free energy of water Pure water = 0 water = lots of free energy no solutes Water with dissolved solutes has lowered water potential (a negative number) Water moves from higher (less negative) water potential to lower (more negative) water potential From area of fewer solutes to more solutes Tension Cohesion Model Explains rise of water even in the tallest plants! Transpiration evaporative pull causes tension at top of plant result of water potential gradient (ranges from slightly negative in soil and roots to very negative in atmosphere) Tension Cohesion Model Column of water pulled up through the plant remains unbroken due to cohesive and adhesive properties of water Tension Cohesion Model Root Pressure Explains rise of water in smaller plants particularly when soil is wet Pushes water up through xylem water moves from soil into roots due to active absorption of mineral ions from soil 5

Root Pressure (solutes) Water enters roots by osmosis (No solutes) Soil Root xylem Stem xylem Leaf xylem atmosphere Water is pulled and pushed through a plant Sugar Translocation

is predominant sugar translocated in Pressure Flow Hypothesis Explains movement of materials in Companion cells actively load sugar into sieve tubes at source requires ATP Pressure Flow

6 Root Pressure (solutes) Water enters roots by osmosis (No solutes) Soil Root xylem Stem xylem Leaf xylem atmosphere Water is pulled and pushed through a plant Sugar Translocation Dissolved sugar is translocated upward or downward in from area of excess sugar (usually a leaf) to a sink (area of storage or sugar use: roots, apical meristems, fruits, seeds) Sucrose is predominant sugar translocated in Pressure Flow Hypothesis Explains movement of materials in Companion cells actively load sugar into sieve tubes at source requires ATP Pressure Flow Hypothesis Turgor pressure gradient produced by water entering at source and water leaving at sink drives flow of materials between source and sink ATP energy pumps protons out of sieve tube elements 6

7 Source ATP Pressure Flow Hypothesis Pressure-flow hypothesis translocation Sucrose loaded and unloaded requires ATP Water moves osmotically Sink 7

Plants. Plant Form and Function. Tissue Systems 6/4/2012. Chapter 17. Herbaceous (nonwoody) Woody. Flowering plants can be divided into two groups:

Plants. Plant Form and Function. Tissue Systems 6/4/2012. Chapter 17. Herbaceous (nonwoody) Woody. Flowering plants can be divided into two groups: Monocots Dicots 6/4/2012 Plants Plant Form and Function Chapter 17 Herbaceous (nonwoody) In temperate climates, aerial parts die back Woody In temperate climates, aerial parts persist The Plant Body Functions