Plant Form and Function Chapter 35 Structure, Growth, and Development

The plant body has a hierarchy of organs, tissues, and cells There are three basic plant organs: Roots Stems Leaves

Roots Fibrous Roots Tap Roots Roots are multicellular organs with important functions: Anchoring the plant Absorbing minerals and water Storing organic nutrients Fibrous Roots Tap Roots Micorrhizae – fungus that forms a symbiotic relationship with some plants

Shoot System: Stems and Leaves Reproductive shoot (flower) Apical bud Node Internode Apical bud Stems – function primarily to display the leaves. Terminal Bud – area of growth at the top end of stem Axillary Buds – area of growth located in the V area between the leaf and the stem (branches) Leaves – main photosynthetic organ in plants Shoot system Vegetative shoot Blade Leaf Petiole Axillary bud Stem Taproot Lateral branch roots Root system

There are three basic groups of plant tissues: Dermal Tissue Single layer of closely packed cells Protects plant against water loss and invasion by pathogens and viruses Cuticle – waxy layer in leaves Vascular Tissue Xylem and phloem Ground Tissue Any tissue that’s not Dermal or Vascular tissue Pith – ground tissue located inside vascular tissue Cortex – ground tissue located outside the vascular tissue

Plants have 5 major types of cells: Parenchyma Most abundant present throughout plant most metabolism (photosynthesis) Collenchyma Grouped in cylinders, supports growing parts of plant Strings of celery (vascular tissue) is supported by collenchyma cells Sclerenchyma Exists in parts of the plant that are no longer growing Tough cell walls utilized for support Xylem Phloem

Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm Fig. 35-10a Figure 35.10 Examples of differentiated plant cells Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm

Collenchyma cells (in Helianthus stem) (LM) Fig. 35-10b 5 µm Figure 35.10 Examples of differentiated plant cells Collenchyma cells (in Helianthus stem) (LM)

Sclereid cells in pear (LM) Fig. 35-10c 5 µm Sclereid cells in pear (LM) 25 µm Cell wall Figure 35.10 Examples of differentiated plant cells Fiber cells (cross section from ash tree) (LM)

Vessel Tracheids Pits Tracheids and vessels (colorized SEM) Fig. 35-10d Vessel Tracheids 100 µm Pits Tracheids and vessels (colorized SEM) Figure 35.10 Examples of differentiated plant cells Perforation plate Vessel element Vessel elements, with perforated end walls Tracheids

longitudinal view (LM) 3 µm Fig. 35-10e Sieve-tube elements: longitudinal view (LM) 3 µm Sieve plate Sieve-tube element (left) and companion cell: cross section (TEM) Companion cells Sieve-tube elements Plasmodesma Sieve plate Figure 35.10 Examples of differentiated plant cells 30 µm 10 µm Nucleus of companion cells Sieve-tube elements: longitudinal view Sieve plate with pores (SEM)

Meristems generate cells for new organs Apical meristems Are located at the tips of roots and in buds of shoots. Sites of cell division that allow plants to grow in length (primary growth) Lateral meristems results in growth which thickens the shoots and roots (secondary growth)

Primary Growth lengthens roots and shoots Cortex Vascular cylinder Epidermis Key to labels Zone of differentiation Zone of cell division Includes apical meristem New cells produces Root cap is located in root Zone of elongation Elongation of cells Zone of maturation Cell differentiation Cell become functionally mature Root hair Dermal Ground Vascular Zone of elongation Apical meristem Zone of cell division Root cap 100 µm

Secondary Growth add girth to stems and roots in woody plants Two lateral meristems Vascular cambrium Produces secondary xylem (wood) Secondary phloem Cork cambrium Produces tough covering that replaces epidermis early in secondary growth Bark includes all the tissues outside the vascular cambrium.

Growth, morphogenesis, and differentiation produce the plant body Morphogenesis – the development of body form and organization. This is the process of cell specialization

Resource Acquisition and Transport in Vascular Plants Chapter 36

Transport occurs by: Short-Distance Long-Distance Diffusion Active transport Cotransport – the coupling of the steep gradient of one solute (H+) with a solute like sucrose Long-Distance Bulk flow – the movement of water through the plant from regions of high pressure to regions of low pressure Aquaporins

Water Potential Water potential is a measurement that combines the effects of solute concentration and pressure Water flows from regions of higher water potential to regions of lower water potential Water potential is abbreviated as Ψ and measured in units of pressure called megapascals (MPa) Ψ = 0 MPa for pure water at sea level and room temperature

How Solutes and Pressure Affect Water Potential Both pressure and solute concentration affect water potential The solute potential (ΨS) of a solution is proportional to the number of dissolved molecules Solute potential is also called osmotic potential Pressure potential (ΨP) is the physical pressure on a solution Turgor pressure is the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast

Measuring Water Potential Consider a U-shaped tube where the two arms are separated by a membrane permeable only to water Water moves in the direction from higher water potential to lower water potential

(a) 0.1 M solution Pure water H2O ψP = 0 ψS = 0 ψP = 0 ψS = −0.23 Fig. 36-8a (a) 0.1 M solution Pure water Figure 36.8a Water potential and water movement: an artificial model H2O ψP = 0 ψS = 0 ψP = 0 ψS = −0.23 ψ = 0 MPa ψ = −0.23 MPa

The addition of solutes reduces water potential

(b) Positive pressure H2O ψP = 0 ψS = 0 ψP = 0.23 ψS = −0.23 ψ = 0 MPa Fig. 36-8b (b) Positive pressure Figure 36.8b Water potential and water movement: an artificial model H2O ψP = 0 ψS = 0 ψP = 0.23 ψS = −0.23 ψ = 0 MPa ψ = 0 MPa

Physical pressure increases water potential

(c) H2O ψP = 0 ψS = 0 ψP = ψS = −0.23 ψ = 0 MPa ψ = 0.07 MPa Fig. 36-8c (c) Increased positive pressure Figure 36.8c Water potential and water movement: an artificial model H2O ψP = 0 ψS = 0 ψP =   ψS = −0.23 0.30 ψ = 0 MPa ψ = 0.07 MPa

Negative pressure decreases water potential

Negative pressure (tension) Fig. 36-8d (d) Negative pressure (tension) Figure 36.8d Water potential and water movement: an artificial model H2O ψP = −0.30 ψS = ψP = ψS = −0.23 ψ = −0.30 MPa ψ = −0.23 MPa

Figure 36.8 Water potential and water movement: an artificial model (b) (c) (d) Positive pressure Increased positive pressure 0.1 M solution Negative pressure (tension) Pure water H2O H2O H2O H2O ψP = 0 ψS = 0 ψP = 0 ψS = −0.23 ψP = 0 ψS = 0 ψP = 0.23 ψS = −0.23 ψP = 0 ψS = 0 ψP = 0.30 ψS = −0.23 ψP = −0.30 ψS = 0 ψP = 0 ψS = −0.23 Figure 36.8 Water potential and water movement: an artificial model ψ = 0 MPa ψ = −0.23 MPa ψ = 0 MPa ψ = 0 MPa ψ = 0 MPa ψ = 0.07 MPa ψ = −0.30 MPa ψ = −0.23 MPa

Vegetative Propegation Types of Veg. Propagation Description Examples Bulbs Short Stems Underground Onions Runners Horizontal Stems above ground Strawberries Tubers Underground Stems Potatoes Grafting Cut a stem and attach it to a closely related plant Seedless Oranges

Tropical Tropisms tropism – turning response to a stimulus Phototropism Refers to how plants respond to light Gravitropism Refers to how plants respond to gravity Thigmotropism Refers to how plants respond to touch (IVY, strangler trees Auxins Responses are initiated by hormones. Major plant hormones belong to the class AUXINS

Table 39-1