CAMPBELL BIOLOGY Reece Urry Cain Wasserman Minorsky Jackson © 2014 Pearson Education, Inc. TENTH EDITION 36 Resource Acquisition and Transport in Vascular Plants Ms. Peplin AP Biology

A Whole Lot of Shaking Going On  Plants have various adaptations that aid in the acquisition of resources, including water, minerals, carbon dioxide, and light  For example, Aspen leaves have a peculiar adaption that causes their leaves to tremble even in light wind

 The success of plants depends on their ability to gather resources from their environment and transport them to where they are needed

Concept 36.1: Adaptations for acquiring resources were key steps in the evolution of vascular plants The algal ancestors of land plants absorbed water, minerals, and CO 2 directly from the surrounding water Early nonvascular land plants lived in shallow water and had aerial shoots Natural selection favored taller plants with flat appendages, multicellular branching roots, and efficient transport Evolutionary History :

The evolution of xylem and phloem in land plants made possible the long-distance transport of water, minerals, and products of photosynthesis –Xylem transports water and minerals from roots to shoots –Phloem transports photosynthetic products from sources to sinks

Figure H2OH2O H 2 O and minerals CO 2 O2O2 O2O2

Figure H2OH2O H 2 O and minerals CO 2 O2O2 O2O2 Light Sugar

Shoot Architecture and Light Capture Stems serve as conduits for water and nutrients and as supporting structures for leaves Shoot length and branching pattern affect light capture –There is a trade-off between growing tall and branching Adaptations in each species represent compromises between enhancing photosynthesis and minimizing water loss

 There is generally a positive correlation between water availability and leaf size  Phyllotaxy, the arrangement of leaves on a stem, is a species-specific trait important for light capture  Determined by shoot apical meristem  Alternate (spiral) = 1 leaf per node  Opposite = 2 leaves per node  Whorled = 3+ leaves per node

 The depth of the canopy, the leafy portion of all the plants in a community, affects the productivity of each plant  Directly proportional  Self-pruning, the shedding of lower shaded leaves, occurs when they respire more than photosynthesize

 Light absorption is affected by the leaf area index, the ratio of total upper leaf surface of a plant divided by the surface area of land on which it grows  Values up to 7 are common for mature plants  Any higher would lead to self-prunning

Figure 36.4 Ground area covered by plant Plant A Leaf area = 40% of ground area (leaf area index = 0.4) Plant B Leaf area = 80% of ground area (leaf area index = 0.8)

Leaf orientation affects light absorption In low-light conditions, horizontal leaves capture more sunlight In sunny conditions, vertical leaves are less damaged by sun and allow light to reach lower leaves

Root Architecture and Acquisition of Water and Minerals Root growth can adjust to local conditions Roots are less competitive with other roots from the same plant than with roots from different plants Roots and the hyphae of soil fungi form mutualistic associations called mycorrhizae –Mycorrhizal fungi increase the surface area for absorbing water and minerals, especially phosphate

Concept 36.2: Different mechanisms transport substances over short or long distances There are two major pathways through plants 1.The apoplast 2.The symplast

The Apoplast and Symplast: Transport Continuums The apoplast consists of everything external to the plasma membrane –It includes cell walls, extracellular spaces, and the interior of xylem The symplast consists of the cytosol of all the living cells in a plant, as well as the plasmodesmata

Figure 36.5 Cell wall Cytosol Apoplastic route Symplastic route Transmembrane route Plasmodesma Plasma membrane Key Apoplast Symplast Three transport routes for water and solutes are 1.The apoplastic route, through cell walls and extracellular spaces 2.The symplastic route, through the cytosol 3.The transmembrane route, across cell walls

Short-Distance Transport of Solutes Plasma membrane permeability controls short-distance movement of substances Both active and passive transport occur in plants

Figure 36.6a CYTOPLASM EXTRACELLULAR FLUID Proton pump Hydrogen ion (a) H + and membrane potential H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP − − − − − + membrane potential is established through pumping H  by proton pumps Plant cells use the energy of H  gradients to cotransport other solutes by active transport

Figure 36.6b H + /sucrose cotransporter Sucrose (neutral solute) − − − − − + − + H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ S S S S S S (b) H + and cotransport of neutral solutes Plant cell membranes have ion channels that allow only certain ions to pass

Figure 36.6c H + /NO 3 − cotransporter (c) H + and cotransport of ions H+H − − − − − + − + H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ NO 3 − Nitrate

Figure 36.6d Potassium ion Ion channel (d) Ion channels − − − − + − K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+

Short-Distance Transport of Water To survive, plants must balance water uptake and loss through osmosis Water potential is a measurement that combines the effects of solute concentration and pressure –determines the direction of movement of water Water flows from regions of higher water potential to regions of lower water potential –Water potential is abbreviated as  and measured in a unit of pressure called the megapascal (MPa)   0 MPa for pure water at sea level and at room temperature (assumed value for our class)

How Solutes and Pressure Affect Water Potential Both solute concentration and pressure affect water potential This is expressed by the water potential equation:    S   P The solute potential (  S ) of a solution is directly proportional to its molarity –Solute potential is also called osmotic potential

Pressure potential (  P ) 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 –The protoplast is the living part of the cell, which also includes the plasma membrane   S  P  S  P

Figure 36.7b Initial flaccid cell: Final turgid cell at osmotic equilibrium with its surroundings: (b) Initial conditions: cellular ψ < environmental ψ ψ P = 0 ψ S = − 0.7 ψ = − 0.7 MPa ψ P = 0.7 ψ S = − 0.7 ψ = 0 MPa ψ P = 0 ψ S = 0 ψ = 0 MPa Environment Pure water:

Water Movement Across Plant Cell Membranes Water potential affects uptake and loss of water by plant cells If a flaccid (limp) cell is placed in an environment with a higher solute concentration, the cell will lose water and undergo plasmolysis Plasmolysis occurs when the protoplast shrinks and pulls away from the cell wall

Figure 36.7a Initial flaccid cell: Final plasmolyzed cell at osmotic equilibrium with its surroundings: (a) Initial conditions: cellular ψ > environmental ψ ψ P = 0 ψ S = − 0.7 ψ = − 0.7 MPa ψ P = 0 ψ S = − 0.9 ψ = − 0.9 MPa ψ P = 0 ψ S = − 0.9 ψ = − 0.9 MPa Environment 0.4 M sucrose solution:

If a flaccid cell is placed in a solution with a lower solute concentration, the cell will gain water and become turgid Turgor loss in plants causes wilting, which can be reversed when the plant is watered TurgidWilted

Aquaporins: Facilitating Diffusion of Water Aquaporins are transport proteins in the cell membrane that facilitate the passage of water These affect the rate of water movement across the membrane