Chapter 29 Part 1

Phyllotaxy, the arrangement of leaves on a stem, is specific to each species Most angiosperms have one leaf per node (alternate phyllotaxy) with leaves arranged in a spiral The angle between leaves is 137.5° and likely minimizes shading of lower leaves © 2016 Pearson Education, Inc. 2

The productivity of each plant is affected by the total area of the leafy portions of all the plants in the community Self-pruning, the shedding of lower shaded leaves when they respire more than photosynthesize, occurs when the canopy is too thick © 2016 Pearson Education, Inc. 3

These relationships help absorb water and nutrients more efficiently Roots form mutually beneficial relationships with fungi, called mycorrhizae These relationships help absorb water and nutrients more efficiently © 2016 Pearson Education, Inc. 4

Three transport routes for water and solutes are The apoplastic route, through cell walls and extracellular spaces The symplastic route, through the cytosol (plasmodesmata) The transmembrane route, across cell walls and plasma membranes © 2016 Pearson Education, Inc. 5

© 2016 Pearson Education, Inc. Figure 29.5 Cell wall Apoplastic route Cytosol Symplastic route Transmembrane route Figure 29.4 Cell compartments and routes for short-distance transport Plasmodesma Apoplast Plasma membrane Symplast © 2016 Pearson Education, Inc.

Short-Distance Transport of Solutes Across Plasma Membranes Plasma membrane permeability controls the movement of substances into and out of cells Both active and passive transport occur in plants In plants, membrane potential is established through pumping H+ by proton pumps In animals, membrane potential is established through pumping Na+ by sodium-potassium pumps © 2016 Pearson Education, Inc. 7

The direction of water flow is determined by water potential, a quantity that includes the effects of solute concentration and pressure Water flows from regions of higher water potential to regions of lower water potential © 2016 Pearson Education, Inc. 8

Ψ = 0 MPa for pure water at sea level and at room temperature Water potential is abbreviated as Ψ and measured in a unit of pressure called the megapascal (MPa) Ψ = 0 MPa for pure water at sea level and at room temperature © 2016 Pearson Education, Inc. 9

Pressure potential (ΨP) is the physical pressure on a solution Turgor pressure is the pressure exerted by the protoplast against the cell wall The protoplast is the living part of the cell, which also includes the plasma membrane This pressure helps maintain the stiffness of plant tissues and drives cell elongation © 2016 Pearson Education, Inc. 10

How Solutes and Pressure Affect Water Potential Both pressure and solute concentration affect water potential This is expressed by the water potential equation: Ψ = ΨS + ΨP The solute potential (ΨS) of a solution is directly proportional to its molarity Adding solute reduces water potential, so it has a negative effect. Because of this, solute potential is always negative. © 2016 Pearson Education, Inc. 11

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 © 2016 Pearson Education, Inc. 12

If a flaccid cell is placed in a solution with a lower solute concentration, the cell will gain water and become turgid (firm) Turgor loss in plants causes wilting, which can be reversed when the plant is watered © 2016 Pearson Education, Inc. 13

© 2016 Pearson Education, Inc. Figure 29.6-1 Environment 0.4 M sucrose solution: Initial flaccid cell: yP = 0 yP = 0 yS = -0.7 yS = -0.9 y = -0.7 MPa y = -0.9 MPa Final plasmolyzed cell at osmotic equilibrium with its surroundings: Figure 29.5-1 Water relations in plant cells (part 1: plasmolyzed cell) yP = 0 yS = -0.9 y = -0.9 MPa (a) Initial conditions: cellular y > environmental y © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.6-2 Environment Pure water: Initial flaccid cell: yP = 0 yP = 0 yS = -0.7 yS = 0 y = -0.7 MPa y = 0 MPa Final turgid cell at osmotic equilibrium with its surroundings: Figure 29.5-2 Water relations in plant cells (part 2: turgid cell) yP = 0.7 yS = -0.7 y = 0 MPa (b) Initial conditions: cellular y < environmental y © 2016 Pearson Education, Inc.

© 2016 Pearson Education, Inc. Figure 29.6 Wilted Turgid Figure 29.6 A moderately wilted plant can regain its turgor when watered. © 2016 Pearson Education, Inc.

Short-Distance Transport of Water Across Plasma Membranes Osmosis, the diffusion of free water across a membrane, determines the net uptake or water loss by a cell © 2016 Pearson Education, Inc. 17

Aquaporins: Facilitating Diffusion of Water Aquaporins are transport proteins in the plasma membrane that allow the passage of water Aquaporin channels can open or close to change the rate of water movement across the membrane © 2016 Pearson Education, Inc. 18

Concept 29.3: Plants roots absorb essential elements from the soil Water, air, and soil minerals contribute to plant growth 80–90% of a plant’s fresh mass is water 96% of a plant’s dry mass consists of carbohydrates from the CO2 assimilated during photosynthesis 4% of a plant’s dry mass is inorganic substances from soil © 2016 Pearson Education, Inc. 19

Macronutrients and Micronutrients More than 50 inorganic chemical elements are found in plants, but not all are essential There are 17 essential elements, (essential nutrients) chemical elements required for a plant to complete its life cycle © 2016 Pearson Education, Inc. 20

Nine of the essential elements are called macronutrients because plants require them in relatively large amounts The macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium Nitrogen is the most important nutrient contributing to plant growth and crop yields © 2016 Pearson Education, Inc. 21

Plants with C4 and CAM photosynthetic pathways also need sodium The remaining eight are called micronutrients because plants need them in very small amounts The micronutrients are chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum Plants with C4 and CAM photosynthetic pathways also need sodium Micronutrients function as cofactors, nonprotein helpers in enzymatic reactions © 2016 Pearson Education, Inc. 22

© 2016 Pearson Education, Inc. Table 29.1-2 Table 29.1-2 Macronutrients in plants (part 2) © 2016 Pearson Education, Inc.

Symptoms of Mineral Deficiency Symptoms of deficiency depend on the mineral’s function and mobility within the plant The most common deficiencies are those of nitrogen, potassium, and phosphorus Nitrogen is most limiting to plant growth on a global scale © 2016 Pearson Education, Inc. 24

© 2016 Pearson Education, Inc. Figure 29.8 Healthy Nitrogen- deficient Phosphorus- deficient Figure 29.8 The most common mineral deficiencies, as seen in maize leaves Potassium-deficient © 2016 Pearson Education, Inc.