25.1 Plant Acquire Mineral Nutrients from the Soil Plants are autotrophs that obtain mineral nutrients as ions from soil Collect carbon from atmospheric carbon dioxide Oxygen from water Essential element: plant nutrient, that if absent, causes disruption of normal plant growth and reproduction Categories of essential elements Macronutrients:concentrations of at least 1 gram per 1 kg of plant's dry matter- Six types: Nitrogen/Phosphorus/Potassium/Sulfur/Calcium/and Magnesium Micronutrients:concentrations of >0.1g/kg- Iron/Chlorine/Manganese/Zinc/Copper/Nickel/and Molybdenum Missing nutrients can be provided by fertilizer Benefits from soil Anchorage for mechanical support for shoot Mineral nutrients and water from soil solution O2 for root respiration from air spaces between soil particles Services of other soil organisms, including bacteria, fungi, protists, and animals such as earthworms and arthropods Soil consists of three major horizons (layers of soil) Topsoil Supports plant's mineral nutrients needs Subsoil Accumulates materials from topsoil and parent rock Parent rock(bedrock) Where soil arises Humus: material used as a food source for microbes that break down complex organic molecules and release simpler molecules into soil solution improves texture of soil and provides air spaces, increasing O2 availability  Three ways to restore nutrient content of soil after leaching(washing away) or harvesting crops Shifting Agriculture People move to another location after soil no longer supported plant growth Came back after weathering and accumulation and breakdown of organic matter Today, human population too great and people do not want to move Organic Fertilizers Compost(partially decomposed plant matter) Manure Add nutrients to soil much more rapidly than natural weathering, but still allow for slow release of ions, with little leaching, as materials decompose Leaf proteins → NH4+ → NO3-- Bacteria cause the changes in substance Inorganic Fertilizers Used to supply mineral nutrients directly in forms that can be immediately taken up by plants Chemical → NH4+ → NO3-- bacteria changes NH4 to NO325.2 Soil Organisms Contribute to Plant Nutrition Formation of Mycorrhizae Plant roots produce compounds called strigolactones stimulate rapid growth of fungal hyphae toward root Sites of nutrient exchange between fungus and plants are arbuscules Formation of Nitrogen-Fixing nodules Group of plants called legumes form symbioses with several species of soil bacteria known as rhizobia roots of these plants release flavonoids and other chemical signals that attract rhizobia- flavonoids also trigger transcription of bacterial nod genes- Nod genes-products that synthesize Nod(nodulation) factors- cause root cortex to divide and form primary nodule meristem Bacteroids-form of bacteria that fix nitrogen bacteria enter root via infecion thread Mycorrhizae expand root surface area 10-fold to 1,000-fold can get into pores in soil that are inaccesible to root hairs Primary nutrients plants obtains from mycorrhizae is phosphorus Bacteria have enzyme nitrogenase that converts N2 to NH3, process called nitrogen fixation Carnivorous plants Obtain some nutrients by digesting arthropods Typically grow in boggy soils where little nitrogen or phosphorus is available Digestion(hydrolosis) provies those missing nutrients Parasitic plants Hemiparasites photosynthesize but derive water and mineral nutrients from living bodies of plants Holoparasites completely parasitic and do not perform photosynthesis25.3 Water and Solutes are Transported in the Xylem by Transpiration-Cohesion-Tension Osmosis: movement of water trough selectively permeable membrane toward region of higher solute concentration (lower water concentration) Water potential (psi,Ѱ): tendency of solution(water+solutes) to take up water from pure water across membrane water potential of pure water is 0 Solution with water potential less than zero has tendency to take up water from pure water Lower(more negative) water potential=greater driving force for water movement across membrane Water potential has two components Solute potential- As solutes are added concentration of free water is reduced- More solues=lower water potential- Solute potential is usualy negative Pressure potential- More pressure decreases the tendency of cell to take up more water Solute potential is sum of solute potential and pressure potential measure all three potentials in megapascals (Mpa) Physical structure of many plants is maintained by (positive) pressure potential of their cells if pressure potential drops (i.e plants does not have enough water), the plant wilts Two major challenges when soil solution containing mineral ions passes through root cell plasma membrane Membrane is hydrophobic, whereas water and mineral ions are polar Some mineral ions must be moved against their concentration gradient These challenges overcome by membrane proteins  Aquaporins membrane channels which water can diffuse can change the rate of osmosis but not direction, water always moves to region of more negative water potential Ion channels and proton pumps Transport proteins can move ion with greater concentration than root into plant by facilitated diffusion and secondary active transport Proton pump uses energy from ATP to move protons out of cell Protons cause an electrical gradient, the region just outside of the cell becomes more positively charged than the inside of the cell Proton concentration gradient develops, with more protons just outside the cell than inside the cell Water and ions from soil solution move through roots to xylem by one of two pathways: Apoplast consists of cells walls, which lie outside the plasma membranes, and intracellular spaces apoplast is continuous meshwork through which water and solutes can flow without everhaving to cross membrane Symplast passes through continuous cytoplasm of living cells connected by plasmodesmata movement of water and solutes into symplast is tightly regulated End result is the water and minerals end up in the xylem, which constitute the xylem sap Caspian strip: blocks movement of water and ions through apoplast Leaves must be alive for water to move in the