BIOL 1442 1nd Edition Lecture 4Outline of Last Lecture I: Tissue organization of leavesII: VeinsIII: Vascular cambium and Cork cambiumIV: Growth, morphogenesis, and cell differentiationV: Flower genetics and the ABC hypothesisOutline of Current Lecture I: Adaptation: underground plantsII: Shoot architecture and light captureIII: Root architecture and nutrient acquisitionIV: Short distance transport mechanismsCurrent Lectureo Underground Plants:-Stone plants (Lithops) are adapted to life in the desert-Have modified leaves with specialized “lenses” that limit the amount of sunlight received into the photosynthesizing portion of plant-The success of plants depends on their ability to gather and conserve resources from their environmento Adaptations for acquiring resources were key steps in the evolution of vascular plants:-The algal ancestors of land plants absorbed water, minerals, and CO2 directly from the surrounding water-The evolution of xylem and phloem in land plants made possible the long-distance transport of water, minerals, and products of photosynthesiso Shoot Architecture and Light Capture:-Phyllotaxy, the arrangement of leaves on a stem, is specific to each species-phyllotaxy determined by the shoot apical meristem-Variations: alternate, opposite, and/or whorled-Most angiosperms have alternate phyllotaxy with leaves arranged in a spiral-The angle between leaves is 137.5 degrees-Angle is important because it minimizes the shading of lower leaves by those aboveThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-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-Once index is above 0.7, there is too much shading-Self-pruning happens with leaf are index is too high. o Leaf Orientation:-Leaf orientation affects light absorption-Horizontal vs vertical leaves-Orientation depends on direction of sunlight to maximize exposureo Root Architecture and Acquisition of Water and Minerals:-Soil is a resource mined by the root system-Root growth can adjust to local conditions-Plants can’t take nitrogen form air (air consists of 78% nitrogen), so they take if from soil in form of nitrate (NO-3)-For example, roots branch more in a pocket of high NO-3 than low NO-3 (If pocket of low NO-3, roots will shoot straight through pocket without branching)-Roots are less competitive with other roots from the same plant than with roots from different plants-Reason unknown, must be some chemical signaling-Roots and the hyphae of soil fungi form mutualistic associations called mycorrhizae-Allows for even more surface area for plant to absorb as much water andminerals as possibleo Different mechanisms transport substances over short or long distances:-There are two major pathways through plants-The apoplast-The symplasto The Apoplast and Symplast: Transport Continuums:-The apoplast consists of everything external to the plasma membraneIt includes cell walls (microfibril strands of cellulose made of glucose), extracellular spaces, and the interior of vessel elements and tracheids-The symplast consists of the cytosol of the living cells in a plant, as well as the plasmodesmata-Three transport routes for water and solutes are-The apoplastic route: substance travels through the cell wall-The symplastic route: substance travels through cytosol via plasmodesmata-Substance will have to cross a plasma membrane once: when it first enters the plant cell-The transmembrane route: a combination of both apoplastic and symplastic routeso Short-Distance Transport of Solutes Across Plasma Membranes:-Plasma membrane permeability controls short-distance movement of substances-Both active and passive transport occur in plants-In plants, membrane potential is established through pumping H+ by proton pumps-Short-distance only because these processes are too slow for moving up stems- Plant cells use the energy of H+ gradients to cotransport other solutes by active transporto Details of Figure 36.7 in slides:a) H+ and membrane potential: ATP-dependent proton pumps establish both a membrane potential and a pH gradientb) H+ and cotransport of neutral solutes: H+/sucrose cotransporters load sugar into the phloem before it travels throughout the shoot systemc) H+ and cotransport of Ions: H+/NO-3 cotransporters allow plant roots to absorb nitrated) Ion channels: Ion channels open and close in response to voltage or chemical signals and allow specific ions to diffuse across membraneso Short-Distance Transport of Water Across Plasma Membranes:-Osmosis determines the net uptake or water loss by a cell and is affected by solute concentration and pressure-Water potential is a measurement that combines the effects of solute concentration and pressure-Water potential 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 Ψ and measured in a unit of pressure called the megapascal (MPa)-Ψ = 0 MPa for pure water at sea level and at room temperatureo How Solutes and Pressure Affect Water Potential:-The water potential equation: Ψ = ΨS + ΨP-The solute (osmotic) potential (ΨS) of a solution is directly proportional to its molarity (measuring concentration of solute)-The greater the molarity, the more negative the ΨS-ex. drinking through a straw is negative pressure-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 protoplastThe protoplast is the living part of the cell, which also includes the plasma