Transport in Vascular Plants

Transcription

1 Note that the following is a rudimentary outline of the class lecture; it does not contain everything discussed in class. Uptake of Nutrients Transport in Vascular Plants Dicot Leaf Cross Section Stomata Open stomata Increase Increase Control of Stomatal Opening and Closing guard cells buckle outward when orientation of causes cells to increase in length more than two guard cells attached at, increase in length causes generally stomata open during and closed at opening coincides with need for Role of Potassium in Stomatal Opening and Closing transport of across membrane and (vacuole membrane) causes changes stomata open when guard cells accumulate and the cells water potential; causes become exodus of from guard cells causes Internal Transport Problem 1:

2 Problem 2: Lateral Transport of Water & Minerals in Roots pathway movement through cell walls, between plant cells, not across cell membranes an extracellular pathway pathway H 2 0 moves from cell to cell via areas where the of cells together slower process than via pathway Endodermis 1 layer of cells (6 sided) surrounding stele in/on walls of 4 sides suberin prevents H 2 0 etc. from passing through of adjacent cells forces H 2 0 and dissolved minerals to follow allows plant to select what substances pass into stele and up into plant Lateral Transport of Water and Minerals in Roots Transport of Xylem Sap Xylem sap water, mineral ions ( ), trace amounts of other molecules BIOL

3 How does xylem sap rise against gravity, without help of any mechanical pump, to reach heights of more than 100 m in the tallest trees? Several steps (mechanisms) needed to achieve this Water Potential A measurement of the combination of solute and Greek letter Distilled water in an open beaker has a water potential of will be dealing with water moves across a membrane from a solution with Ψ to a solution with Ψ units called (abbreviated MPa ) Active Transport Water moves easily into of endodermal cells Mineral uptake into (through membrane) of endodermal cells is and Harmful minerals are excluded by membrane Endodermal cell membrane proteins minerals against their concentration gradient using Once in symplast of endodermal cells minerals move easily into stele and then into xylem through connecting cells Root Pressure BIOL

4 and subsequent accumulation of minerals in xylem results in a solution (xylem sap) with Ψ lower Ψ causes of water Water and minerals that have entered xylem are and cannot leave the stele because of Continued increase of minerals and in xylem causes a build up of pressure forces " water and minerals up root and stem inside xylem This process explains Terminology Water loss - water moves from interior to exterior of leaf caused by evaporation attraction between water molecules water molecules stick to one another forming attraction between water molecules and other molecules water molecules adhere to sides of capillary action Surface tension Cohesion-Tension Model BIOL

5 of water to atmosphere is replaced by water from, which is replaced by water from the continuous stream As water molecules leave, they drag other water molecules along with them Due to of water molecules to one another, a continuous of interacting water molecules is formed in the from the roots to the leaves to xylem vessel walls fights forces pull water upward through, all the way from roots Ascent of Water Guttation the morning after a windless night droplets maybe seen on tips of grass blades or leaf margins of some small, not to be confused with roots of some plants keep accumulating during night root pressure pushes into shoot system because rate is low, more water enters leaves than is excess is forced out as Summary Only of water used by plant used in photosynthesis and plant growth Most of it is lost in BIOL

6 provides the for lifting water up stems leaves Transpiration rate is regulated by Lecture 5 Transport in Vascular Plants Single corn plant can transpire of water in growing season Stomata when water uptake is than rate Water loss is a result of, since stomata must be open for Transport of Phloem Sap sucrose up to ; amino acids; minerals; transport of food in plant organ in which sugar is produced by either leaves are sugar sources organ that is net or of sugar e.g. BIOL

7 may be or depending on season Sugar during summer when storage organ is carbohydrates Sugar in early spring after breaking dormancy, when its starch is to sugar and to growing tips Hypothesis Direction that phloem sap travels is predicts that of sugars is from to sink usually receives its sugar from is loaded into phloem near sites of, or, using supplied by cells or other nearby cells Movement of water containing dissolved and other in phloem requires Pressure Flow in a Sieve Tube of sugar into sieve tube at source reduces in sieve tube members from surrounding tissues moves into sieve elements due to low potential Absorption of generates a pressure that forces sap to flow along tube The pressure gradient in tube is reinforced by of sugar and consequent loss of from tube at sink BIOL

8 In the case of leaf to root, xylem recycles from sink to source Transport in phloem can be, although individual sieve elements can only transport in at any one time Pressure Flow Hypothesis Experiments have shown that this is mechanism of translocation in angiosperms To test hypothesis researchers used that feed on phloem sap probes with a that penetrates a sieve-tube member -like mouthpart As sieve-tube pressure force-feeds, they can be severed from their which serve as taps exuding sap for hours Researchers measured the flow and sugar concentration of sap from at different points between a source and sink RESULTS the closer the was to a sugar source the the sap flowed the its sugar concentration CONCLUSION The results of such experiments support the pressure flow hypothesis Uptake of Nutrients Lateral Transport of Minerals and Water in Roots Plant Mineral Requirements Macronutrients - some BIOL

9 component of nucleic acids, amino acids, chlorophyll, etc. Lecture 5 Transport in Vascular Plants component of nucleic acids, ATP, phospholipids (membranes) Cofactor for many enzymes e.g. involved in cell wall structure & cytoplasmic control functions component of two amino acids e.g. Micronutrients - some involved in synthesis of chlorophyll component of chlorophyll Plant Nutrition & Mycorrhizae In return modified roots consisting of mutualistic associations of fungi and roots benefits from a steady supply of sugar donated by host plant increases of water uptake and mineral absorption supplies to host plant BIOL

10 Farmers & foresters often seeds with of mycorrhizal fungi to promote formation of mycorrhizae Types of Mycorrhizae E mycelium of fungus forms a over surface of root fungal hyphae extend from into soil, absorbing water and minerals, especially. hyphae also extend into spaces of root cortex providing extensive surface area for nutrient exchange between fungus and host plant. E No forms around root, but microscopic fungal hyphae into root Within root cortex, the fungus makes extensive contact with plant through branching of that form providing an enormous surface area for nutrient swapping penetrate cell walls, but not, of cells within cortex Plant Nutritional Adaptations some plants use other organisms in ways unusual nutritional adaptations in plants Epiphytes cup - rosette of overlapping leaves BIOL

11 some ferns produce " " that collect litter roots go into soil in basket eg. Parasitic Plants photosynthetic nonphotosynthetic Carnivorous Plants derive some or most of their nutrients from trapping especially usually grow in places where soil poor in especially found in on Carnivorous Plants BIOL