Resource acquisition and transport in vascular plants Overview of what a plant does Chapter 36 CO 2 O 2 O 2 and and CO 2 CO 2 O 2 Sugar Light Shoots are optimized to capture light and reduce water loss Large leaves in tropical forests Small leaves in dry environments Alternate phyllotaxy limits overlapping of leaves in lower light environment and O 2 CO 2 Opposite phyllotaxy may be advantageous in high light environments 1
Leaf orientation optimizes light conditions Roots are optimized to absorb and anchor Taproot systems anchor tall plants More branching in areas of high resources Less branching in roots of self Mycorrhizae enhance root absorption Substances move through the apoplast and/or the symplast Movement of substances across cell membranes Proton pumps set chemiosmotic gradient, which is then used for cotransport Ion channels open in response to chemicals, pressure or voltage The trade-off for a plant having a low aboveground surface-area-to-volume ratio would be A. low water loss but high respiration rate. B. low water loss but reduced photosynthetic capacity. C. low water loss but increased vulnerability to herbivory. D. low water loss but decreased water absorption capacity. low water loss but high r... low water loss but reduc.. low water loss but incre... low water loss but decre... The most important determinant of evolutionary pressure affecting leaf shape and size is A. light availability. B. soil nutrient levels. C. water availability. D.average yearly temperature fluctuations. light availability. soil nutrient levels. water availability. average yearly temperat... 2
A root tip encountering a patch of soil rich in nitrogen is most likely to A. stop growing. B. grow faster. C. form lateral branches. D.increase production of root hairs. The generation of an electrochemical proton (H+) gradient across membranes allows for A. passive uptake of water. B. accumulation of ions against their concentration gradient. C. long-distance transport of salts and amino acids. D. increased enzymatic activity on membranes. stop growing. grow faster. form lateral branches. increase production of r... passive uptake of water. accumulation of ions aga... long-distance transport o... increased enzymatic activ... Water moves by osmosis Water potential drives direction of water movement Water moves from areas of higher water potential to areas of lower water potential Water potential is designated as ψ and is measured in Mpa Water potential is determined by solute concentration and physical pressure Ψ = ψs + ψp The addition of solutes decreases water potential Turgor pressure and wilting Bulk flow Plasmolysis For long distances, plants rely on bulk flow for transport Bulk flow is movement of liquid in response to a pressure gradient Bulk flow is independent of solute concentration 3
Moving water and into the xylem Movement of water and in the xylem move by bulk flow driven by transpiration Is water pushed into the plant or pulled to the top? There is some pushing of water by root pressure due to pumping of into xylem, but pressure is small Guttation Cohesion-tension hypothesis explains how transpiration pulls water up Briefly, transpiration causes the pull with negative water potential (pressure), then cohesion transmits the pull along the entire plant Cohesion is the attractive force between each water molecule Adhesion helps move water as well Adhesion is the attractive force between the water molecule and the xylem wall Transpirational pull goes from the stomata, through the xylem, through the roots, all the way into the soil solution Loss of cohesion and subsequent air bubbles cause cavitation 4
Stomata balance need for CO2 for respiration with water loss through transpiration 95% of water loss is through stomata Stomatal density controlled by genetics and by environment Desert plants have less stomata than forest plants Stomatal density has decreased since 1927 due to increases in CO2 Control of stomatal opening and closing Triggers to stomatal opening/closing Turgid guard cells open stomatal opening Triggered by opening of K+ channels In the morning Blue-light receptors CO2 depletion Internal circadian clock Due to environmental stresses Wind High temperature ABA produced in response to water deficiency, which then causes stomatal closing Adaptations in xerophytes CAM photosynthesis Translocation is movement of photosynthetic product Phloem sap moves sugars from source to sink Phloem sap also contains amino acids, hormones and 5
Sugar is loaded into phloem usually through active transport Phloem movement is bulk flow by positive pressure Using aphids to study phloem sap Water can enter roots through two pathways, apoplastic and symplastic routes. How do these pathways differ? A. The apoplastic route is for water and the symplastic route is for nutrients. B. The apoplastic route is for nutrients and the symplastic route is for water. C. The apoplastic route does not involve transport across a cell membrane but the symplastic route does. D. The apoplastic route is used in xylem and the symplastic route in phloem. The apoplastic route is f.. The apoplastic route is fo... The apoplastic route doe... The apoplastic route is us.. Which of the following best describes bulk flow in the xylem of a tall tree? A. Pressure flow B. Diffusion and osmosis C. Capillary action D.Cohesion and tension Pressure flow Diffusion and osmosis Capillary action Cohesion and tension In vascular plants, how is the sucroserich phloem sap transported? A. From the roots to the leaves B. From the leaves to the roots C. From sucrose source to sucrose sink D.Only diffuses locally From the roots to the leaves From the leaves to the roots From sucrose source to s... Only diffuses locally 6
Sugar maples are tapped for their sugar-rich sap in the early spring. This sap is transported in and is moving from the. A. xylem; leaves B. xylem; roots C. phloem; leaves D.phloem; roots xylem; leaves xylem; roots phloem; leaves phloem; roots 7