Plant Anatomy 2006-2007

Basic plant anatomy Root - anchor plant in soil, absorb minerals & water, & store food Shoot (stem) – transport water up to the leaves and transport sugars down to roots Leaves – photosynthesis, gas exchange, transpiration

Roots 1 2 3 Different types of roots (you do not need to know this!) fibrous roots (1) mat of thin roots that spread out tap roots (2) 1 large vertical root root hairs (3) increase absorptive surface area 2 3

stolons (strawberries) Modified shoots stolons (strawberries) rhizome (ginger) tuber (potato) bulb (onion)

Leaves simple vs. compound

colored leaves (poinsetta) Modified leaves tendrils (peas) spines (cacti) succulent leaves colored leaves (poinsetta)

Summary Question Why are the leaves, shoots, and roots considered “interdependent” structures? sugars water & minerals

Plant Tissues Dermal Ground Vascular single layer of tightly packed cells that covers & protects plant (the “skin”) Ground bulk of plant tissue Sugar storage Vascular transport system in shoots, roots, and leaf veins Two types: xylem and phloem

Vascular tissue Xylem Move water and minerals (ex: nitrogen, phosphorus, and sulfur) up from roots towards the leaves Dead cells at functional maturity only cell walls remain need empty pipes to efficiently move H2O

Phloem: food-conducting cells Carry sugars from the leaves down the shoot and throughout the plant

Phloem Living cells at functional maturity cell membrane, cytoplasm control of diffusion lose their nucleus, ribosomes & vacuole more room for specialized transport of liquid food (sucrose) Cells sieve tubes sieve plates — end walls — have pores to facilitate flow of fluid between cells companion cells nucleated cells connected to the sieve-tube help sieve tubes

Water & mineral absorption in roots Water absorption from soil osmosis aquaporins Mineral absorption active transport aquaporin root hair proton pumps H2O

Mineral absorption in roots (ctd.) Proton pumps active transport of H+ ions out of cell creates membrane potential difference difference in charge drives cation uptake creates an H+ gradient Enables cotransport of other solutes against their gradient The most important active transport protein in the plasma membranes of plant cells is the proton pump , which uses energy from ATP to pump hydrogen ions (H+) out of the cell. This results in a proton gradient with a higher H+ concentration outside the cell than inside. Proton pumps provide energy for solute transport. By pumping H+ out of the cell, proton pumps produce an H+ gradient and a charge separation called a membrane potential. These two forms of potential energy can be used to drive the transport of solutes. Plant cells use energy stored in the proton gradient and membrane potential to drive the transport of many different solutes. For example, the membrane potential generated by proton pumps contributes to the uptake of K+ by root cells. In the mechanism called cotransport, a transport protein couples the downhill passage of one solute (H+) to the uphill passage of another (ex. NO3−). The “coattail” effect of cotransport is also responsible for the uptake of the sugar sucrose by plant cells. A membrane protein cotransports sucrose with the H+ that is moving down its gradient through the protein. The role of proton pumps in transport is an application of chemiosmosis.

Mycorrhizae increase absorption Symbiotic relationship between fungi & plant symbiotic fungi greatly increases surface area for absorption of water & minerals increases volume of soil reached by plant increases transport to host plant

Water Movement Through Xylem – Transpiration Xylem moves water / minerals up to the leaf ; then water evaporates through the stomata (transpiration) Transpiration by the lower water potential of air (compared to the plant roots), which creates negative pressure to pull water up from roots to shoots Water moves up the xylem tube by capillary action… refresh my memory… what forces cause capillary action? What property of water are these forces related to?

How do plants control the rate of transpiration? Turgor pressure in guard cells controls water loss through stomata (holes on the bottom surface of the leaf) When K+ is transported into guard cells, water follows… why? (use the term osmolarity in your response) Turgid cell = stomata open Loss of K+ and water makes guard cells Flaccid = stomata close

Leaf cross-section with open stomata

Control of transpiration Balancing stomate function always a compromise between photosynthesis & transpiration leaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO2 for photosynthesis

Sugar Movement Through Phloem Phloem sap (in the form of sucrose!) moves from source (where it’s made – leaf cells ) to sink (where it’s stored/used – root cells) Driven by positive pressure Companion cells help move sugars by active transort from leaf cells into the sieve tube elements What does a high sugar content do to the water potential in the sieve tubes? What should water do? (move in or out of the sieve tube?)

Sugar Movement Through Phloem (ctd.) Water pressure in the sieve tube moves sap down What does removal of the sugar at the “sink” do to the water potential in the sieve tubes? What should water do? (move in or out of the sieve tube?)