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Carbohydrate etc. Transpiration Translocation Water and Minerals Figure 34.1 Apical bud The shoot system produces carbohydrates (etc.) by photosynthesis. These solutes are transported to the roots in the phloem tissue: Translocation Axillary bud Node Carbohydrate etc. Internode Node Shoot system Leaves Branch Stem Transpiration Translocation The root system removes water and minerals from the soil environment. These solutes are transported to the shoot in the xylem tissue: Transpiration Lateral roots Root system Water and Minerals Taproot

Dicot circulation: stem anatomy Dicots start with one ring of bundles… Figure 34.19 Dicots start with one ring of bundles… Let’s take a closer look at the vascular tissues ©1996 Norton Presentation Maker, W. W. Norton & Company

Cell Divison: More Xylem and Phloem Dicot stem anatomy: vascular bundle phloem fibers Support of Stem functional phloem Translocation vascular cambium Cell Divison: More Xylem and Phloem xylem Transpiration As a dicot grows, how does it add vascular capacity to become a tree? ©1996 Norton Presentation Maker, W. W. Norton & Company

Carbohydrate etc. Transpiration Translocation Water and Minerals Figure 34.1 Apical bud Axillary bud Node Carbohydrate etc. Internode Because these pathways involve solutes in water passing in the adjacent tissues of a narrow vascular bundle, this is a circulation system! Transpiration and Translocation The water is moving up the xylem, and down the phloem, making a full circuit! Node Shoot system Leaves Branch Stem Transpiration Translocation Lateral roots Root system Water and Minerals Taproot

Mendocino Tree (Coastal Redwood) Sequoia sempervirens Compare Figure 35.5 Mendocino Tree (Coastal Redwood) Sequoia sempervirens Ukiah, California 112 m tall (367.5 feet)! This tree is more than ten times taller than is “theoretically possible” based solely upon the length of the column of uncavitated water. How could this be achieved? http://www.nearctica.com/trees/conifer/tsuga/Ssemp10.jpg

Transpiration in a tall tree has at least 3 critical components: Evaporation: pulling up water from above Capillarity: climbing up of water within xylem Root Pressure: pushing up water from below

Transpiration: root pressure (osmotic “push”) Compare Figure 35.8 Solutes from translocation of sugars accumulate in roots. Water from the soil moves in by osmosis. Accumulating water in the root rises in the xylem. Water escapes from hydathodes. guttation ©1996 Norton Presentation Maker, W. W. Norton & Company This is not “dew” condensing!

Transpiration: root pressure (osmotic “push”) Compare Figure 35.8 http://img.fotocommunity.com/photos/8489473.jpg The veins (coarse and fine) show that no cell in a leaf is far from xylem and phloem (i.e.water and food!). The xylem of the veins leaks at the leaf margin in a modified stoma called the hydathode. These droplets are xylem sap. Root pressure accounts for maybe a half-meter of “push” up a tree trunk.

Capillarity: maximum height of unbroken water column glass tube vacuum created The small diameter of vessels and tracheids and the surface tension of water provide capillary (“climb”). Cohesion of water, caused by hydrogen bonds, helps avoid cavitation. A tree taller than 10.4 m would need some adaptations to avoid “cavitation” gravity pulls water down 10.4m atmospheric pressure keeps water in tube water

Transpiration: evaporation (“pull”) Transpiration can lift the mercury above its normal cavitation height! vacuum water mercury Water evaporating from a porous clay cap also lifts the mercury! 76 cm mercury

This is a cross-section of a “typical” leaf: Syringa vulgaris (lilac) soil mineral entry evaporative cooling means the solute concentration increases!

Translocation is Bidirectional XYLEM PHLOEM Compare Figure 35.17 Lower pressure Apical Bud sucrose sucrose H+ Translocation is Bidirectional XYLEM PHLOEM Transpiration is Unidirectional High pressure sucrose Leaf H+ Translocation is Bidirectional Lower pressure sucrose Root sucrose H+

Transpiration Carbohydrate etc. Transpiration Translocation Apical bud Axillary bud Node Evaporation: Water evaporates from mesophyll into atmosphere. Water molecules are pulled up the xylem by virtue of cohesion. Carbohydrate etc. Internode Node Shoot system Leaves Branch Capillarity: Water climbs in the xylem cell walls by adhesion. Water molecules follow by cohesion. Stem Transpiration Translocation Lateral roots Root Pressure: Water moves into the root because of solutes from phloem. Pressure pushes the water up the stem. Root system Water and Minerals Taproot Figure 36-3 Page 793

Translocation Carbohydrate etc. Transpiration Translocation Apical bud Axillary bud Node Leaf = Source Photosynthesis produces solutes. Solutes loaded into phloem by active transport. Water follows by osmosis, increasing pressure. Carbohydrate etc. Internode Node Shoot system Leaves Branch Stem Transpiration Translocation Root (etc.) = Sinks Solutes removed from phloem by active transport. Water follows by osmosis, reducing pressure. Lateral roots Root system Pressure = Bulk Flow The pressure gradient forces phloem sap away from leaves to all sinks (bidirectionally). Water and Minerals Taproot Figure 36-3 Page 793