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©1996 Norton Presentation Maker, W. W. Norton & Company Radish seedlings have roots with long root hairs that increase the surface area for water and mineral uptake

Dicot Mature Root Structure - Anatomy Epidermis Cortex Vascular Cylinder Ranunculus acris - buttercup Make root hairs for cation exchange Storage of starch Selective mineral uptake and conduction

Root Vascular Cylinder and Cortex Ranunculus acris - buttercup Cortex Endodermis Xylem Phloem Pericycle Selective mineral uptake via these “window cells” Storage of Starch, etc. Sieve Tube Cell conducts organic molecules Companion Cell keeps the sieve tube cell alive! Divides to make branch roots Conducts minerals and water up to shoot system

Xylem cells lack cytosol when mature and functional, and thus are dead. Which human parts are made of dead cells at maturity? A.Hair shafts. B.Finger nails. C.Epidermal surface cells. D.All of these are dead at maturity.

Osmosis: passive movement of water from pure to saltier area cytoplasmic solutes more concentrated soil solutes more dilute cell membrane Water potential lowWater potential high cell wall water flow Do solutes cross the membrane? Virtually not; the bilayer is impermeable to solutes, and transport proteins keep solutes concentrated in the cell This passive movement obeys the 2 nd Law of Thermodynamics!

Root hairs are responsible for cation exchange soil particles covered with capillary water and minerals water voids with air space root hair penetrates soil spaces epidermal cell cortex cell H+H+ Ca 2+ H+H+ intercellular gas space to endodermis and vascular cylinder then up the xylem to the shoot Fig pp

Root Vascular Cylinder and Cortex Ranunculus acris - buttercup Cortex Endodermis Xylem Phloem Pericycle Selective mineral uptake via these “window cells” Storage of Starch, etc. Sieve Tube Cell conducts organic molecules Companion Cell keeps the sieve tube cell alive! Divides to make branch roots Conducts minerals and water up to shoot system

xylem inside cortex outside endodermis suberin- waxy barrier to apoplastic movement cell membrane proteins (active transporters) determine which minerals may be taken up The endodermis is thus responsible for selective mineral uptake. minerals cannot go between cells minerals must go through cells Important?: All human minerals in food come via this path!

Mineral uptake: Active transport against concentration gradient cytoplasmic solutes more concentrated soil solutes more dilute cell membrane Water potential lowWater potential high cell wall water flow Ca 2+ ATP ADP + P i Ca 2+ Calcium transport protein Osmosis: passive movement of water from pure to salty area too expensive? Possible solute diffusion gradient

Which tissue conducts water and soil minerals up the plant? A.Epidermis. B.Cortex. C.Endodermis. D.Pericycle. E.Phloem. F.Xylem.

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

Solute availability is pH dependent nitrogen molybdenum iron pH of soil water 4 acidic7 neutralalkaline 10 Element Concentration The optimal pH?

Which pH would be optimal (ideal) for mineral availability? A.4. B.A little below 7. C.7. D.A little above 7. E.10.

Solute availability is pH dependent nitrogen molybdenum iron pH of soil water 4 acidic7 neutralalkaline 10 Element Concentration optimum

©1996 Norton Presentation Maker, W. W. Norton & Company Dionaea (Venus’ fly trap) leaves have evolved three trip hairs on each half-blade, an electrical potential is produced, osmosis causes the trap to snap shut, This fly is about to touch the second trip hair… Soil pH is less than 4

©1996 Norton Presentation Maker, W. W. Norton & Company The trap halves have folded together, and the marginal spines have turned inward…the compound action makes an effective trap…have you ever tried to catch a fly?

©1996 Norton Presentation Maker, W. W. Norton & Company Saracennia (pitcher plant) leaves hold water to drown insects and mine their minerals Soil pH is less than 4

©1996 Norton Presentation Maker, W. W. Norton & Company Drosera (sundew) uses sticky pads that look like nectaries but are actually glandular hairs secreting botanical “super glue” with digestive enzymes: Remember that carnivorous plants are not eating insects for energy or carbon… they are mining the insects for minerals unavailable from the acidic bog soil.

©1996 Norton Presentation Maker, W. W. Norton & Company Mycorrhizal fungi assist with nutrient uptake root fungal mycelium

©1996 Norton Presentation Maker, W. W. Norton & Company Anabaena heterocysts fix nitrogen and support bacterial growth as amino acids (organic nitrogen) leaks out into the surrounding water…vegetative cells provide carbohydrate too. Can you distinguish heterocysts and vegetative cells?

Rhizobium needs anaerobic conditions to convert N 2 into NH 4 +. Legumes produce heme based molecules and have rapid respiration to eliminate oxygen from root nodules that house the bacterial “symbiosis.”

©1996 Norton Presentation Maker, W. W. Norton & Company Here are legumes with Rhizobiumand without Rhizobium

In shrubs like this tea plant (Camellia sinensis), the root system will be more tap root than fibrous root. Notice the diameter of this tap root compared to this man’s waist! But shrubs also generally have some compromise for uprooting forces…feeder roots extending laterally.

Tropical soils are nutrient-poor. Roots must traverse the surface for minerals, so roots grow on the surface (no tap root). So, to keep this tree standing upright, the roots grow in diameter but only in the vertical dimensions to form ridge roots…called buttress roots. These roots inspired gothic cathedral architects to design buttress walls. How do buttress roots work?

Buttress roots inspired supports for long city walls and cathedral walls to prevent collapse. The foundation is critical!

Pandanus utilis - screw pine Prop roots such as these inspired flying buttresses.