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Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral Intake Conduction (Xylem and Phloem) Storage of Materials.

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Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral Intake Conduction (Xylem and Phloem) Storage of Materials.

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Presentation on theme: "Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral Intake Conduction (Xylem and Phloem) Storage of Materials."— Presentation transcript:

1 Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral Intake Conduction (Xylem and Phloem) Storage of Materials Branching Anchorage

2 Notice how the growing zone has no root hairs or lateral roots! Growth among soil particles would result in shear forces. Zone of Maturation - cell differentiation Protoderm Ground Meristem Provascular Zone of Cell Elongation - cell expansion Zone of Cell Division - new cells by mitosis Root Cap - penetration, padding

3 Mucilage Slough Cells

4 Root Tip Senses Gravity Auxin Hormone Produced Auxin Accumulates on Lower Growth Inhibited on Lower… Relative to Upper Root Curves Downward Gravitropism Root Hairs Increase Surface Area Root Hairs Secrete Acid (H + ) H + Cation Exchange w/Minerals Mineral Uptake into Roots Water and Mineral Uptake

5 ©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

6 Osmosis: passive movement of water from pure to polluted area cytoplasmic solutes more concentrated soil solutes more dilute cell membrane Water potential lowWater potential high cell wall water flow

7 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 vascular cylinder

8 Dicot Mature Root Structure - Anatomy Epidermis Cortex Vascular Cylinder Ranunculus acris - buttercup

9 What does all of this autumn color (leaf senescence) have to do with roots?

10 Root Vascular Cylinder and Cortex Ranunculus acris - buttercup Cortex Endodermis Meta- xylem Phloem Pericycle Proto- xylem Endarch: protoxylem is inside the metaxylem Exarch: protoxylem is outside the metaxylem

11 haplostele siphonostele eustele solenosteledictyostele atactostele leaf gap leaf trace cortex cortex phloem xylem cortex pith cortex phloem xylem pith dicot stem monocot stem Protosteles: actinosteleplectostele Specialized Versions dicot root monocot root

12 ©1996 Norton Presentation Maker, W. W. Norton & Company Apoplastic Symplastic

13 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

14 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 polluted area too expensive?

15 Root Anatomy: Dicot Root Cross Section Epidermis - root hairs, mineral and water intake Cortex - storage, defense Endodermis - selective mineral uptake Pericycle - lateral root formation (periderm) (Vascular Cambium - makes 2° tissues ) Phloem - CH 2 O delivery from leaves Xylem - conduct water and mineral upwards Casparian strips in radial walls One Vascular Cylinder (Phloem + (Cambium) + Xylem) Radial Xylem-Phloem Arrangement Exarch Xylem Maturation Tetrarch (this example)

16 Monocot Root Cross Section Smilax-catbrier Pith Xylem/Phloem Arr? Xylem Maturation? ______arch?

17 How is this section different? Smilax - catbrier

18 A closer look… What do these features tell you? Starch Cutin/Suberin Mitochondria Sieve Tube Element Companion Cell Vessel with Lignin Xylem Parenchyma Lignified Pith Parenchyma

19 What is the Pericycle doing? Root Cap Zone of Cell Division Growing out through cortex In fibrous root systems, there is much lateral root formation. Here you can see two root apices initiating from the pericycle. Notice their connection to the ridges of xylem

20 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 mans waist! But shrubs also generally have some compromise for uprooting forces…feeder roots extending laterally.

21 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 tall baobab tree standing upright, the roots grow in diameter but only in the vertical dimensions to form ridge roots…called buttress roots. My wife here is as large as I am so you can see these roots are a meter tall! These roots inspired gothic cathedral architects to design buttress walls.

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

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25 Avicennia germinans (black mangrove) pneumatophores


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