Root Structure and Function Penetration of Soil Gravitropism Downward Growth Water and Mineral Intake Conduction (Xylem and Phloem) Storage of Materials.
Presentation on theme: "Root Structure and Function"— Presentation transcript:
1Root Structure and Function Penetration of SoilGravitropism Downward GrowthWater and Mineral IntakeConduction (Xylem and Phloem)Storage of MaterialsBranchingAnchorage
2Zone of Maturation - cell differentiation ProtodermGround MeristemProvascularZone of Cell Elongation - cell expansionNotice how the growing zone has no root hairs or lateral roots!Growth among soil particles would result in shear forces.Zone of Cell Division - new cells by mitosisRoot Cap - penetration, padding
4Gravitropism Root Tip Senses Gravity Auxin Hormone Produced Auxin Accumulates on LowerGrowth Inhibited on Lower…Relative to UpperRoot Curves DownwardWater and Mineral UptakeRoot Hairs Increase Surface AreaRoot Hairs Secrete Acid (H+)H+ Cation Exchange w/MineralsMineral Uptake into Roots
6Osmosis: passive movement of water from pure to polluted area cell membranecell wallwater flowcytoplasmic solutesmore concentratedsoil solutes more diluteWater potential lowWater potential high
7Ca2+ Ca2+ Ca2+ Root hairs are responsible for cation exchange cortex cellroot hair penetrates soil spacesepidermal cellsoil particles covered with capillary waterand mineralsintercellular gas spaceCa2+Ca2+H+Ca2+H+to vascular cylindervoids with air spacewater
9What does all of this autumn color (leaf senescence) have to do with roots?
10√ Root Vascular Cylinder and Cortex Endodermis Cortex Phloem Pericycle Ranunculus acris - buttercupEndodermisCortexPhloemMeta-xylemEndarch: protoxylem is inside the metaxylemExarch: protoxylem is outside the metaxylemProto-xylemPericycle√
13The endodermis is thus responsible for selective mineral uptake. xylem insidecortex outsideminerals cannot go between cellsThe endodermis is thus responsible for selective mineral uptake.minerals must go through cellscell membrane proteins (active transporters) determine which minerals may be taken upsuberin-waxy barrierto apoplasticmovement
14Mineral uptake: Active transport against concentration gradient cell membranecell walltoo expensive?Calcium transport proteinADP + PiCa2+Ca2+Ca2+ATPwater flowcytoplasmic solutesmore concentratedsoil solutes more diluteWater potential lowWater potential highOsmosis: passive movement of water from pure to polluted area
15Root Anatomy: Dicot Root Cross Section Epidermis - root hairs, mineral and water intakeCortex - storage, defenseEndodermis - selective mineral uptakeCasparian strips in radial wallsPericycle - lateral root formation (periderm)(Vascular Cambium - makes 2° tissues)Xylem - conduct water and mineral upwardsPhloem - CH2O delivery from leavesOne Vascular Cylinder (Phloem + (Cambium) + Xylem)Radial Xylem-Phloem ArrangementExarch Xylem MaturationTetrarch (this example)
17How is this section different? Smilax - catbrier
18A closer look…What do these features tell you?StarchCutin/SuberinMitochondriaSieve Tube ElementCompanion CellVessel with LigninXylem ParenchymaLignified Pith Parenchyma
19What is the Pericycle doing? Root CapGrowing out through cortexZone of Cell DivisionIn 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
20But shrubs also generally have some compromise for uprooting forces…feeder roots extending laterally.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!
21Tropical 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.