Dynamic Plant Roots & Water Acquisition Functions of Primary History of Plants Systems Roots Plants invaded the land around 400 mya. 1) Anchor the plant 2) Absorb water 3) Absorb minerals Adaptations for living on land: 4) Store surplus sugars > Root for anchor & absorption 5) Transport water, > Cuticle to prevent drying out minerals and sugars and hormones > Stomata i.e. pores for gas exchange 6) Produce some > Conducting vessels hormones 7) Interact with soil fungi > Unique reproductive structures. and bacteria 1 Relevance of Roots • Sources of food Roots as food – Carrots, sugar beets, turnips, horseradishes, Most are biennials cassava (tapioca), yams, sweet potatoes High in carbs. • Spices Vitamins e.g. beta – Sassafras, sarsaparilla, licorice carotenes • Dyes • Drugs – Aconite, ipecac, • Insecticide - Rotenone Parts of a Root Root Cap -very tip of the root, it protects the apical External Anatomy meristem as the root pushes through the soil. of a Root Root Hairs - increase the surface area of the root. Cortex -site of food storage for roots. Casparian Strip -waxy waterproofing material in the walls between cells of the endodermis. Pericycle -give rise to branch roots. Vascular Cylinder -conducting tissues for water and dissolved materials. 2 Root Structure Region of Maturation Internal Anatomy Cortex - Parenchyma cells between epidermis and vascular cylinder of a Root – Mostly stores food Cross section of dicot root Root Structure Root Structure Region of Maturation Region of Maturation Endodermis - Inner boundary of cortex, consisting • Vascular cylinder - Core of tissues inside of a single-layered cylinder of compact cells endodermis • Cell walls with suberin bands called casparian strips on – Pericycle - Outer boundary of vascular cylinder radial and tangential walls – Forces water and dissolved substances entering and leaving the central core to pass through endodermis Region of – Regulates types of minerals absorbed endodermis and pericycle in dicot root – Continues to divide, even after mature – Forms lateral (branch) Lateral root formation Enlargement of vascular cylinder of dicot root roots and part of the vascular cambium 3 Tissues Layers Roots From outside to the inside Types: >Epidermis Tap > Cortex Fibrous > Endodermis/Casparian Strip Adventitious > Pericycle - prop > Vascular Bundle - butressed > Pith - aerial Root Development Root Development - II • Upon germination, Or , after radicle formation, embryo’s radicle adventitious roots may arise that develop into a grows out and fibrous root system . develops into first • Adventitious roots do not root. develop from another root, – Radicle may but instead from a stem or leaf. develop into thick taproot with • Fibrous roots - Large number of fine roots of similar thinner branch diameter Fibrous root system roots. > Monocotyledonous plants > Dicotyledonous Taproot system (monocots) and some dicots plants (dicots) 4 Specialized Roots Specialized Roots • Aerial Roots • Contractile Roots – Orchids - Velamen – Pull plant deeper into roots, with epidermis the soil several layers thick to • Lilly bulbs, dandelions reduce water loss – Corn - Prop roots • Buttress Roots support plants in high – Stability in shallow soil Buttress roots of wind tropical fig tree • Tropical Trees – Ivies (English ivy, Virginia creeper) - Parasitic Roots Aerial roots aid plants • No chlorophyll and dependent on in climbing Orchid aerial (velamen) roots chlorophyll-bearing plants for nutrition Specialized Roots Pneumatophores – In plants with roots growing in water – Spongy roots that extend above the water’s surface and enhance gas exchange between atmosphere and subsurface roots Mangrove pneumatophores 5 Obtaining nutrients Required Nutrients • Roots extract water and minerals from the soil. Plants require nutrients: • Only minerals dissolved in the soil water are Carbon Nitrogen available to the plant. Hydrogen Magnesium • Most minerals are moved into the cells of a plant Oxygen Calcium via active transport. Phosphorous Potassium • The plants receive oxygen and carbon (from CO2)via diffusion into the leaves, stem and roots. Mineral and Water Uptake by Roots Importance of the Casparian strip*: > Restricts movement of dissolved minerals. * Aka Endodermis 6 Plant Partnerships I Ecological Connections Mycorrhizae - root-fungus relationships that Mangroves provide: help plants to secure scarce nutrients such as > protection nitrogen & phosphorous. This relationship allows the plant to extract and absorb minerals > erosion control in its environment. > sediment trap > habitat The fungus in return is > CO2 bank supplied sugars, amino acids and vitamins that it needs from their host plants. Mycorrhizae “fungus roots” Ecto – external fungal associations Plant Partnerships II Endo – internal fungal associations Bacteria-Filled Nodules - Symbiotic bacteria that live in nodules (swellings) in the roots of legume plants. These nitrogen-fixing bacteria can take up nitrogen converting it to ammonium and nitrate ions. >The plants use these nitrogen ions for manufacturing amino acids, nucleic acids and chlorophyll. >The bacteria in turn receive sugars, which it needs for metabolic processes. 7 8.